Day 1: In your glass or ceramic container, mix the flour and water. The mixture will be very thick and pasty. Do not thin it out! The starter needs that flour for fermentation and energy.
Day 2: Look for signs of fermentation: tiny bubbles on the bottom of the starter, pinprick sized bubbles on top. If you don't see any signs after 24 hours, ensure your starter is being in an area that is at least 75º F.
Feeding the starter days 3 and beyond
Day 3: Remove 1/4 cup of starter (60 g) and discard it. Add 1/4 cup of warm, filtered water (60g) stirring, then mix in 1/2 cup of unbleached, all-purpose flour (60 g). I find it's easier to mix if you add the water first. Watch for signs of activity - larger bubbles and a hungry starter that's thinner in texture.
Day 4: Your starter might have a strong smell when you open the container to feed it. That's all normal. Remove 1/4 cup of starter (60 g) and discard it. Add 1/4 cup of warm, filtered water (60g) stirring, then mix in 1/2 cup of unbleached, all-purpose flour (60 g).
Day 5: Remove 1/4 cup of starter (60 g) to discard (see below). Add 1/4 cup of warm, filtered water (60g) stirring, then mix in 1/2 cup of unbleached, all-purpose flour (60 g). Your starter will probably be very active and may be doubling in size within 4-6 hours of a feeding.If your sourdough starter is very active and doubles in size within 6 hours you can use today's discard in a low-rise recipe like or homemade tortillas. Or wait until day 7 and use your starter for baking a loaf of traditional sourdough bread or sourdough sandwich bread.
Day 6: By now, your starter should resemble a sponge 12 hours after feeding. It should be doubling in size 4-6 hours after feeding. If not, see my troubleshooting tips. Feed starter normally: remove 1/4 cup of starter (60 g) as the discard (use or toss), and add 1/4 cup of warm, filtered water (60g) stirring, then mix in 1/2 cup of unbleached, all-purpose flour (60 g).
Day 7 and beyond: If your starter is fully active, has been doubling in size within 4-6 hours after feeding, it's ready! If not, keep feeding it for a few more days, following the same schedule.To use it for baking, feed it as usual 12 hours beforehand: remove 1/4 cup of starter (60 g) and set aside for baking, and add 1/4 cup of warm, filtered water (60g) stirring, then mix in 1/2 cup of unbleached, all-purpose flour (60 g).
Notes
To maintain your starter, feed it regularly. Discard (or use) 1/4 cup (60g) of starter, add 1/4 cup (60g) water, and 1/2 cup (60g) all-purpose flour.How often you feed it depends on how often you'll use it:For weekly or less frequent use, keep your sourdough starter in the refrigerator. Take it out 12 hours before baking. Depending on how much starter you will need for the recipe, discard (or save for later) half and feed your starter.For daily use, keep your sourdough starter on the counter and feed it once a day. Use it for baking 8-12 hours after feeding.