SB E61+PID, Episode 1: A rude awakening about temperature stability

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boren

#1: Post by boren »

Edit: Skip this thread and head directly to Episode 2. The results here are not really useful to draw any conclusions. The only valid conclusion is that measuring temperature while flushing water doesn't tell you anything useful about temperature during coffee extraction.

I spent an hour and a half testing my Quick Mill Alexia Evo temperature at the boiler and grouphead, following this discussion about test methodology. Note that I flushed water to mimic pulling shots, but didn't actually use coffee. This would have been too wasteful. You can find the results here.

All in all, I'm highly disappointed and am really hoping there's something off about my test methodology or my PID configuration that can be corrected to get better temperature stability. The results however do reaffirm my suspicion (based on pulling many shots in the last 3 years) that the temperature stability of the machine leaves a lot to be desired.

Observations:
  • Even with frequent flushes, the grouphead temperature only stabilizes after 60 minutes.
  • The differences in temperature between 2 seconds into a flush and the peak temperature of the flush was on average 4.7c and could go as high as 9.3c. Only in 1 of 4 shots was the gap 2c or less.
  • The temperature difference after a 6" flush vs one that's long enough for the temperature to stabilize (or until I gave up) was on average 2.1c and can be as high as 5.5c.
  • The brew pressure gauge sometimes shows high pressure after the flush (it can be as high as 7 bar). This is with the pump idle and the lever moved all the way bottom position to drain excess water. I also tested temperature of subsequent flushes, 2 minutes apart after releasing this pressure. I tried this by moving the lever slightly up, right before the microswitch engages, and by releasing water from the steam wand. The first method resulted in colder than normal flushes, while the second method resulted in temperature being hotter than normal.
Takeaways:
  • The machine needs at least 1 hour of warm up before it's ready to be used.
  • The brew pressure gauge may be faulty, or the group thermometer may be installed incorrectly (I don't recall the odd post-brew/post-flush pressure readings before installing it).
  • The odd pressure readings are best ignored. Trying to release pressure without using the pump only resulted in even less stable temperature.
  • Overall temperature stability is unacceptable. Is this normal for machines with an E61 grouphead and a PID? Should I move on to a non-E61 machine to get better stability?

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Jeff
Team HB

#2: Post by Jeff »

My E61 HX was a minimum of 40 minutes to stabilize, then a flush routine to control the brew temperature. The E61 group, by its design, spills heat. It was designed for an HX, not for direct connection to the brew boiler. To get flow through the thermosiphon, you need a temperature differential. It is much greater on an HX sitting there with a hot HX than with a brew boiler. If you're looking for better than a couple degrees C, it's not a great option. The "saturated groups" followed quickly after the E61 in commercial machines.
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Bluenoser
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#3: Post by Bluenoser »

Edit: Sorry had a whole post assuming you had an HX, but yours is single boiler.. My E61 HX takes 40 minutes to stabilize. Your pressure gauge is likely near the pump and just measuring residual pressure when you close the lever. If this is true, its reading is of no value for extraction.. It is just used to set the OPV.

But I will say that there are so many factors that affect an E61. Convection currents, time from your last extraction, etc. And the E61 will change the brew water temp as it runs through it. There is no closed loop control here.

boren (original poster)

#4: Post by boren (original poster) »

Jeff wrote:My E61 HX was a minimum of 40 minutes to stabilize, then a flush routine to control the brew temperature. The E61 group, by its design, spills heat. It was designed for an HX, not for direct connection to the brew boiler. To get flow through the thermosiphon, you need a temperature differential. It is much greater on an HX sitting there with a hot HX than with a brew boiler.
Then why do they even make non-HX machines with E61 groupheads, let alone claim that they offer better temperature stability? If this is "by design" then it really does make me think it's time to move on to a non-E61 machine.
If you're looking for better than a couple degrees C, it's not a great option. The "saturated groups" followed quickly after the E61 in commercial machines.
Apparently so. The Lelit Elizabeth for example doesn't cost that much more than my machine but uses a saturated grouphead. It clearly has way better temperature stability even with a tiny 0.3L boiler.

