Problems maintaining temps in cooler mash tun

[cheesebach]

I've been all grain brewing 5g batches for a little over a year now, and maintaining mash temps within a reasonable range has been my biggest struggle for me so far. The first hour of my brew day has turned into a stressful process of opening the cooler to check my temps 30 min into the mash, finding that the temp has dropped by 3 degrees already, and then scrambling to try to boil enough water as quickly as possible to get my temps back on target for the last half of the mash.

I'm using a blue Coleman Xtreme 52 Qt cooler (which I've read should have good thermal properties) with a bazooka screen and SS ball valve. I've been preheating my mash tun on my last 4-5 batches but haven't seen any significant improvements over my first couple batches. Typically I've lost 2-3 degrees when I open the cooler briefly to check the temp at the 30 min mark. This weekend, I tried a test with just using 5 gallons of water (picked a typical volume for a mash on a 5 gallon batch). I added the water at 163F, let the cooler preheat for ~20min with lid closed, then stirred and recorded my starting temp of 159.2F. I set my timer for 60 minutes, and checked and was at 154.6F. I let it go for another 60 minutes (2 hours total after preheating) and was at 149.4F.

These temp drops seem to be about 4X what other users using rectangular coolers typically report. Is the 52 Qt cooler just too large to use for 5 gallon batches in the 5-7% abv range at a 1.3 qt/lb mash thickness? Would switching to a 10G cylindrical cooler likely help since the surface area would be reduced? Are there any other mods people do to their rectangular coolers to get better performance out of them? Let me know if you have any ideas/suggestions for me - thanks!

 

[kristiismean]

It does not matter. the first 20 minutes are all that really matter. Don't open the lid. leave it closed. leave it for 40 minutes, or an hour. or 2, most of the conversion is done in the first 20 minutes anyways. the fact that it drops to 148 is still acceptable.

That said, as small as you can go the better. 10 gallons is better than a 13 gallon cooler like you have. the less air in there the less heat is pulled away from the liquid/wort/soon to be wort...

 

[imasickboy]

First:

The thicker the mash, the better it will retain heat. Ignore your water-only test results. Water alone doesn't hold temp very well. Consider trying 1.15:1 instead.

Second:

Preheating is helpful, but try to preheat at a higher temp, for a shorter duration. I preheat my 5 gallon cooler with about 1.5-2 quarts of water, between 180 and 212 degrees. My 10 gallon gets 3-4 quarts of preheat water. Be aware that the hotter the water, it may warp the inside of your cooler a bit, if you're sensitive to the aesthetics of things like that. And since water doesn't hold temp well, I only preheat about 5-10 minutes before I am ready to add my grain and strike water. Dump the preheat water, and immediately add your important stuff.

Third:

Air doesn't hold temp, period. You have way too much "headspace" in your cooler. Find a piece of insulating foam you can cut to fit just inside of your cooler, and lay on top of your mash, then close it up. Or, use a smaller cooler.

 

[JonM]

Air doesn't hold temp, period. You have way too much "headspace" in your cooler. Find a piece of insulating foam you can cut to fit just inside of your cooler, and lay on top of your mash, then close it up. Or, use a smaller cooler.

This. Definitely this. You can put a sheet of foil between the mash and the foam to keep the foam from getting gunky (I use a crockpot liner bag to wrap the foam in my round Rubbermaid cooler.) it works great.

 

[smyrnaquince]

Find a piece of insulating foam you can cut to fit just inside of your cooler, and lay on top of your mash, then close it up. Or, use a smaller cooler.

I did this with a thick piece of styrofoam wrapped in aluminum foil (shiny side out).

My lid was hollow (5-gallon round igloo cooler). I cut a small hole in the top and filled it with styrofoam pellets from an old hot seat, then sealed the hole with duct tape.

I preheat with water hotter than strike temp (using Beermsith adjusted to my equipment), then after 10 minutes I add my grain and stir for 2 minutes. If you don't stir enough, your temperatures will not be consistent throughout the mash.

Checked my temps for one or two mashes, was happy enough, and now no longer check.

 

[JonM]

If you're cutting foam, save yourself a lot of headaches and get or borrow one of those foam cutters. They look like a jigsaw with a heated wire instead of a blade. It runs on a D-cell or two. Pretty cheap at hobby stores.

Cutting foam with a blade makes a mess.

 

[cheesebach]

Thanks for all the suggestions so far! I understand that practically, the temperature loss may be a non-issue with all the conversion happening in the first 20min or so. It's still enough to drive me crazy though when I read about people using similar coolers to mine for 5 gallon batches and losing only 1-2 degrees loss over a 60+ minute mash!

