Combine 100 grams of freshly milled flour and 80 grams of water in your clean jar. Stir until smooth, then cover loosely. Leave it at room temperature for 24 hours. You may not see much change yet. This is the quiet stage where wild yeast and bacteria begin settling in.
Discard half of your mixture. You can save the discard for one of our sourdough discard recipes if you’d like to avoid waste. Add 50 grams of flour and 50 grams of water, then stir well. You may start to notice small bubbles or a slight rise, which is a good sign of early activity.
Continue feeding every 24 hours using equal parts fresh milled flour and water. By Day 4 or 5, your starter should smell pleasantly sour and begin doubling in size between feedings. If your kitchen is cooler, fermentation may take a little longer. Every home environment is different, so simply keep feeding and watching for steady activity.
By now, your starter should be bubbly, airy, and rising reliably after each feeding. Place a rubber band around the jar to track its rise. Once it doubles within 4 to 6 hours of a feeding, it is ready to use.