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Maintaining Mash Temp

Hey all. I just brewed my first AG beer last night and found that my mash temp dropped from 152 to 140 in less than 15 minutes. Is this possible or is my thermometer playing tricks on me? I just can’t seem to believe that this could happen…I was working in my 40 degree garage after all. I also missed my 152 mash with 162 strike water…what? I did rap the tun with a few light blankets, but really thought the cooler would hold a better temp than that. Any thoughts?

You really really really have to stir everything really good to get the temperature consistant througout the entire mash.
You probably hit a warm spot initially and vise versa 15 minutes later.
Or you drunkenly poured a bag of ice in the tun and forgot?

What did you brew up?

I brewed the Dead Ringer kit (Two Hearted Clone). 12 lbs of grain…in a 60 qt. coleman xtreme cooler. Do you think that the cooler is too big? I want to be able to do 10 gallon batches and that is why I purchased the 60 qt.

Did you preheat the mash tun. You can put the heated water in then close the lid for a minute then add the grain. I didn’t preheat it on a partial mash brew and I lost about the same you did. Now I pour in about 1 1/2 gallons of almost boiling water and close the lid then heat my mash water. I then dump out the hot water and add the mash water then the grain, stir really well and check the temp. I now only lose 1-2 degrees in the hour. I am using a 10 gallon Rubbermaid drink cooler.

I mash 5 gallon batches at 1.25 qt/# in a 28 qt cooler.
What ratio were you mashing at?
If not already you could go to 1.5 or 2 qt/# to get some thermal mass in there.
If you missed your target temperature by a few degrees I could see losing another few degrees to heating up the insulation in the cooler if the cooler was 40 degrees.

I did heat it up with about two gallons of 180 degree water…perhaps I could have used boiling water. I probably did hit a cold patch with the thermometer. Thanks everyone for posting…I will monitor it more closely next batch.

I will heat all my mash water to ~180 and put it in the cooler. When that temp drops to ~160 I will add the grain. It normally stabilizes at ~150 from there.

No need to add boiling water and then toss that down the drain. A waste of water and fuel to heat it.

Adding boiling water to an empty cooler will shorten it’s life. The plastic is stable to about 180°F, but the lining will gradually separate from the insulation, warp, and possibly crack if it is repeatedly exposed to boiling water.

I just did the calculation for my tun and I would need strike water near 170°F to hit 152°F for 12# of grain at 40°F (assuming it had been left in your garage). It would be less if the tun was preheated, but your tun is larger than mine, so it would require more heat.

I suspect that your tun wasn’t heated enough by the brief exposure to the pre-heat water and that the water was probably cooled significantly when put in a 40°F tun. Even if my tun was preheated to 152°F, assuming the grain was 40°F, I would need 166°F water to hit 152°F.

What I’m getting at is that I think you are simply seeing the heat loss to the mass of the cooler over the first 5-10 minutes. You are probably going to need to use hotter strike water, start at a higher mash temperature, and plan on hitting your target after 5-10 minutes. Or, you can use Nighthawk’s technique, where you add your strike water to the tun for ~15 minutes (allowing the tun to be thoroughly preheated) shooting for the temperature that, when combined with the grain, will give you your mash temperature.

You also might think about insulating your lid. Its easy enough to drill the lid and add some spray-in foam.

I use my boil kettle for my mash tun - heat everything up together and then put it into my custom made insulated box. I usually preheat the box the night prior before brewing with my sparge water but when I don’t, it’s efficient enough to not trouble me much. The box loses about 1 degree per hour. I can post pictures if you’d like.

the 60qt cooler for 5gal should be fine. i use a 70qt extreme and batch sparge. i ran your numbers using
cause i’m too lazy/i mean busy to make a spreadsheet with Denny’s/Palmer’s formula(s). essentially, for 7gal preboil with 12lbs grain at 40°F and a water/grist ratio of 1.6 qt/lb and a target mash of 152°F you should have 4.8gal of 170°F strike water. i usually have pretty good luck with this calculator, and i generally do overnite mashes. i maybe lose about 5°F so i try to go hot by adding the temp loss to my initial strike temp.

also +1 for insulate lid. Baratone posted something about that awhile back. use great stuff expanding foam and get some plastic plugs from home despot for about 75cents ea.

