Mash Tun not holding temperature well

[thejuanald]

I have had a problem in the last two batches I've brewed with my mash tun not holding temps very well. I have a 10 gallon cooler that I bought from Home Depot and converted to a MLT.

My normal process is to heat up strike water to temperature (the last beer was 163F to get to a final mash temp of 152 according to Beersmith), close the lid to allow the tun to adjust to the temp of the cooler, add the grain while mixing furiously, then seal it up. I hit the temps just fine at the start, but coming back after 20 minutes to check, the temp has dropped a few degrees. What I ended up doing was just adding a bit of hot water to try and bring up the temp but that doesn't seem like a practice I want to keep doing.

This is being done inside so I wouldn't think the fact that it's freezing outside would be much of a problem.

I don't understand why it's not able to hold temp very well because it held it just fine not that long ago. Any ideas or am I glaringly doing something wrong?

 

[UNIbrewster]

Are you preheating your mash tun with boiling water before adding mash water and grain?

 

[tlucarelli]

I will say I'm a bit on the newer side as well, and I'm still learning "best" techniques for mashing, but I had a similar issue with my 10 gallon cooler converted MLT. What I found is that while I'm heating up my mash water, I fill the cooler with maybe an inch to 2 inches of hot water and seal it. Then, when I've hit my strike temp, I empty the cooler and add the mash water. This basically "conditions" the cooler to be ready for hotter water and honestly I haven't had temp issues since.

 

[phyllobeddo]

I have a red Rubbermaid 10 gallon cooler converted to MLT. I had the same problem as well. The best thing I have have found so far is to fill it up with 2.5 gallons to 3 gallons of hot tap water (I guess boiling would work better) while I heat my strike water on the stove. That helped heat retention for me. I still lose a couple of degrees, though.

 

[GrogNerd]

if you're not hitting strike temps, try heating the tun as described above

if you're losing temps during the mash, it most likely is thru the lid. I place a layer of aluminum foil on top of the grain bed during the mash, then leave it there and it helps keep from disturbing the grain bed while vorlaufing. lose only a degree during an hour-long mash

 

[ndinh]

Like the above post said, you need to pre-heat your cooler. I'll heat up my mash water to 165F for example and then run 1 gallon of it into my cooler. Close the lid and let that sit for 10 minutes. Drain the 1 gallon out and put back in HLT. Heat HLT again, if necessary to get back to 165F and then mash in (half the grain amount each time). Just brewed this past weekend and temp stayed at 152F for the full hour in my igloo round cooler.

 

[kombat]

+1 on pre-heating the MLT. On any brew day, the very first thing I do is set up my mash tun, pour half a bucket of piping hot water from the tap, dump it into the mash tun and close the lid. Then I get to work drawing my strike water, lighting the burner, milling the grain, etc. When my strike water reaches temperature and my grain is all milled, I dump the hot water out of the cooler, add the strike water, and stir in the grain. The foil-on-top-of-the-grain-bed trick helps hold temperatures and prevent disturbing the grain bed during recirculation/vorlaufing.

 

[Natdavis777]

When I used to use a cooler, I would beat my strike water to ~175F and add to the MLT. After 10 minutes or so, I would open up and stir the water until I got to my strike temperature. Then I would dough in. Usually held temps consistently

 

[porterpounder]

Pre-heating is a good start. You can also drill a few small holes around the outside edge of the lid (don't drill through completely) and injection some spray-foam insulation as the cooler body, but not the lid, is insualted. That helped me maintain temp better with the same setup.

 

[thejuanald]

Thanks all for the information! I was not preheating my cooler, but I figured since I hit the temperatures just fine at the start that it was fine. It makes sense that the cooler is absorbing the heat and the temps drop over time. Once they equilibrate I'm sure the temps would stay pretty well.

I will also look into insulating the lid, I did not know it wasn't insulated as well, thanks for the tip. For now I will do what GrogNerd suggested and put some foil on top of the grain bed to try and keep the temperature during the mash.

So my question now is, in heating my mash tun before I add my strike water, I will probably have to adjust my strike water temperature in Beersmith because I will get a lot less heat loss when I add the grain now that the entire tun is preheated, right?

 

[JonM]

I had the same problem, and I tried to insulate the lid with expanding foam. It didn't work and made a mess. The better way to go is to get rid of the headspace (in addition to preheating). I took some 3/4 inch styrofoam and cut out a couple circles roughly the inside diameter of the cooler. I put them in a crockpot liner bag and shove the whole thing into the tun so it just touches the grain bed. I barely lose a degree over the course of the mash.

 

[cobrem]

For lid insulation, I just throw a folded up towel on top. Probably not as good as foam insulation, but good enough and pretty "two birds with one stone"y when you consider the need for a close-by towel for mopping up any spills later in the process.

 

[tlucarelli]

Honestly I think you will be fine without touching your lid. I hit my temps perfect and maintain them now. No need to adjust the qty of water or adjust beersmith calcs IMO. My grains are usually stored in my basement too so I go a couple degrees higher than my strike temp just in case but I usually end up stirring or adding cold water to get back down. Just try it once without adjusting and then see how it goes. If you need to you can adjust accordingly but you won't know until you try.

 

[eelpout]

It doesn't sound like the cooler not "holding" temperature is the problem. It sounds more that your are just not hitting the temp you want.

You said you use beersmith. Beersmith really needs you to dial in your system before it can accurately predict what your cooler will settle at. Make sure the weight is right.
And most importantly, everytime you brew make sure the grain temp and cooler temp are correct.

 

[thekraken]

It seems to me that your goal should be to get the strike water to settle at the calculated strike temp while in the cooler. Heat your water up about 10 degrees or so past strike temp, pour it into your cooler, and let the cooler absorb what heat it will for 10 minutes or so. Then let the temp settle down to where beersmith said and dough in. If it settled too cool then try pull out a sauce pots worth, bring that to a boil, add it back to the mlt, wait for it to settle, so on and so forth.

 

[kh54s10]

Another thing that helps hold the temperature during the mash, after pre-heating, it to wrap the whole thing up in blankets. I have to do this when brewing on my porch during the winter.

 

[Jim311]

Another thing that helps hold the temperature during the mash, after pre-heating, it to wrap the whole thing up in blankets. I have to do this when brewing on my porch during the winter.

You could also buy some foam sheets or insulation from a home improvement store and wrap it up, and I bet it would be cheap.