Measuring Fermentation Temperature

[lael]

I know this site thrives on conjecture and hearsay, so I hope I don't break the mold with posting actual data. But yes yeast is exothermic (heat generating) during fermentation, and can raise the fermentation temperature buy several degrees over the ambient temp. The attached examples were done in a chest freezer controlled by a brewpi (www.brewpi.com). The wort temperature during early ferment is significantly higher then the surrounding air. A fan in the freezer would have probably equalized the temp a bit, but it clearly shows that where you are measuring your temp makes a difference

Site thrives on conjecture - remember reading a similar comment in how to brew and laughing.

Do you use one of the brewpi's?

 

[verysupple]

That makes sense, a static liquid wouldn't pose the same issues, in regards to the deadspace between the inside of the thermowell and the probe I guess Heat transfer paste would work as a good conductive medium between the two.

Maybe that'd work, although the only thermal paste I'm used to working with is for computer CPUs and that's designed to be used in a very thin layer, not a thick clump. If you had some industrial type paste (if that exists) that might work.

I think the best solution is to simply get a thermowell that's the right size for you probe.

 

[verysupple]

I drop the probe in so that it hits the end of the thermowell (which is positioned in the middle of my 30l fermenter, and goes down about halfway). Stainless on stainless - I'd imagine that translates a reasonably accurate temperature of the surrounding wort.

Yeah, that should work fine because the probe and thermowell should be in equilibriuim. The issue is if you're relying on air to transfer heat between the thermowell and probe.

 

[bmarshall]

Does +/- 1 deg really make much difference?

 

[Ducatiboy stu]

Not really if you get it below 18-20*c.

Remembering that the yeast will create it own heat.

 

[verysupple]

Does +/- 1 deg really make much difference?

If it's consistently 1 deg out then it's not a problem. You can adjust the ferment temp up and down as required to get the desired result. If it's not consistent then it does make a difference.

If you have your probe stuck to the outside of the FV and it consistently reads 1 deg lower than the actual temp then that's fine. However on the homebrew scale, no two ferments ever create the exact same amount of heat at the exact same rate, so the error in the measurement will be different for every ferment. The problem comes when you actually have no idea what the real temp is.

 

[bmarshall]

There couldnt be drastic differences in ferment temp from different varieties of yeast and amount of sugars in the wort for homebrew volumes. Commercial volumes may vairy a bit though.
Be good to see a small and large volume ferment with same amount of sugars, and two with same volume ferment with different amount of sugars. Then vice versa with yeast varietys.

 

[Dips Me Lid]

Maybe that'd work, although the only thermal paste I'm used to working with is for computer CPUs and that's designed to be used in a very thin layer, not a thick clump. If you had some industrial type paste (if that exists) that might work.

I think the best solution is to simply get a thermowell that's the right size for you probe.

Yeah I'd agree the right sized probe for the well is paramount, industrial type pastes are available for this use as well, not sure what the losses from direct contact between metals to contact via heat transfer paste would be, but I'm guessing the accuracy would be close enough.

 

[superstock]

I was doing an experiment today with using different materials for the swamp cooler covering and only had water in the fermenter, so I pulled the temp probe out of it's insulated (wet suit ) pocket on the side of the FV and dropped it through the airlock hole into the water. The result------- in the pocket 21.7'c, in the water 21.8'c-------so it seems to me that a temp probe in a well insulated & tightly fitting pocket reads the wort temp pretty accurately.

 

[breakbeer]

I still find it hard to believe that people aren't measuring the temp of the actual wort & rely on a small bottle of water or something taped to the side of the fv

If you're gonna do something, do it properly

 

[Glot]

An interesting concept. Actual data. Sorry.

 

[vortex]

I was doing an experiment today with using different materials for the swamp cooler covering and only had water in the fermenter, so I pulled the temp probe out of it's insulated (wet suit ) pocket on the side of the FV and dropped it through the airlock hole into the water. The result------- in the pocket 21.7'c, in the water 21.8'c-------so it seems to me that a temp probe in a well insulated & tightly fitting pocket reads the wort temp pretty accurately.

So it should. The wall of the fermenter will equalise with the wort temp pretty quickly.

That said, I have a thermowell in my wort - though I didn't notice much difference between that and when I sat the fermenter on it.

New fermentation controller will have graphs and logging. Data geek wants to know.

 

[lael]

Would love more data from people that have thermowells / place the probe in the wort. Fascinating they were only marginally different.

