Originally Posted by usfmikeb
I wouldn't do that. Better off just covering whatever mash vessel you're using with an old comforter or something.
The idea here being to eliminate the effects of dead air space within
the mash vessel to a significant degree.
As a practical example, I'm thinking of upgrading from my 36 quart xtreme cooler to a 62 quart model to be able to do the occasional 10 gallon batch or the monster 5 gallon batch. But there's a whole lot of dead air space in a 62 quart cooler when I'm only doing a 5 gallon batch of a low gravity beer, and I imagine this will always be a detriment to maintaining mash temp. Preheating the cooler for a 5 gallon batch would be a challenge too, since I'd need to be using a lot more water to preheat than I'd need to mash. If I could close off that air space within the cooler with some kind of insulatated barrier, I'd think I'd only have to preheat with whatever mash water I needed and would be able to lock into within a degree over the course of a 60 min mash.
Wrapping foam insulation with a food grade substance of some kind seems to be on the right track. I'd like to probe the clever minds of HBT for some good ideas. (Aluminum foil and saranwrap both good ideas?)
In general, what are folks with oversized mash tuns doing to maintain their temps?