Promoting coffee discussion.
|
|
coffee-forum.com Promoting coffee discussion. |
> commercial specialty coffee roasters. Well I just saw this on an > advertising for a Diedrich: > > * Hourly volumes are based on maximum loads every 15 to 18 minutes > with a lo shrinkage of 12-15% depending on degree of roast. > * The roaster does not roast with convective heat. Diedrich > utilizes radiant heat toghether with low roasting temperatures to > minimize shrinkage. > * Simple to operate, easy to maintain. > * Simultaneous quick air cooling while roasting next batch > * Consistent and reliable > * Manufactured in U.S.A > > So a commercial goal is to reduce "shrinkage" or water loss (first 2 > points). I've never heard that this correlates in any way with taste, > it seems to me purely a commercial ($) issue. > > Jon Based on this little information, I'd have to agree. Dan |
investigating how to reduce all the cost elements that went into a product. One of their products was a line pressure sensitive tapes, and we used to joke that if they continued reducing the thickness of the backing as well as the amount of adhesive they would end up with just the core and the package. They did succeed in improving both the profit and the quality of the their tapes, but there were some failures and unhappy customers along the way. Maybe the Diedrich is in the "let's try it and see" phase of development. It would be interesting to know how long it has been on the ket and what their customer base is. One would hope that they have thoroughly tested the affect on taste etc, but when chasing the bottom line it's easy to make mistakes and sink a product because the ket wasn't properly consulted. Ken Russell "Jon A. Solworth" <solworth@RemoveThisNow.cs.uic.edu > wrote in message news:h1efg1-qrc.ln1@parsys.cs.uic.edu... |
<solworth@RemoveThisNow.cs.uic.edu > wrote: > * Hourly volumes are based on maximum loads every 15 to 18 minutes >with a lo shrinkage of 12-15% depending on degree of roast. >So a commercial goal is to reduce "shrinkage" or water loss (first 2 >points). I've never heard that this correlates in any way with taste, >it seems to me purely a commercial ($) issue. weight loss during roasting is a very real issue for roasters. coffee is bought and sold by the pound. for some roasters, it becomes too much of an issue. how much water is lost during a roast on a diedrich can be influenced by a few things, but generally it's pretty consistent (no wild deviations for any given coffee). further, the numbers do appear to be less than what one encounters with other roasters. most of my 'normal' roasts run 14-15% loss. do i sweat the 1% here and there, trying to find ways to reduce the loss? no. i use weight loss as just another roast monitoring tool, along with color, temperature, and taste. but for roasters who do millions of pounds a year, a 1% or 2% reduction in loss can be significant. so, say you have a 12 kilo Roaster X and you're thinking of upgrading to a 24 kilo roaster. your 'normal' roast loss is 16%. if you can get a comparable roast profile and cup profile from a diedrich, and only have 14% loss while doing so, that might be a deciding factor in their favor over a 24K Roaster X. --barry "what's wrong with commercial roasters being concerned with a 'commercial ($) issue'?" |
> --barry "what's wrong with commercial roasters being concerned with a > 'commercial ($) issue'?" Nothing. I just want to indicate that even quality roasters have pressures on them other than quality. In general, I'm interested in the relative quality of home roast vs. specialty commercial roaster. Also, some say the best way to get high quality coffee is to emulate the specialty roasters, but that only makes sense if they have the same goals. How does water content effect taste? |
<solworth@RemoveThisNow.cs.uic.edu > wrote: > Nothing. I just want to indicate that even quality roasters have >pressures on them other than quality. this is only a problem when quality succumbs to those other pressures. >In general, I'm interested in the >relative quality of home roast vs. specialty commercial roaster. they can be comparable if you know what you're doing and start with quality beans. >Also, some say the best way to get high quality coffee is to emulate the >specialty roasters, but that only makes sense if they have the same goals. if you're thinking that weight loss is a tool by which you can emulate a particular roaster, i think you're barking up the wrong tree. you get high quality coffee by buying high quality green and roasting it "properly". there's a lot of latitude in that last sentence, and for a reason: there's a lot of latitude in roasting. > How does water content effect taste? during the roast, moisture content affects the rate of heat transfer. it also provides a reaction agent for many of the chemical processes which occur during the roast. after roasting, it can affect the rate of staling. |
I am, by profession, a systems guy. I study computer systems, how they work, and how to improve them. These habits carry over into the world of coffee, for better or worse. So I am interested in the factors that make good quality coffee. But this is problematic. Some issues seem arbitrary: for example, do I give a 1/4 turn to polish the espresso in the portafilter or two full revolutions. And some are contradictory. The Itailan Nationale says an espresso is .75-.92 oz: American sites say 1-1.5 oz. This seems an enormous variation. I know you eventually get to what you like, but you need some guidance to find a path which is close enough. So, what is the essence of Roasting? What drives quality? I would guess its the temperature ramp made relatively stable. So what is it? (I was using minimizing shrinkage as an issue which is not aimed at increasing coffee quality, and hence is irrelevant for the home roaster). Jon Barry Jarrett wrote: > if you're thinking that weight loss is a tool by which you can emulate > a particular roaster, i think you're barking up the wrong tree. you > get high quality coffee by buying high quality green and roasting it > "properly". there's a lot of latitude in that last sentence, and for > a reason: there's a lot of latitude in roasting. > |
<solworth@RemoveThisNow.cs.uic.edu > wrote: > So, what is the essence of Roasting? What drives quality? I would >guess its the temperature ramp made relatively stable. So what is it? it's a very simple rule: it's all in the cup. if you find that 1/16 turn whilst tamping, accompanied by standing on a bucket, results in a better tasting shot, then *that's* what determines quality. ;) as for roasting: it depends. it depends upon the roaster, it depends upon the bean, and it depends upon what the roaster (person) wants out of the bean. there are generalities, of course, but the details largely don't translate. what drives quality? the cup. the essence of roasting? the cup. it's all about the cup. |
> > it's a very simple rule: it's all in the cup. - Steve "Damn! 70 lines of snippage which essentially said, "It's all in *your* cup," but which all seems redundant at this point." |
You're damn right....al On Fri, 20 Feb 2004 03:16:49 GMT, Barry Jarrett <barry@rileys-coffee.com > wrote: >On Thu, 19 Feb 2004 19:54:49 -0600, "Jon A. Solworth" ><solworth@RemoveThisNow.cs.uic.edu> wrote: > > > So, what is the essence of Roasting? What drives quality? I would > >guess its the temperature ramp made relatively stable. So what is it? > >it's a very simple rule: it's all in the cup. > >if you find that 1/16 turn whilst tamping, accompanied by standing on >a bucket, results in a better tasting shot, then *that's* what >determines quality. ;) > >as for roasting: it depends. it depends upon the roaster, it depends >upon the bean, and it depends upon what the roaster (person) wants out >of the bean. there are generalities, of course, but the details >largely don't translate. > >what drives quality? the cup. >the essence of roasting? the cup. > >it's all about the cup. |
with any business you will find roasters throughout the spectrum of choices. We have never worried about shrinkage and factor it into our production costs. Others will try to minimize it even down to 3% these days. Still others will add water back into the roasted coffee to create more weight. With all that said "it is all in the cup". We run 16% - 20% shrinkage just to get the taste profile that suits our business. Peter Bernard Java Roasters Inc. sprsso <Acritzer@cfl.rr.com > wrote in message news:<oeie30djini8fg45frour4m9l8cqdr9nn1@4ax.com>... > You're damn right....al > > > > On Fri, 20 Feb 2004 03:16:49 GMT, Barry Jarrett > <barry@rileys-coffee.com> wrote: > > >On Thu, 19 Feb 2004 19:54:49 -0600, "Jon A. Solworth" > ><solworth@RemoveThisNow.cs.uic.edu> wrote: > > > > > So, what is the essence of Roasting? What drives quality? I would > > >guess its the temperature ramp made relatively stable. So what is it? > > > >it's a very simple rule: it's all in the cup. > > > >if you find that 1/16 turn whilst tamping, accompanied by standing on > >a bucket, results in a better tasting shot, then *that's* what > >determines quality. ;) > > > >as for roasting: it depends. it depends upon the roaster, it depends > >upon the bean, and it depends upon what the roaster (person) wants out > >of the bean. there are generalities, of course, but the details > >largely don't translate. > > > >what drives quality? the cup. > >the essence of roasting? the cup. > > > >it's all about the cup. |
> Nothing. I just want to indicate that even quality roasters have > pressures on them other than quality. In general, I'm interested in the > relative quality of home roast vs. specialty commercial roaster. I would say that my best home roasting is on par with Barry's everyday product. I use his Decatur Street Blend as my espresso blend of choice and I'm learning not to underroast it by using his roast as an example, and my taste buds as an arbiter between the two. This premise assumes that Barry's roast methodology is the "right" one, but I think he works very hard at his roasting, takes a pretty systematic view of testing the results (cupping) and comes up with a very good product. That begs the question of why home roast if commercially available products are so good, and the answer is that it's pretty hard to find a roasting company that is gonna agree with your taste buds on everything, you can save some money (hah, gain some skill at an artistic craft and have some fun along the way. > Also, some say the best way to get high quality coffee is to emulate the > specialty roasters, but that only makes sense if they have the same goals. > > How does water content effect taste? Dunno about the answer to water's effect on taste, but I do think that the presence of water in the roasting environment has a significant impact on final product weight. My roaster is a small (1kg capacity) commercial drum roaster that is heated electrically. The roasting environment is quite dry by comparison to gas fired roasters since one of the priy combustion products is water vapor. I think this contributes a lot to the weight loss fraction that my coffees seem to experience. I'd guesss that weight loss for my coffees is around 20%. From a heat transfer point of view, any roasting process will experience convective heat transfer to some degree. Radiation heat transfer can be enhanced by heating surfaces so that they emit radiation towards the drum, and the fraction of heat transferred to the coffee via radiation can be enhanced, but convection can't be eliminated. For that matter, I'm not sure why one would want to, unless one was attempting to seal the roasting environment to capture water vapor that outgassed from the beans during the roast (?). I would think that radiative heating of a drum might be a very good way of heating it evenly, which is maybe what they are shooting for. -Greg |
