How Autofill Degrades Shot Temperature Stability

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Ken Fox

#1: Post by Ken Fox »

I decided to waste a couple more days repeating the shot temperature thermometry on my two PID-modified Cimbali Juniors last week. A new test I devised was designed to measure shot temperatures delivered in the face of variable intervals in-between shots, with frothing mixed in. I did not do exactly the same test on both machines but it was pretty obvious that my almost 11-year old pourover Vibe Junior was much more temperature stable during this type of test than was my current vintage Rotary D1 Junior. I have found from earlier testing that the rotary machine "recovers" faster than does the vibe machine, and hence the inter-shot interval is 30 seconds longer on the vibe than the rotary. Here are representative shot temperature curves, with legends, that show what I mean:

On the old Vibe:

Image

On the Rotary:

Image

Granted, the two machines are different, but they share identically sized boilers, identical groups, and identical heat exchangers. Both were PID'd in essentially the same manner. Why the difference? the only obvious difference that should matter for shot temperature stability is boiler AUTOFILL, present in the plumbed-in rotary but absent in the vibe machine, whose boiler must be manually refilled with the aid of a sightglass. Autofill tends to be sensitive and anyone who owns a machine with autofill knows that the autofill kicks in at unpredictable times. Anything that diminishes boiler fill (like frothing, or using boiler water for drinks) will increase autofill activity.

I discussed these findings initially with Jim Schulman, who agreed that the autofill was the likely culprit in making the plumbed in rotary machine less temperature stable on a complex shot series that included frothing. We discussed possible ways to defeat this such as having a switch one would use to defeat the autofill normally but allow the autofill to work once daily, or however often one desired or when one chose (i.e. not when making espresso drinks). The risk of that of course is that you forget to turn the autofill on again so the element eventually burns out when you empty out the boiler. Of course there are other options such as putting in on a timer, something Jim also brought up.

I had a conversation with Michael Teahan in Los Angeles today, who as always is a fount of espresso knowledge. Rather than using an on-off switch, Michael suggested using a relay to make sure the autofill doesn't actuate DURING A SHOT, but functions otherwise. He mentioned additional options for making this sort of thing work, such as slowing down the inflow into the boiler from the autofill, but the relay seemed the easiest to impliment.

Before actually trying to impliment this modification, however, I thought it would be worthwhile to repeat the shot series with the autofill bypassed. Here is a picture of the autofill circuit in my machine, on the left side of the boiler:

Image

The autofill probe (as can be seen) is insulated in a sleeve and sticks into the boiler where it contacts boiler water; when it does, it completes a circuit with ground, and turns off the autofill as it senses the correct level. Here is how I defeated it, temporarily for purposes of conducting this experiment:

Image

The temporary wire bridges the circuit and shuts off the autofill. This was confirmed by draining 8 oz of boiler water out and seeing that the boiler autofill did not actuate. I then reversed the change (removed the wire), obviously with the machine unplugged, then replugged in the machine and the autofill immediately acutated for about 15 or 20 seconds to refill the boiler.

With the autofill disabled, I repeated the shot series exactly as before. Here are the new shot curves:

Image

As you can see, the shot temperature curves are now more tightly grouped, with a reduction in both the maximum and minimum shot temperatures. I haven't done any mathematical evaluation of these data, but visually it appears to me that the variability in shot temperature has been reduced by at least a third.

What remains to be determined is what is the best way to get this level of improvement in actual shot temperatures without risking burning out the element or causing a housefire :P My impression is that a simple relay, powered by the input solenoid wires (as suggested by Michael Teahan) is the right approach, however I'll have to install one and test again to confirm that this very simple modification in fact has the desired result.

ken
p.s.: This is crossposted on alt.coffee; please do not respond in both threads
What, me worry?

Alfred E. Neuman, 1955

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#2: Post by Compass Coffee »

If I understand you correctly your autofill 'can' kick in during a shot? No, that would not seem good for the shot. I'm 99% certain that has never happened during a shot pull on my rotary Bric'. Including when pulling and steaming concurrenlty. After a shot and IIRC during steaming yes, but I don't recall it ever happening during a shot. I'll run a long series of back to back simulated shots (w/thermofilter so at shot flow rate) to verify.
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Ken Fox (original poster)

#3: Post by Ken Fox (original poster) »

Compass Coffee wrote:If I understand you correctly your autofill 'can' kick in during a shot? No, that would not seem good for the shot. I'm 99% certain that has never happened during a shot pull on my rotary Bric'. Including when pulling and steaming concurrenlty. After a shot and IIRC during steaming yes, but I don't recall it ever happening during a shot. I'll run a long series of back to back simulated shots (w/thermofilter so at shot flow rate) to verify.
From my conversation with Michael Teahan, there are machines that have been made whose electronics prevent the boiler from autofilling during a shot; it is certainly possible that your machine is one of those. When a shot is actually being pulled, there would be no way to know whether the boiler was autofilling since you can't see it and the pump is going to make it's noises whether it is making a shot, filling the boiler, or both. Depending on the amount of water that can move into the boiler per unit time and the size of the boiler plus location of the probe, it could be that your autofill cycles are short enough that you'd have no clue of this happening simultaneous with a shot unless the boiler fill overlapped the end of the shot.

