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Date: 05 Mar 2007 12:33:07
From: gscace
Subject: Pressure Profiling Update 1
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Here's an update on the last few days of progress with brew pressure
profiling. First, I have a greatly enhanced tolerance for caffeine.
Besides that...
I've fooled around with profiles a bit. What I've learned is that a
person can drive himself half crazy if he has a very tuneable system
and no practical knowledge on which to draw. If he's half crazy to
begin with, the combination produces someone who is full-crazy. This
can be bad. I've also formed the opinion that there is something to
soaking the coffee cake at a low pressure and then ramping the
pressure up. Right now the pre-infusion cycle is set to 2 bar for 3
seconds, with a subsequent ramp to from 2 bar to 9 bar over a 4 second
interval. Liquid coffee appears evenly over the perforations on the
bottom of a brew basket just as the pressure begins its rapid rise. I
like this preinfusion cycle over a straight line rampup in pressure
for 7 seconds from startup to 9 bar because it produced more crema in
the limited pairs of shots I brewed alternating between straight line
ramp, and low pressure wetting with faster ramp.
Those who have observed many shots worth of extractions squeezed
through a bottomless portafilter are familiar with the cone of coffee
that hangs off the brew basket during the "meat" of the extraction.
The liquid appears quite viscous for a time, hanging off the bottom in
a hyperbolic shape, eventually thinning out and becoming lighter in
color at the end of the extraction. When this happens the hyberbolic-
shaped cone seems to 'withdraw" toward the brew basket as the fluid
gets runnier. It seemed reasonable to try to control the volume flow
rate of the extraction toward the end of the brew cycle in an effort
to make the liquid flow more orderly, and maybe more viscous as well.
So I programmed various downslopes in pressure at the end of the brew
cycle, arriving at a profile that includes the previously described
pre-infusion cycle, a constant pressure period of 7 seconds at 9 bar,
then a downslope for 20 seconds to 6.5 bar. The flow rate of liquid
in the downslope is reduced when compared to the constant pressure
case, and the color is darker at the end of the extraction.
Extractions seem to take a little longer, using the visual clues that
I'm used to using as a guide for when to stop brewing.
One thing that I've learned for sure is that there is a fundamental
difference between what I'm doing with the profiling pump, and how
pressure profiling works in a lever machine. In a lever machine, the
spring-loaded piston drives water through the cake. The pressure of
the water is determined volumetrically. By this I mean that the
pressure is dependent on the position of the piston, which means that
pressure is directly related to how much water has been forced through
the coffee. In the system that I am investigating, the pressure is
related to elapsed time. One could grind very coarsely and push a
whole lot of water through the cake in 7 seconds, yet at 7 seconds
elapsed time the pressure will have just peaked at 9 bars. On the
other hand, if the coffee is extremely coarse in the lever machine,
then at 7 seconds elapsed time, the pressure will be much reduced
compared to a proper extraction. And the amount of water
corresponding to that specific pressure value (and forced through the
coffee) will be identical to the case in which the coffee grinds are
correctly sized. In the system that I'm using, it appears that the
time-based profile has to get matched to the grinds size so that the
pressures vary in time appropriately within the extraction (I dunno if
I know what "vary appropriately" completely means yet, but I maybe
know a little more than I did last week). I'm finding out that not
only am I matching grinder settings to collected volume, viscosity,
color and crema, I'm matching the grinder settings to the pressure
profile as well. This adds another parameter to the mix, but it's not
unmanageable and I'm getting more comfortable with it.
I've also learned that there are pressure issues at play in all pump-
driven espresso machines that affect orderly pressure ramping at the
start of brewing and may or may not have a small effect on coffee
taste. Relatively cold water is pumped to the brewing water reservoir
(boiler or heat exchanger) in espresso machines without feedwater pre-
heat. The water is heated within the reservoir, and the pressure
within the reservoir increases due to thermal expansion of the liquid
water. When the group solenoid is activated, the water pressure is
instantly released and a small spurt of water flows onto the coffee.
I've reduced the effect of this to a large degree, but I haven't
eliminated it entirely. I think that the way to almost completely
eliminate it might be to install a normally open solenoid-actuated
valve inline with the pressure-relief line from the brew boiler to the
pressure-relief valve in the drain box. I would connect the valve to
the pump circuit, so that the valve would close when the pump is
activated. Rather than adjust the pressure-relief valve to the
recommended 12 bar, I would adjust it to crack open at 2 bars. When
adjusted in this way, the boiler would maintain only 2 bars pressure
when idling. The solenoid valve would close on pump actuation,
allowing pressure to build to brewing pressure levels. At the end of
the brewing cycle (pump de-activation), the solenoid valve would re-
open, again limiting boiler pressure to a low level.
