Mash Equations for 10 gal Rubbermaid Coolers

I've got the same 10 gal big orange Rubbermaid Cooler that just about everyone has on HBT. I've been hit or miss on more than a few of my mash temps. I use Beersmith and it gives me a ball park but it never equates for cooler temp because of the lid, sides, etc. As many of you know, the cooler will hold temp for easily over an hour without 1 degree fluctuation. It's just hitting the initial temp that's the problem.

What I'm proposing is a spreadsheet that tells you how much water at what temp will go into your cooler for your amount of grain. I'm proposing that we do everything in pounds/ounces and ferinheit. I'm also proposing that we do this with the assumption that your grain is at room temp and you have not preheated your cooler. I know it's easier to preheat but we'll have an inconsistant variable by not knowing how much you've actually added to your cooler for how long and and what temp to do the preheating.

I'll collect the data once it gets to a sufficient size and report in spreadsheet style.


Here's my first equation for the mild that I'm brewing today:

(7 pounds 11 oz) in 2.5 gal of 168F water = 158F Mash temp
(16 pounds) in 5 gal of 167F water = 154 mash temp

Well....I have the Rubbermaid (Home Depot branded) 10 gal. "big orange" cylindrical cooler, and I've had difficulty not losing 4 degrees in an hour mash. Yes, I preheat, yes I mix thoroughly with paddle, yes I cover the cooler with a heavy blanket, yes I keep it up off the floor, and yes I put a block of foam over the brass ball valve to keep from losing heat that way...and it'll still go from 152F - 148F in the hour. After three batches, I finally insulated the lid (which comes with NO insulation) with some of that "Great Stuff" product in the ærosol can, and we shall see when I brew next time.

I guess I'm a lucky one. I've never done any of those things and I do fine. Hopefully that will cure your problems.

The thing is, I mash in with a preheated cooler, which then would change the temperature of the necessary strike water so your spreadsheet wouldn't work for me.

I never lose more than a degree or two, so I'm uncertain as to why you are, rico. That seems really strange. Of course, one of the "insulators" is the grain itself, so in a very small batch, I can see it losing a little heat. I don't use any extra insulation, don't cover the ball valve, etc, so I'm surprised your experience is so different that mine.

eschatz, it seems like this would be more of a issue for the "add water to grain" crowd than the "add grain to water" crowd. Which are you? Beersmith and other strike water temp calculators (online, etc.) always get me really close on mash temps. I add grain to water.

why would it make a difference? you end up with the same temp whether you add the grain first or second. it could be that I'm just stupid. actually it's probably that I'm stupid but I'm not getting this. I've seen people debate this before but I've never given it much attention.

Are you estimating the temperture of the grain correctly? I find that when my mash temp is off a couple degrees, it's usually on a day where my garage has fluxuated by a big swing and the grain in the bag is warmer or colder than I thought.

I dont know. I've never really thought about it. I believe my grain to be room temp. I don't know anything that would make me think otherwise.

I agree with the grain temp issue. I have the same cooler (the Home Depot version) and have never lost more than 1-2 degrees, even over a 90 minute mash. I don;t use beersmith though, I use beer alchemy. I set ambient to 75F and heat to about 8 degrees over that. I put the lid on and let it sit for 5-10 minutes and take temp. Once it reaches what Beeralchemy says it should be, I dough in. I'm almost always on target, sometimes a little high, so i add cool water. I have never covered te cooler, or done anything else to prevent heat loss.

eschatz said:

why would it make a difference? you end up with the same temp whether you add the grain first or second. it could be that I'm just stupid. actually it's probably that I'm stupid but I'm not getting this. I've seen people debate this before but I've never given it much attention.

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So, you add water to grain? Not trying to bring up the old this vs. that battle. Either way you end up with beer.

Just seems to me that it's easier to heat strike water (I start with 175ish water) and add it to the MLT, let that water heat up the cooler insulation material or whatever it is you're using as a MLT, and let everything equalize (mine drops ~10* in this process, getting me to around 165*). Then gradually let the temp drop by waiting or stirring for a minute down to my calculated strike temp.

That's when I add the grains, give it a good stir, wait another minute for things to equalize, and take a temp reading. It's been pretty close on the batches I did in my cooler MLT. Make a note of how far off you are and adjust up or down on the strike temp next time.

I tend to err on the high side rather than low so that I can add a wee bit of cool water to adjust down to my target mash temp if necessary. It's easier than adding boiling water to bring it up if I'm low to start with.

