Sourdough starter needs to be fed constantly to keep the cultures active. But if you add more flour and water today, then more flour and water tomorrow—and on and on—you’ll end up with a starter big enough to occupy your kitchen. That’s where discard comes in: the portion of starter you, well, discard before feeding.
But don’t interpret discard as throwaway. For starters (pun intended), it’s a matter of food waste. Small amounts of discard swiftly add up in the trash, compost bin, or drain, especially if you feed your starter daily. Why toss something that you can put to good use?