Hey Eric!

A few questions I can't seem to find in the archives. Is the temperature we're seeing with your thermometer the actual brew temperature or is it somewhat less with the group head soaking up some of the water temp before it hits the puck? I suppose there is some heat loss, maybe a few degress?

Typically right now, 2 days into using it, it seems that there is a spike in temp in the neighborhood of 10 df for me(Bezzera Unica SBDU) from idle when brewing, at least most of the time. Sometimes a little less.

PID is set for 91c (196f), group idles around 197f and I see a spike up to 208f while brewing after a long idle. Back to back shots, within a few minutes of one another, brings the peak temp down considerably to around 200-201 while brewing.

Any thoughts?

Edited: I now see "we" just went through this very subject in Temperature Differential between Eric's Thermometer and Brew Temperature with Madrooter. Most of the information seems to pertain to HX machines and flushing though.

I don't know about that thermometer (I recommend in-basket measurement), but more generically, just like with a HX, if you want a lower brew temp, either lower the boiler temp or flush. Which one depends on how you want to effect the temperature profile.

jonr wrote:I don't know about that thermometer (I recommend in-basket measurement), but more generically, just like with a HX, if you want a lower brew temp, either lower the boiler temp or flush. Which one depends on how you want to effect the temperature profile.

Good points. I guess, naively, I thought because it's a single boiler with a PID that I would have rock solid brewing temperatures. Wrong! I suppose the size of the boiler is the main reason, it's only .5 liter, why I'm seeing the variation I am. Which is really not a bad thing, now that I know it and can control it with HX like flushing.

I suppose the size of the boiler is the main reason, it's only .5 liter, why I'm seeing the variation I am.

That's a good size to give you a proper temperature decline during brew (although it also depends on how the controller behaves, smaller can work well also). But you have a lot of metal exposed to ambient temperatures - you need to compensate for this.

I'm still somewhat unsure of what the difference in temperature is between what I see on the thermometer and then what temperature is actually making it to the puck.

While this is, obviously, not your machine, the results should be close. The boiler size for this PARTICULAR VBM is 0.75 litres.



A grouphead temperature of 197 F is close to ideal. I would do a very short screen flush and brew immediately.

A grouphead temperature of 197 F is close to ideal. I would do a very short screen flush and brew immediately.

1. Ok then, if 197 F is "close", what is the "ideal" idle grouphead temperature?

2. Why the short screen flush, then brew?

You need to specify exactly what brew basket temperature profile you want. And probably buy a brew basket temperature probe to verify that you are getting it (or close, you have limited controls).

A flush should bump up the early brew temperatures (vs the depression seen until 7 seconds above).

Why the short screen flush, then brew?

Because it is my belief that most neglect to do a short screen flush after brewing which is most proper. If you happen to operate counter to my belief, then a grouphead temperature reading of 197 F should produce a tasty shot. Varied beans/bean blends react differently to temperatures and it is best to try a particular bean at, say, +3 and -3 degrees to see if you can discern a difference.