Originally Posted by ntfinkbe
Yes you can fit 10 gallons and that much grain in a15 gallon pot but you have to account for grain absorption. I think I had around 13 gallons when I added the grain and it was a little too much. So I drained some and added the right amount later to account for the boil off.
That's why a two pot process is good if you already have a smaller pot. Any volume you lose to grain absorption you can make up with the higher temp sparge volume. Its a good idea to mash close to the max volume of your pot. Otherwise you have more air space between the grain and the lid and it will not hold temp as well. You don't want too big of a pot or you will need to insulate it.
My process is something like this doing 5 gallon batches in a 7.5 gallon pot:
1. Start with 5.5 gallons of water
2. Mash grain for 60 minutes at temp
3. turn on heat, stir like crazy and bring it up to 170 for 10 minutes
4. Pull bag and put it in 2 gallons of 175 degree water for 10 minutes.
5 squeeze bag and dump that into brew pot.
6. that usually gives me about 6.5 gallons for the boil
7. leave grain draining in the smaller pot and use those runnings to make up for evaporation during the boil
8. This gives me around 52 12 oz beers on bottling day