# Minimising Fridgemate Temp Fluctuations?



## Bizier (6/2/09)

Hi all,

I have a fridgemate and I am concerned about the +/- 1 degree C either side of desired temp, and then the range above or below that will trigger your cooler or heater to work.

I have considered insulation to knock the spikes off the temp fluctuations, but I am worried that the exothermic reaction of the yeast will be exacerbated and raise the temp significantly.

I currently use 2 fermenters in a large fridge, so I can't use a large water bucket etc to act as a buffer, there is simply not enough room, though it would be nice.

Does anyone have tips re: any methods for stabilising temps?

Cheers
Dan


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## cubbie (6/2/09)

Have a look at this thread. There is a fair bit of temp control talk in the back few pages.

There are a fair few differing opinions, choose the one you like the best.


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## Thirsty Boy (6/2/09)

If you have the temp probe taped or otherwise stuck to teh fermentor... you will be accurately measuring the temperature of your beer... BUT you will also be forcing the beer temperature to fluctuate. The fridgemate has a minimum of a 1 differential, so by stickign the probe to the fementor.. the fermentor must change temperature by that differential. so if you have 19 as a set temp, then the beer is forced to swing from 18 to 20 and back. A minimum of 2.

If you have the probe hanging in the air of the fridge... the air inside the fridge is what does the swinging around, it will change temperature much more rapidly than the temperature of all that liquid... and all things being right, its average temperature will be your set-point. Then all you need to do is keep an eye on the difference between the setpoint of the fridge and the actual temp of the fermentor. If I am controlling my fermentation temperatures in this way, I tape an cheap ikea thermometer to the fermentor to monitior its actual temp, so I can tweak the fridgemate's set temp to give me my desired fermentor temp. The fermentor's temperature stays remarkable stable even while the fridge temp swings around.

TB


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## SpillsMostOfIt (6/2/09)

If your wort is several degrees away from where you want it to be, it makes sense (to me) to closely link the probe to the wort. Once it is where you want it to be, I think that hanging the probe in free air or just sitting it on top of the fermenter is the way to go for the reasons TB stated.

I have been taping the probe to the plastic fermenter *above* the liquid level to give me something somewhere in between. It seems to work for me.

The wort I pitched yeast into today is in a Bunnings fermenter with the unmodified lid screwed on (sans gasket). I am sitting the temp probe on the lid.


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## Bizier (6/2/09)

SpillsMostOfIt said:


> Bunnings fermenter with the unmodified lid screwed on (sans gasket)



I am unsure if it is brilliant or lazy minds that think alike, but that is my exact current setup. Though I have a thick towel under one fermenter with the probe held there, or I wedge it between the two and insulate with a bunch of blutac.


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## KillerRx4 (6/2/09)

Thirsty Boy said:


> If you have the temp probe taped or otherwise stuck to teh fermentor... you will be accurately measuring the temperature of your beer... BUT you will also be forcing the beer temperature to fluctuate. The fridgemate has a minimum of a 1 differential, so by stickign the probe to the fementor.. the fermentor must change temperature by that differential. so if you have 19 as a set temp, then the beer is forced to swing from 18 to 20 and back. A minimum of 2.
> 
> If you have the probe hanging in the air of the fridge... the air inside the fridge is what does the swinging around, it will change temperature much more rapidly than the temperature of all that liquid... and all things being right, its average temperature will be your set-point. Then all you need to do is keep an eye on the difference between the setpoint of the fridge and the actual temp of the fermentor. If I am controlling my fermentation temperatures in this way, I tape an cheap ikea thermometer to the fermentor to monitior its actual temp, so I can tweak the fridgemate's set temp to give me my desired fermentor temp. The fermentor's temperature stays remarkable stable even while the fridge temp swings around.
> 
> TB



+1
I've been doing it like this for a couple of years & have got it pretty well worked out. During rigorous fermentation -3 deg from target temp gets me on target.
A decent digital thermometer taped to the fermenter that displays to 0.1deg helps alot. I wish the fridgemate controlled to 0.1 or even had a deg F option.


