All right folks, maybe you can help a brew-brother out here. When I used to use a cooler I'd hit my mash temps +/- 1 degree. Switched to SS pot with false bottom and ever since, I've been having trouble.
The space under the false bottom is almost exactly five quarts. So to calculate temp of strike water, first I calculate the amount of water. Let's say I'm making an ale with 12 lbs of grain. So 12*1.25 is 16 qts. Add 5 for the space under the false bottom, which gives us 21 qts. What is my ratio for the purpose of temperature control? 21/12 is 1.75. Plug that in for my ratio. So the formula gives me a strike water temp of 161 to mash at 150. I heat my water, dump in the grain and it comes down to 157. I leave the pot out uninsulated for half an hour to get the temp down to 150 then wrap it up for the rest of the mash. But it will be sweeter than I was going for.
Possible reasons why:
Thermometer not calibrated right. But that doesn't make a lot of sense. If it can't tell the difference between 157 and 150 that's one thing. But this is essentially not being able to tell the difference between a drop of 11 degrees and a drop of 4 degrees, which doesn't seem like a calibration issue.
Thermometer lag. Maybe the temperature was rising fast enough that when I took the mash tun off the burner, the temp stabilized but the thermometer was behind and was still rising. This doesn't make a lot of sense either. All my thermometers have pretty fast response and would not take that long to register the right temperature. Of course I was gaining a few (five? more?) degrees per minute while warming the mash water. So, maybe.
Thermometer too high. Maybe the thermometer is installed too far off the bottom of the pot, and the heat hadn't risen to it yet. The thermometer is installed right above the false bottom, maybe 3-4 inches from the bottom of the pot.
So.. what say you? Next brew day I am going to assume the temp will only fall 4 degrees, and not change anything else, and if it works I'll stick to it. But I'd like to get some ideas of why this is happening.