WRT taste - I've been mostly investigating a lot of the physical
effects of variable pressure on the extraction, and learning about how
to do it. I've been doing this because varying pressure doesn't make
the coffee suck. It tastes good enough to warrant spending the time
learning about the system, and I am enjoying the taste and the
learning process. Yesterday I pulled a couple of shots for a third
party both with the profile described above, and without any profile
at all. There was a difference in taste. Next weekend I hope to do
some blind testing in which I brew shots for folks with both profiled
and non-profiled pressure, seeking to learn if the difference can be
reliably detected and which shots are preferred.
-Greg Scace
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Date: 06 Mar 2007 11:50:55
From: gscace
Subject: Re: Pressure Profiling Update 1
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On 6, 2:02 pm, "DavidMLewis" <DavidMLe...@mac.com > wrote:
> On 5, 12:33 pm, "gscace" <gregory.sc...@nist.gov> wrote:> I've also formed the opinion that there is something to
> > soaking the coffee cake at a low pressure and then ramping the
> > pressure up. Right now the pre-infusion cycle is set to 2 bar for 3
> > seconds, with a subsequent ramp to from 2 bar to 9 bar over a 4 second
> > interval. Liquid coffee appears evenly over the perforations on the
> > bottom of a brew basket just as the pressure begins its rapid rise. I
> > like this preinfusion cycle over a straight line rampup in pressure
> > for 7 seconds from startup to 9 bar because it produced more crema in
> > the limited pairs of shots I brewed alternating between straight line
> > ramp, and low pressure wetting with faster ramp.
>
> Very nice work, Greg! I'm curious, though, about how this fits in with
> the stuff that Jim Schulman and Ken Fox published here last year. If I
> recall correctly, they found that a pre-infusion at less than 3 bar
> didn't completely saturate the puck, but only wet the outside of it.
> They determined that, if I recall correctly, by just pre-infusing,
> then knocking the pucks out and cutting them in half. Does your system
> behave differently?
>
> Best,
> David
Thanks for bringing that up. I'll have to revisit their work and I'll
try to cut some cakes apart to see what's going on at 3 secs into the
pressure buildup. The answer is that I really don't know if my stuff
is different, but I presume not really at the early stages of the
extraction and I should see the same thing as they did.
-Greg
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Date: 07 Mar 2007 08:42:08
From: Ken Fox
Subject: Re: Pressure Profiling Update 1
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"gscace" <gregory.scace@nist.gov > wrote in message
news:1173210655.697711.143610@t69g2000cwt.googlegroups.com...
> On 6, 2:02 pm, "DavidMLewis" <DavidMLe...@mac.com> wrote:
>> On 5, 12:33 pm, "gscace" <gregory.sc...@nist.gov> wrote:> I've also
>> formed the opinion that there is something to
>> > soaking the coffee cake at a low pressure and then ramping the
>> > pressure up. Right now the pre-infusion cycle is set to 2 bar for 3
>> > seconds, with a subsequent ramp to from 2 bar to 9 bar over a 4 second
>> > interval. Liquid coffee appears evenly over the perforations on the
>> > bottom of a brew basket just as the pressure begins its rapid rise. I
>> > like this preinfusion cycle over a straight line rampup in pressure
>> > for 7 seconds from startup to 9 bar because it produced more crema in
>> > the limited pairs of shots I brewed alternating between straight line
>> > ramp, and low pressure wetting with faster ramp.
>>
>> Very nice work, Greg! I'm curious, though, about how this fits in with
>> the stuff that Jim Schulman and Ken Fox published here last year. If I
>> recall correctly, they found that a pre-infusion at less than 3 bar
>> didn't completely saturate the puck, but only wet the outside of it.
>> They determined that, if I recall correctly, by just pre-infusing,
>> then knocking the pucks out and cutting them in half. Does your system
>> behave differently?
>>
>> Best,
>> David
>
> Thanks for bringing that up. I'll have to revisit their work and I'll
> try to cut some cakes apart to see what's going on at 3 secs into the
> pressure buildup. The answer is that I really don't know if my stuff
> is different, but I presume not really at the early stages of the
> extraction and I should see the same thing as they did.
>
> -Greg
>
What a difference a year makes:-)
Jim has made some observations on extractions and pucks in his recent work
dealing with dosing that are probably relevant. When we did our study on
preinfusion last year, I was (and still am) updosing my baskets with around
18g in a double. Jim's recent work has involved dosing considerably less
coffee into the portafilter. If I understand emails he's sent to me
correctly, channeling is considerably less likely to occur if one doses 12
or 14g vs. 16 or 18g in a double. One would have to assume that more is
going in with water flow and puck saturation during infusion and preinfusion
than simply whether channeling occurs or not.
