Sourdough Starter

Sourdough starter cultures are more than just yeast. They also contain families of bacteria that produce lactic and acetic acids which create sourdough’s characteristic flavor. Amylase enzymes in the yeast break the flour’s starches into simpler sugars that the bacteria consume, and the bacteria transform some of those sugars into forms more digestible by yeast. When in balance, this microbial community out-competes other organisms, and the symbiotic sourdough starter culture thrives.

Starting from Scratch

The yeast and bacteria occur naturally in flour and the environment, so if you don’t have a friend who can pass along a little starter, you can create it yourself. You’ll need a week or two to achieve a healthy, balanced culture. These steps create a 100% hydration starter, where water and flour are kept in a 1:1 ratio by weight, and it will be unique because of the mix of microbes particular to your own kitchen.

Start by weighing out 60 grams each of flour (about ½ cup) and water (about ¼ cup). Avoid bleached and self-rising flours; but you can use whole wheat, rye, bread, all-purpose, or a mixture of grain-based flours. Stir the flour and water together in a container, cover, and leave out unrefrigerated for 48 hours.

On the third day, start feeding once a day: weigh out 60 g of the mixture, discard the rest, and stir in 60 g each of flour and water. After two once-a-day feedings, the mixture should be starting to develop bubbles. Begin feeding twice a day using the same regimen. When the starter doubles in volume a few hours after feeding, it’s ready. The process may take longer in non-Florida climates, but eventually, you’ll have a healthy starter.

Getting Ready to Bake

If you’ve kept to the 60:60:60 regimen, you have about 180 g of starter. Most recipes I’ve seen call for about 220 g (about 1 cup stirred down), so you’ll need more for baking. Weigh 120 g of culture into a quart container, and stir in 120 g of water (about ½ cup) and 120 g of flour (about 1 cup). When the starter inflates to at least twice its volume, it’s ready for baking.

If your culture has been in the refrigerator, allow some extra time to get it revved up. Two to three days before you intend to bake, take the starter out of the refrigerator, transfer to a quart container, and let it come to room temperature. Stir in 120 g each of flour and water. Continue feeding twice daily using the 120:120:120 regimen until it doubles in volume and you’re ready to bake.

After you’ve extracted the starter needed for your recipe, you should have enough left over to keep the culture going. If you intend to bake again soon, continue feeding using the 120:120:120 regimen twice daily.

Storage and Feeding

For long-term storage, keep the starter in the fridge and feed weekly. Weigh 60 g of starter into a clean container, discard the rest, then add 60 g each of flour and water. Mix thoroughly and return to the fridge. I have a pair of tall wide-mouth 20‑ounce jars with screw-on lids for this. I keep the lid loose so excess gas can escape. A chopstick works great for stirring.

A robust starter that’s several months old can survive for two or three weeks without feeding. (I’ve sometimes forgotten, but a feeding brings it back to life.) If a layer of fermentation liquid forms on top, stir it back in before weighing out a portion for the next feeding.

A young starter is less resilient, but any culture neglected for too long can get moldy or develop a musty smell: the healthy balance has been lost, other microbial agents have taken over, and you’ll need to start again.

There are other methods of keeping starter. A mature starter can be frozen, or it can be dried and stored as flakes to be revived later. You can also create starters that are less than 100% hydration. I haven’t tried any of these methods yet myself.

Using Sourdough Discard

Rather than throwing away starter, you can save the discard in a separate container in the fridge for up to a few weeks, and then you can add it to other baked goods. (But chuck the discard if it gets moldy, smells musty, or looks discolored.)

If you kept to the feeding regimen, the starter discard is one part water and one part flour, so you can easily substitute some starter for a portion of these ingredients in a recipe. E.g., 120 g of starter could replace 60 g of flour (about ½ cup) and 60 g of water (about ¼ cup).

In small amounts, this works well for quick breads, pancakes, and even some cake batters and cookie doughs, contributing richness and character. However, keep in mind that the yeast and bacteria have been breaking down the flour, so substituting too much starter may not provide enough structure for your dough or batter.