Fermentation produces heat??? Or not!

[lyonshead]

I recently purchased a Taylor thermometer with a submergible probe, allowing me to monitor my actual fermentation temp for the first time. The previous method was to tape an insulated a419 probe to the side and just trust that I was close to the real temp.

My latest setup had the Taylor submerged and the a419 stuck to the side while controlling a fermwrap. Just so happens that the time of year has my basement at a consistent 64*. My target temp was also 64 so I was worried that the temp increase caused from fermentation would have me well over my temp and the fermwrap would really be pointless, as I would need to be cooling the wort, not heating it. Not so my friends!

As it turns out my beer has not moved a single degree the entire time. The Taylor measures degrees in .1 increments. I have seen fluctuations from 64.2 to 64.8 and that is it. The Johnson probe reads 64 on the outside and hasn't kicked on the fermwrap one time. Basically my efforts for temp control are pointless because the current basement temp is perfect!

My point in all of this, however, is what's the deal with the idea that fermentation increases the temp of your wort. That very clearly did not happen here. Is this a myth to drop in the bucket with all the others??

 

[hunter_le five]

Did you check to see if the wort was actually fermenting?

All kidding aside, if your measurements are accurate this is indeed interesting. I've always been under the impression that internal fermentation temps could exceed ambient temps by up to 10 degrees - a far cry from what you're seeing.

What kind of beer and yeast? Just curious.

 

[ajdelange]

Yes, fermentation produces heat. You can look in a brewing text and find out just how much. It is not enough to cause a temperature rise unless the surface to volume ratio is small (large volumes). This is why it is not noticeable at home brew scale.

 

[lyonshead]

Ha absolutely fermenting. Been monitoring very closely.
1.050 pale ale, very straight forward recipe.
US-05 properly rehydrated and pitched into 64 degree wort!

I'm with ya! That's what I've always HEARD and to this point believed!

 

[RmikeVT]

I active ferment in a swamp cooler. I did an experiment where I measured the swamp water temp and then the fermentation temp in the middle of the fermentation column. I found the temps to be with in a degree of each other. Concluding that the water in the swamp cooler is very effective at maintaining the internal temp of fermentation.

For my typical US-05/WLP001 Pale Ale fermentation, I like to keep ferm temp around 66-68. I usually start the swamp water (water bath) around 64*, once fermentation gets going into full swing, usually about 24 hours, it raises the entire bath temp up to 66-68 (ambient is 64) and maintains it until fermentation slows down at which point the swamp water drops back down to a little less than ambient. So, my experience says that fermentation definitely generates considerable energy.

Are you measuring ambient temp and wort temp with the same instrument? If not have you calibrated both instruments too each other? I am pretty surprised at your observation.

 

[RmikeVT]

Yes, fermentation produces heat. You can look in a brewing text and find out just how much. It is not enough to cause a temperature rise unless the surface to volume ratio is small (large volumes). This is why it is not noticeable at home brew scale.

Are you talking about actual fermentation temperatures rising? They definitely increase at the homebrew level. Depending on gravity of wort, yeast and ambient temps the internal fermenation temperature can be 5 to 10 degrees above ambient air temps if not controlled.

BYO just did an article on it, recently.

 

[lyonshead]

I have calibrated both instruments. But even if I hadn't it wouldn't seem to matter. Neither instrument (ambient or wort) has fluctuated. If they were independent of one another, they are still reading steady temps regardless of fermentation. I took a mercury thermometer into the room as well just to double check the air temp... 64 degrees!

I will say that I have not taken a final gravity reading yet. I'm quite curious now though. The fermentation is 7 days in and from my view through the Carboy and exp with this yeast, it was wrapping up last night/this morning. Everything about this ferment appeared standard

 

[lyonshead]

Are you talking about actual fermentation temperatures rising? They definitely increase at the homebrew level. Depending on gravity of wort, yeast and ambient temps the internal fermenation temperature can be 5 to 10 degrees above ambient air temps if not controlled.

BYO just did an article on it, recently.

I read the same article... That's why I felt compelled to start this thread! I have a tendency to take the word of those more experienced as gold! but my results just don't match what the experts say

 

[ajdelange]

As I noted earlier you can look in a brewing text and find out how many joules per second are released by an actively fermenting wort and from there do the math to figure how much rise you will get for a particular wort mass, fermenter geometry and thermal impedance. There will be a rise but for 5 gallons it isn't likely to be much and, of course, most of the rise would be at the core so you'd want to get your probe down into the core to see it.

As for the 'experts' I have seen some amazing things published. I haven't seen this article in particular so can't comment.

