Correct Mash Tun Specific Heat for 10 gal Cooler?

I, like many, use a 10 gallon Rubbermaid cooler as a mash tun. I've found that the strike water temps generated by BeerSmith are always too high. After poking around I discovered the value for "Mash Tun Specific Heat" is 0.30 and that this means the software is assuming I lose heat more quickly than I actually do. I've googled and searched this forum and cannot find a simple answer to this question:

What is the proper Mash Tun Specific Heat to enter in BeerSmith 2.0 for a 10 Gal cooler?

Really...no one has figured this out?

klnosaj said:

Really...no one has figured this out?

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I'd love to know a specific answer to this as well, but so far haven't found it on Brad's site or this one...or anywhere else for that matter. I did weigh my cooler with the FB and bulkhead/ball valve sans lid so at least I have that entry updated, but I'm still using the default .3 for the specific heat.

I do plug in the starting MLT and grain temps and all that, but I usually miss my desired mash temp by a couple/few degrees. I've learned to hold back a gallon of strike water so I can sub some cooler or hotter water near the end of mashing in to bring it into spec...

Cheers!

Not sure if this will help or not, but what I do is pre-heat my 10 gallon cooler with one gallon of boiling water and close lid. I let that sit in there for a little while (20 minutes) and then I add my strike water minus the gallon already in there and then add my grains adjusting temp like normal. I then set my Thermal mass to zero on my software and all my figures seem to come out pretty damn spot on. Hope this makes sense.

jeremybrown9 said:

Not sure if this will help or not, but what I do is pre-heat my 10 gallon cooler with one gallon of boiling water and close lid. I let that sit in there for a little while (20 minutes) and then I add my strike water minus the gallon already in there and then add my grains adjusting temp like normal. I then set my Thermal mass to zero on my software and all my figures seem to come out pretty damn spot on. Hope this makes sense.

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Well, of course it makes sense - you've totally taken the heat lost in warming up the tun out of the equation

But that also totally misses the point. With the right inputs, BS should be able to tell you the precise temperature to use for the strike water that will account for all of the pertinent criteria, including heat lost to bringing the tun up to temperature. Which was the point of the thread...

Cheers!

OK, I asked my neighbor, who uses Beer Alchemy, what he uses and he said that he inputs 2 lbs 3 oz and his numbers are dead on. He uses a 10 Gallon Rubbermaid cooler.

Can't you just figure it out yourself in BS? By that, I mean use the temps you measured on your last batch (where the numbers were off) and adjust the TM value accordingly to hit the measured strike temp. I am able to do that in Beer Alchemy, but prefer the preheat method now as I find it more reliable. Also, I think that it is fair to say that every cooler is slightly different and one value may not work flawlessly for everyone, so a little tweaking is necessary for your system.

day_trippr said:

Well, of course it makes sense - you've totally taken the heat lost in warming up the tun out of the equation

But that also totally misses the point. With the right inputs, BS should be able to tell you the precise temperature to use for the strike water that will account for all of the pertinent criteria, including heat lost to bringing the tun up to temperature. Which was the point of the thread...

Cheers!

Click to expand...

Yeah...I do use the pre-heat method but it's not the answer to my question. I'm also having problems with BS generating incorrect temps for infusions. My mash-out was supposed to be at 168F but using the numbers generated by the program I ended up at 160F. I wonder what accounts for that error.

I'm a bit surprised that no one has the answer to my first question. There are so many math-orientated people around here that I thought for sure one of them could throw me this bone.

OG2620 said:

Can't you just figure it out yourself in BS? By that, I mean use the temps you measured on your last batch (where the numbers were off) and adjust the TM value accordingly to hit the measured strike temp. I am able to do that in Beer Alchemy, but prefer the preheat method now as I find it more reliable. Also, I think that it is fair to say that every cooler is slightly different and one value may not work flawlessly for everyone, so a little tweaking is necessary for your system.

Click to expand...

Actually, it occurs to me that there is no one number to use. Different amounts of water and grain will stack up against the cooler's heat syncing ability in differing proportions. Preheating has always seemed to be the best solution.

That's exactly why I preheat to the strike temp calculated when I enter 0 for my MLT T/M value in beer alchemy.

Again, back calculate for your T/M value with the actual temp values from your last batch. That should get you close.

If you do a search for calculating thermal mass you will find a process to find what works for your setup.

It's too much for me to try to duplicate here. But it did give good numbers for my software to work with.

You would need to know what your tun is made of. What kind of plastic, what is the ratio of the different parts. Do you have a copper manifold or plastic? What temperature is the tun at when you put the strike water in? Is it the same as the grain temp? This website has the specific heat of several different types of plastics http://www.engineeringtoolbox.com/specific-heat-capacity-d_391.html You can see the math will get quite complicated. You will need to find the temperature loss when you add a mass of water to the tun. This is easy enough with a thermometer. The time the water sits in the tun won't matter. Assuming that all the heat from the water goes into the cooler and none is lost to the air (difficult to do) then the formula you would use is:

1*(G*3785.4118)*TW=SHC*MC*TC

G=gallons of water
TW=temperature change of the water
SHC=specific heat of the cooler (you will need to solve for this variable)
MC=mass in grams of cooler
TC=temperature change of the cooler
3785.4118=conversion from gallons of water to grams of water


Good luck calculating the temperature change of your cooler. Maybe you could use one of those stick on strip thermometers. I would wrap your cooler in about 50 blankets and even then you will loose heat to the blankets and the air inside the cooler.

Maybe you could just mash a batch of wort. Write down the temperature difference from your target step temperature in BS. Then adjust your cooler specific heat in the equipment window so the recipe matches the actual temperature you got when you did your mash. Now you know an estimate of your cooler specific heat. This way seems easier.

And there it is. That's genius. :rockin:

I did a similar experiment with a temperature probe that records the temp every 30 seconds. I ran it for 2 hours and my tun looses roughly .09 degrees F per minute. LOL, which isn't very efficient. Once equalized it seems to be a straight line for heat lost per minute. There was an equalization period at the beginning when I did my cold tun data collection. However, my tun took about 15 minutes to equalize but I have a copper manifold at the bottom. Also, I found the method for pouring the water into the tun makes a difference when calculating the infusion water temp. You want to get it in as fast as possible with as little heat loss. Otherwise, you need to add a degree or two for the transfer. I'm using a hose but I've seen some people transfer into a bucket then into the tun.

Thanks for the read!