Mash Cooler Improvement

I did my first AG about two weeks ago with a rectangular cooler as my mash tun. When I preheated the mash container I could see the steam from the boiling water escaping out of the back. Slightly worried, I poured out the boiling water, added my grain and then the heated water. I stirred to ensure no air pockets and closed the lid. 20 minutes later I returned to stir again and saw that the temperature had dropped from 153 to 149. I didn't open the mash tun from that point on and hoped for the best. We'll see how it turns out in a few weeks.

The Mash Tun itself is just a rectangular cooler with the stainless steel braid as the manifold (is that the right word?). I pumped the lid full of "great stuff" (more like sucky stuff, I still have that crap on my hands) to aid in the heat retention. My question is, what other steps can I take in my mash tun construction to ensure that I keep as much heat as possible? I was thinking some kind of foam weather stripping and drilling a hole for a permanent thermometer. Thoughts? Thanks

I think it's possible you didn't get it well enough mixed in the first place and that would account for your reading. And just stop opening it to stir! Stirring is unnecessary and you lose heat every time you open the cooler.

I am also using a rectangular cooler for a mash tun, but have not experience the temperature drop you have. The three times I've used it, the temp in my garage has been mid eighty's, so that may have something to do with it. After I dough in, and get the temp where it want it, I close the lid and place a larger blancket over the cooller, the something heavy on the lid. I have been pleased to check it after an hour, and it has only lost one degree. I did not mount a permanent thermometer because it would be a source of heat loss and with a plastic cooler, I cant just fire up the gas to bring the temp up. I would say insulate as best you can, close the lid, and dont open it until your done.

I remember my dad, when teaching me about BBQing, would say "If your lookin, you aint cookin."

IMO the best way to preheat a cooler mash tun is to add your strike water about ten to fifteen degrees over strike temp. Let is sit for 10 - 20 minutes and the cooler will heat up while the strike water drops to strike temp. Sounds like you were a bit low when you mashed in.

Most any coooler will have marginal temp loss if preheated this way

I've read about the wrapping in a blanket technique, I'll give it a shot. Thanks for the advice

I'll echo what wilserbrewer said. Your cooler was still pulling heat when you doughed in. You either need to learn how much heat the cooler will pull and strike at that temp or go in way hot and let it cool down to your strike temp. I doubt the cooler is letting 4F out unless your ambient temp is 20F.

Bobby_M said:

I doubt the cooler is letting 4F out unless your ambient temp is 20F.

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Even if he can see steam coming out around the lid? I'd imagine that with a leak big enough you could see a 4*F degree loss over an hour.

I lose about 2 degrees in an hour with no visible leaks. Preheating will help, but if steam's getting out there's an issue somewhere. I wouldn't spend any money fixing up the cooler, since Coleman Xtreme's (what I use) are so cheap; you probably spent almost half as much on the can of Great Stuff as it would have cost for a new cooler! Try preheating (it's easier for me to just add about a quart of boiling water rather than overheating my entire strike water and then waiting, but that's just how I've learned to do things). Try throwing a big old blanket on top. Leave the lid closed, just check the temp at the end of the mash to see how much you lost.

illin8 said:

Even if he can see steam coming out around the lid? I'd imagine that with a leak big enough you could see a 4*F degree loss over an hour.

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Which leads me back to my original thought of perhaps some sort of foam weather stripping around the edge to give it a better seal. I've never read anything about that but I wonder if it would work. Thoughts?

Strikes me as likely to get messy; weather stripping that's gotten covered in wort sounds like a ***** to clean. Things don't have to be perfectly sanitized (pre-boil), but I'd try something on the outside of the cooler (blanket) first.

I usually just throw a towel or two over the top of my cooler to help. I usually get steam out of the lid seam too, but never any dramatic temp drop. I only measure when I dough in and when I am about to sparge and see what my temp loss was for reference. Normally I was getting 2-3 deg in the winter and that is pre heating with 1 gallon of boiling water while I heat my water for the mash.

My 70qt extreme leaks steam thru the front handle at the beginning of the mash...when you push the front-side of the cooler in, it stops. I thought about using a strap to keep it tight, but after a little while it stops...I don't know if its the plastic swelling from the heat but I haven't done anything about it.

don't forget to preheat the cooler before you add the strike water....the cooler will pull out a lot of heat as will the grain.....it took me two or three batches before I figured out how to get the right temps for my cooler

The best improvement you could make is going to a cooler that's advertised to keep ice for 5 days. If the lid had no foam, the rest of the box is minimally insulated.

KerryD said:

The best improvement you could make is going to a cooler that's advertised to keep ice for 5 days. If the lid had no foam, the rest of the box is minimally insulated.

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The 70 qt Coleman Xtreme is rated to keep ice for 5 days.

illin8 said:

The 70 qt Coleman Xtreme is rated to keep ice for 5 days.

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That's what I have (although a 9-gallon model). It wasn't much money, $20 or $25 IIRC, which is why I say don't spend much money on things like Great Stuff and weatherstripping to fix up an old one.

