Mash-tun cooler temperature drop

Hi all,

Perhaps this post should go in the beginners section. If so, moderators, feel free to move this thread.

I've done (or am in the process of) 4 extract brews so far (and 2 apfelweins, but they're more like assembling rather than brewing) and I'm wanting to go all grain now.

I've done a fair amount of reading about all grain and decided to make mash tun out of a cooler. I had the 5 or 10 gallon debate and decided to get a 10+ cooler so I could eventually make higher gravity 10 gallon batches if I eventually want to. So I found an Igloo 50qt square cooler at Target for $20. This cooler appealed to me because the squarishness instead of rectangularishness. It seems like there would be less surface area on top for heat to escape. All the other coolers were the rectangular type. Plus it was $20. I thought the insulation was probably questionable at best because it isn't the thick stuff like the 5-day Coleman Exteme Coolers have.

I don't know if this link will work or not, but here it is: link


Anyway, I drilled a hole and put a brass valve outside and barbed connector on the inside and made a manifold out of 1/2" CPVC. Then I did some testing of the drop in temperature over 1/2 hour with 4.5 gallons of water that started out at 155F. Here are my results:


01/03/09
Initial test:
* Poured 4.5 gallons of water at 155F into cooler
* After ~1 minute, the water was at 150F
* After 1 hour, the water was at 140F

01/05/09
* Lid of cooler has had "Great Stuff" expanding insulation shot into it a couple of days ago
* Poured 4.5 gallons of water at 156F into cooler
* After ~1 minutes, the water was at ~152F
* After 1 hour, the water was at 145F

* With blanket thrown on and cooler still warm inside from last test before dumping water in
* Poured 4.5 gallon of water at 155F into cooler
* After ~1 minute, the water was at 150F
* After 1 hour, the water was at 145F

So my question is: Does anyone else have experience with this type of temperature drop and find it acceptable?

I've read elsewhere that the grain should help retain the heat quite a bit. Does anyone know if that is true? Can I expect my 5F drop in temperature to be more like 2F?

Also, I left the lid closed for the entire hour during this test. If I'm opening it to stir every 15 minutes, it seems like it would only get worse.

Thanks for the help.

kcstrom

I believe the grain will help hold some heat, but I think your biggest problem in not preheating the cooler. During your 1 minute temp check the cooler is still likely absorbing heat and not yet reached equilibrium. Try adding boiling water to the cooler, swirling, leave it for a few minutes, and draining. Then add your 155F water. I better you will get less of a temp drop.

Thanks for the response fifelee. The third test that I tried the cooler was still very warm the from the 140F water that I drained out of it from the previous test. I left the lid closed while heating the water up to 155F again. Perhaps it dropped more than I thought in that time.

Even disregarding the initial 5F loss in temperature, it still lost 5F over the course of the next hour after it has stabilized at 150F. Does that sound fairly normal for 4.5 gallons of water?

kcstrom

Reports from a number of people here suggest that the Igloo coolers aren't nearly as good at holding heat as the Coleman Extreme or the round beverage coolers. But injecting some foam into the lid should help tremendously.

Regardless, I also suspect that much of your temperature drop is associated with the cooler absorbing heat because it was not pre-heated. I always let mine sit for a good 5 - 10 minutes after adding strike water. It takes a while for things to equilibrate. I bet if you took your readings at 1 min, 10 mins, and 70 mins, you wouldn't have seen as much of a drop over the 1 hour window.

I'll test again tomorrow by preheating with water at the same temp as I want it to stay around for the 1 hour test.

Thanks.

ckstrom

Don't try to calibrate a mash tun using just water. The heat retention qualities of a grain bed should not be underestimated.

Your first batch or two will be trial and error. You will learn that your setup has a 15 degree drop (an example)...but holds just fine once sealed up.

Give it your best effort and have some boiling and cold water nearby to make some tweaks when you strike. Soon enough, you'll know exactly the formula to use for strike temps. For my 10-gallon batches, it's my grain weight, plus my desired mash temp...plus 5 degrees.

So a 20 pound grist targeting a 154 mash temp would mean I strike with 179 degree water.

When I mash in I add near boiling water, close the lid for about ten minutes, then stir until it comes down to my strike temp and add the grain. Usually somewhere in the mid 160s for a 152 mash. This preheats and allows a more precise strike temp by preventing temp loss from transferring hot water.

As stated, preheating is one thing that can help here. Going too hot can warp some coolers. I use 180 degree water in mine for pre-heating and sometimes pre-heat a half an hour or more before I dough in.

I bought that exact cooler for sparge water and noticed that it didn't hold heat very well. (I need to turn it back into a regular cooler) If you need to use it for an MLT I suggest making a blanket for the sides and lid out of reflextic (spelling?) insulation from Home Depot or Lowes. The walls are pretty thin on it compared to some others.

kcstrom said:

I'll test again tomorrow by preheating with water at the same temp as I want it to stay around for the 1 hour test.

Thanks.

ckstrom

Click to expand...

If you preheat with 155 water the cold cooler will equalize at something much lower than 155. Then when you add more 155 water you will start losing heat right away. But if you heat the cooler to maybe 180 with near boiling water then you have a much longer window before your temp starts to drop. Now the hotter cooler may add a little heat to the mash, but it will be so small I doubt you will notice.

Don't add boiling water to your cooler. Most are made of plastic that is not rated to high temperatures. They will warp.

The alternative is use steam injection. https://www.homebrewtalk.com/f51/easy-steam-infusion-mash-system-25974/