Fermentation...air temp or wort temp?

I do not have a temp controller. To ferment at cooler temps, I have to put in a cooler on basement floor, sometimes using ice bottles. In general, when i read in recipes the fermentation temperatures, is it referring to air temp or wort temp? I'm a rookie, I've always assumed it was air temp.
But, when reading other threads about swamp coolers I have my doubts. Getting ready to brew a batch that says to ferment in lower 60's. just wanted to check and make sure I understood.

Yes, your assumption was wrong. You need to control the temperature of the wort. When fermentation occurs it creates extra heat. If you do a swamp cooler you will have to change ice bottles more frequently at first.

Get a large plastic tub and 6-10 inches of water. If you use a stick on strip thermometer you do not want to submerge it. Rotate ice bottles to keep the wort temperature in the low to mid sixties and keep the temperature as stable as possible.

I dont have a strip thermometer on my fermentor. My recipe calls for fermentation temps in the lower 60's. So, I assume I'll need to keep the swamp water in the upper 50s? Need to get a thermo on my fermo!!

Thanks for the help!! I need to get a thermometer to stick on my fermometer!

Right concepts, but the process may be flawed.

Who thinks a strip of plastic ("Fermometer") stuck on the outside of a glass vessel can represent the temperature of the contents of the vessel better than it represents the temperature of the air around it?

Got to couple the sensor to the thing you want to know the temperature of. The wort.

A piece of tape on the outside of the glass carboy is much likely to be closer to the surrounding air temp than the wort inside the vessel.

Don't want to burst bubbles, but if you think about the heat sources, sinks and paths, this isn't that hard.

Cheers!

CryoEng said:

Right concepts, but the process may be flawed.

Who thinks a strip of plastic ("Fermometer") stuck on the outside of a glass vessel can represent the temperature of the contents of the vessel better than it represents the temperature of the air around it?

Got to couple the sensor to the thing you want to know the temperature of. The wort.

A piece of tape on the outside of the glass carboy is much likely to be closer to the surrounding air temp than the wort inside the vessel.

Don't want to burst bubbles, but if you think about the heat sources, sinks and paths, this isn't that hard.

Cheers!

Click to expand...

Good point. There's a difference (small as it may be) in using a sensor taped to the bucket and insulated vs. one of those strip thermometers. I suspect that the strip (which I haven't used) would give you a fairly good reading on the vessel temp, but could be influenced somewhat by the air temp.

For the thread starter, if you can keep the water in the tub about 60-62*F for the first 4-5 days and then let it rise after that into the middle 60's to finish, you should be golden. Having it in a tub of water creates a large heat sink which influences the fermenter temp more than air will.

Will that give me a wort temp of of mid to low 60's or so I need to get water temp lower in upper 50s in order to drop wort temp to lower 60s? Thx

I use water to cool my fermentor. My set-up has the water level even with the beer. Even with the most violent fermentation the temperature difference is about 1.7° F. One degree is more typical for high krausen, winding down to zero as the fermentation finishes.

Don’t worry about the accuracy of the LCD strip, they’re pretty good, just don’t get it wet. You can read them to about a degree Fahrenheit. The conductivity of the water is about twenty times that of air. The temperature difference between the air and the beer is a few degrees at most, sitting in water. The air temperature won’t significantly affect the reading.