My impression is that all of this stuff, including the dynamics of puck
saturation and at what preinfusion pressure, is going to be highly dependent
on dosing and the grind needed to achieve certain shotmaking parameters over
time (e.g. shot volume produced over X period of time).
The sumy statement is that we found a need for 3 bar+ with 18g in a
double basket, with the coffee ground to produce 1.25-1.5oz over roughly 30
seconds time. If Greg doses and grinds differently, I think the study on
puck wetting would need to be revisited to determine whether in fact 3 bar,
or some other value, is needed.
ken
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Date: 12 Mar 2007 14:44:37
From: jim schulman
Subject: Re: Pressure Profiling Update 1
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On Wed, 7 2007 08:42:08 -0700, "Ken Fox"
<morceaudemerdeThisMerdeGoes@hotmail.com > wrote:
>What a difference a year makes:-)
>
>Jim has made some observations on extractions and pucks in his recent work
>dealing with dosing that are probably relevant. When we did our study on
>preinfusion last year, I was (and still am) updosing my baskets with around
>18g in a double. Jim's recent work has involved dosing considerably less
>coffee into the portafilter. If I understand emails he's sent to me
>correctly, channeling is considerably less likely to occur if one doses 12
>or 14g vs. 16 or 18g in a double
Most of my recent work has been about the relation of dosing to solids
extraction.
However, both I and everyone else who tried low doses noticed two
things -- the dwell time is longer with doses that do not touch the
showerscreen compared to those that do. The puck turns into a paste
when there's room enough so it cannot expand into the screen. This
paste is self repairing, and makes chanelling almost impossible. The
casual Italian approach to levelling and tamping is based on filling
deep baskets with not too much coffee.
I think the pre-infusion part of Greg's work is of far less interest
than the profiling during the shot. If one wants to do shots where the
puck swells into the screen and remains relatively dry, there is no
doubt that some sort of preinfusion is going to make life easier.
Since various preinfusion mechanisms on pump machines have been
available for the past 45 years, there's already more than enough
anecdotal evidence that beyond this mechanical benefit, it has only
minir influence on mouthfeel or taste.
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Date: 16 Mar 2007 11:02:46
From: Neal Reid
Subject: Dose / sweetness relation
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In article <htabv29jhjcol3p3sti45o1une1ap6igdi@4ax.com >,
jim schulman <jim_schulman@ameritech.net > wrote:
> However, both I and everyone else who tried low doses noticed two
> things -- the dwell time is longer with doses that do not touch the
> showerscreen compared to those that do. The puck turns into a paste
> when there's room enough so it cannot expand into the screen. This
> paste is self repairing, and makes chanelling almost impossible.
I've been trying to compose a query for a couple of days; Jim's
post prompts me to DO it rather than think about it...
For reasons beyond the scope of the query, I recently decided to
try 15 gm shots, slightly more finely ground than my normal 16 gm
doubles - all else held constant. (the basket is a standard
Rancillo double - won't hold much more than 16 and still lock into
my machine)
I have not noticed a dwell time difference - but I HAVE
consistently noticed a sweeter drink. Some of the
back-of-the-mouth complexity is gone (likely still there but
overwhelmed by the increased sweetness) but I think I prefer it.
Is it me - or in relation to the above, does it make sense?
n
--
M for N in address to mail reply
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Date: 16 Mar 2007 21:53:19
From: Andy Schecter
Subject: Re: Dose / sweetness relation
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Neal Reid wrote:
> I recently decided to
> try 15 gm shots, slightly more finely ground than my normal 16 gm
> doubles - all else held constant. (the basket is a standard
> Rancillo double - won't hold much more than 16 and still lock into
> my machine)
>
> I have not noticed a dwell time difference - but I HAVE
> consistently noticed a sweeter drink. Some of the
> back-of-the-mouth complexity is gone (likely still there but
> overwhelmed by the increased sweetness) but I think I prefer it.
>
> Is it me - or in relation to the above, does it make sense?
It makes sense, perhaps, for a light-roasted coffee.
Since 15g vs 16g is a pretty small change, have you tried blind tasting the
shots to see if you can consistently tell them apart?
