Posted by Steve Bellner on March 22, 2004 at 20:01:36:
I have been recently doing decoction mashing, and I have consistently been too low of a temperature when I recombine the decoction with the main mash. As is pointed out in the FAQ, I lose a couple of degrees when pulling the mash, and I account for that with a lower stop temperature. But this weekend, I made a recipe where my mash schedule called for a 40-minute boil with a thick decoction, and I had to add some water mid-boil to keep it from drying out and scorching. I was trying to hit 64 C at the end of the decoction, but only made it to 60C.
So I went back to Promash and started playing with the schedule. To hit 64 requires 5.22 qt. of thick mash. This was what I did during the brew. I then varied the temp. down to 60, and Promash reports only 3.76 qt. are required. This is a difference of about 1.5 qt. Is it possible the error occurs because the actual mass returned to the main mash has been reduced by the boiling losses? This seems reasonable to me. If this is the case, do most decoction brewers top off the decoction with fresh water towards the end of the mash?