Science of Sourdough

After the initial mix, you will feed your starter white flour — both all-purpose and bread flour work — just make sure it is unbleached and look for one that has a protein content between 11 to 12 percent for best results.

To ensure you don’t bring unwanted mold or bacteria into your starter, sterilize your jar by running it through a hot dishwasher wash cycle, or for canning jars, boil for 10 minutes.

A kitchen scale is optional but if you plan on keeping up your sourdough starter for a long period of time, it will make the feedings a bit easier, less messy, and faster.

Add 1 cup (4 ounces) whole-wheat or rye flour into a very clean 1-quart jar along with 1/2 cup (4 ounces) warm tap or filtered water between 65 to 80 degrees F. Stir well until all the flour is moistened and the dough resembles a thick paste. Cover loosely with the lid or plastic wrap. Set out at warm room temperature (75 to 80 degrees F) for 24 hours.

You will not likely notice much of a difference in appearance in the starter after the first 24 hours other than some condensation and a wheat-like aroma. You will need to begin feeding it to encourage growth. Use a rubber spatula to measure out 2/3 cup (5.5 ounces) of the starter and add it to a stainless steel or glass mixing bowl; discard any remaining starter. Add 1 cup (4 ounces) all-purpose or bread flour along with 1/2 cup (4 ounces) warm tap or filtered water between 65 to 80 degrees F to a stainless steel or glass mixing bowl. Stir well to combine all ingredients, making sure all the flour has been incorporated and the starter is well mixed. Return the starter to the jar. Cover again loosely with the lid or plastic wrap. Set out at warm room temperature (75 to 80 degrees F) for 24 hours.

On day 3 you should notice some activity in your starter. The mixture should look bubbly and it will probably have risen some. It will have a fresh, slightly tangy aroma. Now you'll feed the starter twice a day. It’s best to arrange the times to conveniently work with your schedule. Keep them as evenly spaced apart as possible — every 12 hours is the goal. To feed the starter, give it a couple of good stirs to release any bubbles. Measure out a heaping 1/2 cup (4 ounces) starter and place it into a stainless steel or glass mixing bowl; discard any remaining starter. Add 1 cup (4 ounces) all-purpose or bread flour along with 1/2 cup (4 ounces) warm tap or filtered water between 65 to 80 degrees F to a stainless steel or glass mixing bowl. Stir well to combine all the ingredients, making sure all the dry flour has been incorporated and the starter is well mixed. Return the starter to the jar. Cover again loosely with the lid or plastic wrap. Set out at warm room temperature (75 to 80 degrees F). Repeat the process 12 hours later and every 12 hours for the next 2 days.

You may notice the activity in your starter will vary between feedings over the next 2 days. It should consistently look bubbly and sometimes foamy before each feeding. By day 5 it will have nearly doubled in size before you feed it. The aroma should be pleasantly sour and slightly yeasty.

By day 5 or 6, your sourdough starter should be strong enough to use in your first loaf of bread. Check the signs: The starter should be nearly doubling in volume between feedings and look very bubbly and slightly foamy at the surface. It should also have a strong, but pleasant acidic aroma. If you don’t feel your starter is ready, continue feeding it in 12-hour increments for another day or two.

For frequent bakers: If you are baking with your starter more than once a week, keep it at cool room temperature (65 to 50 degrees F) and feed it once a day as instructed above.

For occasional bakers: If you are baking once a week or less, you want to slow the starter's growth by storing it in the refrigerator. To prep your starter for cold storage, give it a regular feeding then let it ripen at warm room temperature until you see a good amount of activity, 3 to 4 hours. Then store in the refrigerator. Check the starter at least every other day and feed it weekly as instructed above, making sure to let it ripen at warm room temperature before you refrigerate it again. A refrigerated starter should smell pleasant and sour, and you’ll see some bubbles on the surface. You should NOT see watery liquid on the surface or smell alcohol. If you do see liquid, try feeding it more frequently.

Q: I missed a feeding. Now what?
Feed your starter every 12 hours at room temperature for a day or two to bring it back to life. I left a starter in the fridge for two months when I fled my apartment at the start of the pandemic — when I came back, I fed it three times and baked a lovely loaf of bread!

Q: Does the type of flour matter?
Yes! Use whole-wheat flour to create the starter — the extra nutrients will help kick-start the process. I use unbleached all-purpose flour for feedings. The fresher the flour, the better the results; you want to capture the wild yeasts that exist on the flour.

Q: Do I have to discard some of the starters?
You need to keep the amount of starter in the jar consistent or it will grow exponentially and take up space. You don’t have to discard it though: You can give some away, or you can add some to pancakes or waffle batter for sourdough flavor (you’ll still need a leavener).

Q: How do I know if my starter is dead?
If the starter doesn’t rise when you feed it, it is likely inactive. You can probably bring it back to life after a few feedings; if it takes many feedings, you are basically just growing a new starter, which is fine, too!