[quote=“Slothrob”]Adding boiling water to an empty cooler will shorten it’s life. The plastic is stable to about 180°F, but the lining will gradually separate from the insulation, warp, and possibly crack if it is repeatedly exposed to boiling water.

[quote=“Nighthawk”]I will heat all my mash water to ~180 and put it in the cooler. When that temp drops to ~160 I will add the grain. It normally stabilizes at ~150 from there.

Great information here for all concerned.
I will watch my preheating temperatures more. I’m glad that I didn’t actually have boiling water. I don’t want to shorten the life of my cooler. I am going to try the hot water and wait for it to cool method next brewday. I may also insulate my lid although I am not losing much temperature so far.

I throw at least two blankets over my cooler mashtun, one of which is thick wool, for the entire mash, which results in a mash temp drop of typically 1 to 3 degrees, depending on how long I mash and how cold it is - I brew outside, including in winter.

The second cooler mashtun I built, I chose a 5-day cooler knowing it is well-insulated, but both of my Rubbermaid coolers hold temp very well. When I add my strike water to the cooler, I go a bit hot and close the lid for about 5 minutes to let the heat stabilize to ensure my strike water is the correct temp before stirring in the grist. Once I close the lid, I will open it briefly to check pH, but that is just to make sure I hit my mark with additions to the strike water per my calculations in Bru’n Water. Also, I use a high quality electronic thermocouple instant read thermometer with a long stainless steel probe, which means I can check temps quickly, accurately, and as regularly as I want and it isn’t a PITA. I’m a check and check again kinda guy when it comes to dialing in temps, but once I’m there, baby, the lid stays closed until the timer buzzer sounds.

You raised two primary problems with all grain brewing:

  1. Do my thermometers work? That’s something that you need to sort out on your own. Personally, I prefer liquid lab-spec thermometers. They’re cheap enough that you can have a few of them in the mash and they’re balls on accurate. But they’re slow. Others prefer digital thermometers, the good ones are expensive and fast; the cheap ones are also fast, but next to useless. Don’t bother with cheap digital thermometers.

  2. Insulation and the continuity of mash temperature is the second issue. I’m a fan of dry beers so I don’t mind starting my mash low and letting it slip lower. If, however, you’re on the malty side of things, it sounds like you’re going to want to invest in some insulation, if you’re going to be brewing in that cold garage. Alternately, you may wish to invest in a heating source. A heatstick is a cheap, cooler friendly way of maintaining mash temps and doing step mashes in cold ambient temps without resorting to a fired mash kettle. It’s a cheap, easy solution that might prove handy.

Edit: Also, missing your mash temp isn’t all that unusual if your grains are cold. Remember to move them inside the house several days before you crush them. Your software assumes they’re at ambient temperature. But if they’ve been living in the garage at 44F, that predicted mash temp is going to be waaaaay off.

Moreover, keep a log of mash in temps. Until you develop a thermal mass number for your system, your software isn’t going to be very useful.

Thanks for all the great tips. For the record, I did have my grain stored at room temp for a few hours leading up to mash time. I think that I will try to heat the strike water to 180 and then wait until it drop down to 168 and see how that works out…sounds really smart to me.

My last brew, I added hot water at 174F to my mashtun, and the mashtun and dry grist (separate from each other) had stayed inside the house overnight and up until time to mash, so they weren’t cold. At 42F outside weather temp, the transferred strike water ended up at 166.5F in the cooler. After closing the lid I left it to stabilize and after 7 minutes the strike water was 165F. My desired strike water temp was 164, but I added the grist at 165 and just stirred the mash a little extra (3 minutes) to get from the initial mash temp of 153F to my desired dough-in mash temp of 151.5F. These are actual temps from my notes which I take carefully since like I said I’m pretty careful about dialing in my mash temps. I work like this every brew and basically always nail my mash temp. If my strike water temp comes in too low in the cooler after transfer from the hot liquor tank (also my kettle), I’ll remove and reheat some of that water from the mashtun and re-add it until it’s where I want it before stirring in the grist. Another good reason to add grist to water and not the other way around. :wink:

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