Sourdough Bread Explained: A Working Guide From a Hot, Humid Kitchen

Sourdough is wildly context-driven. A loaf that takes eight hours of bulk fermentation in a cool New York kitchen takes three in Goa. Most online guides ignore this — they hand out one timeline, one folding routine, one fermentation length, and pretend climate does not exist. It does. Everything downstream depends on it.

Why Sourdough Is Context-Driven

Four variables determine almost everything about how a sourdough behaves.

• Temperature. Sourdough microbes have a sweet spot around 22–28°C. Below 20°C, fermentation slows dramatically. Above 30°C, both yeast and LAB speed up, but yeast stresses first.

• Flour composition. Whole-grain flours ferment 30–40% faster than refined bread flour — more enzymes, more nutrients, more wild microbes on the bran.

• Starter maturity. A six-month-old starter behaves nothing like a two-week-old one. Older starters are faster, stronger, more predictable.

• Humidity. Overlooked but real. High ambient humidity slows surface drying, which matters during long bulk fermentations.

Once these four are read correctly, the whole process becomes legible. A Brooklyn timing chart is meaningless in Goa — and vice versa.

The Science: Yeast and Lactic Acid Bacteria

A sourdough starter is a living culture of two microbe families working in symbiosis.

Wild yeast (primarily Saccharomyces cerevisiae) does the leavening. It metabolises flour sugars and produces CO₂ that lifts the dough.

Lactic acid bacteria (primarily Lactobacillus species) do the flavour. They produce lactic acid (mild, dairy-like sourness) and acetic acid (sharp, vinegar-like sourness). The ratio between the two decides whether a bread is mellow or tangy.

The two organisms keep each other healthy. LAB lower the pH, creating an environment hostile to competing microbes but hospitable to yeast.

Cooler temperatures favour LAB — sour, slow-rising loaf. Warmer temperatures favour yeast — faster rise, milder flavour.

Building a Starter From Scratch

A new starter takes 14–20 days to become bake-ready, varying with climate. The defining feature of starter-building is that the feeding schedule changes as the starter matures. A young starter eats slowly. A vigorous one is constantly hungry.

• Days 1–2. 50g whole wheat flour + 50g room-temperature water in a glass jar. Stir smooth, cover loosely, wait 48 hours.

• Days 3–6 (once daily). Discard most, keep 50g. Feed 50g flour + 50g water. Bubbles by day 4; predictable rise-and-fall by day 6.

• Days 7–9 (twice daily). Feed morning and evening as the starter rises and falls faster.

• Days 10+ (three to five feedings at peak). A vigorous starter in a warm climate rises to peak in 4–5 hours.

By the end, the starter is mature. Move to once-daily at room temperature, or weekly in the fridge with a feed before each bake.

Maintaining an Established Starter

Once mature, the daily ritual simplifies:

1. Discard most (keep 50g).

2. Feed 50g flour + 50g water.

3. Stir smooth. Cover loosely.

4. Use within 4–8 hours when it has roughly doubled.

The float test — drop a spoonful in water. If it floats, it is bake-ready.

Our Recipe

A basic loaf for our kitchen:

• 350g bread flour

• 150g whole wheat flour (70/30 split — works well in our climate)

• 375g water (75% hydration — slightly higher because whole wheat absorbs more)

• 100g active starter (20%)

• 10g salt (2%)

Produces one 750g boule. 100% bread flour handles easier but produces flat-tasting bread. 100% whole wheat is flavourful but dense. The 70/30 blend is where climate, gluten, and flavour meet.

The Phases — Our Goa Timeline (25–28°C ambient)

The whole sequence: about 4 hours of bulk fermentation plus an overnight cold proof.

Phase 1: Autolyse (30–60 min). Mix flour and water until no dry flour remains. Cover. Rest. Gluten begins forming; enzymes break starches into sugars.

Phase 2: Add starter and salt (5 min). Pinch the starter and salt into the dough. Fermentation officially starts.

Phase 3: Three folds (90 min). Stretch-and-fold at 30, 60, and 90 minutes. Wet hands, lift one side, stretch up without tearing, fold over the middle. Rotate the bowl a quarter turn. Repeat four sides.

Phase 4: Final rest (90 min). Left alone. By the end: 50–70% volume increase, slightly domed top, bubbles around edges, slow spring-back when poked.

Phase 5: Pre-shape and bench rest (20–30 min). Turn onto a lightly floured surface. Fold edges toward the centre to form a loose round. Rest.