--
-Andy S.
http://www.flickr.com/photos/andy_s/sets/
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Date: 17 Mar 2007 11:25:00
From: Neal Reid
Subject: Re: Dose / sweetness relation
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In article <45fb49ff$0$4898$4c368faf@roadrunner.com >,
Andy Schecter <schecter@remove.me.rochester.rr.com > wrote:
> Neal Reid wrote:
> > I recently decided to
> > try 15 gm shots, slightly more finely ground than my normal 16 gm
> > doubles - all else held constant. (the basket is a standard
> > Rancillo double - won't hold much more than 16 and still lock into
> > my machine)
> >
> > I have not noticed a dwell time difference - but I HAVE
> > consistently noticed a sweeter drink. Some of the
> > back-of-the-mouth complexity is gone (likely still there but
> > overwhelmed by the increased sweetness) but I think I prefer it.
> >
> > Is it me - or in relation to the above, does it make sense?
>
> It makes sense, perhaps, for a light-roasted coffee.
>
> Since 15g vs 16g is a pretty small change, have you tried blind tasting the
> shots to see if you can consistently tell them apart?
A little over 5% is not a small change to MY taste.
I can honestly say that I COULD taste the difference blind - it is
startling. However, after a bit more work with the stuff (it's my
own blend of 50% Brazil fairly light, 25% Kenya AA and 25% Sidamo
both dark but not oily (thanks to Jim S for starting me down the
path that lead here) I've found it's a sweeter that usual batch.
I've tried 14 through 17 gm shots (volume & time held 'constant'
via grind) - and still find the smaller, finer loads sweeter than
the larger - and that the larger loads have more complexity.
I'll explore each SO independantly and see if it really is an
element of this batch...
--
M for N in address to mail reply
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Date: 06 Mar 2007 11:02:29
From: DavidMLewis
Subject: Re: Pressure Profiling Update 1
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On 5, 12:33 pm, "gscace" <gregory.sc...@nist.gov > wrote:
> I've also formed the opinion that there is something to
> soaking the coffee cake at a low pressure and then ramping the
> pressure up. Right now the pre-infusion cycle is set to 2 bar for 3
> seconds, with a subsequent ramp to from 2 bar to 9 bar over a 4 second
> interval. Liquid coffee appears evenly over the perforations on the
> bottom of a brew basket just as the pressure begins its rapid rise. I
> like this preinfusion cycle over a straight line rampup in pressure
> for 7 seconds from startup to 9 bar because it produced more crema in
> the limited pairs of shots I brewed alternating between straight line
> ramp, and low pressure wetting with faster ramp.
>
Very nice work, Greg! I'm curious, though, about how this fits in with
the stuff that Jim Schulman and Ken Fox published here last year. If I
recall correctly, they found that a pre-infusion at less than 3 bar
didn't completely saturate the puck, but only wet the outside of it.
They determined that, if I recall correctly, by just pre-infusing,
then knocking the pucks out and cutting them in half. Does your system
behave differently?
Best,
David
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Date: 07 Mar 2007 14:48:34
From: Danny
Subject: Re: Pressure Profiling Update 1
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DavidMLewis wrote:
> Very nice work, Greg! I'm curious, though, about how this fits in with
> the stuff that Jim Schulman and Ken Fox published here last year. If I
> recall correctly, they found that a pre-infusion at less than 3 bar
> didn't completely saturate the puck, but only wet the outside of it.
> They determined that, if I recall correctly, by just pre-infusing,
> then knocking the pucks out and cutting them in half. Does your system
> behave differently?
>
> Best,
> David
>
Well, my lever machines preinfuse at boiler pressure (1.1 - 1.2 bar, I
assume, unless there is some pressure-increasing gizmo in the
grouphead, since it only has a small orifice to allow water into the
group), but after 8 or 9 seconds if I remove the pf without pulling
the shot the cake is wetted right through. I just tried it, and a
messy job it is too :)
--
Regards, Danny
http://www.gaggia-espresso.com (a purely hobby site)
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Date: 12 Mar 2007 14:46:47
From: jim schulman
Subject: Re: Pressure Profiling Update 1
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On Wed, 07 2007 14:48:34 +0000, Danny
<danny@nospam.gaggia-espresso.com > wrote:
>Well, my lever machines preinfuse at boiler pressure (1.1 - 1.2 bar, I
>assume, unless there is some pressure-increasing gizmo in the
>grouphead, since it only has a small orifice to allow water into the
>group), but after 8 or 9 seconds if I remove the pf without pulling
>the shot the cake is wetted right through. I just tried it, and a
>messy job it is too :)
The water isn't flowing through a gicleur, solenoid, distribution
block, etc etc -- it's just 2 ounces of water sitting squarely over 1
to 2 ounces of coffee -- you could probably turn your boiler down to
0.5 bar and still soak the puck.
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