24/10/14 - Updated to include Experiment 6.
28/10/14 - Updated to include Experiment 7.
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Hi,
I have been using an STC1000 hooked up to a fridge and brew belt for a good number of years, and have been (mostly) really happy with the beer I have been producing.
The setup I use looks fairly complicated, but is actually quite simple – the STC probe sits in the wort, and the brew belt sits around the bottom of the fermenter:
Apart from checking the STC read-out every now and then, I’ve never really tested how well the STC works in keeping the beer at a constant temperature, but it appears to perform really well from the read-out alone.
Now, a few months ago I was reading an interesting discussion here about where you should place the STC probe to achieve best temperature control.
One chap was adamant that the probe should be placed inside the air-space of the fridge…and to be honest, he made a really good case for it. The idea being that, if you place the probe in or on the actual beer, you guarantee that your beer will fluctuate in temperature between the high and low settings on the STC. Whereas, if you put the probe in the air-space, the beer will adopt the ‘average’ temperature of the fridge, and is much less likely to fluctuate.
Having always routed the probe into the wort myself, I decided to test where to best place the probe to maintain a steady beer temperature. I know this experiment has been done before, but I wanted to see for myself.
I have so far tested five different set ups, and will describe the results below. However, first some caveats:
- The ‘beer’ in these experiments is actually just 20L of water (+3 campden tablets). Therefore, no exothermic fermentation is actually taking place. The purpose of this experiment is just to see which setting gave the best control over a stable mass of liquid.
- The fermentation fridge is kept in my garage, which at the moment fluctuates from about 12 to 20 °C.
- The thermometers used are attached to a Raspberry Pi, with a short python script polling for temperature readings. I attempted to calibrate each of the probes against the STC, but noticed there were slight differences even after calibration (less than 0.2°C).
- For each setup, the experiment was conducted for about 24 hours.
The different set ups were:
1) STC Probe in the Beer, BrewBelt for heat
2) STC Probe in the Beer, 60w Tube Heater for heat
3) STC Probe on side of fermenter, BrewBelt for heat
4) STC Probe on side of fermenter, 60w Tube Heater for heat
5) STC Probe in fridge space, 60w Tube Heater for heat
6) STC Probe in Small Reservoir (400mls water), 60W Tube Heater for heat
Graphs of the results:
1) STC Probe in the Beer, BrewBelt for heat
2) STC Probe in the Beer, 60w Tube Heater for heat
3) STC Probe on side of fermenter, BrewBelt for heat
4) STC Probe on side of fermenter, 60w Tube Heater for heat
5) STC Probe in fridge space, 60w Tube Heater for heat
6) STC Probe in Small Reservoir (400mls water), 60W Tube Heater for heat
7) STC Probe on side of fermenter, 60w Tube Heater for heat, Fridge turned OFF
Discussion:
Firstly, it seems that no matter where the probe is placed, a high level of temperature control is achieved.
The largest fluctuation I saw in any of the experiments was 0.75°C [EDIT] this was written before I had results from experiment 6 & 7 [EDIT]. As a scientist who works with expensive analytical equipment (which also operates fine temperature control), I’d say this is a pretty incredible degree of control from domestic equipment.
Given this, the choice now is based on the requirements of the individual brewer.
If the desire is to have the absolute finest control over temperature, the 4th experiment looks best: stick the STC probe to the wall of the fermenter, and use a tube heater to heat the fridge space. This keeps the beer temperature within 0.19°C, and turns the fridge on every 80 mins or so.
If the desire is to prevent over-cycling of the fridge compressor, the 2nd experiment looks best: put the STC probe in the actual beer, and use a tube heater in the fridge. The beer is kept within 0.75°C and the fridge turns on 2-3 times in 24 hours.
A compromise between good temperature control and few fridge cycles would be experiment 1: STC probe in the beer, and a BrewBelt heating the fermenter. This kept the beer within 0.44°C, and turned the fridge on every 4 hours.
I would say, however, that hanging the STC probe in the fridge space alone resulted in problems. Firstly, it took a long time (over 8 hours) for the beer to settle on a constant temperature. During that period the fridge cycled very quickly (every 40-50 mins), but slowed once the beer was steady. Once the beer was steady, the control was very precise, but not more so than experiment 4. It seems like there are no benefits to putting the probe in the space, rather than attached to the fermenter.
24/10/14 - Added experiment 6 results: Putting the STC probe in it's own small reservoir seems to have adverse effects. There are larger temperature swings in the fridge space, which isn't really a problem in itself (and the fridge cycle isn't as fast as experiment 5), but the result is that the beer takes a huge amount of time to settle - over half a day. On top of that it undershoots the target temp by nearly half a degree.
28/10/14 - Added experiment 7 results: Turning the fridge off has pretty amazing results! There are no fridge cycles - obviously - and the actual beer temp is mainted within 0.06°C. An amazing degree of control. However, the beer was maintained a bit below the target temp (~19.7°C), and I'd be inclined to say that this wouldn't work well unless ambient temperature was a good few degrees below your target temperature. Also, I'd worry about letting fermentation go ahead without any ability to quickly cool the wort.
Here are the conclusions in a table:
For my own brewing, I will be changing to the set up in experiment 4 for now (probe on fermenter, tube heater).
For the future:
Other things to test would be…
- Test on actual fermenting beer. The exothermic properties of fermenting wort would have an effect on temp control
- Test on heating/cooling rates. Which experiment set up would most quickly correct a shift in beer temperature?
Best regards,
Andy