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## WarmBeer (6/2/09)

Would putting your temperature probe in a glass of water in the same fridge allow better temperature control? The time taken to change the temperature of ~250ml water is going to be far less than 21 lt wort, but it will insulate better from fluctuations due to opening of the fridge door.


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## chappo1970 (6/2/09)

Totally agree with all above with hanging the probe in the fridge....

Althought I have only done 5 brews with the newly acquired Temprite. I am somewhat of a self confessed nerd and have been experimenting with the whole set up to ascertain the best position for the probe. Yes, I have waaayyyy to much time on my hands I know! :huh: 

I have put the probe in the fermenter, taped it to the side above and below the beer level and just plain hung it up. I also measured outside ambient temperature vs fermenter temperature vs inside fridge temperature.

Interestingly what I found is if you have the probe either taped to the side below the beer or in the beer itself, the fridge's inside temp will rise and fall quickly against the outside ambient temp, that's a given I know. But because of the water volume in the fermenter (I am guessing so correct me if I am wrong by all means), the beer temp will slowly rise and conversely will cool slowly. In much the same manner as trying to bring 23lts to the boil, it happens painfully slowly. Which means that your Temprite/fridge is slower to react to rising temps and has to run longer to maintain that preset constant temp +/-1deg. Because the Temprite won't kick in and or turn off the fridge before it hits the upper and or lower presets your wort temperature oscillates constantly between those presets even more so when we have had the very high outside ambient temps of late. In other words your beer will constantly oscillate +/- 1.5 degs. Plus your fridge runs for much longer, I found mine running for nearly 3 hours to bring the beer back to temp.

When the probe was hung up the fridge and or taped above the wort level, I found that the fridge ran more constantly, but in much shorter bursts 10-15mins per hour, to maintain the the +/- presets. But the beer temp stayed very very steady +/- 0.2 deg from the middle of the presets. Eg the beer temp oscillated between 18 and 18.2 deg throughout the fermentation. Where as with the in the beer method the beer Temp oscillated between 17.7 to 19.3 degrees over a simular fermentation period.

I guess as long as your not constantly openning and or using the fridge for other things then there would be no need to insulate the probe from temperature variations in fact you want your temprite to react quickly so as to keep your beer at a more constant temp.

I really do suggest that the best place for the probe is either on top of the fermenter lid or hanging in the air space above them as high in the fridge as possible. This will cause your fridge to work more fequently for shorter periods but the beer temp will be much more steady and constant over the fermation period. But like everything in the world it's just a matter of the individuals preference and what makes sense to them. Happy brewing!

Cheers 

Chappo


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## SpillsMostOfIt (6/2/09)

Bizier said:


> I am unsure if it is brilliant or lazy minds that think alike, but that is my exact current setup. Though I have a thick towel under one fermenter with the probe held there, or I wedge it between the two and insulate with a bunch of blutac.



It cannot possibly be brilliant minds...

I can fit four Bunnings/Coopers fermenters in my fermenting fridge (I've had three in there, which is probably enough) and so hanging the probe in free-air is the most sensible thing if I have three different batches of wort into which the yeast is pitched at different times.

Happily, whatever you do with a fridge and a temperature controller has to be better than not.


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## chappo1970 (6/2/09)

Spills you are dead right mate. Having a tempmate in the first place already has you in front!  


The the way I notice Ross has a retail thread on tempmates. It's like he knew of this thread? :huh: cue the twilight music...


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## Bizier (6/2/09)

This makes very good sense to me.

I think a thermostat probe in the wort is a great idea, but not for a device that has a 3 degree celsius acceptable operating temp.


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## niggles (6/2/09)

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:





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.










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. 




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:


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## Mantis (6/2/09)

Wow, that would be the best first post I have ever seen. 
Great work and thanks for all the info
:beer:


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## puffer_pics (6/2/09)

Niggles, 

I would like to see you do the same temperature monitoring with the sensor resting on the fermentor held with some electrical tape, Thats how i do mine. ! i fugure the temperature addition from the fermentation would increase the temperature inside the fermentor v's the temperature that you have in the small volume of water. Aditionally the fermentor is plastic and therefore is an insulator of heat to a degree.

