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Fermentation Fridge - Thermocouple Placement?

philm63

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Just put a batch of APA in the primary this weekend and dropped it into my new chest freezer complete with a Johnson Control. My issue is the thermocouple does not stick to the side of the glass carboy - I used good quality duct tape - it just falls right off! I thought I cleaned the surface fairly well.

So I dropped a second carboy in there and wedged a piece of cardboard between them effectively holding the thermocouple against the primary - isolating it from the second carboy by the piece of cardboard. Crude, yes, but it seems to be working fine. For now.

My question is this; does anyone have a better method of fixing the thermocouple to the side of a glass carboy in such a manner that it will stay there on its own with good pressure against the glass for accuracy?

And are there "best locations" for a thermocouple in the fermentation fridge? I currently have it on the outside of the carboy centered top to bottom.
 
Try some aluminum tape...  worked really well for me.  It's a little expensive for this application, but this tape comes in handy for other jobs around the house. 
 
Wouldnt worry too much about it.  As long as the ambient temp in the  cooler is at least 2-3 degrees lower than target fermentation temp you should be ok.
 
Thanks for the info, always appreciated.

Perhaps I'm looking too far into this; but being an engineer who does product safety testing for a living (including commercial refrigerators for food safety), I tend to dig deep.

Understanding the variability of the internal temperatures in a chest freezer regarding both vertical and horizontal gradients, and having only one thermocouple from which the controller gets its info, if I were to hang it in there just about anywhere (I tried this when I first got it) I'd be reading the air temperature in only one area under a no-load condition meaning it would fluctuate wildly as the thermocouple by itself does not represent a significant thermal mass. If I added a brass slug to the thermocouple it would stabilize things a bit, and while the gradients could still an issue, proper positioning of the slug could reduce this effect also.

Knowing this; my theory was that if I attached the thermocouple directly to the carboy, seeing how it represents a significant thermal mass compared to the total internal volume (7 cubic feet), it would act as a good steady load from which to regulate the temperature. Besides; the carboy and its contents are the very thing whose temperature we're trying to control as best as possible, no?

Feel free to smack me if I'm digging too deep.

 
I use a small piece of bubble wrap and paper towel to cover the probe, then cover it with mailing tape.    then I just set it at 1 or 2 degrees cooler than my desire ferm temp. There's a good article in the latest Brew your own mag that goes into great detail on this subject.
 
abarnard said:
Wouldnt worry too much about it.  As long as the ambient temp in the  cooler is at least 2-3 degrees lower than target fermentation temp you should be ok.

I do not agree with this statement at all.  A typical profile looks like this:

Day0:  beer = ambient
Day1:  beer = ambient + 3
Day2:  beer = ambient + 5
Day3:  beer = ambient + 7
Day4:  beer = ambient + 5
Day5:  beer = ambient + 3
.....

For some beers (hefe's, and big beers over 70 pts) I see up to 12F difference between ambient and the beer temp. 

I use blue masking tape or metalic aluminum tape.  Don't forget to put a 1/2" layer of insulation on top of the temp probe after you tape it down.  I use double layers of carpet pad, or a cut up camping pad.  In this configuration your probe will read within 1/2 degF of the internal beer temperature.

(also engineer)
 
philm63 said:
Thanks for the info, always appreciated.

Perhaps I'm looking too far into this; but being an engineer who does product safety testing for a living (including commercial refrigerators for food safety), I tend to dig deep.

Understanding the variability of the internal temperatures in a chest freezer regarding both vertical and horizontal gradients, and having only one thermocouple from which the controller gets its info, if I were to hang it in there just about anywhere (I tried this when I first got it) I'd be reading the air temperature in only one area under a no-load condition meaning it would fluctuate wildly as the thermocouple by itself does not represent a significant thermal mass. If I added a brass slug to the thermocouple it would stabilize things a bit, and while the gradients could still an issue, proper positioning of the slug could reduce this effect also.

Knowing this; my theory was that if I attached the thermocouple directly to the carboy, seeing how it represents a significant thermal mass compared to the total internal volume (7 cubic feet), it would act as a good steady load from which to regulate the temperature. Besides; the carboy and its contents are the very thing whose temperature we're trying to control as best as possible, no?

Feel free to smack me if I'm digging too deep.

You've got the right idea, Phil.  If you want to control the beer temp, you need to measure the beer temp.  The activity of fermentation generates quite a bit of heat.  So, your controller will have to work hard before fermentation starts, and after fermentation finishes....but, in the middle the yeast will do a lot of the work themselves.

In the future, you will want to get more controllers.  One for the air temp inside your fridge, and one for each beer.  I use heating pads to heat each carboy or bucket while keeping the air temp down at 45F or so.  I can ferment several different beers at several different temperatures this way...
 
Thanks, Tom. All good Stuff.  I know based on good ol' physics the fermentation, if very active, will generate heat so controlling that in the first few days is crucial to reducing potential negative effects from higher temperatures such as fusel alcohols.

Your methods look like they'll fit the bill nicely, thanks again.

 
tom_hampton said:
abarnard said:
Wouldnt worry too much about it.  As long as the ambient temp in the  cooler is at least 2-3 degrees lower than target fermentation temp you should be ok.

I do not agree with this statement at all.  A typical profile looks like this:

Day0:  beer = ambient
Day1:  beer = ambient + 3
Day2:  beer = ambient + 5
Day3:  beer = ambient + 7
Day4:  beer = ambient + 5
Day5:  beer = ambient + 3
.....

For some beers (hefe's, and big beers over 70 pts) I see up to 12F difference between ambient and the beer temp. 

I use blue masking tape or metalic aluminum tape.  Don't forget to put a 1/2" layer of insulation on top of the temp probe after you tape it down.  I use double layers of carpet pad, or a cut up camping pad.  In this configuration your probe will read within 1/2 degF of the internal beer temperature.

(also engineer)

Tom,  thanks for the info.  My experience with refrigeration comes from 20 yrs in foodservice.  Set the walkin cooler around 38 for internal food temp of 40.  With the ongoing reaction of the yeast it makes sense  the beer temp will vary over time.  Does air movement effect your above figures?  Food cools faster when forced air is used so would the addition of a fan in the ferm chamber help to remove more heat from the fermentor reducing how hard the controller works? 
 
I too was having problems with taping the sensor to a carboy and found it a nuisance. 

What I do now is to use an adjustable flat bungee cord wrapped around the carboy.  I put a couple of small squares for dense foam material over the sensor, also strapped under the bungee.

Works fine and takes seconds to put on and off. 

I also use a brewhauler and  a simple 2x4 rolling gantry crane with a boat winch and pulley arrangement to handle kegs carboys in and out of the chest freezer to avoid accidents as I have back problems.  That works great too!


Brian
 
I use blue painters tape.  I have some blue tape around the edges of some thermal bubble wrap (from home depot) I dry the carboy, place the thermocouple between the insulation and the carboy and quickly rub the edges of the tape to the carboy.

I do it this way with glass and plastic carboys (I only use plastic now).  It always sticks and stays. 

I have a 6" computer fan on a 12V wall wart circulating air.  This helps wick away heat generates by the fermentation. 
 
I use the painters tape too, and use a piece of styrene with a valley notched in it to hold the sensor for 5 gallon batches.  The painter tape doesnt leave glue residue on your carboy.  For 10 g I use a skinny hollow styrene rectangle, insert the sensor in the hollow space.  The rectangle is open on the 2 sides facing the carboys and I wedge it between the 2 carboys.
 
Got plenty of painter's tape in the basement, probably even a bungee cord or two, and I'm sure I could dig up some dense insulation material somewhere - plenty of viable options - thanks for the tips!

A small fan, eh? Seems to me circulating the air should negate the gradient issue altogether helping to stabilize temperatures in the carboy much faster. And wouldn't circulating air also reduce humidity? I'm thinking mold here. I can see condensation on the walls inside the freezer, and if left unchecked at temperatures in the mid-to-high 60's, we'd have mold for sure. Any ideas on this one?
 
abarnard said:
Tom,  thanks for the info.  My experience with refrigeration comes from 20 yrs in foodservice.  Set the walkin cooler around 38 for internal food temp of 40.  With the ongoing reaction of the yeast it makes sense  the beer temp will vary over time.  Does air movement effect your above figures?  Food cools faster when forced air is used so would the addition of a fan in the ferm chamber help to remove more heat from the fermentor reducing how hard the controller works?

Absolutely, a fan will increase the rate of heat uptake by the surrounding air.  It will also improve the rate of heat exchange with the walls of the freezer.  Its a relatively linear function of air flow rate. 

philm63 said:
A small fan, eh? Seems to me circulating the air should negate the gradient issue altogether helping to stabilize temperatures in the carboy much faster. And wouldn't circulating air also reduce humidity? I'm thinking mold here. I can see condensation on the walls inside the freezer, and if left unchecked at temperatures in the mid-to-high 60's, we'd have mold for sure. Any ideas on this one?

Air circulation won't do much (if anything) for humidity.  The air relative humidity will stabilize at near 100%.  As the fermentation progresses some water will volatilize off with the CO2, which will put more water into the atmosphere.  Unless the water laden air has someway to escape that extra water is going to condense onto the colder walls of the cooler.  If the air were to dry out (in some unknown way) the condensation would re-evaporate and work to keep the RH near 100%.  So, if your walls are wet, your RH is going to be very high. 

I've heard of some people using damp-rid to absorb excess water....but, I can't attest to its effectiveness....and I have my doubts.  Without a RH meter, and some controlled experiments...its hard to know for sure.

I have an AC unit in my walk-in which works as a dehumidifier.  The condensation on the coils is drained out to the evaporator side and blows out with the hot exhaust.  So, this isn't a problem I've had to solve. 

 
Somebody tipped me off to plumbers putty.  Makes your probe stick to a sweaty carboy instantly, insulates at the same time, is re-useable, and its cheap to boot.
 
If your temp controller's sensor is taped to the fermenter, and if there is a 2-to-3 degree difference in your cooling (or heating) on and off temperatures, your beer will be constantly varying between the cut-on and cut-off temperatures. If your temp controller is sensing the air temperature, your beer will be fluctuating a fraction of the difference between the cut-on and cut-off temperatures.

I've read that some yeasts are highly offended by temperature variations. That raises several questions: Do I believe everything I read? (Not for several decades.) How much variation does it take to affect yeast activity? How much does the temperature of the beer vary if the ambient air is varying 2-to-3 degrees? What am I missing here?
 
durrettd said:
If your temp controller's sensor is taped to the fermenter, and if there is a 2-to-3 degree difference in your cooling (or heating) on and off temperatures, your beer will be constantly varying between the cut-on and cut-off temperatures.

You are correct.  You solve that particular problem by using controllers with tighter tolerances than 2-3 degrees.  An STC-1000 have a minimum differential of 0.3 C or 0.54 F.  If you heat AND cool...then the total swing is 1.1F. 

Second, if you keep the beer in a cold room (10F or so below desired beer temperature), then you only have to HEAT the beer to hold the temperature...and let it cool naturally.  This approach drops the total swing back to ~1/2 F. 

If your temp controller is sensing the air temperature, your beer will be fluctuating a fraction of the difference between the cut-on and cut-off temperatures.

In the short term, this is true...assuming that the beer is not producing any heat of its own.  My experience says that its about 1/3rd of the air temp swing.  That said...it is HIGHLY dependent on local factors: size of the batch, fermenter material, size of the fridge, mass of the fridge, etc. 

The other issue to consider is the "assumption" in bold above.  Its not a valid assumption.  An active fermentation produces a LOT of heat.  A completed fermentation produces NONE.  The beginning and the end produce somewhere in between.  The amount of heat depends on how active the fermentation is.  the more vigorous the fermentation, the more heat.  Hefe yeast is notoriously active.  I have seen hefe fermentation raise the temperature of the beer 12 F above the air temperature at the peak of fermentation.  A more typical number is around 5 F, though.

If you hold a constant AIR temperature, then the extra heat of fermentation will simply raise the temperature of the beer by the amounts described above.  So, you are holding your fridge at 60F, and the hefe raises another 12F for a BEER temperature of 72F.  In fact if a Hefe yeast were allowed to get up above 68F or so, it might take off like a rocket and produce even more heat...maybe landing above 75F.  Now you have a bubble-gum flavored beer.

Or....you anticipate this temperature rise...and set your fridge to 50F.  50F is too cold for the Hefe yeast to get started and ferment vigorously...so it ferments very slowly (if at all).  Thus it produces only a couple degrees of temperature rise.  Your hefe ends up fermenting at 53F (or so).  Now you have zero Hefe flavors...and the fermentation may not complete.

These effects are most pronounced with Ales. 

I've read that some yeasts are highly offended by temperature variations. That raises several questions: Do I believe everything I read? (Not for several decades.) How much variation does it take to affect yeast activity? How much does the temperature of the beer vary if the ambient air is varying 2-to-3 degrees? What am I missing here?

Some yeasts are ABSOLUTELY affected by temperatures, and temperature variations.  Some not so much. 

Kolsch yeast is notorious for dropping out of suspension if subjected to frequent, rapid, large, temp swings. 

I cannot get Cal Ale to ferment below 65F...even that I have a hard time with. 

hefe yeast I've described above.

Saison yeasts are notorious for quitting early without a significant rise in temperature over the ferment.  But, you can't START high, or they will produce nasty high-order alcohols. 

Most belgian strains produce very different flavors over a very small temperature range. 

http://www.whitelabs.com/beer/BelgianYeastStrains.pdf

I'm playing around with WLP570 right now.  And I promise the chart above is very accurate for that strain.

So, if you want to target a specific flavor from a belgian yeast, you have to control the BEER temperature withing a degree or two during the first 72 hours of fermentation---after that it doesn't matter as much.  But, this is during the lag and ramp phases of fermentation where the heat produced by the yeast is increasing.  Without good sensing of the beer temperature, you'd never be able to hold the needed temp range.

You don't have to believe what I'm writing....go do the experiments yourself.  You will quickly find that sources like Jamil Z, White Labs, and Wyeast are very reliable...and won't need to continue to prove everything they say to yourself.  I don't quote information from any source other than the ones I just listed.  I've done a few tests of my own, and I've never managed to do anything except confirm the results reported by these authorities. 

At this point, I take those sources information at face value.  Any experiments I might try, in this regard, are limited to assessing a specific desired recipe characteristic rather than trying to completely characterize a yeast.  If I want spicy, I target the spicy temp range.  If its too much/not enough, I adjust a degree or two on the next iteration.


 
I use those flat elastic bungie cords that you can now buy with the plastic hooks on the end.

The elastic is maybe an inch or more wide.  The ones I have are adjustable so I can easily use them on different size carboys or on kegs.  I just wrap the bungie around the container,  clip the hooks together and put the probe under a small pad of foam insulation and secure it under the bungie tight  against the container.

Never really tried tape, this just seemed and easy way to do it.

Brian
 
 
Tom,

Nobody told me when I stared brewing that I was going to have to THINK!

Thanks for doing the hard work to research and quantify so many of the moving parts of brewing. Thanks also for the endorsement of Z and the yeast labs.

Dan
 
I have to second that. I learn as much from Tom's post as I learn from many books I have read on brewing beer.
 
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