 

[Scooby Tha Newbie]

Nice thread good info. I will go with the stubble cooler on the out side idea (2.5deg less than ferment temp dialed in). Easy simple and ticks all the boxes

 

[beerkravin]

is measuring the ambient temperature of your fermentation area (read: fridge) less ideal than measuring the temperature of the wort itself?
measuring the ambient requires something to activate the heat\cool cycle. If the fridge itself is chilling the wort, then what's heating it back up?
The temperature outside the fridge. the heat provided by the ferment itself. the heating side kicks in to balance it out. yeast doesn't like a lot of fluctuation, a stable warmer temp or a stable cooler temp will give you more consistency.

Ambient
Fridge cools ambient > When Ambient hits desired temp > cooling stops > drops below ambient > heating starts > start again.

the logic in this involves 'Thermal Dynamics'. while the ambient temp can fluctuate back and forth quite rapidly, the mass of the wort will fluctuate much slower keeping it more stable. or for a simple analogy if i had boiling hot water and freezing cold water and sprayed you with each alternately fast enough, it would mostly feel warm to you because your body needs time to heat or cool accordingly, somewhere in the middle is 'warm'

Wort
Fridge cools ambient > ambient cools wort > wort hits desired temperature > Cooling stops > Drops below ambient > heating starts > start again

the difference here is that second step, "ambient cools wort". if I freeze something, or heat something, both the cool and the heat need to penetrate the mass to heat or cool it evenly. while fermenting, your wort is spinning, stirring and being circulated by the yeast, but that's still a lot of mass to heat or cool to hit temperature.
the fridge will keep cooling until the mass is at the ideal temp, but in doing so, theoretically the ambient would be cooler than the mass due to the fridge still running while we're waiting for that mass to cool. the same goes for the heat.

so what you have with ambient is fast temperature swings back and forth, which I think would be slower, but much more gentle at raising or lowering the temperature of your wort. with measuring your wort, you'll get to the temperature quicker but you'll probably find there will be bigger swings while the heating and cooling kicks in and out adjusting the mass of 23+L of wort.

if you can get your wort to the temp you want BEFORE you pitch your yeast, i think the difference between the two is negligible as once you reach that desired temp, fluctuations are going to be minor either way you choose. probably be easier to split hairs.

to test it you would need two calibrated thermometers. one to measure the ambient and one to measure the wort, monitoring the differences between the two.
i would be surprised if the difference was +/- 2C

 

[zarniwoop]

OK at the risk of putting some further science in this...

We're basically dealing with a thermal system here with the wort the being both the heat source and the target measurement point. As you move further away from the wort through various materials (side of the fermenter wall, stainless steel thermowell etc) you will encounter thermal resistances of varying values, if the wort is generating heat then as you pass through each resistance the temperature will drop as some of the heat is absorbed by this interface (resistance), how much it drops will depend on the level of resistance and how much heat energy is passing through it, but the better the conduction properties of the interface the less temperature drop, i.e. if the wort is 25C and generating heat then it might be 24C on the other side of a metal thermocouple with thermal paste but only 23C on the other side of a plastic fermenter. Once the wort stops generating heat the difference will be significantly lower as they will reach thermal equilibrium as there is no heat energy coming from the wort to generate a thermal difference across the interface. There may be a slight difference owing to the varying insulating levels of the fridge.

Bottom line when the wort is generating heat you're better off measuring the actual wort, when it's not it probably doesn't matter.

 

[Glot]

But that takes all the voodoo out of making a good beer
A good clear explanation though.

 

[O-beer-wan-kenobi]

So if heat rises, is the top part of then wort warmest or the bottom?
If it is bottom fermenting yeast is the bottom warmest?
What position should the temperature be taken? Top, middle, bottom?

 

[lael]

Yeah, that's why I'm interested in hearing more from people who actually have the thermowells. I'm guessing there is a difference in from the steel, but realistically I doubt any people have managed or attempted to get thermal paste to the end of a long narrow tube ( good luck...) Which means the air inside the thermo well also acts as an insulator too, right?

So, I'm curious to hear from more people what the temp is inside the thermo well, taped to side under insulating material (foam/neoprene sound like the most common) and directly in the wort (with great sanitisation of course!)

Any other people have them?

 

[zarniwoop]

Sadly I no longer have access to multi-channel temperature data loggers or else I could have stuck probes all over/in my next batch. Anyone else got any kit?