A sourdough starter is filled with naturally occurring yeast. So you can only kill it in two ways. One, heat it to above 138 degrees or something close as that's where regular yeast in a bottle or package gets dead. Two, starve it for so long that it can't come back. But even with the second, I've seen starters come back from pretty dire straights before, so prior to singing a mournful goodbye song to your neglected starter, try feeding it once a day for a few days before declaring that its hopeless.
Sourdough goes through several stages. First it eats all of the starches in the flour that you add and then it goes into a more anaerobic stage where it begins to give off alcohol as a by product. This is what you see when the starter has sat for several days without being feed – a layer of alcohol and a thicker layer underneath. Not to worry, just feed it and it will be fine.
To feed it, add 1 cup water and 1 cup flour to the starter and mix or shake well. Your starter will adjust most easily to a regular schedule of feeding, which you could do optimally twice a day. That's never once happened to my starter and it still works beautifully. I just feed it as often as I bake bread which is once or twice a week. Because I don't feed it that often, I keep it in the refrigerator to slow down the fermentation.
Gonna go get my hands sticky with dough now.
© 2009 Anne Mahle