If this helps.......things I've done to minimize heat loss.

First is preheat. You don't really have to use super hot water.....hot tap water is fine........you just need to make sure you top off the cooler and leave it in there for at least an hour......it takes a surprising amount of time for all of the materials to absorb the heat. If you just add near boiling water for a couple of minutes.......all you are doing is heating the inside plastic.....you want to have it in there long enough that the insulation can absorb the heat. Also why you want to top the cooler off.......as if you only put a gallon or so in it........the heat transfer above the water line will not be anywhere near as efficient.........and the insulation on the otherside of the plastic will still be near the original temp and ready to absorb that heat from your mash.

When I used a square cooler, it leaked a lot around the lid seal (steam came out of it). I also found that I lost a lot of heat when working with it and had to have the lid wide open because of the fixed hinges. So I cut the lid hinges off, so that I could always have the lid at least partially covering it, and I took a strip of rubber (not the foam type weather stripping, but rubber) and permatexed it to the lid. After that.......it sealed so tight that you could actually watch the cooler expand, until it would momentarily break the lid seal and "burp" a patch of steam.....then reseal itself. FYI, this will create such a tight seal that if you are interrupted and called away for several hours......the mash will still be surprisingly hot......but the vacumn created by the cooling is such that you have to use some effort to open the lid and break the seal.

Head space.......the more head space you have, the faster/more heat loss (less thermal mass.......blah blah blah). One reason why I use a 7 gallon round rubbermaid for smaller grain bills, a 5 gallon for light grain bills, and my square one for bigger grain bills. Also, kind of applicable to this.......based on the reading of some of the folks on here, I started mashing a lot thinner........1.5 to 1.8 quarts per lb to increase my efficiency. This also has the added benefit of increasing the thermal mass, and leads to a greatly reduced heat loss as well in my experience.

I generally lose about 1.5 to 2 degrees over a 90 minute mash in either the round or the square. This is up from a 2 to 3 degree loss over 60 minutes from when I mashed at 1 or 1.2 quarts per lb and used the square cooler for everything.

ewbish said:

First is preheat. You don't really have to use super hot water.....hot tap water is fine........you just need to make sure you top off the cooler and leave it in there for at least an hour......it takes a surprising amount of time for all of the materials to absorb the heat. If you just add near boiling water for a couple of minutes.......all you are doing is heating the inside plastic.....you want to have it in there long enough that the insulation can absorb the heat. Also why you want to top the cooler off.......as if you only put a gallon or so in it........the heat transfer above the water line will not be anywhere near as efficient.........and the insulation on the otherside of the plastic will still be near the original temp and ready to absorb that heat from your mash.

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I don't necessarily agree with this. Not saying that your method doesn't work, just that it's not the only way. A little bit of hot water, sloshed around (which helps clean stuff up as well) works just fine for me, even only letting it set for five or ten minutes. I'm nowhere near patient enough to let my mash tun preheat for an hour! I'll argue that a small amount of very hot water works just as well as a large amount of very warm water. Proof is in losing less than 2° in a 60 minute mash, which is about as good as is gets.

the_bird said:

I don't necessarily agree with this. Not saying that your method doesn't work, just that it's not the only way. A little bit of hot water, sloshed around (which helps clean stuff up as well) works just fine for me, even only letting it set for five or ten minutes. I'm nowhere near patient enough to let my mash tun preheat for an hour! I'll argue that a small amount of very hot water works just as well as a large amount of very warm water. Proof is in losing less than 2° in a 60 minute mash, which is about as good as is gets.

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No, 'course it's not the only way........lot's of combinations of coolers, materials, new coolers, old coolers, construction etc. For example......a SS braid or copper manifold connected by metal directly to a metal ball valve will act as a heat sync and rather efficiently move heat from the bottom of the MLT to the external fitting. A PVC manifold w/ a plastic valve will transfer a lot less, so will a false bottom connected to the ball valve by vinyl tubing. Lots of little pieces play a roll in the heat loss game, you've got to find the right combination and heating time for your particular kit. If you have heat loss from one factor that you can't control......you make it up by adjusting something you can......and a thourough preheat is one easy way to manipulate your overall heat loss.

Seriously though, it's not a matter of patience.........first thing I do is fill the MLT with hot water in the bath tub.......then I start the coffee maker, make sure I have suitable selection of brew day beverages at the appropriate serving temp, set up my brew station, and start heating my strike water et all. By the time I'm ready to strike.......the MLT is plenty preheated.

If you topped your particular cooler up......you'd probably cut that 2 degrees in half in 60 minutes, but all things considered.......2 degrees is pretty irrelevant so no need to bother.

Yea, no way am I going to preheat my cooler for an hour. I do the heat the strike water about 12* higher than my strike temp, put the lid on for 5-10 minutes, then take the lid off and let the water come to my strike temp. Usually takes ~5 minutes with a little stirring, then dough in and hit my mash temp on the nose. I lose right around 1* in an hour mash.