<g > -- *********************************************** Ed Needham To Absurdity and Beyond! "Nunc Aut Nunquam" homeroaster ... d.o.t ... com *********************************************** "Greg Scace" <gregory.scace@nist.gov > wrote in message news:8ca075ee.0402200749.e9a3144@posting.google.com... <SNIP > I'd guesss that weight loss for my coffees is around 20%. <SNIP > |
> weight loss during roasting is a very real issue for roasters. coffee > is bought and sold by the pound. Gotta sorta disagree here. Sure, from the roaster's perspective, coffee is sold by the pound, but it's bought by the bag. Weigh some of your incoming bags and tell me that every one of them actually weighs what it's supposed to. No, I haven't actually done this, but in keeping a spreadsheet on green deliveries, roasts, inventory, etc., I often had to manually correct when the end of the bag came before it was supposed to. > how much water is lost during a roast on a diedrich can be influenced > by a few things, but generally it's pretty consistent (no wild > deviations for any given coffee). further, the numbers do appear to > be less than what one encounters with other roasters. most of my > 'normal' roasts run 14-15% loss. Again, I say that moisture content is more significant in weight loss than roaster design. > I don't know if do i sweat the 1% here and there, > trying to find ways to reduce the loss? no. i use weight loss as > just another roast monitoring tool, along with color, temperature, and > taste. Exactly. >but for roasters who do millions of pounds a year, a 1% or 2% > reduction in loss can be significant. Hmmm... If I have $100 and lose a dollar, doesn't that have the same impact that losing $10 out of $1000 has? I believe if 1% is insignificant, then it's insignificant no matter what it's 1% of. Wait. Ephiphany. If I lose $1, I only have $99 left. If I lose $10, I'm WAYBETTEROFF cause I still have $990 !!! Now, which would you rather have. 99% of $100, or 99% of $1000? See! It's MUCH better to lose 1% of a million lbs. than it is to lose 1% of a thousand lbs.! ;-) > so, say you have a 12 kilo Roaster X and you're thinking of upgrading > to a 24 kilo roaster. your 'normal' roast loss is 16%. if you can > get a comparable roast profile and cup profile from a diedrich, and > only have 14% loss while doing so, All else being equal, I don't believe you can... that is, unless you actually put much credence in product brochures. ;-) > that might be a deciding factor in > their favor over a 24K Roaster X. Then I have only one word for them... - Steve "would still rather own a Diedrich than not own a roaster at all" |
<steve@SNIP-THIS.twoloonscoffee.com > wrote: >>but for roasters who do millions of pounds a year, a 1% or 2% >> reduction in loss can be significant. > > Hmmm... If I have $100 and lose a dollar, doesn't >that have the same impact that losing $10 out of >$1000 has? I believe if 1% is insignificant, then it's >insignificant no matter what it's 1% of. At 1% out of 10 million, you can afford to hire an engineer (preferably one who doesn't like coffee) to reduce it. -- Jim (jim_schulman@ameritech.net) |
<steve@SNIP-THIS.twoloonscoffee.com > wrote: >inventory, etc., I often had to manually correct when >the end of the bag came before it was supposed to. ooooh, yeahhh... there's an "allowance" for enroute sampling, bag leak, etc. i'm not sure what the exact number is, but bags are seldom "full weight". > Hmmm... If I have $100 and lose a dollar, doesn't >that have the same impact that losing $10 out of >$1000 has? I believe if 1% is insignificant, then it's >insignificant no matter what it's 1% of. okay, so if you save 1% you might be able to buy a fancy dinner once a year. if folgers saves 1%, they could buy a new corporate jet. ;) > All else being equal, I don't believe you can... >that is, unless you actually put much credence in >product brochures. ;-) i was trying to do a 'ceteris paribus' to show why weight loss figures might be effective keting data. my personal feeling is that roasters are largely individual 'beings', with their own quirks and behaviors. |
"Barry Jarrett" <barry@rileys-coffee.com > schreef in bericht news:o0ba305evmfkqc75u4tns5mfgs0k1238n7@4ax.com... > On Thu, 19 Feb 2004 13:05:53 -0600, "Jon A. Solworth" > <solworth@RemoveThisNow.cs.uic.edu> wrote: > > > * Hourly volumes are based on maximum loads every 15 to 18 minutes > >with a lo shrinkage of 12-15% depending on degree of roast. > > >So a commercial goal is to reduce "shrinkage" or water loss (first 2 > >points). I've never heard that this correlates in any way with taste, > >it seems to me purely a commercial ($) issue. > > weight loss during roasting is a very real issue for roasters. coffee > is bought and sold by the pound. for some roasters, it becomes too > much of an issue. > > how much water is lost during a roast on a diedrich can be influenced > by a few things, but generally it's pretty consistent (no wild > deviations for any given coffee). further, the numbers do appear to > be less than what one encounters with other roasters. most of my > 'normal' roasts run 14-15% loss. do i sweat the 1% here and there, > trying to find ways to reduce the loss? no. i use weight loss as > just another roast monitoring tool, along with color, temperature, and > taste. but for roasters who do millions of pounds a year, a 1% or 2% > reduction in loss can be significant. > > so, say you have a 12 kilo Roaster X and you're thinking of upgrading > to a 24 kilo roaster. your 'normal' roast loss is 16%. if you can > get a comparable roast profile and cup profile from a diedrich, and > only have 14% loss while doing so, that might be a deciding factor in > their favor over a 24K Roaster X. > > --barry "what's wrong with commercial roasters being concerned with a > 'commercial ($) issue'?" > > Indeed, indeed, but than again, use some more Vietnam and you are smiling again . . . . -- Ivo van der Putten www.ivanderputten.nl www.ongebrand.nl |
> "Barry Jarrett" <barry@rileys-coffee.com> schreef in bericht > news:o0ba305evmfkqc75u4tns5mfgs0k1238n7@4ax.com... > > On Thu, 19 Feb 2004 13:05:53 -0600, "Jon A. Solworth" > > <solworth@RemoveThisNow.cs.uic.edu> wrote: > > > > > * Hourly volumes are based on maximum loads every 15 to 18 minutes > > >with a lo shrinkage of 12-15% depending on degree of roast. > > > >So a commercial goal is to reduce "shrinkage" or water loss (first 2 > > >points). I've never heard that this correlates in any way with taste, > > >it seems to me purely a commercial ($) issue. > > > > weight loss during roasting is a very real issue for roasters. coffee > > is bought and sold by the pound. for some roasters, it becomes too > > much of an issue. > > > > how much water is lost during a roast on a diedrich can be influenced > > by a few things, but generally it's pretty consistent (no wild > > deviations for any given coffee). further, the numbers do appear to > > be less than what one encounters with other roasters. most of my > > 'normal' roasts run 14-15% loss. do i sweat the 1% here and there, > > trying to find ways to reduce the loss? no. i use weight loss as > > just another roast monitoring tool, along with color, temperature, and > > taste. but for roasters who do millions of pounds a year, a 1% or 2% > > reduction in loss can be significant. > > > > so, say you have a 12 kilo Roaster X and you're thinking of upgrading > > to a 24 kilo roaster. your 'normal' roast loss is 16%. if you can > > get a comparable roast profile and cup profile from a diedrich, and > > only have 14% loss while doing so, that might be a deciding factor in > > their favor over a 24K Roaster X. > > > > --barry "what's wrong with commercial roasters being concerned with a > > 'commercial ($) issue'?" > > > > > > Indeed, indeed, but than again, use some more Vietnam and you are smiling > again . . . . Where wuz the smiley face :) |
Brent "Barry Jarrett" <barry@rileys-coffee.com > wrote in message news:o0ba305evmfkqc75u4tns5mfgs0k1238n7@4ax.com... > On Thu, 19 Feb 2004 13:05:53 -0600, "Jon A. Solworth" > <solworth@RemoveThisNow.cs.uic.edu> wrote: > > > * Hourly volumes are based on maximum loads every 15 to 18 minutes > >with a lo shrinkage of 12-15% depending on degree of roast. > > >So a commercial goal is to reduce "shrinkage" or water loss (first 2 > >points). I've never heard that this correlates in any way with taste, > >it seems to me purely a commercial ($) issue. > > weight loss during roasting is a very real issue for roasters. coffee > is bought and sold by the pound. for some roasters, it becomes too > much of an issue. > > how much water is lost during a roast on a diedrich can be influenced > by a few things, but generally it's pretty consistent (no wild > deviations for any given coffee). further, the numbers do appear to > be less than what one encounters with other roasters. most of my > 'normal' roasts run 14-15% loss. do i sweat the 1% here and there, > trying to find ways to reduce the loss? no. i use weight loss as > just another roast monitoring tool, along with color, temperature, and > taste. but for roasters who do millions of pounds a year, a 1% or 2% > reduction in loss can be significant. > > so, say you have a 12 kilo Roaster X and you're thinking of upgrading > to a 24 kilo roaster. your 'normal' roast loss is 16%. if you can > get a comparable roast profile and cup profile from a diedrich, and > only have 14% loss while doing so, that might be a deciding factor in > their favor over a 24K Roaster X. > > --barry "what's wrong with commercial roasters being concerned with a > 'commercial ($) issue'?" > > |
<solworth@RemoveThisNow.cs.uic.edu > wrote: >So a commercial goal is to reduce "shrinkage" or water loss (first 2 >points). I've never heard that this correlates in any way with taste, >it seems to me purely a commercial ($) issue. oh, btw, weight loss during roasting does correlate to taste, for any given roaster. |
<barry@rileys-coffee.com > wrote: >oh, btw, weight loss during roasting does correlate to taste, for any >given roaster. So when I roast in the summer and sweat off a few pounds in the hot sun, do I have better taste than when I roast in the winter and don't sweat off any weight... doh! The rich! |
