The sourdough calculator that thinks in ratios

What is sourdough?

Sourdough is bread leavened by a living culture of wild yeast and lactic acid bacteria rather than commercial baker's yeast. That culture — the starter — is simply flour and water that has been fermented and kept alive by regular feeding. The wild yeast produces carbon dioxide that lifts the dough, while the bacteria produce lactic and acetic acids that give sourdough its tang, its keeping quality and its distinctive open, chewy crumb.

Because the leavening is alive, sourdough responds to temperature, time and the ratio of ingredients far more than yeasted bread does. Learning sourdough is really learning to read fermentation: how warm dough behaves, how much rise means "ready," and how the same formula behaves differently in a July kitchen versus a January one. This is exactly why a calculator helps — it fixes the ratios so you can focus on the variables that actually change day to day.

What is baker's percentage?

Baker's percentage is the language professional bakers use to write formulas. Every ingredient is expressed as a percentage of the total flour, and flour itself is always 100%. Water at 75% means 75 grams of water for every 100 grams of flour; salt at 2% means 2 grams per 100 grams of flour. The percentages routinely add up to more than 100 because they are all relative to flour, not to the whole dough.

The power of this system is scaling. Once a formula is written in percentages, you can make one loaf or fifty and every ingredient stays in exact proportion. It also lets you compare recipes fairly: two loaves at "75% hydration, 20% starter, 2% salt" will behave alike regardless of batch size. This calculator works entirely in baker's percentages, then converts them into real weights for your chosen dough size.

Understanding hydration

Hydration is the ratio of total water to total flour, written as a percentage. It is the single most influential number in a sourdough formula. Lower hydration (60–68%) gives a firm, easy-to-handle dough and a tighter crumb, which is forgiving for beginners and ideal for sandwich loaves and bagels. Higher hydration (75–85%) produces a slack, sticky dough and a wild, open crumb, but demands confident handling and strong flour.

Crucially, hydration must include the water and flour already inside your starter. A 100-gram starter at 100% hydration adds 50 grams of flour and 50 grams of water to the dough, changing its true hydration. This calculator accounts for that automatically, so the hydration you set is the hydration you actually get. If you have ever followed a recipe and found the dough wetter or drier than expected, unaccounted starter is usually why.

Starter hydration explained

Starter hydration describes the water-to-flour ratio of the starter itself. A 100% hydration starter — equal weights of flour and water — is the most common and the easiest to maintain, pouring like thick batter. A stiffer starter (50–60% hydration) holds more acetic acid, ferments a touch slower and tends toward a sharper, more complex sourness; a wetter one leans milder and more lactic.

Whatever hydration you keep, the calculator splits your starter into its flour and water components and subtracts both from the amounts you add to the final dough. That means you can switch from a 100% to a 70% starter and your dough's overall hydration stays exactly where you set it, because the maths adjusts the added water to compensate.

Choosing flour types

Flour choice shapes structure, flavour and how much water the dough needs. Strong bread flour (12–14% protein) forms robust gluten, holds gas well and supports high hydration and open crumb — it is the reliable default. All-purpose flour is lower in protein and gives a softer, slightly less airy loaf, well suited to sandwich breads. Whole wheat and rye contain bran and germ that absorb more water and cut through gluten strands, so they drink more liquid but rise less; most bakers blend 10–30% of them into a white base for flavour without sacrificing lift.

Spelt and einkorn are ancient wheats with delicate, extensible gluten. They make wonderfully flavourful bread but tolerate less water and less mixing before the dough turns slack, so lower hydration and gentle handling pay off. The calculator's auto-hydration option nudges your starting hydration toward a sensible range for the flour you pick — a launch point to adjust from, not a rule.

Salt percentages

Salt does far more than season. It tightens and strengthens the gluten network, slows fermentation to a manageable pace, and suppresses off-flavours so the wheat and tang come through cleanly. Most sourdough sits between 1.8% and 2.2% salt by flour weight, with 2% the dependable default: for 500 grams of flour, that is 10 grams of salt.

Cutting salt much below 1.5% lets the dough ferment too fast and become slack and sticky, while pushing past 2.5% noticeably slows the yeast and firms the crumb. If you are baking in a very warm kitchen, a slightly higher salt percentage can buy you a more controllable fermentation window.

Bulk fermentation

Bulk fermentation is the first rise, after mixing and before shaping, when the dough develops most of its strength, flavour and gas. It typically runs 3–6 hours at room temperature, but time is a poor guide on its own because fermentation speed depends heavily on dough temperature and starter quantity. Warmer dough and more starter finish faster; cooler dough and less starter take longer.

