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Date: 23 Jun 2006 17:17:36
From: Ken Fox
Subject: The Impact of Frothing on HX Temperature Stability
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I'd always assumed that once you start frothing milk, you can kiss goodbye
the temperature stability of your heat exchanger. This only makes sense,
afterall, given all the heat that goes out through the steam wand. I'd
never bothered to even look at shot temps while frothing with my Scace
Device. Although I love my Fluke, having to type data into a spreadsheet,
and then transfer it into a graphing program is a real PITA, and I wasn't
willing to give Fluke another $150 for their rip off downloading software.
Omega has a cheaper (and deservedly so, I'm afraid to say) datalogger, the
HH506RA, which comes with poor quality downloading software that *works*,
and the whole package costs about the same as the Fluke software alone. I
decided to buy one because I collect data from my roaster and my espresso
machines regularly and typing the numbers in just sets off my tennis elbow
(I don't play tennis, but I got it anyway).
I decided to do 5 separate "walk up shots" on my PID'd Cimbali Junior D1
rotary machine, 3 years old, modified with the afforementioned PID and a
delay timer that allows 3+ bar preinfusion followed by a full pressure (9
bar) extraction. My machine can froth enough milk for a cappucino in about
8 seconds but I decided to set up the experiment with 15 seconds of frothing
as some may be slower and/or want to froth more milk.
http://img.photobucket.com/albums/v429/kfoxfoie/JrD1PreinfusionHeatOn.jpg
This graph was obtained by flushing the group 50ml (my standard and
programmed flush), then pulling a 30 second simulated shot with the Scace
Device and Omega HH506RA datalogger. At the midpoint, 15 seconds into the
shots, I opened up the steam valve all the way, and left it open for the
remainder of the shot. Each shot was separated by more than 10 minutes, up
to an hour and a half in one case.
http://img.photobucket.com/albums/v429/kfoxfoie/JuniorD10minuteorMoreWalkUpFrothing.jpg
What you see here is essentially no impact at all of frothing on shot
temperature on any of the five datalogged shots. I don't believe that this
finding comes from the presence of the PID in this machine, rather I think
it is the inherent design of Cimbali heat exchanger machines. How
transferable this information is to other heat exchanger designs made by
other manufacturers, I do not know, and hope that others will test.
ken
p.s. this is crossposted on home-barista.com; please don't respond in both
threads, or you will annoy the proprietor of said website:-)
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Date: 23 Jun 2006 21:26:04
From: Jack Denver
Subject: Re: The Impact of Frothing on HX Temperature Stability
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This is good news but not surprising. On the readout of my PID, steaming
enough milk for a couple of caps drops the boiler temp a few degrees (maybe
down to 118C from the 122C setpoint) but within a short time after steaming
is done it is restabilized back at the setpoint. If you figure out the
amount of water that gets vaporized to steam a few ounces of milk, it is
only a few grams, so not all that much heat is lost from the system
(compared with say pulling a cup of hot water out the water wand and having
it replaced by the autofill - test that one if you want to see temps bounce
around). Since the HX would "see" very little variation in temperature, it
stands to reason that shot quality would not be affected. In a commercial
setting where you are steaming gallons of milk for lattes, the situation
might be different.
"Ken Fox" <morceaudemerdeThisMerdeGoes@hotmail.com > wrote in message
news:4g3b48F1l86rgU1@individual.net...
> I'd always assumed that once you start frothing milk, you can kiss goodbye
> the temperature stability of your heat exchanger. This only makes sense,
> afterall, given all the heat that goes out through the steam wand. I'd
> never bothered to even look at shot temps while frothing with my Scace
> Device. Although I love my Fluke, having to type data into a spreadsheet,
> and then transfer it into a graphing program is a real PITA, and I wasn't
> willing to give Fluke another $150 for their rip off downloading software.
>
> Omega has a cheaper (and deservedly so, I'm afraid to say) datalogger, the
> HH506RA, which comes with poor quality downloading software that *works*,
> and the whole package costs about the same as the Fluke software alone. I
> decided to buy one because I collect data from my roaster and my espresso
> machines regularly and typing the numbers in just sets off my tennis elbow
> (I don't play tennis, but I got it anyway).
