Measuring brew temperature

#1: Post by **bean74** » May 6th, 2022, 7:50 pm

My PID kit came with instructions to set an 8°C offset into the controller, to account for temperature drop between boiler and brew head. Easy enough to input, although I'd argue the temperature drop can never be any constant value, it will vary during the course of the brew cycle. I guess the person who engineered this PID pegged that as some average value to use.

But how does one measure temperature, and at what point and time is that temperature critical? I would guess the goal is to maintain the same temperature at the puck throughout the brew temperature, but I haven't a clear idea as to how folks are actually measuring temperature at this location.

Educate me!

#2: Post by **Jeff** » May 6th, 2022, 9:04 pm

Without getting into craziness, I think the two important things are repeatability and being able to know roughly how much of a change you make might be. If you're interested in a less-rough calibration, you can crank up the PID until you get flash boiling at the group. (Let things settle a while to make sure the group temperature has stabilized.) That's roughly your local boiling point.

During the shot? It does what it does for virtually all machines out there. You can buy or rent an expensive "Scace device" that approximates a puck. It's amusing, but hard for me to justify unless you've got multiple cafes and want to make sure "97" on all your machines is very close to the same.

#3: Post by **baldheadracing** » May 6th, 2022, 10:32 pm

bean74 wrote:My PID kit came with instructions to set an 8°C offset into the controller, to account for temperature drop between boiler and brew head. Easy enough to input, although I'd argue the temperature drop can never be any constant value, it will vary during the course of the brew cycle. I guess the person who engineered this PID pegged that as some average value to use.

But how does one measure temperature, and at what point and time is that temperature critical? I would guess the goal is to maintain the same temperature at the puck throughout the brew temperature, but I haven't a clear idea as to how folks are actually measuring temperature at this location.

Educate me!

I believe that you are assuming that keeping the same temperature throughout a shot is a good thing. It can be, but there are other possibilities.

I think of temperature throughout a shot following a profile, just like a pressure profile or a flow profile.

Consider the temperature and pressure profiles of the following two excellent machines:

(EC -> Espresso Coffee)
The Aurelia pump machine delivers a flat pressure profile and a flat temperature profile (and we also know that the machine will follow these curves throughout the multiple pulls of the WBC test procedure). The Athena Leva spring lever machine gives a declining pressure profile and a declining temperature profile.

Which machine gives better tasting coffee? It depends on the coffee and the individual doing the tasting. I know what I like

.

May 7th, 2022, 8:38 am

Thanks for the perspective, guys. As someone just exploring these details for the first time, I guess my goal is to have a reasonable idea of actual temperature, to aid me in trying to replicate recommended recipes from others. That's always a good way to learn anything new, copying what those with more experience have already figured, Newton's old "if I have seen further..." approach.

I like the flash boiling method. Another home-grown option I'd considered is a cheap pressured portafilter, which are a dime a dozen for my Gaggia Classic, drilled to accept a thermocouple. A sort of redneck Scace device, I suppose...

#5: Post by HB » May 7th, 2022, 9:37 am

Or the foam cup method. Or just lay a thermocouple across the puck using a thin wire that will slip between the gasket and portafilter. Search the forums, these are some of the oldest topics.

Seeking low tech way to measure brew temperature (2005)
What's necessary to make a thermocoupled portafilter? (2009)

HB wrote:

You can also do decent "over the lip" measurements with 30 gauge thermocouple wire. The portafilter basket will eventually wear through the wire's casing, but the wire is thin enough for the grouphead gasket to seal. Just lay the wire across the top of the puck, route the wire around the lugs, and measure. Below is a plot comparing the two:

Click here for discussion

From Scace Thermofilter Temperature Device in 2005.

#6: Post by **yakster** » May 7th, 2022, 2:25 pm

You can also dial in by taste and note on your PID what temps work best for which blends.

All these tools are there to get you to the best flavor, but you can also work backwards from the best flavor.

#7: Post by **cafeIKE** » May 7th, 2022, 8:12 pm

And shots vary per one, so make haste slowly