The temperature profile of a commercial lever group - Page 6

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cafebmw
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#51: Post by cafebmw »

regarding the commercial Gaggia machines:
i still have to record a temperature profile of my machines. but i doubt that the change in temperature is a big one. the groupheads are 26 lbs of brass. just alone for the mass of the grouphead the temperature profile should be quite flat.
when i turn off the machines for maintainance it takes more than an hour for the groupheads to cool down.

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drgary
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#52: Post by drgary »

Oliver:

I would be surprised if you don't have a big temperature drop. If the group runs cooler than the boiler water, which it probably does, the massive size of the group would make that happen with delicious results in the cup. Believe me the Prestina's 14+ lb. group holds temperature a long time.

Gary
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peacecup
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#53: Post by peacecup »

Drgary wrote this in the $1000 lever thread:
The secret sauce in these commercial lever groups may be that the group idles at a temperature below the boiler water that extracts the first flavors at high temp and then declines steadily 20 to 30 degrees over the pull. I learned this just two days ago when applying a thermocouple inside the coffee cake on the Prestina.
What exactly are you revealing here? All boilers are at about 240F at 1 bar boiler pressure. The groups are much lower. The boiler water cools dramatically when it leaves the boiler and enters the group. This should continue throughout the duration of the shot. The longer the water stays in the group the cooler it gets. No surprise there. More relatively cool brass (i.e. Conti) means more cooling of course.

Perhaps this does not apply to the Pavoni or even the Elektra or Cremina. It does apply to the home levers I've used, Sama and Caravel. The longer the shot takes the cooler the water. This is due to the shape of the Sama group (tall, narrow, and heavy, compared to the Pavoni) and to the thin steel "group" on the Caravel.
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drgary
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#54: Post by drgary »

I think there's a different temperature profile with these much larger groups, also more consistency because of the sizes of boiler and group. More comparative measurements will tell us if this is so and how they differ.
Gary
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allon
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#55: Post by allon »

I think it's more revealing to observe that the group idles below the brew temperature. When you pull a shot, you get 240 degree water (probably a bit lower since it cools on the way to the group) flooding the group, giving you a hot preinfusion, then cooling as the shot is pulled. The hot (but not brew temperature hot) group buffers the super hot water and you end up with the water cooling and the group heating and end up in the right range.
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samuellaw178
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#56: Post by samuellaw178 replying to allon »

What you described is what the Pavonis, Creminas and Elektras do too. Super hot water from the boiler fills the below-brew-temp grouphead and cools it to brewing temp. This is why they will overheat in the first place. Are you saying the commercial group(Conti) work in the similar principle too?

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drgary
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#57: Post by drgary »

With the Pavoni at least the group also acts as a heat sink but temperature rises during the shot because the Pavoni group is small. Boiler water probably has to start cooler than with a commercial lever to avoid a burnt shot. My Pavoni is dialed in at 0.85 bar. I hear that people with commercial levers tend to run them at higher pressure. This would only work with a massive group able to dissipate the extra heat. We need more measurements to compare these machines. I sure am tasting something different.
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samuellaw178
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#58: Post by samuellaw178 »

Edited: After looking at the graph more closely, it does seem to rise a little in the first part of shot.

From Dennis's data in Olympia Cremina Temperature Study, Part 2, it seems that the water temperature stayed relatively constant and dropping slightly at the very least with the grouphead temperature of 180F. I am guessing the drop would be more drastic with a cooler grouphead.



This was what he used:


Anyhow, from these preliminary observation, it seems like there may be some other mystery factors in play with the commercial spring lever - decreasing temp and pressure do not seem to account for all the differences in taste.

cafebmw
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#59: Post by cafebmw »

ok, i just recorded the temperature profile on my 73 gaggia orione wit a 26 lbs brass grouphead.
and what a surprise!!

A: 19 gr coffee; 6 sec pre-infusion; pressurestat dead band 0.9-1.2 bar;
B: 19 gr coffee; 6 sec pre-infusion; pressurestat dead band 0.95-1.25 bar;
extraction time both A and B circa 39 seconds.

time....... temperature/F
sec........ A........ B

1......... 145........ 153
6......... 155 ....... 164
10....... 174......... 177
15....... 178......... 183
20....... 178....... 184
25....... 178....... 184
30....... 179....... 185
35....... 180....... 186
40....... 182....... 187
45....... 184....... 187
50....... 185....... 187
(sorry for the strange editing, couldn't do the list any other way)

at T=1 sec the temperature is more or less the dry puck's temperature in equilibrium with the PF.
temp rises with the pre-infusion and reaches an equilibrium at T(A)=10 sec resp. T(B)=15 sec and stays then quite stabile. that means after the puck's saturation at (most likely) T=10 sec there is a temperature RISE of around 10F. no temperature drop off!! that actually surprises me, i expected a drop of 10F.

now i'm wondering about the KVDW idrocompresso's temp profile....

P.S.
my boiler is insulated with 5/8" industrial felt (except the boiler end plates). a great amount of heat therefore is dissipated through the group head (like a heat sink) whereas on a naked boiler the heat dissipates at the boiler surface itself before it reaches the group head.

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allon
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#60: Post by allon »

Well well well, that IS interesting.
What I'd be interested to see is the temperature of the water above the puck. It might be interesting to remove the group screen and give it a go....

then spend a while cleaning out the group :/

I may have to build a temperature logger....
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