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5 gal. cooler mash/lauter tun capacity

Those of you who use the 5 gallon Rubbermaid beverage coolers as a mash/lauter tun…what size grain bill have you found the cooler can accommodate?

I use a 10 gallon Rubbermaid cooler and I am finding I always have excessive heat loss on 5 gal batches, although I preheat. I believe the amount of empty space in the cooler is largely to blame. 5 gal coolers are fairly inexpensive and I’m thinking of picking one up, but am concerned a 10+ lb grain bill would not fit.

I routinely mash 5-7 lbs in mine. could probably do more, but my stir spoon reaches it limit near this…and mash water is hot on the old hand. :wink:

Edit: with my recent WLAA, it was slightly more than 7lbs per half batch. Worked well and only dipped my hand in once. But then, I used a slightly smaller water/grain ratio than usual too: 1.44 rather than my usual 1.8 according to my brew notes.


You can fit 15 lbs at a 1.0qt per lb ratio. Its full and its thick but it can be done.

The methods your using to preheat may be suspect here.
I have a 10 gallon cooler and make only 5 gallon batches and lose never more than 3f and that would be if I didn’t properly account for and raise my initial temp correctly in -20f weather, which happened early on and now per my bottom specs I learned the proper temps to avoid this. Now I can assume 1f loss and this is for 8# to 23# batches even in sub zero conditions.

Here is what I have found for thermal loss:
At 65f and up, IE: normal room temps I tack an additional 8f to my strike temp needed and it falls correctly. Example: Strike temp needed for grain at 65f to hit 154f = 171 + 8f for cooler loss = 178f total temp of water pumped to mash tun.

At 60f and under I start to use 10f
At 50f and under I start to use 12f
At 32f and under I start to use 15f+

That way you can always check your mash in temp after the cooler properly equalizes and stir down a few points or as I have just let it rest for 1-5 minutes and it cools down to the desired strike temp pretty quickly.

Thanks All. I found the “Can I Mash It” calculator, which says <13 lb grain bill would work at 1.25 qt/gal:

I’m still a newbie and my procedure may be partially to blame, although I think it has more to do with temp monitoring than anything else. Last time I used 180 deg. strike water and let the cooler rest with the lid on for a while (didn’t write down how long, but pretty sure it was 25-30 minutes). I added the grain at 165 and the temp settled in at 153. My temp loss the first 30 minutes was as follows:

60 min: 153
55 min: 153
50 min: 152.2
45 min: 151.3
40 min: 150.1
35 min: 148.9
30 min: 147.7

My theory is that my wire probe is curling and ending up in the thin layer of water on top of the grain bed, rather than penetrating into the grain bed. I cannot tell where it ends up inside the closed container. I will solve this in my next batch by affixing it to a stainless steel rod and inserting through a tiny hold I’ve drilled in my cooler lid. This will give me confidence I’ve achieved proper penetration of the grain bed.

Having said that, I’ve picked up a 5 gal cooler anyway. Small investment. The hardware is the expensive part.

This chart has been floating around the net, it’s pretty useful. I can’t take credit for it, it’s from a guy in NJ; The Overbrook Brewery.

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