The priy goal of all specialty coffee roasting companies is to make great coffee, and to make it on a moneymaking basis. The priy goal of specialty coffee roasting machine manufacturers is to make the very best coffee roasting machines and to make them as a money making proposition to themselves. One of the goals of any company that hopes to be in business next year is to create and ket a product that in some way does a better job than the competition, or at a better price point for the potential customer or both. In claiming that their machine produces a weight loss yield lesser than others the manufacturer in this case is also stating that its batch roasting times are longer than some other specialty roasting machine manufacturers thereby producing fewer batches per man-hour at the roaster, which is not to the manufacturers advantage in making a sale. There are many factors that determine a roasting business' choice of technology including but not limited to resulting Roast Profile in the hand, Resulting Roast Profile in the cup, Fuel availability, local building, fire, emission codes, Price point, floor load, roast technology - Drum: solid or perferated)Fluid Bed etc, ease of operation, ease of maintenance, cost of operation, safety, price, available financing, exchange rates, parts and service, esthetic design, color, customizing possibilities and availability. Plenty of oportunity here for the roasting machine manufacturer to find positive attributes of their equipment to stress in their keting effort. Suffice to say that today's roasting businesses make their decisions for a variety of reasons. The aim of all is to produce the very best coffee they know how at the very best price for the consumer while still making a n honest profit in the bargain. -DNS |
his coffee from the opposition he would probably lift and separate. Sorry for the oblique reference to the famous bra slogan. I guess the shop is just keeping abreast of modern developments. Ken Russell "Jon A. Solworth" <solworth@RemoveThisNow.cs.uic.edu > wrote in message news:h1efg1-qrc.ln1@parsys.cs.uic.edu... |
shrinkage? "Jon A. Solworth" <solworth@RemoveThisNow.cs.uic.edu > wrote in message news:h1efg1-qrc.ln1@parsys.cs.uic.edu... > We've sometime had discussions on this board about the goals of > commercial specialty coffee roasters. Well I just saw this on an > advertising for a Diedrich: > > * Hourly volumes are based on maximum loads every 15 to 18 minutes > with a lo shrinkage of 12-15% depending on degree of roast. > * The roaster does not roast with convective heat. Diedrich > utilizes radiant heat toghether with low roasting temperatures to > minimize shrinkage. > * Simple to operate, easy to maintain. > * Simultaneous quick air cooling while roasting next batch > * Consistent and reliable > * Manufactured in U.S.A > > So a commercial goal is to reduce "shrinkage" or water loss (first 2 > points). I've never heard that this correlates in any way with taste, > it seems to me purely a commercial ($) issue. > > Jon |
> We've sometime had discussions on this board about the goals of > commercial specialty coffee roasters. Well I just saw this on an > advertising for a Diedrich: > > * Hourly volumes are based on maximum loads every 15 to 18 minutes > with a lo shrinkage of 12-15% depending on degree of roast. They're not necessarily saying that your results will be comparable, just that IF (by some miracle) you're able to roast max loads in 15 to 18 minutes, and IF (by some miracle) you only have 12%-15% weight loss, this will be your hourly throughput. It's kinda like the EPA MPG rating on a new car. Now for reality: A 15 to 18 minute roast at max load simply isn't possible on the '94 Diedrich 12K I used to run. Max load took a good 21 minutes for a city+ up to 26 minutes for an Italian roast. I never roasted max loads because of that. Once in a while I'd go 24 lbs. but normally to get an 18 minute roast, I loaded 20-21 lbs. green. Second, the weight loss they quote is ridiculous (for high moisture content beans anyway... maybe they're roasting beans that have sat in Idaho for a few weeks and have dried out to less than 10% moisture content). My "normal" roast (depending on bean) is just before 2nd crack to maybe 10 seconds into 2nd. At that roast level, that Diedrich would yield generally about 15-16% weight loss... For a 20 lb. order, I loaded 24 lbs. green. That would give me my needed weight with about 1/4 lb. left over. 20/24 = 83.3% or 16.7% loss allowance... 20¼ ÷ 24 gives ~15.7% actual loss. > * The roaster does not roast with convective heat. Diedrich > utilizes radiant heat toghether with low roasting temperatures to > minimize shrinkage. How do you get that fast roast time with "low temperatures?" This seems to directly contradict the earlier bullet. Ceramic IR burners mean heat transfer through a very hot drum, so while the drum air temp may well be cooler, the bean surface in contact with the drum has to be hotter then. Is this really a good thing®? > * Simple to operate, easy to maintain. Easy to maintain!!! alkja#$(~&*%jlkjffas ROFL!!! Please, help me up, someone! I don't know which size roaster in particular they're referring to, but the 12K at any rate, was fairly high maintenance (specifically, I mean hard to clean) relative to other designs. I spent at least 4x the cleaning time on the Diedrich that I do on the Quattro. > * Simultaneous quick air cooling while roasting next batch Not unless by "quick" they mean a good 6+ minutes. The Diedrich design has a single blower shared by drum and cooler. At max bin shutter, only 80% of the blower "suction" is going through the bin. My Quattro, otoh, has a dedicated 1.5 HP blower on the bin which cools a full load to under 80°F in 4 minutes. > * Consistent and reliable They did get that one right. The fit and finish of the Diedrichs are excellent. Keep them clean and greased, and they do perform very consistently. The Quattro is more utilitarian grade when it comes to finish. I can't speak to reliability over the long haul, but no problems so far. > * Manufactured in U.S.A Heh. No controversy possible there. Millenium also manufactured in USA, (Roasters Exchange) but some parts are Italian. (dunno if all Diedrich *parts* are also made in USA) > So a commercial goal is to reduce "shrinkage" or water loss (first 2 > points). I've never heard that this correlates in any way with taste, > it seems to me purely a commercial ($) issue. The whole issue of weight loss is one that seems to me to be over generalized. Obviously if you start out with a bean that's 13% moisture, you'll have more loss than the same bean that's been dried to 10% moisture content. Seems to me that storage conditions of your greens would have more effect on weight loss than which roaster you use. The weight losses I get with my Quattro are very close to, even a bit lighter than, those I got with the Diedrich... Last large load I did to just before 2nd crack, 24.6 lbs of green gave me 21.094 lbs roasted. 14.3% loss. (That's 1 lb. for me, 20.094 for the customer. ;-) That's on the high side of the range of Diedrich's claims above, but certainly lower than any Diedrich roast I ever actually experienced. If you told me there was a half percent difference in weight loss between an electric roaster and a gas roaster, I'd probably believe it. All else being equal though, I don't see how Diedrich could claim that their design somehow magically results in significantly less weight loss than others. I don't know what the point of the exercise was, but there you have my 2¢ anyway. :-) -- Steve Ackman http://twoloonscoffee.com |
<steve@SNIP-THIS.twoloonscoffee.com > wrote: > Now for reality: A 15 to 18 minute roast at max load >simply isn't possible on the '94 Diedrich 12K I used to >run. Max load took a good 21 minutes for a city+ up to >26 minutes for an Italian roast. I never roasted max >loads because of that. Once in a while I'd go 24 lbs. >but normally to get an 18 minute roast, I loaded 20-21 >lbs. green. i can't even get a "full load" into my 7k.... just under 13lbs is max, or the beans start falling out the exhaust duct. > My "normal" roast (depending on bean) is just before >2nd crack to maybe 10 seconds into 2nd. At that >roast level, that Diedrich would yield generally about >15-16% weight loss... For a 20 lb. order, I loaded >24 lbs. green. That would give me my needed weight with >about 1/4 lb. left over. 20/24 = 83.3% or 16.7% loss >allowance... 20¼ ÷ 24 gives ~15.7% actual loss. 2nd crack roasts (just before to just into) on mine run 13-15%, depending upon beans (except sumatra, which is way wet to start with). washed centrals generally hit right around 14%. roast times for 12lbs start weight run right around 14-16 minutes. |
> They're not necessarily saying that your results will > be comparable, just that IF (by some miracle) you're > able to roast max loads in 15 to 18 minutes, and IF > (by some miracle) you only have 12%-15% weight loss, > this will be your hourly throughput. > It's kinda like the EPA MPG rating on a new car. In the computer business a measure of performace is "Peak Performance", the meaning of which is "The performance the manufacturer guarantees you will not exceed". I like coffee roasting, but I'm very happy that its a hobby for me and not a business. |
roasters are in it for the money...they want to make more of it. So if you are selling a commercial roaster ONE of your selling propositions (not the only one) is that buying your product will enable the purchaser to do so. I've yet to see any product sold to a commercial account that does not try, if at all possible, to introduce this selling proposition (even if untrue or somewhat far fetched) into its sales presentation. So there's no reason to be shocked, shocked that this is going on. It does not mean that either the manufacture or the roaster is in league with the devil....this is just how the world works. In places where they tried to remove the profit motive from the equation, the result was that people couldn't get coffee at all most of the time. For specialty roasters that are only selling a few ten thousand lbs. per year, a 1% savings in water weight is no big deal (a few hundred $/year) and they are likely selling their product at a relatively high price anyway. For P&G, Kraft, etc. where they are selling 10s of millions of lbs. and the retail price is as little as $2/lb., every penny saved on a can means millions of $ of profit. So not only are they trying to minimize water loss during roast (they do super fast fluid bed roasts that are over in a couple of minutes) , they are spritzing water back into the coffee post roast (for "cooling") and they are gathering up the chaff, compressing it into pellets and putting that in the can too. In short, they are doing the absolute maximum that is legally allowed so that they can still label the product as "coffee". If they could legally grind up the burlap bags and put those in the can, they'd do that too. The average buyer of a Diedrich roaster is far, far away from that kind of mindset, but still, if you want to stay in business it doesn't hurt to keep your eye on the bottom line. "Jon A. Solworth" <solworth@RemoveThisNow.cs.uic.edu > wrote in message news:h1efg1-qrc.ln1@parsys.cs.uic.edu... > We've sometime had discussions on this board about the goals of > commercial specialty coffee roasters. Well I just saw this on an > advertising for a Diedrich: > > * Hourly volumes are based on maximum loads every 15 to 18 minutes > with a lo shrinkage of 12-15% depending on degree of roast. > * The roaster does not roast with convective heat. Diedrich > utilizes radiant heat toghether with low roasting temperatures to > minimize shrinkage. > * Simple to operate, easy to maintain. > * Simultaneous quick air cooling while roasting next batch > * Consistent and reliable > * Manufactured in U.S.A > > So a commercial goal is to reduce "shrinkage" or water loss (first 2 > points). I've never heard that this correlates in any way with taste, > it seems to me purely a commercial ($) issue. > > Jon |
