Digressing over temperature control.

I was comparing how the group of the Strega and the L1 work, and how they arrive to the desired temperature.
For what I could understand from the schematics, the L1 has an HX with group in and out connections.
It sends hot water to the group, that after getting colder goes back to the HX (to warm again), and is replaced with "new" warmer water. They call that a thermosiphon.
This is done continuously, therefore, once the group is warmed up it can be used, and as long as the recovery time is granted, the temperature will remain constant.
I believe that by fiddling with the pressurestat the temperature settings can be altered at will.
I also believe that, through a short flush one may decrease the temperature, when so desired, however not as efficient and accurately as with regulable machines.

The Strega has also an HX but only with an out to the group connection (no return to the HX).
Therefore, warm water from the HX gets to the group, were it looses heat (to the group), and gets reheated, to the factory set temperature, through the two group heat elements.
As the group's final temperature is determined by these heat elements, regulating the pressurestat will mainly influence the steam, and will have basically little or no effect over the brewing temperature.
Decreasing temperature is also accomplished through flushes.

While the L1 has a small advantage, as the default temperature may be regulated through the pressurestat, for what I could see, I believe that both systems should have a similar performance as both have a predetermined, and basically stable, initial brewing temperature.

As I like trying out different beans, that require different temperatures, I price having an accurate temperature control, preferably more precise than by using flushes.

For the time being I'm using a "mixed" method, to decrease temperature to a given point:

1. I leave the machine heat normally, with PF on (it gets really hot to touch).
2. When I decide to brew I pull a long flush (for renewing the HX water, smelling, feeling the lever).
3. Then I prepare everything in my coffee corner (heat cups, weight beans, prepare pitcher, etc), that usually will take me about 5 minutes.
4. Before grinding (or sooner), I take out the PF from the group, and put the other PF, to act as an heat sink.
5. I grind, dose and tamp and, when ready, I feel the PF in the machine.
6. If it's warm but not really hot, it's like a 3-5 seconds flush; hot but still "touchable" (not quite as the other PF was) is equivalent to the 8-10 seconds flush. To me, and for the time being, feeling the temperature appears to be more consistent than by timing flushes.
7. And for the most acidic beans, I just don't do anything and pull my shots (with the first PF) without flushing.

Therefore I manage to have three roughly different brewing temperatures "settings", even while I don't know the actual values that I'm pulling the shots.

As the Strega uses the heating elements to control the group temperature, it has a potential of installing a dimmer or a PID, that might allow to easily set the temperature for each shot. Presently, if I feel the group is hotter than I want it, I turn it off for a couple of minutes (or more) just to cool off.

As I don't possess the necessary skills for this kind of mods, I tend to try what else I have in hand.

Hey, Bernardo!

Just a small detail about Londinium: I don't think one can cool the group with a flush, as the HX is fed by the boiler water. The pstat setting can play some role but as it mess with steam power it's not the better option. Some flow restrictor on the thermosyphon path, better yet a adjustable restrictor (something like Faema Legend have), could do the trick to stabilize the group on different temperatures.

The PID on the Strega group heater would play something like the idea above - you could set the group to a cooler temperature to have cooler extractions. Probably with more control and easy of use than a thermosyphon restrictor on other machines.

Márcio.

The L1 uses a thermosyphon loop that brings water from the boiler through the upper group tunnel & back to the boiler. It is not an HX like the Strega uses. When you pull a shot on the L1 you are pulling water from the boiler instead of fresh water through an HX as on the Strega. Most likely the L1 uses a jet in the upper passage to regulate flow but some builders use an adjustable screw which you could tweak to raise or lower group temperature.

I would consider the Strega flushes a much more convenient method of adjusting the brew water temp then having to open the L1 & adjust the P'stat each time you wanted to change temps/beans. From reading the L1 threads I get the impression that buyers are not interested in trying different temps.

Because I like brewing different blends and different SO's I am also interested in having a predictable way of altering Strega's brew temperature.

For the past several months, what I've been doing is grinding and filling the PF and tamping, then flushing 6-10 seconds to empty the HX, and then timing the seconds from this long flush to pulling the shot. The longer the interval, the higher the temp of the water in the HX used for the shot.

I have, at least by taste, seemed to have been able to achieve some degree of reproducibility in temperature as it affects shot quality. So once I've dialed in the grind and the "wait interval" for a particular bean (or blend), as long as I wait the prescribed amount of time after the long flush, it seems that I can consistently pull balanced shots. Depending on the bean and the level of roast, the typical wait intervals I've used are from 15-45 seconds. Additionally, for wait intervals greater than about 50 seconds, it would appear that I'm at the steady state "pre-flush" brew temp, so for beans requiring that higher range of temps, I generally don't flush, but just pull the shot after tamping and loading. At some point, I'll get around to confirming my observations with a thermocouple and meter, but at least anecdotally, it seems to be working out well.

Is or has anyone else been using the approach? I'd appreciate thoughts and feedback.

Best,

Rick




Is anyone else using this approach

Because I like brewing different blends and different SO's I am also interested in having a predictable way of altering Strega's brew temperature.

By far, the easiest way to do that would be to add a PID control to the resistance heaters on the grouphead. The thread size is M4 (IIRC) and the total cost would be ~ $115 from this guy: http://www.auberins.com/

And this being the key component to replace the existing thermal switch: http://www.auberins.com/index.php?main_ ... ucts_id=21

There is surely a difference between flushing and not flushing the Strega but the intent should be(?) to not flush at all.

The fluctuating group head temperature definitely has an impact on the shot temperature, but I found the flush routine made far more of a difference with a Scace device. I would certainly PID the heaters if I had the motivation. What would be really neat is a manual bypass valve to let you flush the group without having to hold the lever down. This is an option on the KvdW lever machines now, isn't it?

I have a dumb sounding question.

Suppose you use a quick flush, i.e somewhere from 0 to 4 seconds, whatever you think is appropriate. Then make the shots this way repeatedly without worrying about the state of the group or boiler. How much variation are you getting? I find I mostly get consistent performance with only small variations shot to shot, and maybe one shot in six or seven coming out decidedly odd.

You guys may have had breakthroughs consistency, but for me this is pretty much what I get even on the best gear.

Talking about temperature.
I got hold of a fancy temperature reading device and took some measurements today of espresso from my Strega.
So it takes about 30 minutesa to get the machine to reach the point where the readings reach there maxinmum.
However to my surprise the maximum temperature was 180 degrees.(82 C)
This was after the machine was on for 50 minutes.
Don't know if I can get any higher if the machine idles longer .But this is low!
Maybe I should check for a broken heating element?

Alf, as Jim S. asked me once when I had a similar doubt: when the macine is hot and you flush, doesn't the group water come sputtering and boiling out ? If yes, it's at least 97C ... If it doesn't sputter ....

I just let it idle for more than 90 minutes.Pulled shot without cooling flush.Shot started at 97 degrees celsius at the first drop and ended at 92 degrees.Apparently the Strega needs longer than 30 minutes to reach pulling temperature.i've been relying to much on my temperature strip I guess.And yes the water comes out the HX sputtering.For almost two years my morning cappuccinos have been not hot enough.
But they've always been cappuccino's and never espresso's.Apparently milk masks a lot.Or I just got a bad palate.