I think it's important to give a few minutes for temps to equalize before taking a reading. I'd guess a lot of people rush that step. Could be one reason that some people claim to lose 3,4,5* over an hour, when really they're losing it in the first 5 minutes before the temps have balanced out.

I heat my strike water in the HLT to about 10˚ over my strike temp in the MLT, and let it sit in the MLT for about 10-15 minutes, that seems to be about right, give or take a few ice cubes to get more precise. My grain is stored indoors an is usually about 75˚. Maybe it's warmer when just crushed, I should check next time, having a mill is new to me.
I filed my lid with foam, too and that seems to help.

As stated above, I always add the water about 10F higher than the strike temp, let it preheat the cooler and drop to strike temp then add the grain. I'm usually within 0.5 degree of the target mash temp, and it doesn't change over the course of an hour.

I've got the same rig and have trouble hitting strike temp consistently. I use BeerSmith and have done 6 batches or so where I was really anal about measuring grain temps, garage temp, etc. My results were all over the board. I generally lose 2 degrees or so over 60 min., depending on how much stirring I do.

To be honest, I'm sure the manufacturing controls on the amount of insulation in these things is pretty poor. They're made in China, and could come from multiple manufacturers, even with different types and brands of insulation. Wouldn't surprise me if the insulation is from some recycled process that is totally inconsistent.

It's not like we bought highly calibrated lab equipment.

I have the same cooler. I use ProMash, which lets you enter the thermal mass of your mash tun (trial and error), but 0.100 works for me. Then you plug in the amount and temp of your grain, and the water to grain ratio for your mash. It spits out the strike water temp and volumes.

Heat the calculated amount of water to the calculated temp. Add to cooler. Stir in grains.

I hit my temp EVERY TIME...it's so predictable, I'm tempted to stop measuring. And the cooler never loses more than 1F over a 60-min mash, with no special treatment.

I assume all the other brewing softwares do this same strike water temp calculation as well. I can't understand why people still mess around with preheating, guessing, etc.

Seriously, once you dial in the thermal mass of the cooler, it's simple and foolproof.

It appears, from the last several posts, that the variability from cooler to cooler is something I hadn't considered. The thing now is to start collecting more and more numbers with the 'ol refractometer, and see just how much difference a few degrees of temperature loss really makes. I suspect I won't find this as serious as I thought.

rico567 said:

It appears, from the last several posts, that the variability from cooler to cooler is something I hadn't considered. The thing now is to start collecting more and more numbers with the 'ol refractometer, and see just how much difference a few degrees of temperature loss really makes. I suspect I won't find this as serious as I thought.

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Your refractometer/hydrometer isn't going to tell you which of the sugars are fermentable vs. unfermentable, just how much sugar is in solution. The point of controlling the mash temp is to impact the types of sugars created, dextrine or maltose, to impact mouthfeel, fermentability, etc.

I think it's pretty important to be able to hit and maintain your mash temp, especially if you're trying to repeat a recipe with the goal of getting the same result from batch to batch or brewer to brewer. Just another one of those variable that we like to try to control as much as possible...hence the fancy HERMS/RIMS systems that are out there.

Plamer has a good write-up on it: How To Brew Your First Beer: Chapter 14 - How the Mash Makes Wort

I just found an equipment section on Beersmith that uses a 10 gal cooler with turkey fryer. I always knew that program had what I needed. I just needed to find it!

I have the same cooler. I use ProMash, which lets you enter the thermal mass of your mash tun (trial and error), but 0.100 works for me.

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Beersmith has a field for "Mash Tun Specific Heat," defined as cal/gram-deg C. Is this the same as ProMash's thermal mass? I'm curious, because Beersmith's default for these coolers is .3, which is a far cry from .1 that you found. What does ProMash list for stainless?

EDIT: o/t, but Eschatz, does your sig really say mint chocolate stout?

mattmcl said:

Beersmith has a field for "Mash Tun Specific Heat," defined as cal/gram-deg C. Is this the same as ProMash's thermal mass? I'm curious, because Beersmith's default for these coolers is .3, which is a far cry from .1 that you found. What does ProMash list for stainless?

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ProMash also defaults to 0.300. Through trial and error, I found that 0.1 works for me. Give it a shot.

mattmcl said:

EDIT: o/t, but Eschatz, does your sig really say mint chocolate stout?

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Yeah, Matt. It's a beer I did last X-mas. It's in my recipe pull down. Check it out.