I'm with the bird. I would stop putting money into an old cooler and just get another one if it is losing that much heat. Just swap the parts over and use the old one as a regular cooler.

Let me preface this statement by stating that I am not an experienced AG Brewer. I have a 5 gallon drink cooler (round) that I experiment with for partial mash recipes. I use 3 to 5 pounds of grain to mash I had a problem with heat loss even after preheating for 20 minutes with 130 degree tap water. I determined that the large head space in the cooler was causing me to drop heat. I cut a piece of blue board insulation 1-1/2" think into a frisbee shape and just float that on top of my grains. It has really helped with heat retention, I can hold my temperatures for 90 minutes with no noticeable loss in temperature. It seems to me that this would work well in a rectangular cooler as well. I got this idea from someone on this site, so I'm not the only one who does this.

i use a thick blanket. Even when it was 40 degrees i might have lost 2 degrees in an hour

I also use a rectangular cooler and preheat. Since I use a 48 qt cooler I have extra head space that would cause me to loose a lot of heat over an hour. After reading some other threads on the forum I've since cut out pieces of 2 in thick closed cell foam and float that on top of the grains to minimize head space. That helped my issues tremendously.

Ya know, I just don't get it. I use a 10 year old, cheapo, 48 qt. Rubbermaid cooler. I stopped preheating years ago, deciding it was a waste of time if I just took a couple brews to figure out how much hotter I needed my strike water to be if I didn't. And I never lose more than 1-2F over the course of a 60-90 min. mash. I can't for the life of me understand why some of you are having such issues.....

Denny said:

Ya know, I just don't get it. I use a 10 year old, cheapo, 48 qt. Rubbermaid cooler. I stopped preheating years ago, deciding it was a waste of time if I just took a couple brews to figure out how much hotter I needed my strike water to be if I didn't. And I never lose more than 1-2F over the course of a 60-90 min. mash. I can't for the life of me understand why some of you are having such issues.....

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Must be the new coolers just aren't made like the old ones, or maybe not trained yet???:rockin:

Is there any good information on how the present-day coolers are insulated? This could account for some of the observed differences. Even if there were only air between the inner and outer walls of the cooler, air is a pretty decent insulator.....but probably not good enough for mashing purposes.

After a while you get to know your equipment and know how much hotter than strike temp you have to be to arrive at the mash temperature spot on. Once that happens you are good to go.

Put insulation foam into hollow lids and that helps a lot.

Denny said:

Ya know, I just don't get it.

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Yea me too Denny, I use a cheap old coleman plastic cooler that I repurposed for brewing, works absolutely fine. It kills me when I read about people putting boiling water in their cooler to "heat it up", or buy a "Max Cold" or "Extreme" this or that.

Why would I need a 5 Day cooler to mash for 60 - 90 minutes?

Maybe I do get it, people are mashing in and taking a temp immediately rather than letting the grain / water equalize, then blaming a drop in temp on the cooler??

Edit...I would agree that it is helpful to have a cooler that matches the size of the grain bill thereby minimizing head space. I use a 25 or 40 quart depending on batch size / grain bill.

+1, wilserbrewer!

I'll put my 0.02, FWIW (not much as you'll soon find out)

I have a 48qt Ice Cube that I converted to a MLT (free). It is horrible for holding temperature. I'm talking several degrees over an hour. Preheating the MT results in a slow and predictable temperature loss, suggesting that instead of the MT/water coming to equilibrium that heat is continually lost.

I've injected foam into its hollow lid (having to cut and reposition pieces because the lid had built in compartment and can holder holes) with little change in performance. I've fitted a piece of foam insulation to sit on top of the mash with little change in performance.

Finally, I found that if keep the MLT on a cold floor while mashing, the temperature will continue to drop, presumably because the floor is acting as a heat sink of sorts.

The walls of the cooler are thin and I can't imagine there being much insulation (if any) in there.


To summarize: it sucks. Sure the extreme is probably overkill, but there is such as a thing as underkill too. If I had to pick, I'd go overkill.

I know others have had better luck with the Ice Cubes, but I think there are multiple versions on there.

There alot repeat suggestions but...


Here's what I do for my Igloo Cube

• Preheat the mash Tun. Adding boiling hot water for 10-15 minutes.
• Use wal-mart bags stuffed with more bags to take up head space and insulate after mashing-in.
• Use a sleeping bag (still rolled up) and set it on top of the cooler to insulate.
• Depending on my mash time & temp I can calculate a quick infusion step (Rest) if necessary. Boiling 3-6 quarts on a turkey fryer takes no-time.
  • Use the Rest Calculator

I use a 10gal Gott Cooler. About an hour prior to strike I place the cooler on the edge of the bathtub and fill it with tap water from the shower on its hottest setting. (It helps to have a hand held shower nozzle.) After that I just dolly that bad boy (if I have no help) out to brewing area. Right before strike I drain the hot water (which is still steaming) and mash in. I have hit my temps every time.