Phase 6: Final shape (5 min). Flip seam-side up. Stretch four corners outward, fold each side to the middle, roll up. Flip into a floured banneton.

Phase 7: Cold proof (12–18 hours in fridge). At 4°C, yeast activity slows to almost zero; LAB keep working. Dough tightens, structure sets, flavour deepens.

The Bake — Convection Oven With Steam

We bake in a home convection oven with the steel-bowl-and-water method. No Dutch oven needed.

Setup:

• Baking stone or heavy sheet pan on the middle rack.

• Empty steel or cast-iron bowl on lower rack.

• Convection OFF. Preheat the oven to 250°C for 45–60 minutes.

Load and steam:

1. Turn cold dough onto parchment. Score the top with a razor at a 30° angle — one clean sweep.

2. Slide onto the hot stone.

3. Pour 250 ml of boiling water into the empty steel bowl. Close the door immediately.

4. Bake at 250°C, convection off, for 20 minutes.

Second phase:

1. Open briefly to release steam. Remove the steel bowl (heavy gloves).

2. Drop the temperature to 220°C. Turn convection ON.

3. Bake another 25–30 minutes.

Done when the crust is deeply browned (mahogany, not just golden), the bottom sounds hollow, and the internal temperature reads 96–99°C. Cool on a wire rack for at least an hour before cutting — the interior is still setting.

Oven Spring

Oven spring is the rapid rise in the first 10–15 minutes of baking. Three things drive it.

• Yeast hyperactivity. As dough heats from 5°C to 50°C, yeast activity ramps up dramatically before the yeast dies around 60°C.

• Gas expansion. Trapped CO₂ expands as it heats; dough water turns to steam.

• Crust softness. An elastic crust lifts upward. This is why steam matters — without it, the crust hardens in 3–5 minutes and kills the spring.

The score is the controlled expansion point. Without it, the loaf tears at random.

How to Adjust for Your Climate

Our 4-hour bulk works in a 25–28°C kitchen with a 70/30 whole-grain blend. For other climates:

• 18–20°C — 7–8 hours bulk, possibly a fourth fold at 120 minutes.

• 20–24°C — 5–6 hours bulk, three folds at 45-minute intervals.

• 24–28°C (our range) — 3–4 hours bulk, three folds at 30/60/90.

• 28–32°C — 2.5–3 hours bulk, three folds at 20/40/60. Watch for over-proofing.

• Above 32°C — Bulk-ferment in the fridge after one or two folds.

In cooler climates, a more active starter or a warmer proofing spot (top of the fridge, near a lamp) helps.

Troubleshooting

• Dough collapses during bulk. Over-proofed. Shape immediately and cold-proof.

• Dough too slack, won't hold shape. Over-fermented (skip bench rest, shape immediately) or gluten undeveloped (add a fourth fold next time).

• Open holes near the top, dense crumb below. Over-proofed and shaped without enough tension.

• No oven spring. Oven not hot enough, no steam, or dough over-proofed before scoring.

• Crust too pale. Steam phase ran too long, or convection off for phase 2.

• Vinegar-sharp sourness. Cold proof too long, or starter percentage too high.

Frequently Asked Questions

How does climate affect sourdough timing?

Climate determines almost everything. At 25–28°C ambient in Goa, total bulk runs about 4 hours. At 18–20°C, expect 7–8 hours. Above 30°C, bulk-ferment in the fridge after the first fold.

How often do you feed a new sourdough starter?

Once a day for days 3–6. Twice a day from day 7. By day 10, a vigorous starter in a warm climate wants three to five feedings a day. Slow the pace once the starter is established.

What flour mix works best for sourdough?

A 70/30 bread-flour-to-whole-wheat blend balances gluten strength with wild microbes and enzymes. 100% bread flour handles easier but tastes flat. 100% whole wheat is flavourful but dense.

Do I need a Dutch oven to bake sourdough?

No. A convection oven with a hot stone and a steel bowl of boiling water produces the same crust. Steam 20 minutes, then dry-heat convection for the remaining bake.

Where Sourdough Takes You

The first loaf is rarely the best loaf. The first ten are calibration — the bread teaches the baker to read the dough. After that, adjustment becomes intuitive: what to change when the kitchen is 3°C warmer, when the flour is different, when the starter has been in the fridge for a week.

The microbes do the work. The baker manages timing, temperature, and the dough's signals.

At The Vegan School, sourdough runs through the fermentation module — students build a starter from scratch, calibrate to a hot, humid kitchen, and bake their first loaves within days of understanding the science.