-- *********************************************** Ed Needham To Absurdity and Beyond! "Nunc Aut Nunquam" homeroaster ... d.o.t ... com *********************************************** "Jack Denver" <nunuvyer@netscape.net > wrote in message news:2_idnVft1O0Jvavd4p2dnA@comcast.com... <SNIP > If they could legally grind up the burlap bags and put those in |
> with a lo shrinkage of 12-15% depending on degree of roast. > * The roaster does not roast with convective heat. Diedrich > utilizes radiant heat toghether with low roasting temperatures to > minimize shrinkage. > * Simple to operate, easy to maintain. > * Simultaneous quick air cooling while roasting next batch > * Consistent and reliable > * Manufactured in U.S.A > > So a commercial goal is to reduce "shrinkage" or water loss (first 2 > points). I've never heard that this correlates in any way with taste, > it seems to me purely a commercial ($) issue. > > Jon Concerning the taste issue, what the advertisement doesn't say is telling. If the IR produced roasts that improved flavor you can be sure they'd have said so. And, if the IR had no effect on flavor they'd have said that, too. The fact that they don't say anything about flavor tells me there is a reduction in flavor. All of their 'benefits' are about production issues, not about quality. Dan |
<danbollinger@REMOVEinsightbb.com > wrote: >Concerning the taste issue, what the advertisement doesn't say is telling. If >the IR produced roasts that improved flavor you can be sure they'd have said so. >And, if the IR had no effect on flavor they'd have said that, too. The fact that >they don't say anything about flavor tells me there is a reduction in flavor. >All of their 'benefits' are about production issues, not about quality. i think this is a tremendously unfair statement. |
If > >the IR produced roasts that improved flavor you can be sure they'd have said so. > >And, if the IR had no effect on flavor they'd have said that, too. The fact that > >they don't say anything about flavor tells me there is a reduction in flavor. > >All of their 'benefits' are about production issues, not about quality. > > i think this is a tremendously unfair statement. > Unfair? Unfair to whom? Diedrich or their customers? How many mfgrs do you know that go out of their way to advertise or ket their product's faults? Why should Diedrich behave any differently? Dan |
unfair to diedrich, of course. "The fact that they don't say anything about flavor tells me there is a reduction in flavor." utter crap. first, it assumes that there is some paradigm of flavor in the coffee. second, it assumes that all other roasters routinely achieve that paradigm. third, this makes no allowance for taste *preference* -- even *if* a diedrich does produce a _different_ flavor, doesn't mean that it is necessarily better or worse (just different). |
>The fact that >they don't say anything about flavor tells me there is a reduction in flavor. Total bullshit. Try roasting the same beans in a Probat, a Deidrich, a Lilla and and ancient Jabez Burns. If you pay attention to detail, particularly the time/temperature relationship, the end results will be indistinguishable in a blind cupping. I've yet to meet the cupper who can tell what brand of drum machine the coffee was roasted in. -- Alan alanfrew@coffeeco.com.au www.coffeeco.com.au |
<solworth@RemoveThisNow.cs.uic.edu > wrote: > * The roaster does not roast with convective heat. Diedrich >utilizes radiant heat toghether with low roasting temperatures to >minimize shrinkage. This is an interesting (but to me, confusing and possibly misleading) point. Understandably Diedrich are going to tout whatever commercial advantages might be wrought from the differences in their infrared heating design compared to a more conventional convective (rising) heating design. But what exactly is the "radiant heat" being utilized to heat? The drum and the air, or the beans? Iow, my understanding is that, in Diedrich's "IR" model roasters, a gas burner heats some ceramic tiles which in turn then radiate (emit) longer wavelength (IR) heat which in turn is utilized to heat the blown air (via a heated HX through which the air is blown) and the drum (radiantly, from the outside) which in turn, by conduction (priily), heat the beans inside the drum as they are contacted by the blown air and drum. Is this correct? Otoh, assuming that radiant heating is in fact advantageous, would not a roaster design which directly utilizes IR radiation to heat the beans (for example, using an IR heater positioned inside the drum or so as to radiate IR into the interior of the drum) offer even better performance? I'm speaking of something along the lines of a halogen heater radiating directly into the drum, as in the Imex Digirosto shop roaster's design. I realize this might be difficult to implement with a gas burner, and that using electrical power to heat a commercial roaster might be impractical (and more expensive to operate?), but am thinking about whether the roasting performance might be better. See for example US patents 4,691,447 and 4,860,461. M "who agrees 100% that it's what's in the cup what matters"-bob -- To e-mail, take out the "hippo." |
>Iow, my understanding is that, in Diedrich's "IR" model roasters, a >gas burner heats some ceramic tiles which in turn then radiate (emit) >longer wavelength (IR) heat which in turn is utilized to heat the >blown air (via a heated HX through which the air is blown) and the >drum (radiantly, from the outside) which in turn, by conduction >(priily), heat the beans inside the drum as they are contacted by >the blown air and drum. Is this correct? on mine, the "burner" is really a ceramic heating pad, which has small pores through which the gas flows. the pad isn't heated by a burner, rather the pad *is* the burner, only a sort of quasi-flameless one. the air is heated incidentally as it passes through the burner area under the drum (no formal hx at all). >Otoh, assuming that radiant heating is in fact advantageous, would not >a roaster design which directly utilizes IR radiation to heat the >beans (for example, using an IR heater positioned inside the drum or >so as to radiate IR into the interior of the drum) offer even better >performance? I'm speaking of something along the lines of a halogen >heater radiating directly into the drum, as in the Imex Digirosto shop >roaster's design. it would be cool to try. there have been roasters which have an open flame in the center of the drum. i wonder what the maximum mounting angle is for the ceramic burners.... |
heat? same for heat radiated by the glass/plastic/metal/etc roasting columns? "Barry Jarrett" <barry@rileys-coffee.com > wrote in message news:a56e309navkj9i2f84ktdns5bpl1h69n51@4ax.com... > On Sat, 21 Feb 2004 07:53:31 GMT, M-bob wrote: > > >Iow, my understanding is that, in Diedrich's "IR" model roasters, a > >gas burner heats some ceramic tiles which in turn then radiate (emit) > >longer wavelength (IR) heat which in turn is utilized to heat the > >blown air (via a heated HX through which the air is blown) and the > >drum (radiantly, from the outside) which in turn, by conduction > >(priily), heat the beans inside the drum as they are contacted by > >the blown air and drum. Is this correct? > > on mine, the "burner" is really a ceramic heating pad, which has small > pores through which the gas flows. the pad isn't heated by a burner, > rather the pad *is* the burner, only a sort of quasi-flameless one. > the air is heated incidentally as it passes through the burner area > under the drum (no formal hx at all). > > > > >Otoh, assuming that radiant heating is in fact advantageous, would not > >a roaster design which directly utilizes IR radiation to heat the > >beans (for example, using an IR heater positioned inside the drum or > >so as to radiate IR into the interior of the drum) offer even better > >performance? I'm speaking of something along the lines of a halogen > >heater radiating directly into the drum, as in the Imex Digirosto shop > >roaster's design. > > it would be cool to try. there have been roasters which have an open > flame in the center of the drum. i wonder what the maximum mounting > angle is for the ceramic burners.... > > |
radiant >heat? same for heat radiated by the glass/plastic/metal/etc roasting >columns? Nothing newbie about that. Heat is heat, what changes with different roasters is the amount of heat applied to a particular area of the bean per unit time. This in turn <can > change the rate and path of chemical reactions within the bean, and thus alter the end flavour. In my experience of drum roasters (as distinctive from fluid bed roasters, with which I have no commercial form) the same profile will produce the same result, regardless of who built the roaster. The difficulties which can arise are usually due to trying to reproduce a particular profile on a roaster which wasn't originally built to do that sort of thing. -- Alan alanfrew@coffeeco.com.au www.coffeeco.com.au |
<alanfrew@coffeeco.com.au > wrote: >>another newbie question: isn't heating beans with hot air heating by >radiant >>heat? same for heat radiated by the glass/plastic/metal/etc roasting >>columns? > >Nothing newbie about that. Heat is heat Ah, but it's a bit more complicated than that, innit? ; > There are, if you will, different heats (e.g. "white hot" steel is not merely at a higher temp than "red hot" steel, but radiates (emits) light at a different wavelength (which is why it's perceived as a different color). Point is, radiation which heats can have different wavelengths. Roasting coffee with hot air relies upon heated air to transfer its heat to beans into which it comes in contact priily by conduction, not by direct radiation, whereas in radiant roasting the heat is radiated directly from the radiant heat emitter to the beans (although the air surrounding the beans also gets radiantly heated and in turn can transfer its heat to the beans with which it comes into contact). Air is a much better thermal insulator than conductor, especially when it is dry (low humidity). Think about toasting a slice of bread only with hot air instead of exposing the bread directly to heat radiated from heating elements. Coffee could be roasted radiantly in a vacuum (without _any_ air). Fluidized bed hot air roasters and other roaster designs which roast coffee with hot air (e.g. Burns' Thermalo and Bersten's Belaroma) can provide an even roast by contacting the hot air to all the beans and all over the beans. But they are fairly inefficient because they rely upon a poor thermal conductor (air) and thus need to put a lot of heat into the air and pass a lot of air through and over the beans. M "enjoying 'ondol' underfloor heating system in Korea"-bob -- To e-mail, take out the "hippo." |
>Coffee could be roasted radiantly in a vacuum (without _any_ air). forgotten coffee experiment: deep fried coffee beans. |
<barry@rileys-coffee.com > wrote: > >forgotten coffee experiment: deep fried coffee beans. Light roasted coffee with a nice oil sheen? -- Jim (jim_schulman@ameritech.net) |
> forgotten coffee experiment: deep fried coffee beans. Many of the common vegetable oils are smoking in the required 450-475F temperature range. So you might want to use one of the more exotic oils for your experiment: almond, grapeseed, etc. They perform better at high temperatures, but they would add an exotic flavor component, of course. And then there's always Mobil 1. -- -Andy S. picture page: http://tinyurl.com/eh0x |
