What will be the effect of these temperature fluctuations?

Hi, I'm learning a lesson about trying to brew a belgian tripel without proper or precise temperature control. I brewed a 5 gallon batch of extract with OG of 1.070 and pitched 2 Wyeast 3787 packs at 68 degees. Used an aquarium heater set at 68 to keep the temps there because my basement ambient is now 60 degrees. A few hours later the car boy fermometer read 72 so I unplugged the heater and when I got up, the temps were down to 64. I put the heater back in because I was off work yesterday and could monitor the temps and I managed to keep it at 68 until I went to bed. got up at 5:00 AM and the temps were at 64 so I put the heater on again and when I got up for work, the temps were at 72 again. So I turned the heater off again and I guess when I get home tonight, the temps will be around mid 60's. Are these fluctuations within an acceptable range or what problems will they cause? Last evening was 24 hours after pitching and I needed a blowoff but when the temps had dropped overnight, it stopped blowing off. Thanks

Your beer will be fine. Although the primary flavor in a Belgian beer is the yeast, and to get more of that yeasty goodness you ferment at higher temps, but the lower temps will be just fine.

You'll probably end up ok, but you're risking under attenuation by having the temperature swing around like that. The rule of thumb is that if you're better off letting the temperature rise than drop. Once the temperature drops yeast tends to flocculate and go to sleep. Raising the temp back up can rouse them some but repeated cycles of warm/cold will tire them out and they'll stop fermenting before all the sugar is gone.

Belgians beer yeasts tend to do best with warm temperatures anyway so next time I'd start in the high sixties/low seventies and let it rise from there.

Doesn't your aquarium heater have a built in thermostat on it? It should at least enable you to maintain a temperature floor.

Yes, the heater has a thermostat but I set in on the lowest setting and it still raised the temps too much

Yeast are pretty tough creatures, so even with the temp swings you are experiencing, they will probably do their job but you may not get the ester profile you were looking for. In Chris White's new yeast book he states that yeast can start to express heat shock proteins with a rising temp of just a few degrees over a short period of time... the same is true with decreasing temps, with the exception of instead of making proteins they get sluggish and want to drop out of solution.

I think your beer will be fine, but seriously look into getting a dedicated fermentation space with heating and cooling available so that you can precisely control the temperature of your fermentation. I fell into the same trap that lots of people do and spent money on the wort production side of things and really neglected the fermentation side. Needless to say, I was very disappointed with the results because I had no consistency control of the fermentation.

It sounds like you are doing a water bath, so look into a Johnson or Ranco controller to control your heater so that you can have better control over the fermentation and you won't have to mess with it so much. You can easily find them for less than $100 and I think that if you use one you will be much happier with the results of your beer.

Good luck,

Joe