Hi Guys,
Been lurking (& learning) for a while & gotta say I've been very grateful for the info/experience people share on AHB so I guess it's about time made some sort of contribution!
A lot of the stuff everyone's said here makes a lot of sense... here's a bit more data/pics/explanation from my own experience.
OK, so I set up a fermenting fridge a few months back with a Fridgemate. I had decided to order the submersible SS probe to control the temp as well as accurately as possible (geeky engineering type!). A mate of mine worked in air-conditioning, so I also scored a nifty USB temp logger to help monitor the fermentation.
The first fridge-brew was a Hefeweizen pitched at 12deg; set temp 18deg, differential 1deg. Without thinking I connected the Fridgemate directly to the probe installed through the fermenter lid. I stuck the USB probe to the fermenter with Blu-Tack. Here's the data log for the first 6 days of ferment:
View attachment 24565
As Tirsty Boy & Chappo have mentioned, you can see the effect of the large thermal mass of beer. The fridge is only cycling for a short time about once every 30 hours. The exothermic fermentation & heat transfer from the ambient air in the garage (~27deg) then take about thirty hours to trigger the fridgemate. Note the data log shows the beer temp dropping to around 13.7deg after each cooling cycle!! :angry:
If you think about it, this lag makes sense... at the time the probe sees the set-temp minus differential, the fridge turns off. The cold air in the fridge then continues to suck heat from the fermenting beer....Overshoot!!
At this stage, I thought it through & decided to mount a probe to a smaller thermal mass, or leave it hanging in the fridge. Here's a pic of the re-wired setup & fridgemate with two switchable inputs (SS submersible + standard). With the switch, I am able to monitor the beer temp and fridge temp with a flick of the finger.
View attachment 24566
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So, Like Thirsty Boy & WarmBeer suggest, a setup with the probe away from direct contact with the fermenter will give more frequent cooling cycles & a smoother temp log. I found that simply hanging the probe in the air gave very short cycling every few minutes (not good for the fridge life). So far I'm happy with the Blu-Tack/glass of water solution.
Here's the plot for the rest of the Hefe ferment.
View attachment 24569
Note the data logger is still attached to the fermenter - partly exposed to the air, away from the centre of the fermenter (where the heat is being generated) & partly insulated from the beer by the plastic. These things all mean the beer temp should be slightly higher than the log suggests, but also more stable (high thermal mass).
After carefully monitoring a couple brews, I have noticed the beer temp is approx 1-2 deg higher than set temp for ales (high krausen) & 1deg higher for lagers. Of course I have calibrated all thermometers & checked the probes are accurate (easily <1deg).
So, after a few tests and a bit of science, here's my Fridgemate 101:
- If the probe is immersed in the beer, (or stuck to the fermenter below the fluid level for that matter) you get an accurate reading, but poor fridge control (cooling overshoot, unstable temps). Overshoot is inevitable, hence use of proper closed-loop/PID controllers for more accurate control systems (e.g. HERMS/RIMS etc)
- Attaching the probe to a glass of water or other small thermal mass gives stable temp control at the expense of not knowing the exact beer temp.
- Fridge cycling can be adjusted easily, e.g. filling the glass to the top or using a larger/smaller glass.
- Leaving the probe hanging in the fridge will give accurate control, but be careful not to short-cycle the fridge.
- Assuming fermentation is active, the beer will always be warmer than the fridge/probe. On my setup, differences vary mainly upon fermentation activity and are 1-2 deg at high krausen for ales, 0-1deg for lagers.
- Using the Fridgemate as above, it is easy to achieve control to less than +/- 0.5deg
- A twin probe setup is nice, and allows good monitoring/control of fermentation.
So, bit of a long first post, but hope it helps.
Cheers,
Niggles.
PS: BTW I reckon an old fridge and a $50 fridgemate is the best addition to any brewers kit!
Oh, & in case you're wondering, the Hefe ended up a few points under-attenuated (~70% apparent from 1049-1014 with WLP300), but a nice drop all the same. Mmmm...nice & spicy. And a great starter for a Dunkelweizen....
Ahhhh. Science experiments & good beer. :beer: