The Art of Sourdough: From Starter to Loaf

Sourdough bread is having a moment, but the craft itself is ancient. At its core, sourdough is flour, water, salt, and time. No commercial yeast, no additives, no shortcuts.

We spent a week with master baker Tom Reeves at Stone Mill Bakehouse to understand the process, the science, and the quiet satisfaction of baking with wild yeast.

The starter is the bakery

The shop opens to customers at seven, but Tom is already at the bench at five. He pulls a quart jar out of the proofing cabinet and weighs out a hundred grams of the gray, ropy mass at the bottom. To it he adds a hundred grams of stone-milled bread flour and a hundred grams of filtered water, stirs it with a chopstick, and tips it into a clean jar.

"A starter is a living thing," Tom says, sealing the jar with a loose lid. "It responds to temperature, humidity, the flour you feed it. You learn to read it like a gardener reads soil."

The culture in that jar is fourteen years old. It came with Tom from a bakery he worked at in Oakland, and before that from a baker in Petaluma who claims it descends from a starter brought from France in the 1980s. The lineage is technically unverifiable, but a starter holds — once it is established, the same wild yeasts and lactic-acid bacteria persist for decades. Daily feeding is what keeps them dominant over whatever drifts in from the air.

What is actually in there

A mature sourdough starter is not single-organism yeast. It is a stable community of wild Saccharomyces and Candida yeasts living alongside two main species of lactic-acid bacteria, Lactobacillus and Pediococcus. The bacteria produce the lactic and acetic acids that give sourdough its characteristic tang. The yeasts produce the carbon dioxide that lifts the loaf.

The ratio shifts with temperature. Warmer fermentation favors the bacteria and produces a tangier loaf; cooler fermentation favors the yeasts and produces a milder one. A skilled baker uses temperature the way a brewer uses temperature — as the most important variable in the entire process.

The schedule

The process begins days before the bake. A healthy starter is fed twice in the 24 hours before mixing, monitored until it reliably doubles within four to six hours of feeding.

When Tom is ready to mix, he weighs out the dough. A standard country loaf at Stone Mill is 800 grams of flour (a blend of bread flour, whole wheat, and rye), 600 grams of water, 160 grams of leaven (active starter), and 18 grams of salt. The hydration is around 75 percent — wet but workable.

Autolyse

The flour and water meet first, on their own, for an hour. This is the autolyse — a French word that means roughly self-digestion. The flour absorbs the water; enzymes naturally present in the wheat begin to break down starches; gluten begins to develop without any kneading. After an hour, the dough is already softer, more cohesive, and easier to work with than it was at the start.

The leaven and salt go in after the autolyse. From here, the dough is on the clock.

Bulk fermentation

Bulk fermentation is where the magic happens. Over four to six hours at room temperature, the dough is folded every 30 minutes for the first two hours, then left alone. The folding — Tom does what bakers call a stretch and fold, lifting one side of the dough and folding it over on itself — builds gluten strength without aggressive kneading.

The dough changes visibly during bulk. It puffs. It develops a domed top. Bubbles appear under the surface. By the end of bulk, it has roughly doubled, smells faintly sweet, and feels alive.

"You can teach the schedule. You cannot teach the moment when the dough is ready. That part is the bake itself, repeated for years."

Shaping and the cold proof

Shaping is an art in itself. The dough is divided into individual loaf weights, pre-shaped (a loose round to give it structure), rested for 20 minutes, then shaped tightly into the basket — boule for round, batard for oval. A well-shaped loaf holds its structure during the final proof and creates the dramatic ear when scored before baking.

From the basket, the loaves go into the walk-in cooler at 38 degrees Fahrenheit for an overnight cold proof. The cold slows the yeast, lets the bacteria continue working, and produces the deepest flavor of any single decision a sourdough baker makes. Most great commercial sourdough is cold-proofed for 12 to 24 hours.

The bake

The bake happens in a blazing hot oven — Stone Mill's deck oven runs at 480 degrees Fahrenheit with a steam injection at the start of every load. At home, a Dutch oven preheated for 45 minutes does the same job: a heavy lid traps the moisture coming off the loaf and creates the steam that produces a blistered, crackling crust.

The loaves go in lid-on for 20 minutes, lid-off for another 20 to 25. The crust deepens to a mahogany brown — what bakers call bold-baked. Internal temperature should reach 205 to 210 degrees Fahrenheit. Rest the loaf on a wire rack for at least an hour before cutting; the crumb is still setting in those final minutes.

A properly baked sourdough sounds hollow when tapped on the bottom and continues to crackle (the song) for ten minutes after coming out of the oven. That sound is the crust contracting as it cools.

Reading the loaf

A finished loaf tells a baker exactly what happened during the bake:

• A tight, dense crumb means under-fermented dough. Either the starter was sluggish or the bulk was cut short.
• A flat, spread-out loaf means over-proofed dough. The structure collapsed before the crust could set.
• A burst, ragged side means the score was too shallow. The dough found its own escape route.
• A pale crust means under-baked. Pull the next batch later, hotter, or both.
• A perfect ear, an open crumb, and a deep brown crust means the entire chain — starter, schedule, shape, bake — was in tune.

Where to buy it

Real sourdough bread, made with a wild starter and a long fermentation, is harder to find than the marketing suggests. Many sourdough loaves at supermarkets and chain bakeries are conventionally yeasted breads with a touch of acidified flavor for tang.

The tells for the real thing: a producer who can name their starter's age, a fermentation schedule of at least 12 hours, and a list of ingredients that includes flour, water, salt, and starter — nothing else. To find genuine bakeries near you, [browse the Brothh directory](https://brothh.com/browse).

For beginners

For home bakers, Tom's advice is straightforward: "Start with a simple recipe and bake it twenty times before you change anything. You will learn more from repetition than from reading."

The first five loaves will be ugly. The next five will be edible. Somewhere around the fifteenth loaf, you will start to feel the dough rather than reading the recipe. That is when you have actually learned to bake bread.

Good sourdough is a discipline, not a hack. The patience is the point.