How to Make and Maintain a Sourdough Starter — Complete Beginner Guide

A healthy starter contains a symbiotic community of wild yeasts (primarily Saccharomyces cerevisiae and Kazachstania humilis) and lactic acid bacteria (principally Lactobacillus sanfranciscensis and related species). The yeasts produce CO₂ gas that leavens the bread; the bacteria produce lactic and acetic acids that give sourdough its characteristic tangy flavour and extended shelf life.

They co-exist because they occupy different ecological niches: yeasts ferment simple sugars; bacteria prefer complex sugars and byproducts the yeasts leave behind. The ratio of yeast to bacteria — influenced by temperature, hydration and feeding schedule — determines the balance between leavening power (yeast) and sourness (bacteria).

Temperature is the key variable: at 21–24°C, you get a balanced, moderately sour starter. Below 18°C, bacteria dominate (more sour, slower rise). Above 28°C, yeast dominates (faster rise, less sour). This is why sourdough culture varies so dramatically by geography — San Francisco sourdough's famous tang comes partly from the specific local bacteria, partly from the cool, foggy climate.

You need only two ingredients: whole wheat or rye flour (the bran contains wild yeasts; white flour works more slowly) and non-chlorinated water (chlorine inhibits yeast activity — use filtered or let tap water sit uncovered for 30 minutes).

**Day 1:** Mix 50g whole wheat flour + 50g room-temperature water in a clean jar. Cover loosely (don't seal airtight). Leave at room temperature (ideally 21–24°C).

**Days 2–3:** You may see no activity, or small bubbles. The culture is establishing. Discard all but 50g and add 50g fresh flour + 50g water. The 'discard' can be used in pancakes or waffles.

**Days 4–5:** Activity should increase — bubbles, a tangy/yeasty smell developing. Continue the same feeding schedule daily.

**Days 6–7:** A healthy starter should now be doubling in volume within 4–8 hours of feeding and have a domed top and bubbly interior when active. It should smell pleasantly sour and yeasty.

If there's no activity by Day 7, try: warmer location (top of the fridge, near an oven), switching to 50/50 whole wheat and rye flour, or using warmer water.

**Room temperature feeding (if baking frequently):** Feed once or twice daily. Always discard all but 50–100g before feeding. Add equal weights of flour and water (100% hydration). Use within 2–4 hours of peak activity (when the starter has doubled and is domed but not yet collapsed).

**Refrigerator storage (if baking weekly or less):** A starter stored in the fridge goes dormant and needs feeding only once a week. When you want to bake: remove from fridge, discard all but 50g, feed, leave at room temperature 4–8 hours until doubled and active, then use it to build your levain.

**The float test:** Drop a small spoonful of starter in water. If it floats, the starter is active and well-aerated — ready to use. If it sinks, feed it and wait 4–6 more hours.

**No activity after 5+ days:** Temperature too cold, too much chlorine in the water, or too little whole grain flour. Try a warmer spot, filtered water, and switch to 50% rye flour.

**Pink, orange or black streaks:** Contamination — these are harmful bacteria or mould. Discard entirely and start again with cleaner equipment.

**Grey liquid on top (hooch):** This is alcohol produced by the yeast when the starter is hungry — it's harmless. Pour it off or stir it back in, then feed immediately. Hooch means the starter needs more frequent feeding.

**Smells like cheese or nail polish remover:** Too sour, too acidic, or built up acetone from stressed yeast. Increase feeding frequency and/or hydration.

**Smells like vomit:** The starter may have been contaminated with non-beneficial bacteria. If the smell persists through 2–3 feedings, discard and start again.