Sourdough Starter

A sourdough starter is a living culture of wild yeast and lactic acid bacteria maintained with regular feedings of flour and water. Instead of commercial yeast, bakers use a sourdough starter to leaven bread, producing the tangy flavor, chewy crumb, and crisp crust that define sourdough baking.

Some starters have been kept alive for over a century, passed down through generations. The Boudin Bakery starter in San Francisco dates to 1849. I've maintained mine for about four years now. It's gone through neglect, fridge hibernation, and one accidental encounter with dish soap. It survived all of it.

How a sourdough starter works

When you mix flour and water and leave the mixture at room temperature, wild yeast and bacteria already present in the flour begin to colonize the mixture. Over 5-14 days of regular feedings, two groups of microorganisms establish a stable ecosystem:

Wild yeast (primarily Saccharomyces and Kazachstania species) produces carbon dioxide gas. This is what makes the dough rise.

Lactic acid bacteria (primarily Lactobacillus) produce lactic and acetic acids. These acids give sourdough its characteristic tang and also act as natural preservatives. Sourdough bread stays fresh longer than commercially yeasted bread because of them.

The two groups work together. The acids produced by bacteria create an environment too acidic for most competing organisms, while the yeast thrives in it. This symbiosis is why a healthy starter is stable and resistant to contamination.

How to make a sourdough starter from scratch

The sourdough starter ingredients are simple: flour and water. That's it. No commercial yeast, no sugar, no yogurt. The wild yeast and bacteria come from the flour itself and the air in your kitchen.

A few notes on the process. Days 2-4 often produce a burst of activity followed by a dead period. This is normal. The early bacteria that cause the initial bubbling get replaced by the lactic acid bacteria that will dominate long-term. Don't panic when it seems to "die" around day 3-5.

You can use all-purpose flour instead of whole wheat, but whole wheat gets things moving faster because it has more wild microorganisms and nutrients. I started my current starter on 100% rye for the first five days, then switched to a mix of 80% bread flour and 20% whole wheat. The rye kickstarted the fermentation noticeably.

How to feed a sourdough starter

Feeding means discarding part of the culture and adding fresh flour and water. This replenishes the food supply for the yeast and bacteria.

Standard feeding ratio: 1:1:1 by weight. Keep 50g of starter, add 50g flour and 50g water. Use a kitchen scale for accuracy. Volume measurements are too imprecise for consistent results.

Feeding schedule:

Flour choice matters. Unbleached all-purpose or bread flour works well for maintenance. Whole wheat or rye flour accelerates fermentation because it contains more nutrients and wild microorganisms. Many bakers use a mix (80% white flour, 20% whole wheat) for a balance of activity and mild flavor.

Signs of a healthy sourdough starter

It takes 7-14 days to establish a new sourdough starter from scratch, and another 2-4 weeks before it's strong enough to reliably leaven bread. Patience during this initial phase is the biggest factor in success.

Sourdough starter troubleshooting

Sourdough starter vs. commercial yeast

Neither is "better." Commercial yeast is convenient and predictable. Sourdough rewards patience with flavor and texture you can't get any other way. Many bakers keep both in rotation.

What to do with sourdough discard

Every feeding produces discard: the portion of starter you remove before adding fresh flour and water. It doesn't have to be waste. Sourdough discard works in:

• Pancakes and waffles — adds tang and tenderness
• Crackers — thin, crisp, and deeply flavored
• Pizza dough — discard replaces some of the flour and water in a standard recipe
• Quick breads and muffins — adds complexity without long fermentation
• Flatbreads — naan, tortillas, and pita all benefit from discard

Discard doesn't have enough leavening power to rise bread on its own, but it adds flavor and acidity to anything that uses baking soda or baking powder as the primary leavener.

Sourdough starter in Fond

Fond's Bread Studio includes a sourdough starter tracker. Log each feeding, set reminders on your preferred schedule, and track your starter's rise-and-fall pattern over time. When you're ready to bake, Bread Studio calculates the right amount of starter for your recipe based on baker's percentages. You always know how much to pull and how much to keep.

Frequently asked questions

How long does it take to make a sourdough starter?

From scratch, expect 7-14 days before the starter shows consistent rising and falling. It may take another 2-4 weeks of regular feeding before it's strong enough to reliably leaven bread. Whole wheat or rye flour speeds up the early days. Temperature matters too: a warm kitchen (24-26°C) gets results faster than a cold one.

Is a sourdough starter alive?

Yes. A sourdough starter is a living colony of wild yeast and bacteria. As long as you feed it regularly, the microorganisms stay alive and active. A refrigerated starter can often be revived after weeks of neglect with a few days of consistent feeding.

Can you buy a sourdough starter?

You can. Bakeries, online retailers, and some grocery stores sell dehydrated or fresh starters. You can also get a piece from a friend's existing culture. Either way, the culture adapts to your local flour and environment within a few feeding cycles.

Can you make a sourdough starter with all-purpose flour?

Yes. All-purpose flour works fine. It just takes a bit longer to get going compared to whole wheat or rye because it has fewer wild microorganisms. Once established, many bakers maintain their starter on all-purpose flour because it produces a milder flavor.

What does sourdough starter smell like?

A healthy starter smells pleasantly sour, like yogurt, mild vinegar, or ripe fruit. A strong acetone or nail polish remover smell means it's very hungry and needs feeding. If it smells putrid or develops colored mold, discard it and start over.

Can you make a sourdough starter without discarding?

Technically yes, but the starter grows fast. Without discarding, you'd need to add more and more flour each feeding, and you'd quickly end up with a huge quantity. Most bakers discard to keep the volume manageable and the culture healthy. The discard goes into pancakes, crackers, or pizza dough rather than the bin.