I don’t know if Mitsuwa has always carried sake lees, or sakekasu, but they do now, and perhaps it’s more than just coincidence that winter is the height of sake brewing season, and therefore just the right time for this by-product of the process to show up. Why should you care? Well, these are solids left over after the sake is separated from the fermented rice. Fermented rice? You mean koji? That’s right. The same stuff chefs are using to amp the umami of everything from burgers to spaghetti carbonara to baked goods.