Around a year ago, excitement rushed over me when I converted a keg into a mash/lauter tun. I thought it was glorious, and would make my homebrews even better. As I started to brew 5-gallon all-grain batches on an outdoor propane burner, I had some serious frustrations with the system. I could not keep temperatures during the mash! Since I’ve been all-grain brewing for some time now, I know how critical it is to keep steady temperatures for maximum efficiency.
I tried experimenting in a variety of ways, including a heat blanket, keeping the mash on a low flame, or infusing hot water to keep temperature steady. The heat blanket helped, but I was wasting propane to keep the temperature. I always try to be economical when it comes to brewing. So, here’s what I decided to do.
I have an extra pot, a 7.5-gallon stainless steel pot without a ball valve spigot. I mashed in there for an hour, and was able to keep temperatures. I poured the mash into my combo mash/lauter tun, and sparged into that. I started to get great efficiency doing this, but still frustrated that I couldn’t mash and lauter in the same vessel. And then it hit me. Working on a collaborative brew, a 10-gallon IPA (Guntasco IPA), I filled up the whole mash/lauter tun with 25 pounds of grain and roughly 9 gallons of water. We mashed for an hour, and only lost 2 degrees. It dawned on me of why I was losing degrees. There was too much room in the pot for cold air to sneak in and drop the temperature of the mash for a 5-gallon batch. It all made sense.
So, the moral of the story is, know your kettle. Be sure to have appropriate headspace in your kettle. Too much headspace will generally lead to significant temperature drop. Having 2-4 inches of room will provide steady temperatures and great efficiency.