<schecter@rochester.rr.com > wrote: >Barry Jarrett wrote: >> forgotten coffee experiment: deep fried coffee beans. > >Many of the common vegetable oils are smoking in the required 450-475F >temperature range. So you might want to use one of the more exotic oils for your >experiment: almond, grapeseed, etc. They perform better at high temperatures, >but they would add an exotic flavor component, of course. would the oil have to be that hot? the heat transfer would be a lot more efficient with oil. |
> On Sun, 22 Feb 2004 14:45:38 GMT, "Andy Schecter" > <schecter@rochester.rr.com> wrote: > > >Barry Jarrett wrote: > >>> > would the oil have to be that hot? the heat transfer would be a lot > more efficient with oil. Barry, its not only heat transfer efficency, but delta T that controls the process. Could could get a fast raoast to 85 or 90% of the oil temperature, but its delta T (425-400= 25) that drives the time to temperature. |
> would the oil have to be that hot? the heat transfer would be a lot > more efficient with oil. Well, assuming you want a coffee bean endpoint around 450F, the oil of course will have to be a little hotter.... -- -Andy S. picture page: http://tinyurl.com/eh0x |
<schecter@rochester.rr.com > wrote: >Well, assuming you want a coffee bean endpoint around 450F, the oil of course >will have to be a little hotter.... but is that the *real* bean temp at endpoint, or a 'pseudo' bean temp (as carl staub likes to call it) which registers on the measuring device, and which is affected by several non-bean factors? how about 'water roasted' beans, cooked in a pressure vessel? :) that might be an interesting experiment, as the oils and CO2 might be contained within the bean until the cooling stage. mmmmm.... skillet fried coffee... --barry "need a lab, and i don't mean a pup." |
"Barry Jarrett" <barry@rileys-coffee.com > wrote in message news:028i30513n1p44fl1tnbad3sgp84ek6eav@4ax.com... > On Sun, 22 Feb 2004 20:51:32 GMT, "Andy Schecter" > <schecter@rochester.rr.com> wrote: > > >Well, assuming you want a coffee bean endpoint around 450F, the oil of course > >will have to be a little hotter.... > > but is that the *real* bean temp at endpoint, or a 'pseudo' bean temp > (as carl staub likes to call it) which registers on the measuring > device, and which is affected by several non-bean factors? > > how about 'water roasted' beans, cooked in a pressure vessel? :) > that might be an interesting experiment, as the oils and CO2 might be > contained within the bean until the cooling stage. > > mmmmm.... skillet fried coffee... > > > --barry "need a lab, and i don't mean a pup." > That would be fun to try. about 29 bar for 450F, that's do-able. I wonder how thick, say steel, walls would need to be for that kind of pressure. |
> > That would be fun to try. > about 29 bar for 450F, that's do-able. I wonder how thick, say steel, walls > would need to be for that kind of pressure. > > Sounds like KFC to me. (Kentucky Fried Coffee) |
news:028i30513n1p44fl1tnbad3sgp84ek6eav@4ax.com... > On Sun, 22 Feb 2004 20:51:32 GMT, "Andy Schecter" > <schecter@rochester.rr.com> wrote: > > >Well, assuming you want a coffee bean endpoint around 450F, the oil of course > >will have to be a little hotter.... > > but is that the *real* bean temp at endpoint, or a 'pseudo' bean temp > (as carl staub likes to call it) which registers on the measuring > device, and which is affected by several non-bean factors? > > how about 'water roasted' beans, cooked in a pressure vessel? :) > that might be an interesting experiment, as the oils and CO2 might be > contained within the bean until the cooling stage. > > mmmmm.... skillet fried coffee... > from what I've read that was the common way to roast coffee in the early USA. another way might be steam roasting in a pressure cooker where the beans are kept above the water...would probably leave more flavor intact...steaming vegetables leaves more flavor that boiling vegetables. |
achieve the correct final temperature, I think there would a problem with achieving the desirable Maillard reaction that results in the coffee browning and achieving the "roasty/caramel" notes we expect, in the presence of so much water. If you really want to experiment, there are other roasting "fluids" that you could try in addition to air, water and oil - perhaps hot salt or hot sand. In the end, coffee roasting is a form of cooking and you have to look at the methods by which foods are cooked (especially, actually only, cooking methods that result in the food browning). In the end there aren't really many of them - broiling/grilling (infrared heating) , griddle baking (contact heating), oven baking (convection heating with some radiation), pure convection (hot air only) frying in oil. That's more or less it. "Barry Jarrett" <barry@rileys-coffee.com > wrote in message news:028i30513n1p44fl1tnbad3sgp84ek6eav@4ax.com... snip > how about 'water roasted' beans, cooked in a pressure vessel? :) > that might be an interesting experiment, as the oils and CO2 might be > contained within the bean until the cooling stage. > > mmmmm.... skillet fried coffee... > > > --barry "need a lab, and i don't mean a pup." > |
> but is that the *real* bean temp at endpoint, or a 'pseudo' bean temp > (as carl staub likes to call it) which registers on the measuring > device, and which is affected by several non-bean factors? If Carl says it's only "pseudo," who the hell am I to argue? But even "pseudo" is likely to be fairly close to the exterior bean temp, no? I still say the taste of your frying oil is going to obliterate any of the subtler coffee flavors.... -Andy S. picture page: http://tinyurl.com/eh0x |
<schecter@rochester.rr.com > wrote: >I still say the taste of your frying oil is going to obliterate any of the >subtler coffee flavors.... but maybe we'll create *new* and *more exciting* flavors!! --barry "can't distinguish the subtleties of potatos, but sure do like french fries" |
"Barry Jarrett" <barry@rileys-coffee.com > wrote in message news:57gl305tpegidkte6ls7i379vgtbnkm7cn@4ax.com... > On Tue, 24 Feb 2004 01:28:48 GMT, "Andy Schecter" > <schecter@rochester.rr.com> wrote: > > >I still say the taste of your frying oil is going to obliterate any of the > >subtler coffee flavors.... > > but maybe we'll create *new* and *more exciting* flavors!! > > --barry "can't distinguish the subtleties of potatos, but sure do like > french fries" > Ever had deep fried french toast? Yummy! Randy R |
<barry@rileys-coffee.com > wrote: >On Sun, 22 Feb 2004 05:13:27 GMT, M-bob wrote: > > >Coffee could be roasted radiantly in a vacuum (without _any_ air). > >forgotten coffee experiment: deep fried coffee beans. Belgian style, I assume. They don't brown properly unless you fry twice. shall |
news:l7kg301e1k7qnrqhn14oeeh2ejp4cu2a37@4ax.com... > On Sun, 22 Feb 2004 05:13:27 GMT, M-bob wrote: > > >Coffee could be roasted radiantly in a vacuum (without _any_ air). > > forgotten coffee experiment: deep fried coffee beans. > and? what about roasting in hot sand? BTW with so many folks here knowledgeable about so many thing, does any one here know why Szechwan pepper corns roasted in a wok in coarse salt and then oil poured into the salt, would produce a spice oil but with no salt taste even though the salt was totally dissolved? |
> here know why Szechwan pepper corns roasted in a wok in coarse salt and then > oil poured into the salt, would produce a spice oil but with no salt taste > even though the salt was totally dissolved? The question is, "Dissolved where?" Oil is not a solvent. Salt is only dissolvable in one solvent: water (if memory serves). Therefore, the salt was dissolved in the only water present, namely in the pepper corns, leaving the pepper corn's essential oils to mix with the oil. |
amount of dried peppercorns...I am checking right now to see if I can get some salt to dissolve in oil (with a few drops of water) "Dan Bollinger" <NOdanbollingerNO@NOinsightbb.com > wrote in message news:%hn_b.108278$uV3.593100@attbi_s51... > > BTW with so many folks here knowledgeable about so many thing, does any one > > here know why Szechwan pepper corns roasted in a wok in coarse salt and then > > oil poured into the salt, would produce a spice oil but with no salt taste > > even though the salt was totally dissolved? > > The question is, "Dissolved where?" Oil is not a solvent. Salt is only > dissolvable in one solvent: water (if memory serves). Therefore, the salt was > dissolved in the only water present, namely in the pepper corns, leaving the > pepper corn's essential oils to mix with the oil. > > |
wrote: >thanks, makes sense to me except for the large amount of salt and the small >amount of dried peppercorns...I am checking right now to see if I can get >some salt to dissolve in oil (with a few drops of water). try to get the oil to dissolve in water. |
news:rbtl30tkrndhkdo1v424ofo7i8ii2s0m25@4ax.com... > On Mon, 23 Feb 2004 18:06:07 -0800, "dmreed" <dmreed@dmreed.com> > wrote: > > >thanks, makes sense to me except for the large amount of salt and the small > >amount of dried peppercorns...I am checking right now to see if I can get > >some salt to dissolve in oil (with a few drops of water). > > try to get the oil to dissolve in water. > the best I can get with oil and water is an emulsion using some egg yolk...hey I just added some vinegar and spices and now I have salad dressing...at least it was not a waste of oil and water! |
-- *********************************************** Ed Needham To Absurdity and Beyond! "Nunc Aut Nunquam" homeroaster ... d.o.t ... com *********************************************** "dmreed" <dmreed@dmreed.com > wrote in message news:GEI_b.277$id3.153@fed1read01... |
ed@NOSPAMhomeroaster.com says... > "Real" Italian dressing...with coffee beans! > Whoa... good drugs? 8^) Ted -- Please take the 'thisgetsremoved' out of the email before emailing me. |
> > Fluidized bed hot air roasters and other roaster designs which roast > coffee with hot air (e.g. Burns' Thermalo and Bersten's Belaroma) can > provide an even roast by contacting the hot air to all the beans and > all over the beans. But they are fairly inefficient because they rely > upon a poor thermal conductor (air) and thus need to put a lot of heat > into the air and pass a lot of air through and over the beans. Fluid air is inefficient, but I do not believe this is the reason. If you have a heat source, its going to inject that much heat into its surroundings whether the surroundings are good or bad conductors. Where else is it going to go? The problem with fluid air is that the agitation mechanism (the fluid air) is moving a lot of heat out of the roaster into the environment. Imagine a roaster with a very thin mesh for holding the beans with a traditional electric or gas heat source. Almost all the heat would be by convection (air) and it could be made very efficent. Jon |