 

[Facinerous]

I have to agree with Rmike. Having a temp increase above ambient would directly corrilate with OG, yeast strain, and ambient temp. Since the temp you are fermenting at is at the mid-low range of the yeast your fermentation won't be very vigorous.

I did a stout reciently where I fermented at a farely high temp (70 degrees) and I usea fermentation chamber . Even in the midst of night were the temp outside was 45 or so the fermentation was hot enough to continuously raise the temp of my box kicking on my cooler. Needless to say I was impressed.

 

[Wynne-R]

Handbook of Brewing says ‘about 140 kcal/kg of extract’.

So for a 5 gal batch that starts at 1.064 and finishes at 1.015 that would be 12 Plato * 19L = 2.28 kg of extract. 2.28kg * 140 kcal/kg = 319 kcal. So if it went off like a bomb that would heat the beer 16.8C° or 30.0F°. I’d call that significant. Sorry AJ.

Of course real fermentations don’t take place in zero time. The above calculations also don’t account for any cooling to air.

Let’s try to get real. Suppose you have a vigorous fermentation that eats 1/4 of the sugar in four hours. That’s 7 ½ degrees of warming minus any cooling to the air. Plus the fermentation is still chugging along, faster than the air can cool your fermenter.

People on this forum routinely report fermentations 6-8F°above ambient. I believe ‘em.

 

[ajdelange]

I went through step by step calculations re the beer I have in the fermenter now and concluded that the temperature rise would be 12.7 °C under adiabatic conditions spread over the duration of the ferment which for this beer, a Pils, is typically 10 days. As I was posting the whole thing disappeared. I refuse to retype it. This rise amounts to an average power production of about 140 W. I don't consider either the rise or the power to be significant as we are talking over 200 kg of wort. Consider a 55 gal drum with a 140 W heater.

I also observed that the work done by my cooling unit depends only on the ambient temperature - not on the vigour of the fermentation. I thus conclude that in my system at least the yeast's heat contribution is not significant.

I do recognize that if I trapped all the heat that 13 °C could occur and that would be significant so that if you have a fermenter that approaches adiabatic conditions (good insulator, large volume) you can get an appreciable rise. In my small system most of the heat that has to be disposed of comes in from the ambient. In a 1000 bbl fermenter that might be less than the amount produced by the yeast.

 

[Wynne-R]

Fair enough. He got 12.7 °C and I got 16.8 °C on a bigger beer. Same ballpark. I don’t think many of us do 50 gal batches so I’m going back to my numbers.

315 kcal will melt 8 3/4 pounds of ice. Adiabiatic, which means perfect insulator.

Is that significant? It is to me. I use frozen water bottles to cool my water bath cooled fermentor, and it takes at least twice as many when the fermentation is hot.

 

[Yooper]

I do relatively small batches (10 gallons) in separate vessels. A cooler fermentation (under 64 degrees) will maybe rise a tiny bit (1-2 degrees) during active fermentation but I've personally seen a very active 67 degree fermentation rise up to over 75 degrees overnight in a 65 degree room. I tried my best to cool it, but it got up to 77 degrees before I was successful in lowering the temperature.

That may be anecdotal, but since it happened to me and I am not crazy (much), I concluded that a fermentation that is very vigorous does indeed produce heat. Because a warmer temperature increases yeast activity, it got even more active. More activity made it warmer- and I had a nearly explosive situation in the morning.

I've also noticed that I can keep a fermentation cooler than ambient in the basement- simply by putting the fermenter directly on the basement floor. In a 65 degree ambient temperature, the fermentation was 63 degrees even though the ambient temperature taken on the floor was 65 degrees.

I assume the concrete floor helped to cool the wort below ambient a bit.

 

[lyonshead]

This makes a lot of sense, I have been experimenting with us-05 at different temps. Next up is 66* and then 68*. I'll be very interested to see if the 68* ferment takes off into the 70's... The 64* still hasn't moved greater than half a degree

 

[kh54s10]

I don't know about always, but I have a pretty stable temperature in my basement and have seen the fermentation temperature, as per the stick on temperature strip on the Better Bottle, raise up to 10 degrees when I didn't control the temperatures properly.

 

[el_caro]

My point in all of this, however, is what's the deal with the idea that fermentation increases the temp of your wort. That very clearly did not happen here. Is this a myth to drop in the bucket with all the others??

I put down a 1.070 ale nearly 2 hours ago. Pitched at 21°C. Pitched active starter at full krausen and it took off in less than 30 mins. Starsan is already foaming at the airlock. It is now in a fridge with control set for 20°C and the surface temperature of the FV has risen to 22.3°C in that short time.
I expect fridge will take another hour or so to take control of the situation.
Ambient temperature outside the fridge is 19.5°C

Not that I needed convincing fermentation raises temperature of wort.

