7-Day Sprint

Commercial bread uses a single purified yeast strain in a packet. Sourdough uses a community you grow yourself: wild yeasts that produce carbon dioxide and alcohol, and lactic acid bacteria that produce lactic and acetic acid. The yeast inflates the dough; the bacteria acidify it, which gives flavor, helps preserve the loaf, and strengthens the dough's structure up to a point.

To build one from scratch, mix equal weights of whole wheat or rye flour and water in a jar, leave it loosely covered at warm room temperature, and each day discard most of it and feed the remainder fresh flour and water. Whole grain flour is worth using at the start because the bran carries more microbes and more enzyme activity. Expect an early burst of activity from bacteria that will not last, then a quiet stretch, then a real rhythm of rising and falling. Most starters take one to two weeks to become reliable.

A finished starter is judged by behavior, not looks. Ripe means it roughly doubles or more within a predictable window after feeding, smells sharply yogurt-like or beery rather than acetone-harsh, and is full of bubbles through the middle. Until it does that on schedule, it isn't ready to raise a loaf.

A feeding is written as a ratio: 1:1:1 means one part old starter, one part flour, one part water by weight. 1:5:5 means one part old starter to five parts each of flour and water. More fresh food per unit of starter means a longer, gentler climb to peak; less food means a fast climb and a fast crash into over-acidity.

Peak is the moment the starter has risen as far as it will go and is just about to fall. Before peak it's underpowered. Well after peak the yeast have run short of fuel and the acid has built up, so the dough it raises will be slack and sour without much lift. You can see peak as a domed top that has just started to flatten or dimple, and you can hear it as a jar that has gone quiet.

Use the ratio to fit your schedule. A 1:1:1 feed at warm room temperature may peak in four to six hours, which suits a same-day build. A 1:5:5 feed at cooler temperature can be timed to peak overnight so your dough is ready when you wake up. Same culture, different gearing.

In baker's percentage the flour is always 100%, and everything else is stated relative to it. A common loaf is 100% flour, 72 to 78% water, 2% salt, and 15 to 20% ripe starter. So 500 grams of flour means about 375 grams of water at 75% hydration, 10 grams of salt, and 100 grams of starter at 20%.

Hydration is the number that changes how the dough behaves in your hands. Lower hydration around 65 to 70% gives a stiff, easy-to-shape dough with a tighter crumb. Higher hydration around 80% and up gives a slack, sticky dough that can produce a more open crumb but punishes sloppy handling. Different flours absorb different amounts of water: strong bread flour and whole grain flours drink more than supermarket all-purpose, so the same percentage feels wetter or drier depending on the bag.

Salt is not optional seasoning. At around 2% of flour weight it tightens the gluten, slows fermentation slightly so you have a wider margin of error, and makes the bread taste like bread rather than paste. Leave it out and you get a sticky, fast-fermenting dough with a flat flavor.

Two proteins in wheat, glutenin and gliadin, link into gluten once flour is wet. Glutenin gives elasticity, the snap-back; gliadin gives extensibility, the willingness to stretch. You need both. Kneading aligns those links quickly, but simply leaving mixed dough to rest does much of the same work on its own, which is why sourdough bakers rely on rest plus a handful of gentle folds instead of ten minutes of pummeling.

A typical sequence is to mix flour and water and let it rest 30 to 60 minutes before adding salt and starter, then perform three or four sets of folds spaced 30 to 45 minutes apart during the first part of fermentation. A set of folds means lifting one side of the dough, stretching it up, and laying it over itself, then rotating and repeating on all four sides. Coil folds, where you lift the whole mass from the middle and let it tuck under itself, do the same for wetter doughs.

Stop folding when the dough tells you to. Strong dough holds a dome, feels billowy rather than soupy, and pulls off the bowl in a sheet instead of tearing. You can check with a windowpane: stretch a small piece thin enough to see light through it without it ripping. Folding past that point tightens the dough and can drive gas out of a fermentation you want to protect.

Recipes say four hours because the writer's kitchen was at a certain temperature with a certain starter. Yours isn't. Fermentation roughly speeds up as the dough gets warmer and slows as it cools, so a dough at 78°F can be ready in half the time of the same dough at 66°F. This is the single biggest reason home loaves fail: the baker follows the clock and pulls the dough early or late.

Judge the dough instead. Most bakers end bulk when the mass has grown by roughly 50 to 75% for a well-fermented open crumb, though stronger flours tolerate more and whole grain doughs generally need less. Look for a domed surface, visible bubbles at the sides and top, a jiggly feel when you shake the tub, and a slight dome that holds when you tip it. Underfermented dough is dense and tight and will bake into a tall loaf with a gummy, closed crumb. Overfermented dough is soupy, smells sharply sour, tears instead of stretching, and spreads flat in the oven.

The cleanest way to measure is an aliquot jar: pull a small sample of the mixed dough into a straight-sided jar, press it flat, mark the level, and watch the percentage rise there rather than guessing in the big tub. You can also control the pace deliberately by adjusting the water temperature at mixing to land the dough where you want it.

Turn the finished bulk dough onto a lightly floured counter, fold it loosely into a rough round, and let it rest uncovered for 20 to 30 minutes. This preshape lets the gluten relax so the final shape doesn't fight you. Then flip it, fold the sides in, roll it up, and drag it across the bench so the surface pulls tight like the skin on a drum. That tension is what directs oven spring upward instead of outward.

Place the shaped loaf seam side up in a floured banneton or a bowl lined with a floured towel, cover it, and put it straight into the refrigerator for 8 to 16 hours. Cold slows the yeast a lot and the acid-producing bacteria somewhat less, so a long chill deepens flavor. It also firms the dough, which makes a wet loaf far easier to turn out and score cleanly.

Judging final proof is a matter of touch. Press the chilled dough gently with a floured finger: if the dent springs back fast, it needs more time; if it fills back slowly and partly, it's ready; if the dent stays and the dough sighs, it's overproofed and will spread. Baking straight from the fridge is standard and works well.

Preheat a Dutch oven inside your oven at 500°F for at least 45 minutes. Turn the cold loaf out onto parchment, score it with a single confident slash held at a shallow angle about a quarter inch deep, and lower it into the pot. The lid traps the dough's own moisture, which keeps the crust soft and stretchy while the trapped gas expands, the water turns to steam inside the loaf, and the starches set. That window of expansion is oven spring, and it closes within the first several minutes.

Bake covered at 450°F for about 20 minutes, then remove the lid and bake another 20 to 25 minutes until the crust is deep brown. Don't pull it pale. The browning is Maillard reaction and caramelization, and it is where a large share of the aroma lives. If you are unsure, an instant-read thermometer in the center should show roughly 205 to 210°F.

Then wait. Cutting a hot loaf lets steam escape from a crumb that is still setting, which leaves it gummy and makes the bread stale faster. Cool on a rack for at least two hours, longer for a large or high whole grain loaf. When you finally cut, read the crumb: even, open holes and a slightly translucent, glossy interior mean the fermentation and shaping were right, while dense bands near the base suggest underfermentation and a flat, gray, ragged crumb suggests it went too far.