1. Day 1: The Initial Mix. In a clean, large glass jar or container (at least 1-quart capacity), combine 1 cup (240g) of unbleached all-purpose flour and 1/2 cup (120g) of lukewarm filtered water. Stir vigorously with a spoon or spatula until no dry spots of flour remain. The mixture should be thick and pasty. Scrape down the sides of the jar, cover loosely with a lid, plastic wrap, or a clean kitchen towel, and let it sit at room temperature (ideally 70-75F) for 24 hours.

2. Day 2: First Feeding. After 24 hours, you might see a few tiny bubbles on the surface or around the edges, and it might smell slightly yeasty or like wet flour. Discard about half of the starter (approximately 1/2 cup or 120g). Then, feed the remaining starter with 1 cup (240g) of unbleached all-purpose flour and 1/2 cup (120g) of lukewarm filtered water. Stir well until fully combined, scrape down the sides, cover loosely, and return to room temperature for another 24 hours.

3. Day 3: Increased Activity. Today, you should start to see more bubbles and possibly some slight expansion. The smell might become a bit more sour or acidic, which is a good sign. Repeat the feeding process: discard half of the starter, then feed with 1 cup (240g) flour and 1/2 cup (120g) lukewarm water. Mix thoroughly, cover, and let sit for 24 hours.

4. Days 4-7: Daily Feedings and Observing Growth. Continue the daily feeding routine. Each day, discard half of the starter, then feed with 1 cup (240g) flour and 1/2 cup (120g) lukewarm water. By day 4 or 5, you should notice significant activity. Your starter should be consistently bubbling, expanding (doubling in size or more) between feedings, and have a pleasant, tangy, yeasty aroma. It should also have a spongy, web-like texture when stirred. If your kitchen is cooler, it might take an extra day or two to reach this stage.

5. When Your Starter Is Ready for Baking. Your sourdough starter is considered “active” and ready for baking when it consistently doubles in size within 4-8 hours after being fed, has many visible bubbles, and smells pleasantly sour and yeasty. You can perform a “float test” to confirm: drop a small spoonful of starter into a glass of water. If it floats, it’s ready! If it sinks, it needs more time and possibly another feeding or two to strengthen.