How much temperature swing is OK when fermenting?

I asked a very similar question a few years back and got what I think to be some pretty good feedback from @PortLargo and others:
https://www.beeradvocate.com/community/threads/fermenting-temps-fermometer-accuracy.576635/

 

Not sure I'm following your math...I would consider a low of 66 to a high of 68 to be a two degree swing. Is that still too much? IMO, probably.

But that's not how most of us ferment. It's rare to run both a heating and cooling cycle daily. More likely you will be using only one input. In the summer (which is 11 months out of the year for me) you will be in "cool" mode only, i.e. a 1° swing. I cannot recall having temps that require dual modes on the same day.

You can tighten up the spread on an Inkbird by switching to Celsius where you can set a 0.3° differential (~0.5°F). This also allows a set temp with a 0.1° accuracy which is ~0.2° F. Example: if you wanted 67F, then set 19.3 with 0.3 diff...if in cool mode the wort would swing from 66.7 to 67.3F. Is that tight enough? Probably. While that sounds ideal, in the real world I find the wort temp normally overshoots by as much as 0.5F with each cycle. I. E, when the cooling stops the wort still drops a tad as the temps equalize throughout the liquid. YMMV.

Pretty much without exception you can figure out how to dial all this in within a few brew cycles.

 

I honestly couldn't tell you the difference in two beers brewed exactly the same with one fermented within 1 degree and another fermented within 3 degrees, assuming the temperature swing is slow over 24 hours, not over 2 hours. I'd add I don't think a majority of people can. (e.g. S-05 temperature range is 64-82°F, if you ferment in the 70-73 range you won't notice)

IMO, it only matters if you're near the upper or lower range of the yeast and/or what kind of profile your trying to get out of the yeast (e.g. Belgian yeast that has a wide range of esters pending temperature of fermentation, or some yeast liking higher end of temperature range for higher attenuation)

I'd also add that the surface temp of the carboy vs the liquid temp of the center where the probe is located is going to vary so much you're going to do more harm heating/chilling cycling the beer than good. If the center of the beer is at 67'F and the heater turns on, the surface temp of the bucket/carboy could be 70'F before the center ever equalizes at 68'F. Obviously this is a lot less risky if you're using a fridge where you're depending on ambient air temperature rather than a heating mat.

It's better to let the entire batch of beer equalize in temperature slowly. Hence why PortLargo is exactly right in that you should really only be using the heating OR the chilling element to prevent constant and quick changes in temperature.

EDIT: Lagers may be more sensitive to temperature swings than Ales

 

A few things to consider, in addition to the good advice already provided.

• Your Ink Bird is not as accurate as you think it is. There is a good chance the display is a degree or 2 above or below the actual temperature of the wort. If you're trying to dial it in to less than 1 degree, forget it. Especially if you are measuring air temp and not liquid temp. These units are built on a price point. Accurate digital thermometers cost more than the entire Ink Bird contraption (looking at you Therma Pen).
  This is not a really big deal though.
  
  
• Compressor burn out. Cycling the compressor on and off too frequently will significantly shorten it's life. Think of starting in gear from dead a dead stop on a bicycle. The first few revolutions require a lot more energy than maintaining speed.

• I'm of the opinion that as homebrewers we do want to be accurate and replication is important, especially for fermentation. In reality, a 1 degree spread is not noticeable. Maybe if you have the other 99 things nailed down and never variable. But not many of us do.

Cheers

 

+1 to that.

Cheers!

 

+2 to jacks +1.

if I’m in the mid range of the yeast temp, I never worry.

 

What about when yeast are in the lag phase? I would think it's preferable that any temp change occur when yeast are least active, if it happens. ie it's not so bad to raise the temp more quickly during the lag phase of the cycle, no?

Belgian / Saison fermentation for example, might involve raising the temp, and that's an old technique as far as I know. So the level of temperature maintenance noted by OP is specific to a certain objective.

 

I have not made the above mentioned beer so don’t know.

but for what I brew, it’s not a concern.

 

I'm surprised the controller is that accurate they never are. Experience tells me it won't be a problem.

 

For your setup, you are probably good. In general it depends on the yeast and which way you're swinging. If you're fermenting a lager and it gets too cold you can gently rewarm it with no ill effects (you will be doing so anyway for a diacetyl rest). If it gets too warm in the first day or 2 of the fermentation that is bad. Some yeasts are more forgiving than others, e.g Chico ale and the AB or 3470 lager strains.