How to Care for Your Sourdough Starter
It's about temperature and time.
Getting into baking sourdough lands somewhere between adopting a puppy and deciding to start a garden on the commitment scale. Just ask Noam Grossman of Upside Pizza, who uses a sourdough starter rather than commercial yeast, for all of the pizza dough in the shop. Figuring out how to feed the starter so that it would be at its peak during the hours when they needed in was a process of trial and error, with a lot of focus on the temperature of the water and the temperature of the room that the starter was in. When he was starting the place, Grossman placed batches of dough in front of a close-circuit camera so he could monitor their rise from home.
Not everyone needs quite that volume of bread in their lives, but it's instructive in the process of caring for and feeding a sourdough starter, the fermented mixture of flour and water which gives sourdough bread both its trademark tanginess and its leavening agent. "My advice for keeping a sourdough starter," Grossman joked, "is to quite your job and watch it at all times." You don't have to be quite that serious about it; however, there are a few things that will make sure your sourdough starter keeps in peak condition.
Once you have a sourdough starter in your possession, it's important to remember that feeding it essentially activates the yeast in the starter. So if you're someone who bakes a loaf of bread every day, it makes sense to feed the starter once a day and keep it at room temperature. But if you make bread less often, it's just fine to keep the starter refrigerated and feed it once a week. If you make bread only very occasionally, you can even keep it going by drying the starter thoroughly and rehydrating it with water when you want to use it.
What does it mean to feed a starter? Essentially you're just weighing out flour and water and stirring it into the starter, as well as discarding a good bit of the starter. According to King Arthur Flour, you want to add about 4 ounces of flour and four ounces of water to every four ounces of starter, or roughly the same amount of flour and water as you have starter. (The easiest way to figure out the ratio you'll need is with a scale.) If you don't regularly feed your starter, the yeast can die or grow mold, making it unusuable. Visible mold is an indicator that the starter is a goner, as are pink or orange streaks, which are unwanted bacteria. An active, well-fed sourdough starter won't grow mold.
You also need to monitor the temperature of the starter, as the colder it is, the slower it will feed and be ready for use in bread. If a starter gets too hot, the yeast will also die. A well-maintained starter is pretty difficult to kill—in fact, you can often coax them back from the dead. But if your starter isn't bubbling or frothing with the addition of flour and water after a day or so, it's probably time to start over. If a starter is left a long time without a feeding, it develops a liquid on top, which can be stirred back into the starter or discarded. But watch the color of the liquid—if it's pink or orange, it's time to start again.
The core principles of maintaining a starter have to do with time and temperature, but you can also play around with what flour you're feeding it. Grossman prefers a malted flour, you can figure out what makes the most sense for whatever you're using your starter for. Once you start with a starter, it becomes a pretty good hobby, even if you don't quite your day job.