It sounds like the headspace in the 13G cooler is likely not helping the issue for me. However, it seems from other user posts that many here do have good success keeping their temps with coolers larger than 10G on 5G batches. Maybe my particular one just doesn't get a good seal? Can anybody think of something i could do to make it more air tight?

Regarding the wrapped foam suggestions - it sounds as though it would likely help, but I think I may lean more towards just picking up a smaller cooler for normal abv brews since the rectangular ones can be found pretty cheaply. Since 90% of my brews will not even come close to filling up 10 gallons, it seems like it may be a better solution long-term than adding a large piece of foam to wrap up and clean off each brew.

 

[imasickboy]

It's not air exchange that causes temperature fluctuation, it's just the fact that air itself, (even in a sealed environment), cannot easily maintain temperature.

Think about your kitchen. When you use your oven, the air in the room easily changes temperature. Compare that to waiting for your wort to cool if you were just letting it sit on the counter.

I'm not sure where you are, but I have a like-new 5 gallon round cooler in Lancaster, PA that I'll let go for $10. I will not ship it, however. That will easily solve most of your issue.

 

[EtchyLives]

A couple other observations I've noticed in my own brewing: When checking the temp I always stir up the mash really well when checking temps. This makes sure I'm getting an accurate reading and also helps loosen up the sugars (or so I think). I've found drastic temperature differences from when I check the temp before and after a good stirring.

Two: Pre-heated mashtun temps per beersmith are not the same as the temp of the water I used to reheat the temp. I fill my Igloo with boiling water (no warping, yet. HD Cooler FTW!) and let it sit for about 10-20 minutes then dump it out and fill it up with my water. I can't measure the walls of the cooler but when messing with the temps in Beersmith to get my final calculated mash temp to match my actual recordings I've figured out that my vessel temp after being heated with water comes out to 165° to 170°, vice my estimate of 200°. Temperature loss may be less if you dump your water direct from the lauter tun into your mash tun as opposed to what I do (open the valve and let it run in through a hose).

Three: Water temp in the lauter tun. My gauge reads about 3-4° warmer than what my thermopen measures (after a good stir). I haven't spent the time to calibrate my gauge near lauter temps to that of my thermopen, yet and even if you've calibrated to a certain temp it may go out of whack because mechanical gauges do that.

Bottom Line: experiment, measure, experiment, measure, rinse, wash, and repeat.

 

[brew_dawg23]

You might try wrapping your cooler with a blanket or thick towel. My mash tun is a 48 qt igloo marine cooler. After the first couple of batches, I found that the lid wouldn't close as tightly and I could literally feel hot air escaping in a couple of spots. I started wrapping it with towels or blankets after I mash in and it holds temps within a degree for 60 min.

 

[brewkinger]

It does not matter. the first 20 minutes are all that really matter. Don't open the lid. leave it closed. leave it for 40 minutes, or an hour. or 2, most of the conversion is done in the first 20 minutes anyways. the fact that it drops to 148 is still acceptable.

That said, as small as you can go the better. 10 gallons is better than a 13 gallon cooler like you have. the less air in there the less heat is pulled away from the liquid/wort/soon to be wort...

Agree with this except the cooler you have is fine, it just needs to be tweaked and your process as well. (see below)

Preheating is helpful, but try to preheat at a higher temp, for a shorter duration. I preheat my 5 gallon cooler with about 1.5-2 quarts of water, between 180 and 212 degrees. My 10 gallon gets 3-4 quarts of preheat water. Be aware that the hotter the water, it may warp the inside of your cooler a bit, if you're sensitive to the aesthetics of things like that. And since water doesn't hold temp well, I only preheat about 5-10 minutes before I am ready to add my grain and strike water. Dump the preheat water, and immediately add your important stuff.

Air doesn't hold temp, period. You have way too much "headspace" in your cooler. Find a piece of insulating foam you can cut to fit just inside of your cooler, and lay on top of your mash, then close it up. Or, use a smaller cooler.

Also agreed with a couple of caveats and process changes to make life easier. I am a subscriber of 2 basic concepts O.H.I.O (Only Handle It Once) and K.I.S.S (you probably know this one)

Some "tweaks" that you can do to the cooler are:
1) drill a couple of holes in the lid and use that expanding foam insulation spray to fill in. Trim the excess off and then the lid is exponentially better at insulation.
2) Get a piece of REFLECTIX insulation (ask at any home repair business), cut to fit the inside of your cooler and again you have GREATLY increased your insulation against heat loss in that cooler.

