Position of temperature probe

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chrisstuarthall

TheGquaffer
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I have converted a chest freezer into a fermentation container using the usual controller (ATX-800) and have been fermenting two 5 gallon brews.

Something I would appreciate opinion on, where best to position the temperature probe?

I had it taped to one of my bins with the heater in between.

I have now bottled 5 gallons and put the bottles in the chest.

Everyone's thoughts and experiences much appreciated.
 
I have converted a chest freezer into a fermentation container using the usual controller (ATX-800) and have been fermenting two 5 gallon brews.

Something I would appreciate opinion on, where best to position the temperature probe?

I had it taped to one of my bins with the heater in between.

I have now bottled 5 gallons and put the bottles in the chest.

Everyone's thoughts and experiences much appreciated.

Read a interesting article about this somewhere recently... I think it may have been on reddit?

Basically its really hard to position your probe in the perfect position, this is because your fermentation is exothermic and gives out heat making the fermenting beer slightly warmer than its environment.

You've also got to factor in the delay in liquid heating or cooling compared to air.

I work in a lab, the most scientific way we measure fridge temperature is to place the probe in a tube of glycerol. Although this wouldn't help with the exothermic reaction of your fermentation.

I think the article I read suggested attaching the probe to your FV to be the most accurate form of temperature reading.
 
Read a interesting article about this somewhere recently... I think it may have been on reddit?

Basically its really hard to position your probe in the perfect position, this is because your fermentation is exothermic and gives out heat making the fermenting beer slightly warmer than its environment.

You've also got to factor in the delay in liquid heating or cooling compared to air.

I work in a lab, the most scientific way we measure fridge temperature is to place the probe in a tube of glycerol. Although this wouldn't help with the exothermic reaction of your fermentation.

I think the article I read suggested attaching the probe to your FV to be the most accurate form of temperature reading.

Do you know how many degrees C are added by the exothermic reaction?
 
Do you know how many degrees C are added by the exothermic reaction?

It depends on how active your fermentation is, if your brewing something with a low OG then your reaction of fermentation is going to be slower and give off less heat. If your brewing something with a really high OG and you pitch a higher cell count your fermentation is going to go crazy and give off a lot of heat.

Typically your taking 2 - 5 C above ambient temperatures. Up to you if you consider this a problem or not, but if your going to the effort to make a temperature controlled environment I'd maybe factor this in. Especially if your brewing a RIS or something, if your environment is set to 22C, your fermentation vessel will be at 27C... This would produce off flavours.
 
In my brew fridge I have the sensor hanging just off the side wall about 2/3 up. This means I'm measuring air temperature with hopefully a median point. I figure that all instructions for fermentation are based on having the FV in an environment with a particular air temperature so why would I not measure that way?
 
You have to be sure of what the question is i.e. what is it that you are trying to measure.

If you want the wort to be at a specific temp then you need to measure by dangling the probe into the wort. A safer method I use is to have the probe against the side of my FV and covered from the air by a few layers of small-bubble bubblewrap. Not sure how effective that would be with a glass DJ though, as there would be a level of heat transfer from the unprotected glass.
 
I secure the probe to the side of my FV and place several layers of insulation over that. It's not perfect but it can be consistent.

I also think there is a product that has a thermowell in a rubber bung. Basically it's a regular Carboy bung but instead of one hole for the airlock, it has two. The second hole is really a "well" that extends about ten inches down into the fermenting beer. They are designed for glass thermometers but I bet you can probably place the probe down inside of that too.
 
I think the size of the heater or fridge motor must make a big difference. I have worked out I likely need a 10W heater. In fact using 18W so to lift a brew sitting at 5 degrees above ambient 0.5 degrees takes around 1.5 hours it really does not matter where the sensor is when warming up so slowly.

But if heating up quickly then if you tie the sensor to the fermentor behind a sponge like I have done then the walls and air in the fridge will be a lot hotter than the fermentor and when the heater is switched off heat will still be going into the fermentor.

Heating is easy one can select a bulb just the right size but cooling is the problem. You can't alter the size of freezer motor and you don't really want an over shoot. So really with cooling air temperature is the only way.

As yet never needed to cool only heat so my sensor is on side of fermentor and the heating tile is under the fermentor. Up to now when it gets too warm I stop brewing.
 
It depends on how active your fermentation is, if your brewing something with a low OG then your reaction of fermentation is going to be slower and give off less heat. If your brewing something with a really high OG and you pitch a higher cell count your fermentation is going to go crazy and give off a lot of heat.

Typically your taking 2 - 5 C above ambient temperatures. Up to you if you consider this a problem or not, but if your going to the effort to make a temperature controlled environment I'd maybe factor this in. Especially if your brewing a RIS or something, if your environment is set to 22C, your fermentation vessel will be at 27C... This would produce off flavours.

Does Maxwell's third law of thermodynamics not come into play when you have a closed environment?
 
Third law of thermodynamics doesn't come into play until close to absolute zero. By then, I doubt I would be worried about the temp of my wort 😄
 
Since the post above I have replaced the thermostat in my mothers freezer. The sensing tip goes into a pocket and when I came to check temperatures I found a sensor in center of freezer compartment went slightly lower every time the motor cycled on.

Clearly the pocket leads the sensing tip close to the evaporator so it switches the unit off before the main chamber has reached the desired temperature on first motor run, and as this lack of heat is slowly transmitted to the cooling void.

If to heat the void we were to reverse the fridge motor then using the same sensor for heat and cold would work. However at least in my fridge the heater is under the fermentor where the cold air is supplied from the top.

I therefore see a problem in using same sensor for heating and cooling. Clearly you don't want heating and cooling on together so it would require two units. Only when the unit on fermentor is over temperature would the other unit be switched on but the second unit would control near to the evaporator so cooling would be gentle.

OK this may be the ideal as far as control goes but do we really want two temperature controllers? Other option is to restrict the run time of the motor. A simple mechanical timer with every other pin set so max run time is 15 minutes would reduce the cooling by half and allow time for the heat to be absorbed by the fridge. However 15 minutes may be too long.

It's still the same problem the motor is too big. A wine chiller with clearly a smaller motor for unit size would work better. The other problem is heat rises so we cool from the top and heat from the bottom so again unlikely the same sensor can be used for both functions.
 
I do all my fermenting in converted chest freezers. If you have a thermowell port added to the bucket, put it there. Next would be inside a jacket around the bucket. You want the probe to tell you the temp of the wort fermenting, not the ambient air. Also, you should put a fan inside the freezer. Moving the air around helps keep the temp constant inside so you dont have pockets of hot or cold air, and it will keep rust and mold from forming too.
 
Mold or Yr Wyddgrug has formed there is some debate when it got its name and how but it has been called Mold for a few hundred years anyway.

As to control much depends on how quickly you heat or cool. At 10 - 20 watt it does not really matter where the sensor is. As the power increases to 60W then you have to control the heat or cooling source rather than the brew or it will over shoot.

Many do in fact control both having a fridge set to 5 degrees and a second sensor in the brew set to 14 degrees is not so bad as the air will not cool beyond 5 degrees so it will still control quite well. Also of course over cooling is not too much of a problem as it will soon warm up again with no harm done.

Heating is something else though. Even at 18W if I set the temperature to say 20 degrees it will likely hit 22 degrees when ambient (and original brew temperature) is 16 degrees. If however the brew is already sitting over 20 degrees then with a 0.3 degree differential on to off it will hold it at 20 degrees nicely.

I start at 18.5 degrees until I see the fermenting has started then raise 0.5 degrees per inspection until sitting at 21 degrees. At some point as summer approaches I will need to leave the door of the fridge open. At least for early stages when the fermenting its self is producing heat. Since in a fridge/freezer I don't really want to run the fridge motor just want to use the insulating qualities of the fridge to keep it warm in Winter.

Clearly not a problem at the moment but it will be. I made an error got a temperature controller which only has one set of contacts or I could use other set as an alarm. Think I will have to buy a second one with two sets of contacts so it can light a warning light if it gets too hot.
 
imho you want to place the probe measuring the beer temperature close but not too colse to wherever the change is being applied, in most brewfridges with a tube heater thats via air circulation so plastered against the vessel side behind a patch of insulation should work well.

while fermentation is very active the rising of all the co2 bubbles will stir the brew enough to promote an even temperature throughout the brew. tho at the begining or end of the fermentation the activity will not be enough to help in this way and the liquid will change in accordance with whatever input is being applied from the outside in toward the centre a centrally positioned probe in a thermowell may well lead to overheating or overchilling of the perimiter beer before the target registers at the centre of the brew.

if however your applying temperature change via a coil immersed in the brew a centrally mounted thermowell for the probe may be a better option.

by measuring the temperature close to the point of change application, change should be registered in advance of any overapplication, and while hitting target may take a tad longer with more application steps and if chilling waiting for the compressor delays.. the risk of overapplication of any change is minimised.

all i have to back this up is my own observations of a few simple tests i performed measuring the change in temperature in a Stainless steel fv wrapped in heat trace cable, and the core temperature of the still water lagged a fair number of degrees behind that of the perimeter liquid.
 

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