Temperature Stratification in Carboy

Lately I have been trying to nail down my fermentation temperatures. I have noticed that the temperature of my glass carboy varies 3-4º F from the top to the bottom, as measured by an infrared thermometer. Once the fermentation gets going everything is stirred up enough that the variation quickly diminishes to pretty much nothing.

I get pretty good correspondence from the IR to a 12“ partial immersion lab type thermometer lowered into the wort at different depths. There’s a certain amount of guesswork, as I have to reel the analog out to get a reading on the lower depths. I am however satisfied that the IR is giving me a good indication. It could be a degree or so off of the absolute temperature, but the relative temps should be really good.

My tapwater temperature is in the high 80's, so I have been using a lot of ice with the carboy in the good old rope handle tub. Once I put the carboy in the tub with cold water, I obviously can’t use the IR to measure the bottom temperature.

Last batch I apparently used too much ice, as it took 48 hours to start off with an active yeast slurry (S-05). Problem is, while the yeast were napping, the IR was telling me the temperature at the top was a balmy 70º F. The ice water in the tub was being held at 65º F.

I can understand it’s colder in the basement than the attic, but wow, that’s a lot. I also fully appreciate that the delta T is going to be bigger with cold water on the bottom of the tub and warm air at the top.

My question (finally, right?) is; How should I regulate the temperature pre-fermentation? It appears the yeast are napping in the basement. When it warms up a little they take over the house and party.

To put it another way, if I want to pitch at, say 65 º F, where (and how) should I measure this?

Well I would think since the yeast has yet to start and you just areated it you don't have to worry O2 damaging the beer.

I would think you could pick the thing up and shake it a bit to average out the TEMPs. I put my Carboys and bucket on the top of a table, 30 inchs or so, soe I just bearhug them and shake them.

It seems to me you should consider this since you will have such a temp differation when in the ice.

Also once shaken you can see what the true Temp is and then decide if it need to go back in the ice or not.

Well thanks DPBISME, but that’s not gonna happen. I can see how that would alleviate the problem, but it’s all I can do to LIFT a 5 gallon carboy, let alone shake it.

Besides. I’m curious about the science. This must be something the commercial breweries figured out a long time ago. My local brewery uses 100bbl fermenters, and they’re not shakin’ them.

I'll start by answering your question about large cylindroconicals. They have chill bands - jackets which surround the fermenter and through which cold (and I do mean cold) glycol is circulated. This cools the beer next to the band which becomes denser and sinks. The cold beer coming down along the walls displaces warmer, lighter beer which rises up the center of the fermentor and, when it reaches the surface, is pushed over to the sides where it gets cooled and sinks. Thus there is a circulation whenever the chill bands ar running. Heat generated by the fermenting yeast adds to this effect. The beer is not, thus, at uniform temperature throughout but on average all beer gets exposed to the same temperature cycling.

With your carboy I'd suggest sticking electricians tape to the glass and pointing your IR thermometer at the black tape. This insures uniform emissivity and that you are measuring the temperature of the tape (carboy) not the ceiling or a wall as reflected off the glass. You are more interested in relative than absolute temperature here. If you can obtain an electronic (thermocouple or better still RTD) thermometer with a probe that can be sanitized then you can take absolute reading anywhere in the carboy (top, bottom, walls, center).

Instead of shaking the carboy you could sanitize a racking cane and stir with it.

Thanks AJ, for your thoughtful comments. I knew the big ones used glycol, but I hadn’t thought about the placement. Good to know.

I tried the tape and it doesn’t seem to do anything. That’s good, I guess, but a little surprising. I would expect the emissivity of the tape to be higher than the glass.

My current batch is just starting, about 1 bubble/min in the old double bubble airlock. Not enough to do much mixing. With a five gallon carboy sitting in 10cm of 10º C water and I’m seeing 20 ºC at the top of the water and 24 ºC at the top of the beer. I’m having to throw a couple or three ½ liter frozen bottles per hour at it to hold these temps. Apparently a lot of heat being generated in the basement, the part covered by the cold water.

For those that don’t do metric 10cm is four inches, 10 ºC is 50 ºF, 20 ºC is 68 ºF and 24 ºC is 75 ºF.

I’m quite amazed at the dynamics of the situation. It seems the yeast love to surf to the surface riding a carbon dioxide bubble but the majority of the work is happening at the bottom. Somebody should make a movie. Little cartoon yeast going “Yee-Hah, party!”

Wynne-R said:

Thanks AJ, for your thoughtful comments. I knew the big ones used glycol, but I hadn’t thought about the placement. Good to know.

I tried the tape and it doesn’t seem to do anything. That’s good, I guess, but a little surprising. I would expect the emissivity of the tape to be higher than the glass.

My current batch is just starting, about 1 bubble/min in the old double bubble airlock. Not enough to do much mixing. With a five gallon carboy sitting in 10cm of 10º C water and I’m seeing 20 ºC at the top of the water and 24 ºC at the top of the beer. I’m having to throw a couple or three ½ liter frozen bottles per hour at it to hold these temps. Apparently a lot of heat being generated in the basement, the part covered by the cold water.

For those that don’t do metric 10cm is four inches, 10 ºC is 50 ºF, 20 ºC is 68 ºF and 24 ºC is 75 ºF.

I’m quite amazed at the dynamics of the situation. It seems the yeast love to surf to the surface riding a carbon dioxide bubble but the majority of the work is happening at the bottom. Somebody should make a movie. Little cartoon yeast going “Yee-Hah, party!”

Click to expand...

I read this post kind-a fast.... did you say "Party at your house!"?

What should we bring?