mash tun needs a hat

[dcunitedfan]

I just built a 5 gal mash tun using FlyGuy's instructions at https://www.homebrewtalk.com/showthread.php?t=23008

I'm not yet ready to do my first mash, but I did do a test to see how well the cooler maintains temperature. With water in the 150-155F range, it seemed to lose maybe 2-4F in one hour. I did notice that while the walls were pretty cool to the touch, the lid was rather warm. Of course, heat rises, and I don't know if the lid is as well insulated as the rest of the vessel (I suspect not since these things are designed for cold liquids, so the lid insulation is less important there). I was testing with 3 gal of water and no grain, so maybe with the additional thermal mass of the grain, it will be less of a factor. Still, I'd like to keep the temp as stable as I can with some cheap solution congruent with using a cooler instead of a heated metal kettle for a mash tun...

So I'm wondering if anyone else has noticed the same thing and devised some sort of simple solution to help with the lid insulation. I'm hoping that I could cut the heat loss down just by putting a big hat on my mash tun

 

[PT Ray]

The lid is hollow and needs to be insulated. There should be a vent plug in the center, this allows air to come in preventing negative pressure so water will flow freely when dispensed. This will need to be removed and several holes drilled around the circumference. This will allow several access points to fill with spray foam insulator aka Great Stuff. Once filled and allowed plenty of time for the Great Stuff to gas off the holes can be covered with caulk or in my case hot glue. This should insulate the lid and better hold heat.

 

[BierMuncher]

Don't go there. You're about to make a typical error in thinking that plain water should hold temperature as well as a mix of grains and water.

If you're using an orange rubbermaid cooler, you'll most likely loose 1-2 degrees in 60 minutes.

Grains hold temp much better than water. I've gone as long as 90 minutes with my rubbermaid loosing only 3 degrees.

 

[dcunitedfan]

BierMuncher, that's a good point about the grains. But, I'm still thinking that I'll want to do something to help insulate the lid. From what I know about mashing, I'm gaining nothing if I lose heat out the top, even if it's less of a factor when using grains (well, unless maybe the mash temp starts out too high)

I'll have to think about the drill 'n fill method, thanks PT!

 

[david_42]

I recommend you use "door & window" latex foam, not poly. It doesn't expand as much (very little actually) and is less likely to warp the lid.

 

[dblvsn]

I built a 5 gallon version of this and over a 60 minute mash I only lose 1 maybe 2 degrees. Once you add the grains to the water the temperature holds very nicely.

 

[malkore]

I think you're improving something that doesn't really need improving.

i left my grain in the cooler for 6 hours after collecting the final runnings. then I cleaned it and the grain was still hot enough to be uncomfortable to stick my hand into (so probably 115-120F).

during a 60 minute mash I might lose 2 degrees.

Use Promash to help you hit your proper dough-in temp with the right strike water temp.

and always preheat the cooler with 3 gallons of hot tap water (which for me is 122F)

 

[Bobby_M]

I think the best solution, if you really want to hold as much heat as possible, is to make an insulation plug that will fit down inside the cooler snugly and rest on top of the mash. I'm thinking a decent method would a a disc of rigid insulation in a vaccum sealed bag. My reasoning is that the mash heats the air gap, then the air can leak out a little.

If the lid really is hollow, filling it with foam is a cheap way to stop that 1-2F drop at least.

 

[desertbronze]

... If you're using an orange rubbermaid cooler, you'll most likely loose 1-2 degrees in 60 minutes.

Grains hold temp much better than water. I've gone as long as 90 minutes with my rubbermaid loosing only 3 degrees.

I have had the same experience with my coolers. When brewing when it's really cold outside, I just put an old sleeping bag over the cooler. Low-tech, but it works - and no chance of warping the cooler lid with the foam.

 

[Craig5_12]

I say go for it and fill that lid with foam. In the world of brewing, temperature is King! If the Mash Tun only loses one degree (or better yet 0 degrees) throughout the mash, more power too you. Plus...whats it going to cost you? $10?

 

[bitteral]

The lid is hollow and needs to be insulated.

From what I understand, air is an excellent insulator. So if your lid is airtight, it is probably already very effective, maybe even more effective than a foam filled lid.

Now if your lid is not airtight (i.e. with some small leaks), so that the warmed air in the lid can actually physically escape to the outside of the lid, and the cooler outside air can enter into the lid, then you would benefit by having a solid insulating material, like a foam, in the lid. The foam is both a good insulator, but more importantly it would fill the lid so that air could not flow in and out of the lid.

If air is such a good insulator, why do we put insulation in our walls and why do people use these foams around their windows, etc? From what I understand, it is only really because those areas are not airtight, not because air is not a good insulator. The situation with your cooler lid may be different.

 

[Thalon]

I've had the opposite experience with my mash tun. I did the same testing with water and I only lost 2*F over 90 min with straight water. But it seems with the two AG batches I've done with it I've lost about 4-5*F during the 60 min mash. I'm not aware of anything I'm doing differently.. In any case, I had no idea that peep hole was in the lid, thanks for the tips! Hopefully this will help me keep my mash temps.

