I talked a bit about taking care of your sourdough starter yesterday. But what happens if you don't take care of it?
People often worry if they've killed their starter by leaving it in the refrigerator for a long time without feeding it. When it's refrigerated, the yeast slows down and becomes practically dormant. A yellowish liquid usually forms on top, referred to as "hooch" by sourdough folks. Hooch isn't a big deal. Sometimes the hooch starts looking like it has a little black sediment in it. This also isn't a big deal. It's yeast cells that have died off, but chances are that there are plenty more still alive.
Just for the fun of it, I left some starter unfed and at room temperature for a week. At that point it smelled strongly of acetone—not something you'd want to eat. I stirred in some flour and water, and it sprang back to life even better than before. So, it wasn't dead or dying, it was just napping and waiting for a little food and a little stirring.
I've never had a refrigerated sourdough go bad on me completely, but it's possible that you can get mold or really nasty stuff growing in an unrefrigerated one if you leave it undisturbed for long enough. I know, because I have left some starters for quite a while. Some simply fell into a deeper sleep while others developed truly nasty odors and some grew fur. I didn't try reviving any of those—the acetone-smelling one was about my limit. I figure that it's easy enough to grow a new starter if I have to. I might have gone to greater measures to revive one of my foreign starters, though. Maybe.
Sourdough from Scratch
Day Zero: What You'll Need »
Day 1: A Half-Ounce Flour and an Ounce of Water »
Day 2: No Feeding, Just Stirring »
Day 3: Feed Me More Flour! »
Day 4: 100% Hydration »
Day 5: Keep Feeding and Stirring! »
Day 6: Keep Stirring and Feeding! »
Day 7: Feed and Wait »
Day 8: Getting Close! »
Day 9: First Harvest »
Day 10: Second Harvest »
Day 11: Time for Storage »