Strain and simmer the grape must
20 minPour the grape must through a fine-mesh strainer to remove the sediment, then bring it to a boil in a wide pot. Skim off the gray foam that gathers on the surface with a slotted spoon, and continue until no more foam appears; leaving it in makes the grape must pudding cloudy and tart. After 15 minutes, transfer about a couple of cups to a separate bowl and let them cool.