> On Sat, 21 Feb 2004 09:28:36 GMT, "Coffee for Connoisseurs" > <alanfrew@coffeeco.com.au> wrote: > > >>another newbie question: isn't heating beans with hot air heating by > radiant > >>heat? same for heat radiated by the glass/plastic/metal/etc roasting > >>columns? > > > >Nothing newbie about that. Heat is heat > > > Ah, but it's a bit more complicated than that, innit? ;> > > There are, if you will, different heats (e.g. "white hot" steel is not > merely at a higher temp than "red hot" steel, but radiates (emits) > light at a different wavelength (which is why it's perceived as a > different color). > Heat is heat. The white hot steel is hotter than red hot and emits more energy since it is hotter. > Point is, radiation which heats can have different wavelengths. > > Roasting coffee with hot air relies upon heated air to transfer its > heat to beans into which it comes in contact priily by conduction, Actually convection is the mechanism for heating through contact with gasses. > not by direct radiation, whereas in radiant roasting the heat is > radiated directly from the radiant heat emitter to the beans (although > the air surrounding the beans also gets radiantly heated and in turn > can transfer its heat to the beans with which it comes into contact). > Air is a much better thermal insulator than conductor, especially when > it is dry (low humidity). > > Think about toasting a slice of bread only with hot air instead of > exposing the bread directly to heat radiated from heating elements. > > Coffee could be roasted radiantly in a vacuum (without _any_ air). > > Fluidized bed hot air roasters and other roaster designs which roast > coffee with hot air (e.g. Burns' Thermalo and Bersten's Belaroma) can > provide an even roast by contacting the hot air to all the beans and > all over the beans. But they are fairly inefficient because they rely > upon a poor thermal conductor (air) and thus need to put a lot of heat > into the air and pass a lot of air through and over the beans. > > > M "enjoying 'ondol' underfloor heating system in Korea"-bob |
wrote: >M-bob wrote in message news:<c19dqt1mo5@enews1.newsguy.com>... >> On Sat, 21 Feb 2004 09:28:36 GMT, "Coffee for Connoisseurs" >> <alanfrew@coffeeco.com.au> wrote: >> >> >>another newbie question: isn't heating beans with hot air heating by >> radiant >> >>heat? same for heat radiated by the glass/plastic/metal/etc roasting >> >>columns? >> > >> >Nothing newbie about that. Heat is heat >> >> >> Ah, but it's a bit more complicated than that, innit? ;> >> >> There are, if you will, different heats (e.g. "white hot" steel is not >> merely at a higher temp than "red hot" steel, but radiates (emits) >> light at a different wavelength (which is why it's perceived as a >> different color). >> > >Heat is heat. The white hot steel is hotter than red hot and emits >more energy since it is hotter. > You obscure the point. Heat is simply a transitional energy state. The white hot steel has a higher internal energy. > >> Point is, radiation which heats can have different wavelengths. >> >> Roasting coffee with hot air relies upon heated air to transfer its >> heat to beans into which it comes in contact priily by conduction, > >Actually convection is the mechanism for heating through contact with >gasses. > No, convection is the mechanism of heat transfer (transfer of energy away from the source) by mass motion _within_ a fluidic medium. A gas can't transfer energy into a solid (e.g. a roaster drum or a coffee bean) by convection, but can only transfer heat within itself by convection. There has to be conductive transfer at the gas-solid interface. Heat transfer (e.g. to a solid such as a coffee bean) through contact with a gas (e.g. hot air) involves the mechanism of conduction (transfer of energy by agitation between molecules), not convection. In a drum roaster, the drum might be heated by heat transfer from a hot gas, but such heat transfer would be via conduction of energy from the gas to the drum, not by convection. That is, although energy might be transferred through the gas by convection, the energy transfer mechanism from the gas to the solid drum is not convection but conduction. What Diedrich appear to be doing in their IR roasters is the same as in a bbq grill roaster using ceramic tiles heated by a gas flame, utilizing the heated tiles as radiant heat sources for heating the drum by radiant heat transfer in augmentation of or as an alternative to convective (through gas) and conductive (from gas to drum) heat transfer. In a hot air roaster, where the heated air is being forced to flow at a high velocity by a blower (and not by convection), there isn't really a convective heat transfer mechanism involved anymore than there is a radiant heat transfer mechanism, which is to say, only to a miniscule and practically negligible degree. Heating of both the air (by the heater) and coffee beans (by the hot air) is priily if not entirely via conduction. In an espresso machine having an e61 type grouphead heated by a thermosyphon loop, the heated water circulates in the thermosyphon loop due to convection. But the heated water convectively flowing in the loop heats the grouphead by conduction of heat from the water to the grouphead. not by convection. The thusly heated grouphead radiates heat as well as also conducting heat into the air which comes into contact with the exposed grouphead, and as the air is thereby heated it may convect the heat away. M "or did the guvmint rewrite the laws of thermodynamics?"-bob -- To e-mail, take out the "hippo." |
> A gas can't transfer energy into a solid (e.g. a roaster drum or a > coffee bean) by convection, but can only transfer heat within itself > by convection. There has to be conductive transfer at the gas-solid > interface. > > Heat transfer (e.g. to a solid such as a coffee bean) through contact > with a gas (e.g. hot air) involves the mechanism of conduction > (transfer of energy by agitation between molecules), not convection. > very interesting...I would have thought that a cold metal object suspended in a hot gas would heat up...caused me to google again: http://www.hukseflux.com/dictiona.htm |
wrote: ><M-bob> wrote in message news:c1dt5p0240j@enews3.newsguy.com... >> A gas can't transfer energy into a solid (e.g. a roaster drum or a >> coffee bean) by convection, but can only transfer heat within itself >> by convection. There has to be conductive transfer at the gas-solid >> interface. >> >> Heat transfer (e.g. to a solid such as a coffee bean) through contact >> with a gas (e.g. hot air) involves the mechanism of conduction >> (transfer of energy by agitation between molecules), not convection. >> >very interesting...I would have thought that a cold metal object suspended >in a hot gas would heat up...caused me to google again: > >http://www.hukseflux.com/dictiona.htm > > Here's a very basic explanation: http://www.school-for-champions.com/science/heattransfer.htm And here's some food for thought about cooling a hot cup of coffee: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/coocof2.html#c1 M "a whole new way to make iced coffee ; >"-bob -- To reply, delete the "hippo." |
news:403b1b67.24933984@enews.newsguy.com... > And here's some food for thought about cooling a hot cup of coffee: > > http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/coocof2.html#c1 > thanks, however, after looking at the details, I have decided to put the cup of hot coffee on my desk and wait for it to cool down enough for me to drink. |
wrote: >"M-bob" <cbob@hippo.newsguy.com> wrote in message >news:403b1b67.24933984@enews.newsguy.com... >> And here's some food for thought about cooling a hot cup of coffee: >> >> http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/coocof2.html#c1 >> >thanks, however, after looking at the details, I have decided to put the cup >of hot coffee on my desk and wait for it to cool down enough for me to >drink. or you could use that jet-powered kiwi beer cooler! :) |
Comments imbedded. Some stuff snipped > > No, convection is the mechanism of heat transfer (transfer of energy > away from the source) by mass motion _within_ a fluidic medium. The gas surrounding the coffee is such a medium. The motion is caused by the drum rotating, flow of gas out of the roaster by forced convection (fan) and possible flue temperature gradient (natural convection). You are right that the heat transfer from the gas to the solid bean occurs by conduction, but only within the boundary layer. From Frank Incropera and David P. DeWitt, "Fundamentals of Heat and Mass Transfer, Third Edition", John Wiley & Sons, NY, 1990, Page 6: "The convection heat transfer mode is comprised of two mechanisms. In addition to energy transfer due to random molecular motion (diffusiion), there is also energy being transferred by the bulk, or macroscopic, motion of the fluid. The fluid motion is associated with the fact that, at any instant, large numbers of molecules are moving collectively or as aggregates. Such motion, in the presence of a temperature gradient, will give rise to heat transfer. Because the molecules in the agregate retain their random motion, the total heat transfer is then due to a superposition of energy transport by the random motion of the molecules and by the bulk motion of the fluid. It is custoy to use the term convection when referring to this cumulative transport and the term advection when referring to transport due to bulk fluid motion." > > A gas can't transfer energy into a solid (e.g. a roaster drum or a > coffee bean) by convection, but can only transfer heat within itself > by convection. There has to be conductive transfer at the gas-solid > interface. Of course it can. The concept of convection heat transfer from fluids to solids is discussed in detail in the reference cited above. You are right that the transport of heat from the gas to the solid occurs by conduction thru the boundary layer, but this effect is considered part of the convection heat transfer process. > What Diedrich appear to be doing in their IR roasters is the same as > in a bbq grill roaster using ceramic tiles heated by a gas flame, > utilizing the heated tiles as radiant heat sources for heating the > drum by radiant heat transfer in augmentation of or as an alternative > to convective (through gas) and conductive (from gas to drum) heat > transfer. I reckon that radiant heating of the drum might be a very good way to go, particularly if the radiation source is shaped so that the drum sees the radiant surface uniformly and with the radiant surfaces close to "overhead". This would provide quite uniform heating, but would respond to changes pretty slowly - parhaps a problem if one wanted to change the amount of heat being added to the system. Maybe that's not too much of an issue. My roaster is heated by radiation and convection (3 circumferential electric heating elements and gas flow around the drum). The heating elements are pretty slow to respond, compared to a gas flame, but the drum is a real big heat sink and slows response big time. In my roaster, the drum seems to be the thing that dominates system dynamics. Changing the amount of coffee by +- 10% doesn't seem to hardly affect the speed at which the coffee heats. AFA the coffee is concerned, the issue of whether or not the coffee "sees" the radiant heat is moot. the coffee is heated by contact with the drum and by forced convection within the drum. I say forced convection because the drum is rotating and because the fan is forcing air through the roaster to some degree. > In a hot air roaster, where the heated air is being forced to flow at > a high velocity by a blower (and not by convection), there isn't > really a convective heat transfer mechanism involved anymore than > there is a radiant heat transfer mechanism, which is to say, only to a > miniscule and practically negligible degree. Heating of both the air > (by the heater) and coffee beans (by the hot air) is priily if not > entirely via conduction. Actually, by the reference that I cited, heat is added to the gas ALMOST COMPLETELY by forced convection and imparted to the coffee by the same mechanism. From page 7 of Incropera and DeWitt: "We speak of forced convection when the flow is caused by external means, such as by a fan, a pump, or atmospheric winds." The also state "In contrast, for free (0r natural) convection the flow is induced by buoyancy forces which arise from density differences caused by temperature variations in the fluid." > > In an espresso machine having an e61 type grouphead heated by a > thermosyphon loop, the heated water circulates in the thermosyphon > loop due to convection. But the heated water convectively flowing in > the loop heats the grouphead by conduction of heat from the water to > the grouphead. not by convection. The thusly heated grouphead radiates > heat as well as also conducting heat into the air which comes into > contact with the exposed grouphead, and as the air is thereby heated > it may convect the heat away. > > > M "or did the guvmint rewrite the laws of thermodynamics?"-bob Greg (hain't rewritten anything and I don't propose Pi = 3 either) |
