Originally Posted by duboman
Ideally you want to keep as steady a temperature as possible through the active fermentation phase which could be 3-7 days. Temperatures swings can cause stress to the yeast and create off flavors. If the temp gets too cold the yeast will just quit and drop out until warmed back up.
Try placing the vessel in a tub of water to help equalize and maintain the temperature as the volume of water will create an insulating layer
+1; Since the process ultimately depends on the yeast, they have to be kept happy, and every yeast is different. Some respond well to temp variation and others DO NOT.
When I first started brewing, I made Irish Red Ale with Nottingham yeast for my first 3 batches.
On the first one, I made note of the fact that my ferment temp was at the upper end of the range.
On the second batch I focused on keeping it within middle of the range
Third batch (done when it started getting cooler in Vermont) allowed me to keep it at the low end.
All 3 were great beers and each had a different taste that (since all other factors were essentially controlled and reproduced) can be attributed to the yeast.