You've probably landed here because you received some sourdough starter, possibly from me! ;) Unless the starter is very fresh, you will probably need to feed or refresh it before you can use it. Besides, if you go ahead and use up your starter, you won't have any more to use later on.
Your starter will keep for a few months in the refrigerator. If you won't be using it within a day or two of receiving it, go ahead and pop it in the coldbox. Set a reminder on your calendar (or wherever you'll see it in ~2 months) to feed/refresh your starter. The more often you refresh it, the better it will get over time!
A few hours before you plan to feed your starter, let it come up to room temperature. (I usually feed it in the morning, so I just take it out of the refrigerator the night before.)
Personally I bake (and feed my starter) almost exclusively by weight. I feel that is the most accurate way to handle flour. But if you don't have a scale, you can still get good results feeding by volume. These instructions assume you will be feeding by weight. But if you're feeding by volume due to preference or necessity, just follow the same proportions as for weight.
Don't be stingy when feeding! You should always at least double your starter. You can also triple or quadruple it. The various species of yeast and bacteria respond in their own ways to different levels of feeding. (And the local microbes in your area will eventually overtake the existing culture in your starter.) Experiment, take notes, and learn how you prefer to keep your culture.
- Bring your starter to room temperature.
- Weigh the starter. The containers I gave out at Christmas 2015 weigh about 10 g (without lid), so be sure to account for that.
- Get a bowl at least 6 times the volume of the starter culture. (Starter culture is about 1 cup, so your bowl should be at least 6 cups/1.5 quarts.)
- Triple your starter. This should give you enough active culture to make a batch of bread, and still leave some starter for keeping/later use. It also makes for some very easy math! ;) You want to add equal parts bread flour and warm (90-100 degrees F) water for feeding. To triple the starter, measure out the same weight of flour as your starter. Add the flour to your bowl. Then measure out the same weight again in warm water into a measuring cup. (Metric system to the rescue here! A gram of water is 1 milliliter.)
- Mix the water into the flour, a little at a time.
- After all the water has been incorporated into the flour, add the starter to the bowl and mix the culture and feeder.
- Cover the bowl loosely and keep it warm for a few hours. An oven with the light on works well for this.
- Once the starter is bubbly, it's ready to use!
My "go-to" bread book is 'The Bread Baker's Apprentice' by Peter Reinhart. But if you already have Julia Child's 'Mastering the Art of French Cooking', it also has some good advice for bread.
See the license file. Basically, this is a Free Culture license.