> Mass Transfer, The Association Scientifique Internationale du Café http://www.asic-cafe.org/ has many articles about heat and coffee roasting that are right on point and would be better than a book on fundamentals. The articles are for members only, but some of you may qualify as members. I've often received articles free by writing to the authors. Dan |
wrote: >Hi: > >Comments imbedded. Some stuff snipped >> >> No, convection is the mechanism of heat transfer (transfer of energy >> away from the source) by mass motion _within_ a fluidic medium. > >The gas surrounding the coffee is such a medium. The motion is caused >by the drum rotating, flow of gas out of the roaster by forced >convection (fan) and possible flue temperature gradient (natural >convection). You are right that the heat transfer from the gas to the >solid bean occurs by conduction, but only within the boundary layer. > The term "forced convection" is kind of a misnomer imo, although it is so commonly used it has become accepted in reference to the assisted movement of heated gases and fluids (we patent convection oven technology for a client and commonly find the terminology "forced convection" being used in the art for describing fan-boosted circulation of the heated air). Think of "forced convection" as being like adding a circulation pump into an e61 thermosyphon loop. Classically, convection is the mass transfer of heat energy through mass fluidic flow due to a heat-induced density differential within a fluidic mass, and there is really no such thing as "forced" convection; rather there can be "assisted" or "augmented" convection where the flow of a fluidic medium undergoing convection is assisted or augmented by external means (e. g. a mechanically created pressure differential) other than the heat source. >From Frank Incropera and David P. DeWitt, "Fundamentals of Heat and >Mass Transfer, Third Edition", John Wiley & Sons, NY, 1990, Page 6: >"The convection heat transfer mode is comprised of two mechanisms. In >addition to energy transfer due to random molecular motion >(diffusiion), there is also energy being transferred by the bulk, or >macroscopic, motion of the fluid. The fluid motion is associated with >the fact that, at any instant, large numbers of molecules are moving >collectively or as aggregates. Such motion, in the presence of a >temperature gradient, will give rise to heat transfer. Because the >molecules in the agregate retain their random motion, the total heat >transfer is then due to a superposition of energy transport by the >random motion of the molecules and by the bulk motion of the fluid. >It is custoy to use the term convection when referring to this >cumulative transport and the term advection when referring to >transport due to bulk fluid motion." > Without benefit of full text context, it sounds like what they are describing is only the transport of heat within a fluidic mass, not how a fluid transfers heat to a solid. On a more technical level, it really involves quantum physics concepts about how the atoms/molecules of the fluid transfer their energy, which is what is actually occurring at the barrier layer between a heated gas and a solid to be heated thereby. >> >> A gas can't transfer energy into a solid (e.g. a roaster drum or a >> coffee bean) by convection, but can only transfer heat within itself >> by convection. There has to be conductive transfer at the gas-solid >> interface. > >Of course it can. The concept of convection heat transfer from fluids >to solids is discussed in detail in the reference cited above. You >are right that the transport of heat from the gas to the solid occurs >by conduction thru the boundary layer, but this effect is considered >part of the convection heat transfer process. > As mentioned, I don't read anything in the quoted text referring to convective heat transfer from a fluid to a solid, only about how heat is transported through/by a fluidic mass. The conductive transfer of heat within a fluid (what the authors term "diffusion") due to molecular interactions within the fluid might be lumped in with the mass movement of the heated fluid and considered by the authors to be included in the convective heat transfer within the fluidic mass, but conduction of energy thru a boundary layer (from the fluid to a solid or vice versa) is not convection, it's conduction. >> What Diedrich appear to be doing in their IR roasters is the same as >> in a bbq grill roaster using ceramic tiles heated by a gas flame, >> utilizing the heated tiles as radiant heat sources for heating the >> drum by radiant heat transfer in augmentation of or as an alternative >> to convective (through gas) and conductive (from gas to drum) heat >> transfer. > > >I reckon that radiant heating of the drum might be a very good way to >go, particularly if the radiation source is shaped so that the drum >sees the radiant surface uniformly and with the radiant surfaces close >to "overhead". This would provide quite uniform heating, but would >respond to changes pretty slowly - parhaps a problem if one wanted to >change the amount of heat being added to the system. Maybe that's not >too much of an issue. My roaster is heated by radiation and >convection (3 circumferential electric heating elements and gas flow >around the drum). The heating elements are pretty slow to respond, >compared to a gas flame, but the drum is a real big heat sink and >slows response big time. In my roaster, the drum seems to be the >thing that dominates system dynamics. Changing the amount of coffee by >+- 10% doesn't seem to hardly affect the speed at which the coffee >heats. AFA the coffee is concerned, the issue of whether or not the >coffee "sees" the radiant heat is moot. the coffee is heated by >contact with the drum and by forced convection within the drum. I say >forced convection because the drum is rotating and because the fan is >forcing air through the roaster to some degree. > The hot drum is a good conductor and also operates, to a lesser extent, as a radiator, so it heats priily through conduction by direct contact (where beans come into contact with the drum) and also irradiates the bean surfaces exposed to the drum. The heated air can come into contact with more of the bean surface, especially if it can flow interstitially between the beans, but forced air flow is necessary to bring enough of the hot air into contact with the beans. Convection (whether it be natural or forced) is only how the heat in the air gets to the beans, not how the air transfers energy to the beans. >> In a hot air roaster, where the heated air is being forced to flow at >> a high velocity by a blower (and not by convection), there isn't >> really a convective heat transfer mechanism involved anymore than >> there is a radiant heat transfer mechanism, which is to say, only to a >> miniscule and practically negligible degree. Heating of both the air >> (by the heater) and coffee beans (by the hot air) is priily if not >> entirely via conduction. > >Actually, by the reference that I cited, heat is added to the gas >ALMOST COMPLETELY by forced convection and imparted to the coffee by >the same mechanism. From page 7 of Incropera and DeWitt: "We speak >of forced convection when the flow is caused by external means, such >as by a fan, a pump, or atmospheric winds." The also state "In >contrast, for free (0r natural) convection the flow is induced by >buoyancy forces which arise from density differences caused by >temperature variations in the fluid." > Again, I read the quoted text as describing only how heat is transported though the gas, but don't find any explanation referring to heat transfer from the gas to a solid by convection. "Forced convection" only makes the heated gas flow more than it would under "natural convection", not transfer its heat to a solid. Seems to me, atmospheric winds are about as natural as "natural convection" gets. ; > M "what air velocity would we need for frictional heating?"-bob -- To e-mail, take out the "hippo." |
> M "what air velocity would we need for frictional heating?"-bob Don't know the answer, but IIRC, frictional heating increases as the cube of velocity. Do you represent any clients who wish to patent a hypersonic fluid-bed roaster? :-) -- -Andy S. picture page: http://tinyurl.com/eh0x |
schecter@rochester.rr.com says... > M-bob wrote: > > M "what air velocity would we need for frictional heating?"-bob > > Don't know the answer, but IIRC, frictional heating increases as the cube of > velocity. Do you represent any clients who wish to patent a hypersonic fluid-bed > roaster? :-) > That also grinds for Turkish while roasting? Cool. Ted -- Please take the 'thisgetsremoved' out of the email before emailing me. |
<tnjsimpson1@comTHISGETSREMOVEDcast.net > wrote: >In article <W7c%b.84457$n62.11158@twister.nyroc.rr.com>, >schecter@rochester.rr.com says... >> M-bob wrote: >> > M "what air velocity would we need for frictional heating?"-bob >> >> Don't know the answer, but IIRC, frictional heating increases as the cube of >> velocity. Do you represent any clients who wish to patent a hypersonic fluid-bed >> roaster? :-) >> >That also grinds for Turkish while roasting? > and cools beer. |
"Barry Jarrett" <barry@rileys-coffee.com > wrote in message news:plqq309e9got5ag8opetc0ervkirjh888o@4ax.com... > On Wed, 25 Feb 2004 21:33:54 -0500, Simpson > <tnjsimpson1@comTHISGETSREMOVEDcast.net> wrote: > > >In article <W7c%b.84457$n62.11158@twister.nyroc.rr.com>, > >schecter@rochester.rr.com says... > >> M-bob wrote: > >> > M "what air velocity would we need for frictional heating?"-bob > >> > >> Don't know the answer, but IIRC, frictional heating increases as the cube of > >> velocity. Do you represent any clients who wish to patent a hypersonic fluid-bed > >> roaster? :-) > >> > >That also grinds for Turkish while roasting? > > > > and cools beer. > > mmmmm beer . . . Richard "uuuurp" F |
