Mash tun cooler not working well for me

I bought a 52 qt igloo marine cooler and have been using the SS braided line. I have had some terrible numbers lately, so I took some more accurate temp readings tonight. Tonight is a big beer - Bombastic 1.075. Because my efficiency is so low, the LHBS set my efficiency to 65% in proMash.

Almost 20 Lbs of grain, mashed in with about 6 gallons of water at about 164 degrees. I was using a digital thermo that was inside the mash tun. Started great. 153, then 152 about 5 minutes in. Then it started falling quicker. Needless to say, last time I checked I was at 144 with about 12 minutes left in my 60 minute mash.

Should the temp drop this much? I thought it held very constant after you mashed in. Thoughts? What am I forgetting?

Did you pre-heat the cooler?

It shouldnt drop that much.

You might try wrapping the mash tun in a sleeping bag or something else thermally insulated to retain some heat. You also might consider increasing the amount of water (ie, water to grist ratio) you use to mash in. More hot water = more thermal mass = less reduction of heat. It also means less sparge water.

Maybe we'd be better equiped to advise you if you outlined your process step by step.

A cooler isn't likely to lose that much heat in an hour. Are you sure the thermometer is accurate?

Sounds like every time you open it up you lose a degree. Preheat your cooler with a few gallons of 160ish water, wrap that sucker in a blanket, and don't fiddle with it for the whole hour. (edit) Or maybe your not opening it. maybe ghosts are haunting your mashtun, do you live in a haunted house?

brooksy said:

Sounds like every time you open it up you lose a degree. Preheat your cooler with a few gallons of 160ish water, wrap that sucker in a blanket, and don't fiddle with it for the whole hour. (edit) Or maybe your not opening it. maybe ghosts are haunting your mashtun, do you live in a haunted house?

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This. Preheat then add water and grains. Stir the crap out of it and let it sit for ten minutes covered in towels or blankets. The. Check the temp to make sure that you are on target. Leave it alone for the hour wrapped up again.

SouthBay said:

It shouldnt drop that much.

You might try wrapping the mash tun in a sleeping bag or something else thermally insulated to retain some heat. You also might consider increasing the amount of water (ie, water to grist ratio) you use to mash in. More hot water = more thermal mass = less reduction of heat. It also means less sparge water.

Maybe we'd be better equiped to advise you if you outlined your process step by step.

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I always thought that by adding more water to your mash you were more likely to loose heat because the thicker grains retain heat better than just plain old water. It's like oatmeal, which will stay hot on the inside forever, vs a bowl of hot water which will lose temp quickly. So therefore a thicker mash might be your target.

brooksy said:

Sounds like every time you open it up you lose a degree. Preheat your cooler with a few gallons of 160ish water, wrap that sucker in a blanket, and don't fiddle with it for the whole hour. (edit) Or maybe your not opening it. maybe ghosts are haunting your mashtun, do you live in a haunted house?

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This...

Stop opening the mash tun. OR if your like me and want to know the temp, put a small hole in the top of the mash tun and push a LONG thermometer (one of the turkey fryer one's) into the mash tun thru the hole so you dont have to open it up.

I didn't open it at all in the 60 minutes. I'm using a wired thermometer.

We have used the round 10 gallon coolers and maybe lose 1 degree in 90 minutes. On thing that we do it to make sure the water is at Temperature in the Mash Tun prior to adding the grain. If we are shooting for a starting temp of 164, then we will add water at maybe 180 and then add cooling water 1 cup at a time till we get 164. If we need to remove some water to get to the 6 gallons, we will do so. It is much easier to cool water than heat it by additions. We have found this method very useful in not chasing the mash temperature. We have moved on and have a Stout MLT and now use a HERMS system to maintain tempuature, but we still achieve our start temp and volume prior to adding the grain. We also add about 1/2 pound of base malt to any standard 5 gal recepie, although lately we have improved our effiency so we are adding water to get the the projected OG. In fact on our last brew, I used one of the Starter flasks to make a one gallon bonus batch.

cmybeer said:

I always thought that by adding more water to your mash you were more likely to loose heat because the thicker grains retain heat better than just plain old water. It's like oatmeal, which will stay hot on the inside forever, vs a bowl of hot water which will lose temp quickly. So therefore a thicker mash might be your target.

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I lose heat more quickly with a THINNER mash.

Is there a lot of headspace in your tun after adding grain and strike water? If so try taking some aluminum foil and resting it on top of the mash. I lose way less heat since I started using this method.

Do you live in a place where it's still cold at midnight? Fill the cooler with about 2 gallons of 190F water and take it outside. Shine a flashlight around where the lid closes and see if you get steam coming out.

Was the grain sitting out in the garage overnight? How about the cooler?

However, I do agree with the others that using 164F without a preheat is definitely not going to do it. That temp is assuming a certain ambient temp (what temp the cooler is), grain temp, and water/grain ratio.

My guess is most of that heat was lost to the cooler itself and grain, which was probably colder than Promash was assuming. If you think you need 164F strike, heat it to 175 before putting it in the cooler. Then just let the cooler take whatever heat it wants over the next 5 minutes. Also tilt the cooler a bit so that water hits each side wall. Wait until the water gets to 164, stirring with the lid open if necessary, THEN dough in.

Report back.

KraphtBier said:

Is there a lot of headspace in your tun after adding grain and strike water? If so try taking some aluminum foil and resting it on top of the mash. I lose way less heat since I started using this method.

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This is pretty much exactly what i was getting at. The overall density of a thick mash will be higher than a thinner mash, and have a greater thermal mass per unit of volume, meaning it'll retain more heat. Buuuuut, once you take into account headspace in the mash tun, that thermal mass will be radiating its heat into a very not-dense area of air, and could be escaping through the lid/seals, especially if it's not insulated with blankets/sleeping bags/etc or if its being opened repeatedly.

I've never tried the aluminum foil thing, but it seems like it'd work, since it doesnt absorb heat very well.

Great advice. Things learned: 1. Mash at a higher temp regardless of everything - easy to cool, near impossible to heat with my methods. 2. I need to keep using this "remote" thermo. It gives me real time numbers. 3. I need to assume more of a loss in the first 5 minutes (that's where I had the steepest amount of loss). 4. Keep getting practice. Perfect practice makes perfect.

Thanks again.

Naptown said:

Things learned: 2. I need to keep using this "remote" thermo. It gives me real time numbers.

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Are you sure it is accurate? Do you have another one you can check against?

Naptown said:

3. I need to assume more of a loss in the first 5 minutes (that's where I had the steepest amount of loss).

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Maybe you should just stir for the first five minutes, then take the temperature.

cravej said:

Are you sure it is accurate? Do you have another one you can check against?


Maybe you should just stir for the first five minutes, then take the temperature.

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Yes, I have double checked it. I do a lot of BBQ smoking with it. It's solid. Yeah, I think that's my biggest mistake here. I though you mashed in, and were done when there were no clumps. That's just wrong.

Naptown said:

2. I need to keep using this "remote" thermo. It gives me real time numbers.

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Is it possible that the remote probe is laying at the very bottom of the tun, the outside of the cooler, and experiencing more cooling than the rest of the mash? For this reason I prefer a handheld thermo to a mounted unit.

Just for kicks try checking the temp at various locations throughout the mash. Temp should be fairly consistent if the mash is mixed well. I agree with previous posters, if properly preheated, just about any cooler, properly sized, will not lose a significant amount of heat.

All you would ever want to know about preheating a MT here...https://www.homebrewtalk.com/f36/pre-heating-mash-tun-295417/