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BaristaBoy E61

#5: Post by BaristaBoy E61 »

You might be much happier brewing by taste and not by numbers.
Digesting the numbers will only make you sick and leave you with a bad taste.

Brew by taste and slow down enough to 'smell the coffee'.
"You didn't buy an Espresso Machine - You bought a Chemistry Set!"

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HB
Admin

#6: Post by HB »

boren wrote:I spent an hour and a half testing my Quick Mill Alexia Evo temperature at the boiler and grouphead... I flushed water to mimic pulling shots, but didn't actually use coffee. This would have been too wasteful.
That may or may not yield meaningful results. How did you measure temperature? Would you post a video of your methodology? Here's a couple examples of mine:
From ECM Technika IV Profi Review
From La Marzocco Linea Mini Review
Dan Kehn

Bluenoser
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#7: Post by Bluenoser »

boren wrote:Then why do they even make non-HX machines with E61 groupheads, let alone claim that they offer better temperature stability? If this is "by design" then it really does make me think it's time to move on to a non-E61 machine. .
E61 (from 1961) is a time-proven design for commercial machines where Baristas are pulling shots every few minutes, and the E61 characteristics for this workflow keep the brew water pretty close to 200F. Initial heat up was not an issue as they were on all day. However, SO coffee wasn't a thing back in the early 60s, which requires more control over brew water temp management. I think it is a cheap and fairly reliable way to get a somewhat reasonably stable brew water temp. However, manufacturers do not do a good job educating the users on how to effectively use the E61; and they make claims that are not true when they attach a PID.. which hurts their reputation. You can get good espresso from E61 designs, but you generally need to work at it more; and be conscious of how the E61 influences the eventual brew water temp. Also for medium dark and dark roasts, the temperature of the brew water can be in a wider range than for light roasts and E61s work ok here.. depending on how fussy you are.

After your machine is fully warm.. try a quick 3-second flush and then pull your shot.. You can experiment with the PID which will make the brew water hotter/cooler, but only after a 15 minute wait. As BaristBoy said, you can experiment and find a taste you like and then duplicate that workflow each time.

You do want to know when your machine has rebounded. Sometimes after pulling a few shots you'll need to let the water in the Thermosiphon reheat.. Your group thermometer can tell you after a shot when your water has reheated. You don't need a group therm forever.. just to learn how your machine behaves.

boren (original poster)

#8: Post by boren (original poster) »

BaristaBoy E61 wrote:You might be much happier brewing by taste and not by numbers.
Digesting the numbers will only make you sick and leave you with a bad taste.

Brew by taste and slow down enough to 'smell the coffee'.
The whole reason I checked the numbers was that I was experiencing inconsistent results in the cup. With the exact same beans and workflow some shots were great, others not so much. Now that I've done these tests, it's pretty clear why. If this is the level of temperature stability to expect from this machine, then it's time to move on.

boren (original poster)

#9: Post by boren (original poster) »

HB wrote:That may or may not yield meaningful results. How did you measure temperature?
I used a grouphead thermometer (Vidastech E61 Thermometer Pro). Here's a video of flushing water at the 60 minute mark:

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HB
Admin

#10: Post by HB »

There's a few problems with your methodology.

You're measuring upstream of the brew chamber and with a thermometer that reacts more slowly than a bare thermocouple wire. Because of the location, you're measuring the grouphead temperature dynamic, not the actual brew temperature. The "pour" time was significantly faster than a real espresso pour (~12 seconds) and had no dwell time at all.

If you want more reliable data, you can build a DIY thermofilter. Even that's just an estimate, since thermofilters tend to boost stabilizations because their "puck" carries more heat than an actual coffee puck. An even more accurate measure is a themocouple wire across the top of the coffee puck; I used type T 36 gauge wire since it's thin enough to get a seal.

FWIW, in past discussions of temperature stability (or lack thereof), a common mistake is flushing more than necessary or not allowing enough rebound time, leading to a short spike followed by plummeting brew temperature.
Dan Kehn
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