> "Barry Jarrett" <barry@rileys-coffee.com> wrote in message > news:plqq309e9got5ag8opetc0ervkirjh888o@4ax.com... > > On Wed, 25 Feb 2004 21:33:54 -0500, Simpson > > <tnjsimpson1@comTHISGETSREMOVEDcast.net> wrote: > > > > >In article <W7c%b.84457$n62.11158@twister.nyroc.rr.com>, > > >schecter@rochester.rr.com says... > > >> M-bob wrote: > > >> > M "what air velocity would we need for frictional heating?"-bob > > >> > > >> Don't know the answer, but IIRC, frictional heating increases as the > cube of > > >> velocity. Do you represent any clients who wish to patent a hypersonic > fluid-bed > > >> roaster? :-) > > >> > > >That also grinds for Turkish while roasting? > > > > > > > and cools beer. > > > > > > mmmmm beer . . . > > Richard "uuuurp" F Got me to thinking... I may have to put a "donate to your local Roastmaster's Beer Fund" button on my order page. Well, it works for politicians when I file my taxes online, anyhow. As for the design; are we talking a micro-turbine powered grinder? Couldn't you then bleed off some of the post-grind turbine exhaust for for brewing and frothing? Seems like 19 bars would be pretty easy to accomodate. Might need to retrain some baristas, tho! :) -- www.coudycoffee.com - I'm only serious about coffee |
> On 24 Feb 2004 09:00:27 -0800, gregory.scace@nist.gov (Greg Scace) > wrote: > > >Hi: > > > >Comments imbedded again. Some stuff snipped > > > > The term "forced convection" is kind of a misnomer imo, although it is > so commonly used it has become accepted in reference to the assisted > movement of heated gases and fluids (we patent convection oven > technology for a client and commonly find the terminology "forced > convection" being used in the art for describing fan-boosted > circulation of the heated air). > > Think of "forced convection" as being like adding a circulation pump > into an e61 thermosyphon loop. > Yes. > Classically, convection is the mass transfer of heat energy through > mass fluidic flow due to a heat-induced density differential within a > fluidic mass, and there is really no such thing as "forced" > convection; rather there can be "assisted" or "augmented" convection > where the flow of a fluidic medium undergoing convection is assisted > or augmented by external means (e. g. a mechanically created pressure > differential) other than the heat source. Yes. I recall that all convection heat transfer problems are handled in the same basic way, whether "forced" or "natural". > > >From Frank Incropera and David P. DeWitt, "Fundamentals of Heat and > >Mass Transfer, Third Edition", John Wiley & Sons, NY, 1990, Page 6: > >"The convection heat transfer mode is comprised of two mechanisms. In > >addition to energy transfer due to random molecular motion > >(diffusiion), there is also energy being transferred by the bulk, or > >macroscopic, motion of the fluid. The fluid motion is associated with > >the fact that, at any instant, large numbers of molecules are moving > >collectively or as aggregates. Such motion, in the presence of a > >temperature gradient, will give rise to heat transfer. Because the > >molecules in the agregate retain their random motion, the total heat > >transfer is then due to a superposition of energy transport by the > >random motion of the molecules and by the bulk motion of the fluid. > >It is custoy to use the term convection when referring to this > >cumulative transport and the term advection when referring to > >transport due to bulk fluid motion." > > > > Without benefit of full text context, it sounds like what they are > describing is only the transport of heat within a fluidic mass, not > how a fluid transfers heat to a solid. Actually, later in their book, they discuss heat transfer from the gas to the solid, then present some correlations for obtaining heat transfer correlations for a variety of fully developed flow conditions (laminar to turbulent). I think that the book, while very useful for me, is a more practical engineering textbook and a more in depth study of convection specifically would deal with quantum physics. I s'pose I could ask Dave DeWitt. He's actually a couple floors below me in the same building. It's kind of handy here to have such experts floating around. > > On a more technical level, it really involves quantum physics concepts > about how the atoms/molecules of the fluid transfer their energy, > which is what is actually occurring at the barrier layer between a > heated gas and a solid to be heated thereby. > > >> > >> A gas can't transfer energy into a solid (e.g. a roaster drum or a > >> coffee bean) by convection, but can only transfer heat within itself > >> by convection. There has to be conductive transfer at the gas-solid > >> interface. > > > >Of course it can. The concept of convection heat transfer from fluids > >to solids is discussed in detail in the reference cited above. You > >are right that the transport of heat from the gas to the solid occurs > >by conduction thru the boundary layer, but this effect is considered > >part of the convection heat transfer process. > > > > As mentioned, I don't read anything in the quoted text referring to > convective heat transfer from a fluid to a solid, only about how heat > is transported through/by a fluidic mass. The correlations in the book lump that in when finding heat transfer coefficients. > > The conductive transfer of heat within a fluid (what the authors term > "diffusion") due to molecular interactions within the fluid might be > lumped in with the mass movement of the heated fluid and considered by > the authors to be included in the convective heat transfer within the > fluidic mass, but conduction of energy thru a boundary layer (from the > fluid to a solid or vice versa) is not convection, it's conduction. > > >> What Diedrich appear to be doing in their IR roasters is the same as > >> in a bbq grill roaster using ceramic tiles heated by a gas flame, > >> utilizing the heated tiles as radiant heat sources for heating the > >> drum by radiant heat transfer in augmentation of or as an alternative > >> to convective (through gas) and conductive (from gas to drum) heat > >> transfer. > > > > > >I reckon that radiant heating of the drum might be a very good way to > >go, particularly if the radiation source is shaped so that the drum > >sees the radiant surface uniformly and with the radiant surfaces close > >to "overhead". This would provide quite uniform heating, but would > >respond to changes pretty slowly - parhaps a problem if one wanted to > >change the amount of heat being added to the system. Maybe that's not > >too much of an issue. My roaster is heated by radiation and > >convection (3 circumferential electric heating elements and gas flow > >around the drum). The heating elements are pretty slow to respond, > >compared to a gas flame, but the drum is a real big heat sink and > >slows response big time. In my roaster, the drum seems to be the > >thing that dominates system dynamics. Changing the amount of coffee by > >+- 10% doesn't seem to hardly affect the speed at which the coffee > >heats. AFA the coffee is concerned, the issue of whether or not the > >coffee "sees" the radiant heat is moot. the coffee is heated by > >contact with the drum and by forced convection within the drum. I say > >forced convection because the drum is rotating and because the fan is > >forcing air through the roaster to some degree. > > > > The hot drum is a good conductor and also operates, to a lesser > extent, as a radiator, so it heats priily through conduction by > direct contact (where beans come into contact with the drum) and also > irradiates the bean surfaces exposed to the drum. The heated air can > come into contact with more of the bean surface, especially if it can > flow interstitially between the beans, but forced air flow is > necessary to bring enough of the hot air into contact with the beans. > Convection (whether it be natural or forced) is only how the heat in > the air gets to the beans, not how the air transfers energy to the > beans. That's my take as well. I suspect that radiation between the drum and the beans is a pretty small component of the entire heat transfer process since the heat transferred is a function of the difference in absolute temperatures raised to the 4th power. Since the temps are pretty close, it can't be much heat. > > >> In a hot air roaster, where the heated air is being forced to flow at > >> a high velocity by a blower (and not by convection), there isn't > >> really a convective heat transfer mechanism involved anymore than > >> there is a radiant heat transfer mechanism, which is to say, only to a > >> miniscule and practically negligible degree. Heating of both the air > >> (by the heater) and coffee beans (by the hot air) is priily if not > >> entirely via conduction. > > > >Actually, by the reference that I cited, heat is added to the gas > >ALMOST COMPLETELY by forced convection and imparted to the coffee by > >the same mechanism. From page 7 of Incropera and DeWitt: "We speak > >of forced convection when the flow is caused by external means, such > >as by a fan, a pump, or atmospheric winds." The also state "In > >contrast, for free (0r natural) convection the flow is induced by > >buoyancy forces which arise from density differences caused by > >temperature variations in the fluid." > > > > Again, I read the quoted text as describing only how heat is > transported though the gas, but don't find any explanation referring > to heat transfer from the gas to a solid by convection. "Forced > convection" only makes the heated gas flow more than it would under > "natural convection", not transfer its heat to a solid. > > Seems to me, atmospheric winds are about as natural as "natural > convection" gets. ;> And arguably linked ultimately to buoyant forces. > > > M "what air velocity would we need for frictional heating?"-bob Greg (dunno. You tell me) Scace |
-- *********************************************** Ed Needham To Absurdity and Beyond! "Nunc Aut Nunquam" homeroaster ... d.o.t ... com *********************************************** <M-bob > wrote in message news:c19dqt1mo5@enews1.newsguy.com... |
different drum roasters apply heat in different configurations. A thick walled cast drum roaster will perform differently if aggressive air convection is added and will produce a different roast than a steel walled roaster. A thin walled perforated stainless steel drum, different still. Heat is applied in each drum in different ways. Some by air current, some by contact with the drum, some by direct radiant heat from the drum or heat source. Each heat source contacts the bean differently and in different proportions for each roaster causing changes in the cup. Even rotation speed affects which heat source affects the bean more. I'm out of my league in this conversation, but roasting five pound batches at home using a thin walled, perforated stainless steel drum allows me to see how even small changes in my drum setup affect the cup. I improved my roasts by shielding the drum from direct flame. I am in the process of adding a source of blown-in heated air so I can use that as a roasting variable. Using a solid wall drum in my roaster (I have both) brings out different qualities in the roast than using my perfed drum. Had to get my 2 cents in. I'll retreat now and listen to the pros. -- *********************************************** Ed Needham To Absurdity and Beyond! "Nunc Aut Nunquam" homeroaster ... d.o.t ... com *********************************************** "Coffee for Connoisseurs" <alanfrew@coffeeco.com.au > wrote in message news:8xFZb.69461$Wa.26742@news-server.bigpond.net.au... <SNIP > |