Preheating is important but there is no need to dump the preheat water. Instead heat your strike water up to around 170-ish and then dump a couple of gallons in and shut the lid and let the cooler preheat. After 5-10 minutes, dough in and add the rest of your strike water. This will usually get your mash temps down into the mid to high 150 range and then stir rapidly until your temp gets down to where you want it. Cover with insulation, put the lid on, wrap with a blanket (I use an old wool hunting shirt thanks to Unionrdr) and most importantly DO NOT OPEN THE LID.
Leave it be for the 60 minute mash time (although I have checked at the 20 minute point and conversion is indeed complete). I do not try and rush my brew days, there is always something that I can do while the mash is going on. I often bottle a prior batch while I wait.

To summarize, the cooler you have is fine with some additional tweaks, there is no real need for a new cooler (although a round cooler works well)

 

[cheesebach]

It's not air exchange that causes temperature fluctuation, it's just the fact that air itself, (even in a sealed environment), cannot easily maintain temperature.

Thanks again for all the input, but I'm not sure I'm understanding this part correctly. If there were no heat exchange between the inside of the cooler and the outside, the headspace air inside the cooler would quickly heat up and reach equilibrium with the temperature of the liquid, right?

It just seems as though I have more heat escaping from somewhere than I should. If the seal wasn't good so that the hot air inside could get out, this would probably let out a lot more heat than I'd expect to lose through the other less insulated parts, like the lid or ball valve.

 

[cheesebach]

Preheating is important but there is no need to dump the preheat water. Instead heat your strike water up to around 170-ish and then dump a couple of gallons in and shut the lid and let the cooler preheat. After 5-10 minutes, dough in and add the rest of your strike water.

Thanks, brewkinger - this is actually the preheat/dough in process I am using now. For my first few batches, i just filled it with a couple gallons of hot water from the faucet (around 130F) to test for leaks, and then dumped it and added my strike water and grain. After coming in below my target temp by the time everything equalized, I saw another user recommending this method and it's been working well for me over my last 4 batches. Unfortunately, it hasn't helped with the temperature drops after everything is mixed well and I close the lid and wait the 60 minutes.

Some "tweaks" that you can do to the cooler are:
1) drill a couple of holes in the lid and use that expanding foam insulation spray to fill in. Trim the excess off and then the lid is exponentially better at insulation.
2) Get a piece of REFLECTIX insulation (ask at any home repair business), cut to fit the inside of your cooler and again you have GREATLY increased your insulation against heat loss in that cooler.

Thanks for the suggestions. For the REFLECTIX, would you recommend just attaching it to the underside of the lid? I'll try these suggestions before my next brew and see if i get enough improvement from that.

Also, regarding the round cooler - is there any reason they would work any better or be more convenient? I don't think I'd want to go down to a 5 gallon round, since it might be tricky to give a good stir to a 5 gallon mash in a 5 gallon vessel. I'm guessing something in the 7-8 gallon range would probably be ideal for me, but i'm not sure what options I'll be able to find in that range, especially for a round cooler.

 

[brewkinger]

Thanks for the suggestions. For the REFLECTIX, would you recommend just attaching it to the underside of the lid? I'll try these suggestions before my next brew and see if i get enough improvement from that.

Also, regarding the round cooler - is there any reason they would work any better or be more convenient? I don't think I'd want to go down to a 5 gallon round, since it might be tricky to give a good stir to a 5 gallon mash in a 5 gallon vessel. I'm guessing something in the 7-8 gallon range would probably be ideal for me, but i'm not sure what options I'll be able to find in that range, especially for a round cooler.

I cut the piece to fit inside the cooler and it ends up right on top of the actual mash. That way there is minimal air space above the mash to lose heat to.
I have a 5 gal round coooler and I routinely put 4.8 gallons of grist in. Stirring it is possible it just takes patience and a good method.
The reflectix fits right on top of that and then the MEGA-insulated lid on top of that. Not a single degree of heat loss and I once mashed for 3.5 hours and it only dropped 1 degree.
I also have a 10 gal round cooler with a insulated lid and matching reflectix and commonly do bigger beers in that. There ends up being sometimes 8 to 10" of air space above the reflectix and I lose only 1 degree in that as well.

I think that the combination of insulated lid and reflectix is the key.

