Where to Locate Temp Probe in HERMs

I'm designing my next brewstand. It will be a 3 vessel system with a HEX. I plan on using a BCS controller and am trying to determine the best location for the Mash Temp Probe.

Options are:
1) Out of MLT (bottom draining Keggle)
2) Out of HEX
3) At return inlet to MLT

To me it seems the true mash temp is what would be at bottom of grain bed. However, in an automated set up if the original strike temp is undershot, the system may overheat wort to compensate resulting in too high a mash temp in the first 5-10 minutes of mash until temps normalize.

Anyway, appreciate feedback.

IMO, the output of the heat exchanger is the best place, because you don't want enzymes being denatured as they flow through the heat exchanger. Thats typically where the thermocouple is in a RIMS tube as well.

SleepyCreekBrews said:

IMO, the output of the heat exchanger is the best place, because you don't want enzymes being denatured as they flow through the heat exchanger. Thats typically where the thermocouple is in a RIMS tube as well.

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Agreed. In my setup I can switch between the HEX output and the HLT temperature to control the HLT burner, but the HLT sensor is only used to control preheating the HLT before recirculation begins. During recirculation, the HEX output temp is used. If that is correct, the mash temp will necessarily follow.

SleepyCreekBrews said:

IMO, the output of the heat exchanger is the best place, because you don't want enzymes being denatured as they flow through the heat exchanger. Thats typically where the thermocouple is in a RIMS tube as well.

Click to expand...

This. That way you know the temperature of your wort going into your MLT is not too hot. Sure it may cool slightly as it pulls through the grain bed but if your pumping at a reasonable speed you will be recirculating your entire wort every minute or two anyways. I bet if you measured at the top or bottom wouldnt really matter, they should be within a few tenths of a degree fahrenheit.

Thanks for the feedback everyone. I plan to circulate strike volume through the HEX at strike temp pre dough-in, kill pump at dough-in, and then circulate at mash temp for duration of mash. The pre dough-in circ cycle should help pre-heat all HERMs lines which will be insulated anyway. I agree that once the system heat is normalized through the HERMS cycle the differential between wort in vs wort out should be +/- .5*.

As an aside, one thing I've scratched my head over on RIMS set ups, is how much denaturing is happening with direct wort contact to the element. Presumably the flow is sufficient to mitigate, but still there is a portion of wort that is in contact with the element that is being heated well beyond the intended mash temp. Over the course of a typical 60 min mash with say 6-8 gallons of wort, that's a lot of enzymes coming in contact with a very hot element - albeit briefly and buffered by the overall volume. I'm no thermo dynamics expert by any means, though...

I use #3. My HERMS is controlled by a thermocouple positioned at the return inlet to the MT. I also measure the temperature of the wort leaving the MT (thermocouple at MT outlet). I doubt there would be much temp difference between HEX outlet and MT inlet unless the vessels are located a significant distance apart. Depending on batch size, there can be a significant temp lag between MT inlet and outlet as you describe in the original post. In my system, I need to set my temp (MT inlet) 4F above desired mash temp to reach desired temp at MT outlet. YMMV.