I've made lots of brewing mistakes lately. One of the biggest was thinking I had nailed the thermal coefficient of my mash tun. I did an experiment to determine this awhile ago and I believe it came out wrong because my dial thermometer was messed up.
If you use a dial thermometer, check it at boiling and make sure that water boils at 212F. If you use a glass thermometer, ensure that you are submerging it properly. It should be marked for the proper submerging depth.
If your not familiar, to calculate the final temperature of a system from the starting temperatures, you multiply the mass of each part times it's temperature and specific heat, add them all up, and divide by the total mass.
So when I say tun coefficient what I really mean is finding the equivalent amount of water that the tun is equivalent to. So in Excel:
Tun = 0.5
Tun Temp = 72F
Water = 2 Gallons
Water Temp = 160F
Final Temperature =((0.5*72F)+(2.0*160F))/(0.5*2)
As long as you reference your cells right, you will be able to modify the tun value until the final temperature you calculate equals what you measure experimentally.
I found a value of 0.26 for my tun, meaning it's thermal mass is equal to 0.26 gallons of water. I fully calculate my mash temps in Excel, and use 0.051 for my equivalent thermal mass of one pound of malt.
Prior to solving this problem I was thinking about building a RIMS mash tun. No need now! I can mash in and hit my temperature as closely as I am able to measure the temperature of my strike water.
Don't forget to check the accuracy of your thermometers!
