|This is an annual advisory. When warm weather arrives we start getting the calls about over-active fermentations. It's not a random coincidence. It is caused by the difficulty getting your beer cooled adequately, and then keeping it cool during the most active fermentation period when it will actually generate a bit of heat.
First, we must beat again on the benefits of using a wort chiller! Every brewer we know of who has purchased a chiller has come back after its first use and simply raved about how much easier it made cooling and how fast it is. That is not an overstatement... every brewer. In Summer you may need to help the cooling process, even with a chiller, by putting the kettle in a cool water and ice bath after the chiller has cooled the beer to 90 to 100 degrees F. But the point is you MUST cool the beer to UNDER 75 degrees F, and preferably a little cooler because the air temperature in Summer is NOT going to help you.
We can't say that any more clearly, but routinely get the frantic calls that say the beer is 78 degrees and rising... "what am I going to do??". Well, the next time listen to what we are saying and do it right! But relax... we can help you fix your problem. Wrap a wet bath towel around the fermenter. Make sure it makes good contact with the surface of the vessel. Bunge cords may help. Keep that towel wet, even putting the wrapped fermenter into a shallow tray with additional water so it may continue to wick water and the through the evaporation of water help cool the surface of the fermenter. This can cool the beer over many hours as much as 6 to 10 degrees F., depending on air flow and water evaporation rate.
Since the weather is going to stay warmer, you might consider the evaporative cooling technique as a preemptive strike against potential temperature problems... meaning wrap the fermenter with the wet towel as soon as you pitch your yeast. Since we live in a dry climate, evaporation works quite well and wrapping the fermenter in a wet towel is sure to keep the beer cooler and overall more stable against rising temperatures. If you wrap it and the weather is cooler, well, unwrap it. It's the simplest way to avoid warm weather stress.