Originally Posted by jro238
I disagree a bit with some of the other comments. Will a 4F difference make good beer into crappy beer? Hell no. Could it make great beer into good beer? Absolutely.
It will make it more difficult to hit your target final gravity and can definitely cause some headaches when trying to fine tune recipes (especially for beers like large belgians or IPAs that really need to hit their target FG).
I use a normal chest cooler for a mash tun and have found that it will lose somewhere between 3 and 5 degrees over 1 hour if left uncovered. When I cover it with a space blanket and a couple of towels I can hold temperature within 1 degree over an hour. It is a really easy (and cheap) way to eliminate this variable.
I agree with this. I've found the magic treatment for this is to throw one of those old style furniture blankets, the padded, quilted kind, over the top of it. I brewed a couple times this winter, where my garage temps were in the mid 30s and I lost only 1/2 a degree in the mash over an hour.
Without it I have lost up to 3.5 degrees.