I feed it to the pigs and use a little to lacto-ferment things. Some people feed it to their chickens, mine won't bother with it. It can really boost a compost pile. If it is pasteurized whey from a thermophilic cheese and we don't have pigs at the moment, I just toss it down the sink. I mostly make mesophilic raw cheeses, though, so we have LOTS of whey to use, up to 12 gallons a week. Right now I refer to whey as "free bacon."