Basic Sourdough Starter
To make ahead: An established starter, fed weekly, will keep in the refrigerator indefinitely.
Equipment: Kitchen scale, 1.5-quart crock or jar
Tips: Sourdough starters develop more quickly in warmer environments (say, an 85 degrees F summer day) and more slowly in colder ones (a drafty 65 degrees F kitchen come wintertime). The starter may take more or less time depending on your surroundings, so watch for the cues and use the timing given in the recipe as overall guidelines.
If you see an 1/8-inch to 1/4-inch layer of what looks (and smells) like vinegar on top of your starter, it means your sourdough is underfed; feed it twice that day, at the usual 12-hour intervals, to bring it back to form. If the sourdough fully separates (i.e., a 1-inch layer of vinegar is floating on top of a thin, dormant starter), discard and start again.
The sourdough should remain fragrant and slightly bubbly in the fridge. Feed once each time before using to get the starter nice and active.