 

[Bobby_M]

From what I understand, air is an excellent insulator. So if your lid is airtight, it is probably already very effective, maybe even more effective than a foam filled lid.

...
If air is such a good insulator, why do we put insulation in our walls and why do people use these foams around their windows, etc? From what I understand, it is only really because those areas are not airtight, not because air is not a good insulator. The situation with your cooler lid may be different.

Air is a better insulator than some things, but certainly not foam. Foam insulates well because it makes a million tiny air gaps that do not intermix via convection.

An inch of air that is not still is only R-1. An inch of foam is like R-5. That's a nice improvement.

 

[dcunitedfan]

What is clear to me is that the top of the lid is quite warm compared to the sides when it has 3 gal of 150+ deg F water in it. The heat loss is palpable, palpable I say!

As for the design of the lid, it has a small (maybe 1/8") hole at the edge of the bottom rim of the lid. I'm not sure at present if that's the air inlet or not - could also be convinced that the design of the lid is such that it doesn't really form an airtight seal with the vessel itself.

At any rate, I picked up a can of window&door sealant foam, so I think I'll give that a try. Thanks for all of the input, I'll report back when I get a chance to do the deed.

 

[jfrizzell]

I'll report back when I get a chance to do the deed.

Be sure to let us know how the test with the foam goes also...

 

[paranode]

The Igloo MaxCold thing I bought must be better insulated cause I'll tell you neither the sides nor the top seem to get warm. Only my brass valve gets warm. Obviously that doesn't help you any but if anyone else is deciding on what cooler to buy maybe that makes a difference.

 

[bitteral]

Air is a better insulator than some things, but certainly not foam. Foam insulates well because it makes a million tiny air gaps that do not intermix via convection.

An inch of air that is not still is only R-1. An inch of foam is like R-5. That's a nice improvement.

Interesting. So you are saying that the material that makes the foam itself is not necessarily a better insulator than air (as a material itself), but the fact that foam prevents air from convecting, by partioning it into "a million tiny [stationary] air gaps", is what makes it so effective. And that is what makes foam a better insulator than pure air.

I can buy that explanation!

 

[perry]

Lots of good advice here... I'll add mine- get an old sleeping bag, preferably made of cotton so's it don't melt on the burner or whatever, throw it over the top, and call it good. As long as your temps, your stirring, and your patience are intact, your mash will be fine!

-p

 

[dcunitedfan]

It took me a while to finally get to the point of doing my first allgrain batch (which I did yesterday). In the end, I went with the "throw a blanket over it" option. That seemed to help and also the added thermal mass of the grain seemed to help hold the heat better than my early water-only test.

 

[Funkenjaeger]

I think that just cutting out a circle of foam (even something thin, like 1/2") and gluing/taping it to the inside of the lid would help significantly. Even if it's not a perfect fit, it'll still dramatically reduce the area of the lid that's directly exposed to the hot air inside the mash tun.

With that said, though, I agree that it's not really necessary - like others, I lose maybe 1-2 degrees over a 60-minute mash, tops, so I don't feel it's worthwhile to go out of my way to insulate the thing any better - if I had a piece of foam laying around, I might go for it, but I'm not going to go out and buy anything.

I think it's likely that anyone who's losing more than a degree or two during the mash is wrongly attributing it to straight heat loss - not preheating the mash tun and not stirring the mash sufficiently can cause a significant temperature drop in the first 10 or 15 minutes as the mash and mash tun all equalize in temperature. Since I started preheating my mash tun (over-heating strike water a bit, putting in MLT for 5-10 mins, then adjusting to target temp with cold water) and making sure to stir vigorously, I've had great luck maintaining mash temps without modding my 5-gallon cooler at all.

 

[Bobby_M]

The only time I think you'd have higher heat loss is when your tun is way bigger than it needs to be for the batch size (a small 5 gallon batch in a 60qt cooler). If you do that often, it would be nice to cut a piece of rigid foam to the exact contour of the cooler sidewalls so that it sits just about on top of your grain bed. That will keep the heat really well.

 

[foxtrot]

I too was concerned about the lid feeling warm. I think the sides are a little warm, too. So I bought a water heater banket, taped a plastic drop-cloth to cover the exposed insulation side, and cut it up to make a cover for both my MT and HLT. My mashes now lose 0 heat after 60 minutes, and my sparge water is maintained (I'm a fly guy). After mashing and sparging, the drop-cloth side (inside) feels warm so I know I'm keeping some heat in. My be over-kill but any additional control over my system gives me better control over the final product!

 

[BrianP]

+1 on the preheating. insulating the exterior won't hurt but probably isn't necessary (unless may during fall/winter).

 

[boo boo]

I have had the same experience with my coolers. When brewing when it's really cold outside, I just put an old sleeping bag over the cooler. Low-tech, but it works - and no chance of warping the cooler lid with the foam.

I'll second that. I just put a thick towel over the top and don't lose any tempertures that can be noticed over a 90 minute mash.