There is more than one way that boiler autofill can perturb shot temperature; it could occur during a shot, when it would be difficult for the element to overcome, or it could occur shortly before the next shot having essentially the same effect. Putting a simple relay on the autofill circuit would prevent the former problem but not the latter. Making the autofill work manually, with a switch, would prevent both problems but risks damage. Putting the autofill circuit on a timer, if the operator doesn't use boiler water for drinks and if the operator isn't frothing constantly, could allow programming of the autofill to have it kick in at times when the machine isn't apt to be making drinks.

What I did in my little test was to disable the autofill completely. That doesn't tell us whether the improvement was due simply to no autofill actuation during shots, or from the absence of autofill shortly before shots being made; it only implies that without autofill the machine is more temperature stable on a shot series like this. Since the machine could easily figure out if you were making a shot, but can't figure out when you are going to make your next shot, this difference is potentially critical in designing a fix.

ken
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#4: Post by Compass Coffee »

Just ran series of 25-30 simulated lattes ie; pulling a double concurrently steaming 6oz continuing steaming 5-10 sec after shot completed. Autofill kicked in 4 times during the series, each time after shot completed and after completing steaming. Three times right after stopped steaming but well before flash, flush & go so shot temp ok with a slight pause in rhythm, once just as I started flash so waited for boiler to come back up to pressure and started flash, flush & go again. (didn't time the wait but way less than a minute)

I could tell if the Bricoletta autofilling during the shot, different sound than when pulling a shot. Plus watched the boiler gauge which of course takes a dive during autofill. Didn't happen I'm 99.999% certain.

Not conclusive that the Bric' won't autofill during a shot, but good enough for me not to be concerned!

Yes, autofill kicking in just before flash flush&go screwed up timing, had to wait and start flash over.

What was surprising/amazing to me was that while I didn't time the wait between each shot/steaming, all I did was dump the 20oz pitcher, refill ~6oz tap cold water for simulated steaming, remove the thermofilter, flash flush & go. All done without foot movement needed since Bric's right by the sink. No shot temp drop across the series, very short flash before flush&go though. I expected shot temps to drop off because previous shot only series temp testing suggested I needed ~35sec after post shot grouphead flush & wiggle or temps dropped off. Ah, that's the difference. Wasn't doing a post shot flush & wiggle so not drawing new mains cold water into HX as fast so recovery virtually instantaneous combined with steaming keep the 1900w heater element on more. (Boiler ceramic blanket insulated FWIW)
Mike McGinness, Head Bean (Owner/Roast Master)
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Ken Fox (original poster)

#5: Post by Ken Fox (original poster) »

Compass Coffee wrote:Just ran series of 25-30 simulated lattes ie; pulling a double concurrently steaming 6oz continuing steaming 5-10 sec after shot completed. Autofill kicked in 4 times during the series, each time after shot completed and after completing steaming. Three times right after stopped steaming but well before flash, flush & go so shot temp ok with a slight pause in rhythm, once just as I started flash so waited for boiler to come back up to pressure and started flash, flush & go again. (didn't time the wait but way less than a minute)

I could tell if the Bricoletta autofilling during the shot, different sound than when pulling a shot. Plus watched the boiler gauge which of course takes a dive during autofill. Didn't happen I'm 99.999% certain.

Not conclusive that the Bric' won't autofill during a shot, but good enough for me not to be concerned!

Yes, autofill kicking in just before flash flush&go screwed up timing, had to wait and start flash over.

What was surprising/amazing to me was that while I didn't time the wait between each shot/steaming, all I did was dump the 20oz pitcher, refill ~6oz tap cold water for simulated steaming, remove the thermofilter, flash flush & go. All done without foot movement needed since Bric's right by the sink. No shot temp drop across the series, very short flash before flush&go though. I expected shot temps to drop off because previous shot only series temp testing suggested I needed ~35sec after post shot grouphead flush & wiggle or temps dropped off. Ah, that's the difference. Wasn't doing a post shot flush & wiggle so not drawing new mains cold water into HX as fast so recovery virtually instantaneous combined with steaming keep the 1900w heater element on more. (Boiler ceramic blanket insulated FWIW)
I've used my Scace and dataloggers collecting hundreds of shot curves on both of my machines. One thing I have learned is that you need to actually collect all the data with a datalogger; simply looking at numbers as they flash by on a digital thermometer is highly misleading. Many times I've done shot series where I thought the curves would be stable and in fact they were not. The opposite has also occurred many times.