 

[cheesebach]

I cut the piece to fit inside the cooler and it ends up right on top of the actual mash. That way there is minimal air space above the mash to lose heat to.

Thanks again - so the REFLECTIX is actually in contact with the mash? Do you know what material the reflective layers are made of and whether they'd be food-safe at mash temps? I googled a little and found that the interior is polyethylene, but haven't found much about the outer layers.

 

[brewkinger]

The external layers are composed of high purity aluminum and the literature that I have says that it is non-toxic and non-carcinogenic

Check out the documentation HERE

 

[WildernessBrewing]

Tons of good ideas in this thread.

Something really simple to try if you haven't already is just putting something heavy on top of the lid while mashing. I noticed 2-3 degrees less in temperature drop over 60-90 minutes by just wrapping my 48qt coleman mash tun in a blanket and putting a heavy pot or container of water on top of the lid.

 

[str1p3s]

i put a folded fleece blanket on top and underneath and it significantly improved retaining heat. i don't think i lose anything in an hour and it's pretty simple

 

[cheesebach]

Thanks again for all the suggestions here. I tried a few things this weekend, but didn't quite get the results I was hoping for. Even after placing some aluminum foil over the "mash" and throwing a blanket and weight over the top of the cooler, I still lost around 7 to 8 degrees over 120 minutes (opening briefly at the 60 minute mark to check the temp). I'm sure I could improve on this with a little bit of work and some more insulation materials, but I think I'm leaning towards getting a smaller cooler in the 7-10 gallon range for my normal abv beers and keeping the larger one around for any big mashes that exceed that volume.

It was commented earlier in this thread that I shouldn't be concerned about 4 degrees over an hour since all of the conversion happens in the first 20 minutes anyways. Does this really imply though that any temperature changes that occur after those first critical 20 minutes don't have any affect on the end result though? Just looking to better my understanding of what is going on with the enzymes and sugars in there after after conversion is complete, since my several of my beers have finished 3 to 5 points lower than I was expecting and have been wondering to what extent this can be attributed to temperature drops in the later part of the mash.

 

[blizz81]

It was commented earlier in this thread that I shouldn't be concerned about 4 degrees over an hour since all of the conversion happens in the first 20 minutes anyways. Does this really imply though that any temperature changes that occur after those first critical 20 minutes don't have any affect on the end result though? Just looking to better my understanding of what is going on with the enzymes and sugars in there after after conversion is complete, since my several of my beers have finished 3 to 5 points lower than I was expecting and have been wondering to what extent this can be attributed to temperature drops in the later part of the mash.

I would think it can definitely have an effect, and would expect it to be what you are seeing (a beer that finishes more dry than expected). In general terms, most people losing temp are going to lose 0-3 degrees over the course of an hour. Conversion in a non-recirculated mash will depend on crush and time. If / when people say "all the conversion will happen in the first 20 minutes anyways", I would say that's still a general statement...ie, most conversion will happen within the first 20 minutes, and even with that, there won't be a large enough temperature change between minute 20 and minute 60 anyways to cause any appreciable difference.


That's not saying it can't happen, depending on perhaps crush and maybe a larger temp drop. 3-4 degrees in 60 minutes I wouldn't think would cause too much of a difference. If you are going 120 minutes and you're still dragging some conversion out in the latter 60 minutes, that could be open to a different temperature picture than your mash-in temp and could possibly result in more beta amylase. You'll also likely have some spots that are cooler / will lose temp more quickly than others.


My roommate had a pricey "made for homebrewing" mash tun that lost enough temp over 60 minutes that it took generally-unnecessary grain bill formulations to avoid brewing super-dry beers. It can happen. As mentioned, I don't think it's a (noticeable) problem most people have with the standard coolers.

 

[day_trippr]

Why mashing for two whole hours?

Cheers!

 

[smyrnaquince]

Are you thoroughly stirring the mash (at least 2 minutes) before measuring the temperature at mash-in and again before taking your later temperature?

 

[Bobby_M]

Thoughts that may or may not have been addressed in the thread:

1. Don't preheat with water that is not already your strike water. If you need 165f water for the amount and temp of your grain, heat it to 178F, add it to the cooler and cover it and slosh it around for a few minutes. Stir and check the temp and just wait until it hits 165. Now it's preheated.

2. Make sure you aren't waterlogging the insulation. If your bulkhead has a gasket on the outside, get rid of it. You may be leaking but that outside gasket is putting it all into the insulation which causes a LOT of heat loss.

