I did my first decoction last night. I doughed in with 152F water and it stabilized at 144F, which was close to what I wanted (145F). Let that sit for 25 minutes, then pulled (what I thought was enough) thick mash, something like 5 qts for a 7lb grain bill. Boiled for 20 minutes, stirring constantly and added it back. Well, the main mash temp had dropped too low, down to about 136 or so. So adding the boiling decoction back only brought the temp back up to about what I had mashed for 25 minutes at. Damn it! I think there was too much head space in my mash tun (10 gallon cooler for 7lb grain bill). Ended up draining off about a gallon of the thin mash, brought to boil, then added it back. That brought the temp up to 158F like I had wanted. Let that sit for 45 minutes. Then sparged as normal.
I kind of wonder if mashing thin would make it more difficult to bring it up to the next rest, also. I think I mashed with 13qts for 7lbs, so like 1.7qt/lb or something like that. Perhaps I'll mash thicker next time. By the way, this was a 4 gallon batch.
Anyone have any tips or insight on this experience? This was for a schwarzbier, just wanted to try a single decoction.