Prim (m?) is whey that's been cooked down until it caramelizes. It's on the way to mysost. That is it's not cooked down as much. I love the stuff. It's sweet, tangy, malty tasting. When making it the other day, I tased the whey before it got too brown.. it was significantly reduced but still very much a liquid and not at all brown. Anyway, it was DELICIOUS! A bit too sweet.. but I though of all the things I could use that for.. Like to drizzle over ice cream. Yum..