kefir grains - you guys might get into these. Kefir has a flavor
  similar but tangier than yogurt. But you don't use a yogurt
  machine to make these. You use "kefir grains" - a collection of
  healthy bacterias and yeasts that grow, when fed, at room
  temperatures. You put a tablespoon of kefir grains in a quart of
  milk, and in 12 - 24 hrs, you have a fizzy, tangy milk drink. I
  make smoothies with it, pancakes, add honey or just drink it
  plain (I like tangy). I grow my kefir in powdered milk, which
  makes it non-fat and very cheap to make. Look it up on the
  internet - you'll get a kick out of it I think. I got my grains
  from the 'net but you can have some of mine if it looks
  interesting to you. "