Sourdough Starter (7-Day Guide)

Method

1. Day 1: Mix 1/2 cup (60g) flour and 1/4 cup (60g) water in a clean glass jar. Stir until smooth. Cover loosely and leave at room temperature (70–75°F is ideal). Mark the level with a rubber band so you can track the rise.

2. Days 2–6: Every 24 hours, discard half the starter (about half the jar). Add 1/2 cup (60g) flour and 1/4 cup (60g) water. Stir well. Cover loosely. The discard prevents the jar from overflowing and keeps the yeast-to-food ratio balanced. By day 3–4, you should see bubbles and smell a sour, yeasty aroma. This is fermentation — wild yeast and bacteria are colonizing the flour-water mixture.

3. Day 7 (the float test): Drop a small spoonful of starter into a glass of water. If it floats, the starter is active enough to leaven bread — the CO2 bubbles trapped inside make it buoyant. If it sinks, continue daily feedings for a few more days.

4. Maintenance: Once active, feed once a week if stored in the fridge (take it out, discard half, feed, let it rise for 2 hours at room temp, then refrigerate). Feed daily if kept at room temperature. The starter will last indefinitely with regular feeding — some starters are over 100 years old.

Equipment

• Large glass jar or container (at least 1 quart — the starter doubles in volume)
• Kitchen scale (measuring by weight is essential for consistency) Recommended: Escali Primo Digital Kitchen Scale
• Rubber band or tape (to mark the level and track rise)
• Clean cloth or loose lid (the starter needs to breathe)
• Instant-read thermometer (water temperature affects fermentation speed) Recommended: ThermoWorks ThermoPop 2

Chef Notes

• The most important thing: Patience is the only real ingredient. A sourdough starter is a colony of wild yeast and lactobacillus bacteria that you cultivate by feeding flour and water daily. Some starters are active by day 5; others take 10–14 days. Don't give up if nothing happens by day 3.
• Use filtered or bottled water. Chlorine in tap water can inhibit the wild yeast and bacteria you're trying to cultivate. If you only have tap water, let it sit uncovered for 24 hours to off-gas the chlorine.
• The starter will smell sour and yeasty when it's active — like beer or yogurt. If it smells like nail polish remover (acetone), it's hungry and needs more frequent feeding.
• Keep the jar loosely covered, not sealed. The fermentation produces CO2 that needs to escape. A loose lid or cloth secured with a rubber band works.
• Name your starter. Everyone does. It's alive and you're going to be feeding it for years.

Common Substitutions

Ingredient	Substitution	Notes
Yogurt	Sour cream or coconut yogurt	Sour cream is thicker. Coconut yogurt for dairy-free.
Bread	Gluten-free bread or lettuce wraps	GF bread varies by brand. Lettuce wraps for low-carb.

What You're Practicing

Sourdough is applied fermentation science — the same lacto-fermentation principles behind yogurt, kimchi, and sauerkraut. Wild yeast (Saccharomyces) produces CO2 for leavening, while lactobacillus bacteria produce lactic and acetic acids for the signature sour flavor. Understanding this symbiotic relationship is the foundation of all natural fermentation. Visit Techniques for more on fermentation.

The discipline of daily feeding teaches you about maintaining a living culture — the same commitment required for kombucha SCOBYs, kefir grains, and vinegar mothers. Visit Pastry Foundations for more on sourdough baking.