 

[FlyDoctor]

To the OP - what is your FV sitting on? In my Garage I always put it on a grate so it is not touching the floor. The floor is cool concrete and can suck a lot of heat. To really know if your experiential is valid, you need to avoid losses like this.

 

[biestie]

Does fermentation produce heat? Yes, it does. I believe that to be a fact based on everything that I've read.

Will it be noticeable? Depends. Before I added temp control equipment to my homebrewing tool box, I've had some that would rise from the temp at which it was pitched at, even though ambient was lower. I've had some that stay pretty much constant. Where I really ran into trouble was when I was a rookie, and tried pitching higher than recommended thinking that it'd drop overnight. Yeah, not so much. Not only did it not drop, but because it was pitched hot, it only got hotter, and significantly above ambient. None of this is "scientific", but I chose to precisely control my temperatures. I'm sure many would've been fine without it, but it's really nice to be able to set it and forget it. And I also like the fact that if I make a beer that I really love, I can look back on my notes and make again, right down to fermenting at the same temp within a degree.

 

[ajdelange]

That may be anecdotal, but since it happened to me and I am not crazy (much), I concluded that a fermentation that is very vigorous does indeed produce heat. Because a warmer temperature increases yeast activity, it got even more active. More activity made it warmer- and I had a nearly explosive situation in the morning.

All fermentations produce heat. A mixture of alcohol, water and CO2 has less internal energy than the mixture of sugar and water from which it is derived. Much of that energy is released as heat. There is no question about this. The question derives from the rates at which heat is added to or removed from the fermenter. If you put a fermenter with conductive walls in a cool room or on a cool floor more heat flows out per unit of time than is produced by the fermentation and the temperature drops. If you put it in a perfectly insulated fermenter no heat can enter or leave and the temperature goes up. If you put it in a warm room in a container with conductive walls then heat enters through the walls and is added to the heat produced by fermentation and the temperature rises until the temperature of the wort reaches the temperature of the room. Whether the heat produced by the fermentation is significant depends on several things including one's definition of 'significant'.

Increasing wort temperature increases rate of fermentation and, as long as extract is available, causes increased rate of heat production. This is a positive feedback effect and, under the proper conditions of thermal resistance and ambient temperature, can cause the 'thermal runaway' you saw.

 

[Bobby_M]

The best proof I have for exothermic fermentation is a 1.120 OG barleywine that I pitched onto half a yeast cake. My ferm chamber had to run at 58F in the box to keep the wort at 68F. Yes, a 10F delta.

 

[LBussy]

As I noted earlier you can look in a brewing text and find out how many joules per second are released by an actively fermenting wort and from there do the math to figure how much rise you will get for a particular wort mass, fermenter geometry and thermal impedance. There will be a rise but for 5 gallons it isn't likely to be much and, of course, most of the rise would be at the core so you'd want to get your probe down into the core to see it.

As for the 'experts' I have seen some amazing things published. I haven't seen this article in particular so can't comment.

For a guy that has a 5 gallon fermenter it's far more effective to just keep a constant outside temp than to worry about what the temp rise is (or is not) inside the vessel.

I think the amount of energy produced is 516 BTU per pound of ethanol produced. Ethanol is 46.06844 g/mol (or 6.584 lbs/gallon). Take my house ale at estimated 5% ABV, that's .25 gallons of ethanol or 1.646 lbs. This comes out to 849.336 BTU. Since a BTU is enough to heat 1 pound of water 1 degree F, and 5 gallons of water is 41.727 lbs, I have created enough energy to raise 5 gallons by 20 degrees F (excuse the glaring omission of the real weight of wort vs water but it's close enough for this description).

All that is if my numbers/math is right but this is the Internet and someone will correct me quickly if I am wrong.

20 degrees may sound like a lot but that heat is going to go somewhere. The "convection" currents inside a fermenter are pretty considerable and given that peak heat production coincides with peak physical activity inside, the wort is going to transfer heat to the glass, and in turn radiate it's heat pretty easily to the environment. Think about how quickly your coffee cools off; if you are making an effort to ferment in a properly conditioned space you will be fine (unless you get one of those mysterious 12 hour ferments that happen when nobody is looking).

I suppose there will be the odd person who for whatever perfectly reasonable sounding reason is fermenting in a Dewar flask and has to worry about this, but it seems that keeping some moving airspace around the fermenter is a lot easier than trying to condition the inside of the fermenter.

ETA: I guess I should add that advanced brewers have advanced equipment, batch sizes and methods. My post was directed at the poor guy that wanders in here worrying if he needs recirculating coolant coils in his Ale Pale.