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How to calculate mash tun heat specific heat

reim0027

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I had a problem hitting my mash temperature this weekend.  Hopefully, someone can help me with this.

I have a Rubbermaid 70qt extreme cooler.
I have a good, calibrated thermometer.
Goal mash temperature 152F.
13 pounds of grain.

I measured my grain and tun temperature.  They were 72 degrees (perfect day for brewing).
I set my specific heat to 0.300, as recommended for plastic.
I preheated my water to the recommended temperature by BeerSmith (about 167 degrees).
After mixing (and trying to get the temperature the same in all places of the mash tun), my temperature was 160.

Is there an easy way I can test my mash tun to figure out it's specific heat? 
 
You can measure the specific heat of your tun by filling it with a known volume of water at a known temperature and measuring the temperature the water falls to (if the water was hotter than your tun) or rises to (if the water was colder than your tun) and the starting temperatue of your tun.  Water has a specific heat of 1 cal/gram-deg C.  So the heat lost by the water ((change in water temperature in deg C)X(grams of water)) equals the heat absorbed by your tun (water is 1 gram/cc so you can measure volume and convert to weight easily).  Divide heat lost by the water by your tun's weight in grams and the temperature change of your tun (final water temp-initial tun temp)) and you get the specific heat of your tun. 

It's not quite as easy as it sounds, however.  The difficulty comes in controlling losses or gains to the outside - this throws off the accuracy of the measurement and calculation.  It would help to wrap the whole thing in a heavy blanket. You also have to wait long enough to make sure temperatures are stable.    Since your tun is an insulated vessel, it would be best to use water within 10-20 degrees of your mash tun to minimize the difference between the inside and outsde of the tun once the water temp stabilizes.  You'll get a reasonable estimate that I would think would be good enough to use.
 
There is a very cool on-line calculator here: http://www.haandbryg.dk/mashcalc.html#rest that will convert your MLT heat capacity into an equivalent volume of water.

Record the initial temperature of the MLT, and heat a measured quantity of water, pour it into your MLT and give it 5 minutes to reach equilibrium and take the temperature again.  After entering these values the calculator will determine the water volume equivalent of your MLT.  I poured a few cups of water into my cooler based MLT and let it sit for an hour for everything to reach room temp shook things up a bit and took the temp of the water then poured it out.  I then warmed up 3 gal of water to 170 (close to the typical strike temp for a 5 gal batch) and poured it in let it sit for 5 min and took the temp.

Now adjust the settings within BeerSmith.  Convert the water quantity into pounds and enter it into your equipment profile for the "Mash Tun Weight".  Change the "Mash Tun Specific Heat" to 1.0 which the value for water.

It would be great of the tool could do this for you.
 
DaveinPa said:
You can measure the specific heat of your tun by filling it with a known volume of water at a known temperature and measuring the temperature the water falls to (if the water was hotter than your tun) or rises to (if the water was colder than your tun) and the starting temperatue of your tun.  Water has a specific heat of 1 cal/gram-deg C.  So the heat lost by the water ((change in water temperature in deg C)X(grams of water)) equals the heat absorbed by your tun (water is 1 gram/cc so you can measure volume and convert to weight easily).  Divide heat lost by the water by your tun's weight in grams and the temperature change of your tun (final water temp-initial tun temp)) and you get the specific heat of your tun. 

It's not quite as easy as it sounds, however.  The difficulty comes in controlling losses or gains to the outside - this throws off the accuracy of the measurement and calculation.  It would help to wrap the whole thing in a heavy blanket. You also have to wait long enough to make sure temperatures are stable.    Since your tun is an insulated vessel, it would be best to use water within 10-20 degrees of your mash tun to minimize the difference between the inside and outsde of the tun once the water temp stabilizes.  You'll get a reasonable estimate that I would think would be good enough to use.
Thanks for this it is a big help. Just wondering when doing this I transferred 25l from boiler to tun I lost 5.5c just transferring the water. So should I use the boiler temp or the temp of the water once it has been transferred to the tun when working out the tun heat loss? Either way I think its going to be a bit out.. My tun is a 60l double walled stainless vessel with pe foam insulation..

Edit: Also this bit "Divide heat lost by the water by your tun's weight in grams and the temperature change of your tun"
do I divide heat loss(in Celsius) by mash tun weight(in grams). then divide that result by the difference in mash tun temp(Celsius)? Also the mash tun temp change is it taken on inside or outside of tune(guessing inside) cheers.
 
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