Easy Mash Tun Temperature Control

I had a double brew-day a couple weekends ago. I have a very large cooler converted to a mash tun and it has a huge headspace. This makes it difficult for me to maintain my mash temp. I decided to try the foam board on top of the grain bed trick. I think it helped a little on the first batch, but I still lost a few degrees and had to occassionally add boiling water to the mash to bring the temp back up. This results in a thin mash and, I assume, a bit lower efficiency and or some other undesireable effect.

On the second batch I had an idea. Instead of adding the boiling water to the grain bed, why not just put a bunch of boiling water inside a glass container and put it on top of the grain bed. In other words, convert my headspace to a source of heat. It worked perfectly. I just boiled some water right before mash-in, added this boiling water to a pyrex dish my wife has, and set this dish on top of the foam board. I was able to maintain 152 for my full 90 minute mash. The was thicker and my efficiency came out 5% better than the first batch (I know this could be coincidence). Didn't see this tip posted anywhere. Happy brewing.

Did you pre-heat the cooler?
I don't use a cooler any longer, but used to put a couple gallons of 170f, water in for 15 minutes or so to "pre-heat". Otherwise, the cooler will suck the heat out of your strike water. Also, make sure you consider the grain temp when calculating your strike water temp.

I think your idea is pretty clever, just not sure if you tried any common alternatives.

Ed

Yeah, I always pre-heat by going about 10 degrees over my strike temp, closing the lid, and not doughing-in until the temp comes down to the correct strike temp. I use beersmith and it asks for grain temp so I assume it takes that into consideration when giving me my strike temp.

Thanks for your help, though. Sometimes the low-hanging fruit gets passed over pretty easily so I appreciate your reminder.

mattjmac said:

On the second batch I had an idea. Instead of adding the boiling water to the grain bed, why not just put a bunch of boiling water inside a glass container and put it on top of the grain bed.

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pretty clever idea. i've been wondering how i can do this myself. thanks for sharing!