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Fementation Temperature Fluctuation
I've always heard/read that controlling the fermentation temperature is one of the most important things you can do to brew a better beer.
My question is: if you are keeping the fermentation temperature in the optimum range for the yeast, how do temperature fluctuations affect the final product?
For example, I'm currently fermenting an amber ale with US-05. It was pitched around 72 (a bit warmer than I wanted), then I reduced the temp to 68 within an hour or so, and down to 64 within the next three hours. Fermentation has been steady for the past four days, but with the heat outside in the 90s, even with an ice water bath it's been hard to keep my temps steady.
I've been anywhere from 62 to 69 over the past four days (within the suggested range), but typically no more than 3-4 degrees fluctuation in a 3-5 hour period. I've always thought this won't introduce any off-flavors, but I want to make sure I'm not missing anything. I was under the impression that the real danger is when your temps swing by 10 degrees or more and spike over the suggested fermentation range (74+).
This one is sure tee'd up for you Mike. And, it's a good question. I only recently started to control my fermentation temps other than just taking what was given my by the temps in the house. I have been using a water bath, most recently with two batches of Safeale-04, trying with some success to keep the temps about 64. I have had the temps fluctuate, in one case as high as 70 when I checked the temp in the morning. I am curious about the impacts. I know based on reading and on discussions on this forum, that temp control will improve my beer, and that's enough for me to do it. But, knowing it impacts the beer, with no real knowledge of the specifics, doesn't really let me know the true value of my time and efforts.
IMO the two problems are sustained high temperatures causing off flavors and sudden drops in temperature as fermentation slows causing a stalled ferment.
I think you'll be OK as long as you make sure to back off on the cooling as activity slows down. Once they're not as active, they're not making as much heat, so they don't require as much cooling.
I've read quite a few posts regarding fermentation temperatures and how brewers around the country measure and attempt to control them, in hopes of getting the best results from the yeast strains they use. After doing some research on this topic I found the following bit of information on the Brew Your Own website that I wanted to share with you.
According to Mr. Wizard at BYO
"However, in a small fermenter such as a 5-gallon (19-L) carboy the difference between the air temperature and the beer temperature is usually within about 5 ºF (3 °C). So if you have a yeast strain that produces the best beer when fermentation is held at 70 ºF (21 °C) the surrounding air temperature should be around 65 ºF (18 °C). You can periodically monitor this by inserting a thermometer into the fermenting beer."
The reason I found this post so interesting is that it talks about the exact same temperature control setup I have been using at home to ferment and carbonate my beers, all 27 of them. In my upstairs office/brewery where I have been fermenting and carbonating my Mr. Beer recipes I run a small 110 volt window air conditioner set to 70F.
While that BYO excerpt is true for the most part, I'd like to add a couple things.
First, they state there's a 5 degree discrepancy but keep in mind it may be more or less. I've noticed it to be as high as 8 degrees before. This may not seem like a big deal but it can be a big deal to your yeast who behave differently at different temperatures, especially warmer ones.
Secondly, because this discrepancy varies, the easiest and cheapest way to monitor your fermentation temperatures is to use a Fermometer. It's a stick on thermometer, much like the ones on fish tanks, that range from 36-78 degrees Fahrenheit. I remember listening to a Brewing Network podcast (forget which one, mayve the Sunday Session) where Jamil Z was discussing these and quoted some test results that concluded these were accurate +/- 1 degree. And for the money, that's good enough for me. They've served me well over the years and until I turn a fridge or freezer into a fermentation chamber I'll keep on using them in my swamp bucket. Just don't submerge them in water.
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