>
> I decided to do 5 separate "walk up shots" on my PID'd Cimbali Junior D1
> rotary machine, 3 years old, modified with the afforementioned PID and a
> delay timer that allows 3+ bar preinfusion followed by a full pressure (9
> bar) extraction. My machine can froth enough milk for a cappucino in
> about 8 seconds but I decided to set up the experiment with 15 seconds of
> frothing as some may be slower and/or want to froth more milk.
>
> http://img.photobucket.com/albums/v429/kfoxfoie/JrD1PreinfusionHeatOn.jpg
>
> This graph was obtained by flushing the group 50ml (my standard and
> programmed flush), then pulling a 30 second simulated shot with the Scace
> Device and Omega HH506RA datalogger. At the midpoint, 15 seconds into the
> shots, I opened up the steam valve all the way, and left it open for the
> remainder of the shot. Each shot was separated by more than 10 minutes,
> up to an hour and a half in one case.
>
> http://img.photobucket.com/albums/v429/kfoxfoie/JuniorD10minuteorMoreWalkUpFrothing.jpg
>
> What you see here is essentially no impact at all of frothing on shot
> temperature on any of the five datalogged shots. I don't believe that
> this finding comes from the presence of the PID in this machine, rather I
> think it is the inherent design of Cimbali heat exchanger machines. How
> transferable this information is to other heat exchanger designs made by
> other manufacturers, I do not know, and hope that others will test.
>
> ken
> p.s. this is crossposted on home-barista.com; please don't respond in both
> threads, or you will annoy the proprietor of said website:-)
>
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Date: 23 Jun 2006 20:22:10
From: Ken Fox
Subject: Re: The Impact of Frothing on HX Temperature Stability
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"Jack Denver" <nunuvyer@netscape.net > wrote in message
news:_LWdnTDClMkwCQHZnZ2dnUVZ_q-dnZ2d@comcast.com...
> This is good news but not surprising. On the readout of my PID, steaming
> enough milk for a couple of caps drops the boiler temp a few degrees
> (maybe down to 118C from the 122C setpoint) but within a short time after
> steaming is done it is restabilized back at the setpoint. If you figure
> out the amount of water that gets vaporized to steam a few ounces of milk,
> it is only a few grams, so not all that much heat is lost from the system
> (compared with say pulling a cup of hot water out the water wand and
> having it replaced by the autofill - test that one if you want to see
> temps bounce around). Since the HX would "see" very little variation in
> temperature, it stands to reason that shot quality would not be affected.
> In a commercial setting where you are steaming gallons of milk for lattes,
> the situation might be different.
>
Perhaps this seems straightforward to you (and at least one other person who
sent me an email), but I think the reality is far more complicated. Leaving
the frothing wand open for 15 seconds on a large boiler is going to deplete
lots of heat; I know this because my PID probe, which is in the steam column
of my boiler, feeds a drop of about 10 degrees F into the PID readout by the
time I'm done frothing, and that is with an 8-10 second froth, not a 15
second froth. Depending upon where one's probe is located, perhaps there is
a difference in what one would see with a probe located in the water column.
The heat exchanger in my machine holds between 4 and 6 ounces of water in
actual use; I've been told by a Cimbali tech that after the machine has been
operating for several hours steam displaces some of the water and you are
down to the 4 oz. figure. If 50ml (close to 2 oz) is used in the flush, and
then another 75 ml (counting what is left in the puck) is expended to make a
double shot, all within maybe 40 seconds (flush and shotmaking), the heat
exchanger in even my machine (with a larger HEX than most) is going to be
recycled and reheated all within this period. Add this to the loss of heat
as steam and you have a lot of heat loss to be dealt with by a 110v. heating
circuit.
As pointed out by an email I received, steaming will increase the amount of
time one must take between drinks in order for the system to recover,
compared to simple straight shots. I have no doubt of this. At the same
time, frothing milk means you are making a milk drink and this is going to
take more time to assemble than simply taking out a demitasse cup and
serving it to someone; the extra 30 second or whatever recovery time is
probably covered pretty much by the time you will take putting the drink
together before you are ready to make the next one.
I'm surprised that there isn't more curiosity about this issue; on the one
hand I'd be the first to say that temperature stability of the espresso shot
itself is probably less important if the shot goes into a milk drink which
will mask a lot of quality issues in the espresso that would be more obvious
in a straight shot. At the same time, seeing that the whole system is not
perturbed all that much means that the NEXT shot, if it is a straight shot,
has a pretty good chance at being delivered at the temperature you would
want to make it at.
ken
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