Sourdough Starter

Ingredients

• 2 cups unbleached bread flour (about 8 1/2 ounces)
• 2 cups whole-wheat flour (about 8 1/2 ounces)
• 1/4 cup (about 2 1/8 ounces) lukewarm water (80°F to 85°F), plus more for feeding

Steps

1. Combine the bread flour with the whole-wheat flour, stirring them in a medium bowl or an airtight container.
2. In a wide-mouthed quart jar or small bowl, stir 1/4 cup water with 1/2 cup flour mixture (about 2 1/8 ounces) until smooth. Place a kitchen towel over the bowl and leave at room temperature for 3 days. Keep the remaining flour mixture for feeding the starter.
3. After 2 days, check for a dark crust on the starter's surface; if present, scrape it away and discard it. The starter below it should have an acidic smell. If it does not, cover it and leave at room temperature for 1 more day.
4. For a feeding, remove and discard about 2 tablespoons starter, then stir in 3 tablespoons flour mixture and 1 1/2 tablespoons water until smooth. Cover it and leave at room temperature.
5. Continue feeding daily until the starter is bubbly, smells tangy and rises and falls reliably, which takes about 10 days. Its rise and fall—expansion followed by collapse—will occur about 4 to 8 hours after each feeding.