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Really Frustrated - Losing heat in my Cooler!

I’ve been monitoring my mash and realized I was losing heat in the mash tun over 60 min. I brew in a 10-gallon Gott (orange round) cooler. After reading a tip here, I insulated the lid with spray foam insulation. That didn’t seem to help much at all - on my last brew, I lost 4 degrees over an hour.

I preheated with very hot water, shot high on my strike temp, and adjusted with ice cubes until I hit my mash temp. I stirred very well and checked it over the course of 5 min or so, then put the lid on tight. I threw 3 blankets over the top to hold in heat, and still lost 4 degrees! This is really frustrating.

One thing that could be a factor is that the sides of the cooler seem to be separating. There is a bulge running vertically up the inner cooler wall, where it’s separating. I think this is from dumping the hot water in.

Should I just retire that cooler and buy a new one? That would be a bummer, because it’s still in really good shape. I guess I could also start doing a small infusion about halfway through the mash. Let me know what has worked for you.

You shouldn’t fret losing 4F in an hour. Nearly all of the commercially available base malts these day have the diastatic power to convert the starches to sugar in about 10min or less. Even those low in protein like the British pale malts still have the juice to be done with their work long before you get to 30min.

As horrific as this may be to us…its the first moments of the mash that really count for 90%+ of the conversion…so worry more about where you mash-in at and less about where your temps are at the end of your rest. Because of this I only rest for 30min on a STI and then mash-out or vorlauf depending on what I’m doing.

60+min rests will gain you some color and maybe 1%-2% in sugar yield. Mashing out to 170 will help your efficiency more than a longer rest.

Hope this helps.

I agree with troutguy - no need to get frustrated at 4 degrees in an hour, even with all the added amenities. I think you’ll drive yourself crazy and waste time (and money?) trying to prevent this loss. Losing ~4 degrees with a ~152-degree mash is only a ~2.5% heat loss… not bad by any calculation or effort.

Labratory testing shows that rectangular coolers lose less heat. Especially the BLUE ones.

I’m not too concerned about efficiency - I’m worried more about the effects of mash temp on body and fermentability. I recently brewed a nut brown and an oatmeal stout that seemed too thin, and I’m finding that my FG’s are consistently lower than specified in the recipes.


The entire sugar profile will be established within 10-15 minutes…maltose…dextrin…all of them. So if you are have body issues with your finished product, first calibrate your thermometers, then analyze your water profile (sulfate = dry, carbonate=malty).

If you are hitting say 154F at mash-in and are holding near that for 15 minutes then my opinion would be that it is not your mash schedule that is causing dryness/thinness in your finished product. This is assuming all of your recipes across the board are like this…got to be temp inaccuracies or water issues.

Any chance moisture might have penetrated into the insulation?

4degrees over an hour is nothing. RDWHAHB! :cheers:

Solution: internal lid from scrap styrofoam. I get 0 to 1 degree loss in 90 min mash.


@troutguy - thanks for your info on establishing the sugar profile. That eases my mind anyway.

@Baratone - I don’t think there’s any way that water could have gotten into the insulating layer, because the entire thing is sealed on the inside. The holes I drilled in the lid were from the outside. The only possible place would be where the spigot is mounted, but I doubt that’s happening because I’m not seeing any leaks.

@StormyBrew - your solution looks like it certainly works. I was going to say something about chemicals leaching from the styrofoam, but then I thought about all of the styrofoam cups full of nearly boiling coffee I’ve had. So that’s probably not much of a concern. I guess I could give that a shot on my next brew and see if it helps. That would at least let me know if I’m mainly losing heat out the top.

Thanks for all the input. :cheers:

I’ll second that and add- are the aspects of the beers that you’ve made that have led you to this frustration? Do you calibrate your thermometer every brew? For me, I’m willing to bet that my thermometers have a margin of error of 2-4 degrees. If I’m within 3 degrees of my target mash temp 10 min. after dough-in I’m happy. Don’t let the details of brewing at home cloud what you’re after, which (for most of us) is good beer that we made ourselves.

Oh, I’m totally enjoying my beer as usual. I don’t get that hung up on details. I’m just working on refining things and establishing a set of house recipes.

I’m using a digital thermometer that reads correctly, so I don’t think that’s the issue. I’ll consider mashing in 1-2 degrees high next time and see what I get. I also might give the inner styrofoam lid a shot, if I can convince myself that I won’t be leaching out nasty chemicals.

Make sure your thermometers are calibrated at brewing temps also. I had a couple of them that I was using all the time that read good at 32 degrees and at boiling also but were 6 to 7 degrees off in the 140 to 170 degree range. Knowing that now I no longer use those when I brew…I purchased a certified calibrated digital model that I use now.

I’ve noticed similar heat loss from my cooler, actually it can be up to 8 degrees. Yes, it is a blue rectangle! As others have said, I don’t think it is a big deal but I like the idea of the Styrofoam lid. Might try that next time just to see.

mtodd…excellent point. I calibrate my mash tun therm to 150F and my liquor tank therm to 170F.

I have not read all of the posts, so, if this is redundant…

I use the 70 qt. rectangular Coleman for my ten gallon batches. Yes, living in the Wisconsin winter is not as cold as it once was, but it can get chilly.

I have taken a piece of the blue hard insulation that is about two inches thick. I cut it so it fits within the inside of my mash tun. I actually made two of them so I can replace the head space of my cooler no matter what the grain bill calls for.

Once I mash in and stir to my comfort level I now push the insulation into the tun, replacing air. They sit directly above the mash and keep things cozy.

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