The other day, some friends brought over half a loaf of Amish Friendship Bread and a bag of starter. The starter takes 10 days to ferment and then I make my own loaves, and give my extra starter to my friends. It's like those chain letters from the 80s, except it's not annoying and you end up with tasty bread.
There are a couple of rules, though. You can't refrigerate the starter, and you can't use any metal bowls or utensils. I'm not a scientist, but I'm pretty sure both of those things kill the fermentation. This is sort of like sourdough. Good sourdough starter is actually really old. I asked my friend, who is a scientist about this. Okay, not actually about this. I asked her about making yogurt. But you do the same thing. You use some of your last batch of yogurt to make your next batch. I asked why it doesn't go bad, and she said that basically it becomes more yogurty, and then you dilute it when you make your next batch.
(On a similar note, my freshman year of college I conducted a very non-scientific experiment. My roommate and I were up late studying for finals, and I was starving. Somehow, the only thing we had to eat in the dorm room was a container of yogurt, but it had expired. We theorized that unless there was visible mold growing on it, it was safe for me to eat. Our thesis: yogurt just gets more yogurty. Obviously I survived, and I have no fear of eating expired foods.)
Captain America was a bit appalled that we were to leave this bag of mushy dough on the counter for 10 days at room temperature (it IS July in San Diego, but don't worry, it's not in direct sunlight), and then cook it and eat it. But I informed him, it's not gross; it's science!
He's still not so sure, but that means more bread for me! Yum!