Ambient vs Fermentation temps with a chest freezer

[pfooti]

I'm getting a 14 cf chest freezer in the mail soon, which I want to turn into a fermentation chamber (probably going to build Mylo's Mother of Fermentation Chiller eventually, for now it's just putting buckets in the freezer).

When I hook up a thermostat to the freezer, where should I push temps (at first at least) to hit target fermentation temperatures? I've heard that temps in a 5 gallon brewing bucket are typically about 5 degrees above ambient. Assume I don't have a thermowell in the buckets and I have to just make do. Or should I just push the thermostat to about my target temps and leave it be? I'm mostly trying to brew clean american ales with a bit more control- figure on a consistent 60F ambient temp or something, right?

[Bugeater]

Don't worry about a thermowell. Just tape the temperature probe to the side of the fermenter and then cover that with some bubble wrap to insulate the probe from ambient air in the freezer. This will give you virtually the same temperature reading as using a thermowell actually in the wort/beer.

Wayne

[Cliff]

don't forget that fermentation is exothermic.

[cdburg]

I think that you'll be fine not using a thermowell with buckets. The plastic is more of an insulator, so it should be pretty close to the same temperature as the beer. When the freezer isn't running, I've noticed that the thermowell and exterior probes are almost always the same temperature. Using plastic, I would think that they will be pretty close, even when the freezer is running to cool the beer.

If you ever move to glass carboys, I would advise using a thermowell if you really want to be able to control things precisely. I use a chest freezer for a fermentation chamber as well. I've noticed that the freezer cools the glass much more quickly than the liquid in it. If the thermowell is taped to the glass, it's measuring the temperature of it, not necessarily the beer. That's more of an issue when cooling the beer. I bought a thermowell, and I have seen temperature differences as high as 7F between the exterior probe (carboy) and thermowell probe while the freezer is running and the beer is being cooled down. If you used a refrigerator, it might not as big an issue, since it would be cooled more slowly.

I was getting some fusel alcohol in beers that I knew I'd kept cool during fermentation (according to the probe taped to the carboy). Using a thermowell in the carboy solved the issue for me.

[captain carrot]

I tape the probe to the side of the fermenter and tape a piece of foam rubber over the probe to insulate it from ambient temps.
Good Luck!

[spiderwrangler]

If you ever move to glass carboys, I would advise using a thermowell if you really want to be able to control things precisely. I use a chest freezer for a fermentation chamber as well. I've noticed that the freezer cools the glass much more quickly than the liquid in it. If the thermowell is taped to the glass, it's measuring the temperature of it, not necessarily the beer.

As long as your probe (and the carboy glass near it) is insulated with bubble wrap or foam, I'd think that it would still be pretty similar to the internal temp of the ferment?

[cdburg]

If you ever move to glass carboys, I would advise using a thermowell if you really want to be able to control things precisely. I use a chest freezer for a fermentation chamber as well. I've noticed that the freezer cools the glass much more quickly than the liquid in it. If the thermowell is taped to the glass, it's measuring the temperature of it, not necessarily the beer.

As long as your probe (and the carboy glass near it) is insulated with bubble wrap or foam, I'd think that it would still be pretty similar to the internal temp of the ferment?

I always thought so too, but I've found that it's not, in my set up anyway. I've used both bubble wrap and foam rubber to create a pocket over the probe to insulate it from the ambient air, but it still gave a much different reading than the thermowell when the freezer is actually cooling. The freezer is cooling the glass very quickly which then cools the beer. The thermowell is reading the temperature of the glass, from what I can tell. With a plastic container, I don't think it would be as much of an issue, but it is with glass.

Since I've moved to the thermowell for the "cooling" probe, I've been much more pleased with my beers. I also run another Ranco attached to a fermwrap for heating. That probe is attached to the outside of the carboy, so I can see the readings for both locations at any given time. Everyone else's experiences may vary, but I didn't find that taping the probe to the outside of the carboy was as accurate as I would like. A carboy hood with a thermowell through the top has been much more accurate for me.

[pfooti]

Further complicating the measurement of ambient temps is the pretty significant stratification I'm seeing in the freezer itself; I get a two or three point difference between the top and bottom if the temp setting is high enough (60F) that the compressor isn't on very often. I have a feeling I might just move to a thermowell probe eventually. Maybe if I can find a 20gal plastic bucket that would fit in this chest freezer, it'd be worth tricking out. Or maybe just an old 1/2bbl keg.

This particular bucket has one of those LCD thermometer stickers on the outside; readings from that are about 4F higher than what my probe is reading. For now I can just assume that's a constant and program the temp controller appropriately.