The "Sour Mash" part of this recipe comes from mashing in 1/2 lb of the Maris Otter with about 3 cups of water at conversion temperatures, then letting the small mash sour over about three days. Once it was starting to bubble and smell sour, I drained it, sparged with another pint of water through a mesh strainer, and boiled for ten minutes before cooling and adding the soured wort to the primary fermenter. The sour portion of the mash smelled a lot like old sneakers while boiling, but fermented out to a nice extra "twang" of sour and a mild funky undertone not unlike a very mild Belgian.