View Full Version : Fluctuating temperature- Problem?

02-21-2013, 11:03 PM
Hello everyone,

I have a 5 gallon glass carboy brewing some mead. (5 days in)
It is currently in the basement, and since its winter time the low temps in the middle of the night have been hovering around 60 degrees, with its max at around 68 during the day. I figured this was fine since the yeast I'm using (d-47) says it can go as low as 50, so i have a solid 10 degree buffer zone.

Although, I'm about to add a 5 gallon batch of apple wine, which yeast's tolerance is 59-86. I decided to add a small space heater in the closed off area in which I'm brewing, and the temp is consistently fluctuating between 63 and 73, the majority of which spends around 66. Will this fluctuating hurt the yeast? Or is the carboy's mass large enough so the temp will stay relatively consistent in the middle?

Thanks for the advice!

Medsen Fey
02-22-2013, 07:02 AM
At this point you probably aren't going to harm the first batch with temps of 73F but frankly I'd give the second batch a chance at the cooler temps and see how it does. If it is sluggish, then warm it up.

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02-22-2013, 01:46 PM
Fluctuations in the temperature of the must over a range of 5-6 degrees (i.e. +-3 degrees) aren't an issue, but larger swings (10 degrees-ish from one limit to the other) will add some stress to the yeast. As you noted, the temps that you're talking about are the air temps in the room, and there is enough "thermal mass" in 5 gallons of liquid to damp out those swings significantly if they only vary over a day or less time, so you're probably not in any danger from the kind of swings you've got.

Temperature stress on yeast will tend to get them to prematurely stall, causing fermentations to stick at a higher specific gravity than they otherwise would. Thermal stress can also cause some yeast strains to throw excessive amounts of phenolic compounds that can be a source of "chemical" or "plastic" aromas or flavors in the finished mead.

02-22-2013, 02:34 PM
The "swing" in temperature is on about a 45 minute cycle, from highest temp to lowest, though the majority of the time the temp is around 65-68, so I'm optimistically assuming the must is around that temp.

Chevette Girl
02-22-2013, 03:45 PM
Honestly with the amount of time it would take for the 5 gallons to heat or cool appreciably within that temperature range, I don't think this will be any worse that it being a 24 hour cycle.