3. Check for air leaks at the lid. If you have a way to blow air into the drain valve (not while you are brewing), you should be able to hear and feel air escaping out of gaps between the lid and body.

 

[cheesebach]

1. Don't preheat with water that is not already your strike water. If you need 165f water for the amount and temp of your grain, heat it to 178F, add it to the cooler and cover it and slosh it around for a few minutes. Stir and check the temp and just wait until it hits 165. Now it's preheated.

This is a good suggestion, and is exactly the process that I follow. After the my strike water has "preheated" the mash tun, I add the grains and stir everything well until my temp is on target and consistent within a couple tenths of a degree throughout the mash.

3. Check for air leaks at the lid. If you have a way to blow air into the drain valve (not while you are brewing), you should be able to hear and feel air escaping out of gaps between the lid and body.

I've checked that I don't have any liquid leaking into the insulation, but hot air leaking through the lid has been something I've suspected from the start. A bad seal at the lid on my particular cooler could explain why many users are using this same cooler for 5 gallon batches with good heat retention. However, I haven't been able to find any other posts with suggestions on how to fix that other than adding a weight over the top (which didn't help much in my case). I'm thinking some sort of rubber or foam tape that I could attach to the top of the cooler where it contacts the lid might work, but not sure what heat and food safe options there are out there like this.

 

[laredo7mm]

First:

The thicker the mash, the better it will retain heat. Ignore your water-only test results. Water alone doesn't hold temp very well. Consider trying 1.15:1 instead...

This doesn't make much sense to me. Mass retains heat. The more mass you have in the cooler the slower the temperature drop will be.

If I have a 12# grain bill and I mash at 1.15:1 then I will use 3.45 gallons of strike water. Lets say my mash temp is 150° F. So I will have 40.9 pounds of grain and water at 150° F.

If I mash at 1.75:1 that will be 5.25 gallons of strike water so I would have 56 pounds of water and grain at 150° F.

A mass of 56 pounds at 150° will retain heat longer than a mass of 41 pounds at 150°.

 

[doug293cz]

This doesn't make much sense to me. Mass retains heat. The more mass you have in the cooler the slower the temperature drop will be.

If I have a 12# grain bill and I mash at 1.15:1 then I will use 3.45 gallons of strike water. Lets say my mash temp is 150° F. So I will have 40.9 pounds of grain and water at 150° F.

If I mash at 1.75:1 that will be 5.25 gallons of strike water so I would have 56 pounds of water and grain at 150° F.

A mass of 56 pounds at 150° will retain heat longer than a mass of 41 pounds at 150°.

Correct

Brew on

 

[laredo7mm]

This is a good suggestion, and is exactly the process that I follow. After the my strike water has "preheated" the mash tun, I add the grains and stir everything well until my temp is on target and consistent within a couple tenths of a degree throughout the mash...

I have the same problem with heat loss in the mash tun. I use a 10 gallon cylindrical cooler and I insulated the lid with spray foam. It didn't seem to help much. I lose 2 to 3 degrees an hour. I heat my strike water right in the mash tun with a heat stick.

My last beer was a double batch of cream ale so I had 17.69 pounds of grain and 6.25 gallons of water for 70 pounds of thermal mass. I still lost a couple degrees over a 75 minute mash. I am bad about stirring and checking the temp too often though so it doesn't help the situation.

I bought some reflectix last night to try and insulate my boil kettle to see if i can get a good boil with just the 2000W heat stick and no assistance from my stove on a 7 gallon boil.

It failed, but now I have the insulation to make an interior lid to set on top of the mash in the cooler and give that a try as was suggested here earlier.

 

[cheesebach]

3. Check for air leaks at the lid. If you have a way to blow air into the drain valve (not while you are brewing), you should be able to hear and feel air escaping out of gaps between the lid and body.

I took your suggestion to blow air into the drain to check for leaks at the lid (making sure no one was watching as I did this ). There's very little resistance to blowing air in, so I'm thinking this is likely a major source of heat loss. I'm still trying to think of a good method for improving the seal though that would be food-safe at mash temps though. There is a bit of a ledge (maybe a bit under a half in wide) that goes around the entire inside wall of the cooler that I'm thinking I could put to use. Maybe a few sheets of reflectix cut to sit on top of that would work using the pressure of the lid when closed to hold it against the ledge. Another option I had considered was trying to find some sort of foam or rubber tape along the top edge of the cooler that would compress a bit under the lid and to fill in any air gaps.

Let me know if anyone has any ideas for me, and I'll post back if I'm able to find something that works.