Holding Mash Temp for Small Beers

I have a 10 gal rubbermaid cooler I use for my mash tun. It has a stainless steel false bottom. I alsways do 5.5 gal batches. I preheat it before mashing everytime with hot tap water (~120 degrees F). Lately, I've been having a hell of a time getting the damn thing to hold temperature during a mash! On an Irish Dry Stout I'm brewing today, with 7.5 lbs grain and 9.75 qts. mash water, it dropped 10 degrees in 30 minutes! What the hell? I mashed in and hit my temp (152) right on the nose. Came out after 30 minutes to give it a stir and it was sitting right around 142. Does anyone else have this problem with small beers? Heck, it's been a while since I brewed anything over about 1.056, maybe it doesn't hold temperature no matter how full it is. I'm thinking about getting a 5 gal. cooler for all the beers that don't need the 10 gal. I just thought I would have heard something about this if other people were having the same problem, which leads me to believe it's the cooler that is the problem.

Closed-cell insulation is your friend. Cut a piece of two-inch thick foam to the size of your cool and set it on top of the mash. You'll lose nary a degree.

Also I assume the 152 was an average of several different spots in the mash? Not just stick it in one place and say Bingo? If not, this could be your temp swing. There will be hot and cool spots if not extremely well.

flyangler18 said:

Closed-cell insulation is your friend. Cut a piece of two-inch thick foam to the size of your cool and set it on top of the mash. You'll lose nary a degree.

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awesome, that sounds like a great solution. where do i get the stuff and is it food safe?

IrregularPulse said:

Also I assume the 152 was an average of several different spots in the mash? Not just stick it in one place and say Bingo? If not, this could be your temp swing. There will be hot and cool spots if not extremely well.

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yeah, no matter how much i stir, it seems like the bottom is always a degree or two hotter than the top. so i take measurements all around and if im shooting for 152, they'll typically be like 151 on the top, 152 in the middle and 153 on the bottom.

I always put 180F water in my 48-quart mash tun, wait 15 minutes, then adjust to the strike temperature. You might also consider using 2 quarts of water per pound of grain.

david_42 said:

I always put 180F water in my 48-quart mash tun, wait 15 minutes, then adjust to the strike temperature. You might also consider using 2 quarts of water per pound of grain.

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+1, go with a thinner mash! Or double up on the batches and make 11 Gals per brew day! I'd imagine the closed cell insulation and thinner mash would do the trick.

Schlante,
Phillip

I know it isn't too cool in Durham at this time of year, but have you considered that the ambient air temp is quite a bit lower now. Have you used this system in the winter before?

I'd thought of that, but the outside of the cooler doesn't get warm, which makes me think there is no heat exchange through the cooler to the outside air. But I do think I'm going to start mashing inside just in case. It was probably about 60 here today when I was mashing so it really wasn't that cold.