There is no substitute for collecting the data and plotting it out, as big a PITA as that is.

ken
What, me worry?

Alfred E. Neuman, 1955

houdina

#6: Post by houdina »

Does anyone know how having the boiler feed turn on during a shot effects the water pressure on the puck. It would seem sure to cause some fluctuation in pressure, I wonder how much.
Gregg

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#7: Post by Compass Coffee »

Ken Fox wrote:I've used my Scace and dataloggers collecting hundreds of shot curves on both of my machines. One thing I have learned is that you need to actually collect all the data with a datalogger; simply looking at numbers as they flash by on a digital thermometer is highly misleading. Many times I've done shot series where I thought the curves would be stable and in fact they were not. The opposite has also occurred many times.
Fluke I'm using with the Thermofilter doesn't have data logging capabilities. As far as the autofill kicking in during my shot steaming test series I don't need shot data logging to know if autofill engaging while pulling a shot. My eyes and ears work just fine watching the boiler gauge and listening to the Bric'.
There is no substitute for collecting the data and plotting it out, as big a PITA as that is.

ken
Except for taste. Obviously not tasting Thermofilter shots. But since shots taste excellent to me, and as recently as a couple weeks ago hosted a goodly group of home roasting espresso fiends all raving on shots and caps pulled from the Bric' I'm not too worried about my lack of ability to plot graphs of what we're tasting.
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cannonfodder
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#8: Post by cannonfodder »

When I rebuilt my Faema, I removed the auto fill solenoid (actually, it was missing) and used the supply line to mount a brew pressure gauge on the machine, and capped the boiler auto fill input. I attached a 220v orange light to the front of the machine and wired it into the solenoid hookup on the level box.


I have a sight glass which I check every time I turn on the machine, but if the boiler gets low, the wife occasionally uses the water tap to make hot chocolate, the level box trips the orange 'idiot light' right beside the brew button. Then she (or I) just pushes the manual fill button until the light goes out. Works wonderfully, obviously you have to have a plumbed in machine with line pressure greater than your normal boiler pressure for the fill to work. No middle of shot auto fill, or mid steam fill.
Dave Stephens

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#9: Post by cannonfodder »

houdina wrote:Does anyone know how having the boiler feed turn on during a shot effects the water pressure on the puck. It would seem sure to cause some fluctuation in pressure, I wonder how much.
Gregg
On a vibe pump, it kills your brew pressure. On my Isomac I loose almost half pressure, on a rotary, it is usually minimal.
Dave Stephens

Ken Fox (original poster)

#10: Post by Ken Fox (original poster) »

Compass Coffee wrote:Except for taste. Obviously not tasting Thermofilter shots. But since shots taste excellent to me, and as recently as a couple weeks ago hosted a goodly group of home roasting espresso fiends all raving on shots and caps pulled from the Bric' I'm not too worried about my lack of ability to plot graphs of what we're tasting.
This is a technical thread; there is a reason that I posted it here rather than on the "Coffees" forum. I try to divorce my opinion about the importance of fine temperature management from my observations when I post this sort of material, but for the record, I don't think that the great majority of people can taste fine temperature differences in espresso brew temperatures. 2 or 3 degrees F; probably; 0.3 degrees F; I doubt it.

So the fact that you could make what you consider to be a lot of good drinks for a lot of people with your current equipment is irrelevant to what I posted.

My post is about the impact of boiler autofill on fine temperature management. In order to evaluate this, one needs to be able to monitor actual shot temperatures, second by second. This does not mean looking at a digital thermometer, this means datalogging. Without a datalogger, you can't really prove or disprove what I've posted as it applies to your machine.

Once again, I'm not saying that I've concluded that you can taste differences related to these temperatures. What I've said is that IF such varying brew temperatures have an important impact on the shots produced, then it is important to know what those temperatures are. In order to know that, you need to use a datalogger.

As to skill in plotting graphs, $35 will buy you dpot, which will allow anyone with minimal effort to plot shot temperature or other curves. Do I think that this is important to your enjoyment of your espresso machine? I doubt it.

ken
What, me worry?

Alfred E. Neuman, 1955