Cheers Colin

if i hade one of those USB dataloggers id do the experiment.


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## niggles (6/2/09)

Mantis said:


> Wow, that would be the best first post I have ever seen.
> Great work and thanks for all the info
> :beer:



Hi Mantis,

Yep a long post but hopefully useful! I figure I've gotten enough out of AHB so time to give something back. 

I have also modified the setup to include an external cooling loop that runs through the (previously unused) freezer compartment. I'm currently using this to keep a Belgian Wit at 18deg, whilst a Czech Pils & Pivo Cerny are in the fridge at 12. Will detail the setup in a new thread (gear &equipment) shortly!

G'Day Colin,

Yep, I reckon your idead is not a bad way of doing it. The only thing is I'm not sure what the relationship between the beer temp & probe temp on the lid might be. Next brew (lager) I'll try the usb logger up there & get back to you. Since the temp diff is greatest (and presumably most important for flavours) at high Krausen, I'll need to do a new brew first. Gees.. more science experiments resulting in beer  .

Another way of getting a good "average" may be to place the glass of water/probe right next to the fermenter (see my first post). I'm guessing this would result in a good balance between beer temp accuracy (especially for bottom fermenting lagers) & temp fluctuations. Another experiment & more beer? :lol: 

Cheers, Niggles.


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## afromaiko (6/2/09)

Jaycar sell a USB temperature/humidity datalogger for $100 if you think that will help to understand the fluctuation any better.

http://jaycar.com.au/productView.asp?ID=QP6013


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## atkinsonr (6/2/09)

Hi Niggles. Some quality well thought out experimenting there. Well presented too!

Thanks very much!


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## chappo1970 (10/2/09)

Niggles you are a legend. Here I was thinking I am the only nerd here willing to show his inner nerdiness. Seriously good post.

You need to post that thread as an article so others can find it easily. Thanks for the work again!

Bye the Bye? The way you used the data logger and stuff any chance of an explaination of what you used and how your rigged it. Even a how-to so I maybe I could rig something simular. I simply have 2 Tempmates, a home weather station, you know one of those Oregon jobbies (and a thermometer stuck to a garden knome! :lol: Hey it gives me ambient temps) and a power usuage meter I bought from Jaycar to monitor power consumption of the fridges.

Chappo


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## hando (17/7/09)

niggles said:


> 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!!



I have a heater in the fridge in the form of a (low energy) light bulb inside an aluminium box. I use it only in the winter. It's on a timer usually set at 15mins per hour. To prevent the overshoot it could be rigged up to another fridgemate used on the heater mode. It would be interesting to see the data logger record my system... 

It could be anything from pretty good to all over the place :icon_cheers: I got the fridge for nothing and it's old so I'm not concerned about over-cycling it. I am probably less concerned about the power bill than I should be. :unsure: 

Anyway this system could be used effectively with a heater mat or belt too.


I just had an idea about trend monitoring and fully computerised automated control system that could predict overshooting of the temp and activate a heater or the fridge before the overshoot happens based on historical data of the hysteresis for the delays between cause and effect. Anyone want to take up that challenge??


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## Georgedgerton (26/9/09)

niggles said:


> 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!
> 
> ...




So given a lot of time has passed since this excellent post, have any other brewers (by experimenting or experience) have anything further to add, or does niggles have it down to pat


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## Screwtop (26/9/09)

Forgetting any temp recording, I discovered long ago that when I dropped temp to 1C to drop out the yeast, that the beer froze. Now how could this happen if the lowest temp reached was 0C (1 less that the Fridgemate set temp) given that the beer was around 4.8% ABV this should not happen. My simple guess was that the over-run plus thermal lag of the wort was responsible. Since having this happen (2 years ago) I have simply added 2 degrees to the min temp required. Prevents stuck ferments due to yeast dropping out due to low temps too 

Cheers,

Screwy


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