Judge bulk by change, not the clock. Look for a 30–50% increase in volume, a domed and slightly jiggly surface, some bubbles at the edges, and a smooth, billowy feel. Under-fermented dough bakes dense and gummy; over-fermented dough goes slack, tears and loses its ability to hold a shape. The temperature-versus-time table on this page gives realistic starting estimates, and the calculator adjusts them for your room temperature and starter percentage.

Cold proofing (retarding)

Cold proofing, or retarding, means resting the shaped loaf in the refrigerator — usually 8–16 hours at 3–5°C — instead of proofing it entirely at room temperature. The cold slows the yeast dramatically while the bacteria keep working, which deepens flavour and builds a more complex, pleasantly sour profile. It also firms the dough, making it far easier to score cleanly and giving a more dramatic ear and oven spring.

Retarding is as much a scheduling tool as a flavour one: mix and bulk during the day, shape in the evening, and bake cold straight from the fridge the next morning. Most cold-proofed loaves go into the oven without any warming-up, which is one reason bakers love the method for fitting bread around real life.

Dough temperature

Dough temperature is the hidden lever behind consistent results. A few degrees warmer or cooler can shift bulk fermentation by an hour or more, so professional bakers aim for a desired dough temperature (DDT), often around 24–26°C for sourdough. The main tool for hitting it is the temperature of your mixing water, because you can control that precisely while flour and room temperature drift.

For hand mixing: water temperature = (DDT × 3) − flour temperature − room temperature − starter temperature. If a machine adds warmth from mixing, include a friction factor and multiply DDT by four instead.

The calculator's DDT tool does this for you: enter your target dough temperature and the temperatures of your flour, room and starter, and it returns the water temperature to use. In a warm kitchen this often means noticeably cool water; in winter, warm.

Stretch and folds

Rather than kneading, most sourdough builds strength through a series of gentle stretch-and-folds during the first part of bulk fermentation. Every 30–45 minutes, wet your hand, lift one side of the dough, stretch it up and fold it over the centre, then rotate and repeat on all four sides. Three or four sets across the first two hours is typical.

Folding aligns and strengthens the gluten, redistributes warmth and gas, and turns a shaggy, slack mass into a smooth, elastic dough that holds its shape. Early folds can be firmer; as the dough gains structure and air, handle it more gently to avoid degassing it. Higher-hydration doughs generally need more folds to build enough strength.

Scoring

Scoring is the cut you make in the surface just before baking. It is not only decorative: it gives the loaf a controlled place to expand, so the dough bursts open where you intend rather than tearing randomly at a weak seam. A single confident slash at a shallow angle creates the classic raised "ear"; more intricate patterns are best kept shallow so they open cleanly.

Use a very sharp blade or a lame, score in one smooth motion, and work with cold dough straight from the fridge, which holds its shape and cuts crisply. For a bold ear, angle the blade about 30 degrees to the surface; for even overall expansion, a simpler cross or square works well.

Baking methods

The goal of home baking is to mimic a professional steam-injected deck oven: intense heat and trapped moisture early for maximum oven spring, then a dry finish for a deep, crackling crust. A preheated Dutch oven is the simplest way to achieve this — the lid traps the loaf's own steam for the first 20 minutes, then comes off so the crust can set and colour. It is forgiving and reliable, which is why it is the default here.

A baking stone or steel gives excellent bottom heat and lets you bake several loaves, but you must add steam yourself with a tray of boiling water or ice. Steam ovens and commercial decks offer precise steam injection at the moment of loading. Whatever the method, a thoroughly preheated surface and strong early heat matter more than the exact equipment.

Steam baking

Steam in the first phase of baking keeps the crust soft and elastic just long enough for the loaf to spring fully, and it gelatinises the surface starches into a thin, glossy, crackling shell. Without it, the crust sets too soon, limiting rise and leaving a dull, thick exterior. In a Dutch oven the covered environment supplies its own steam; with a stone, add a preheated cast-iron tray and pour in boiling water, or throw in a handful of ice cubes as you load.

After 15–20 minutes, remove the steam source or lid so the oven dries out and the crust can brown and crisp. Baking a further 20–35 minutes uncovered, depending on loaf size, develops colour and flavour; a deep mahogany crust generally tastes better than a pale one.

Common mistakes

The most frequent problems trace back to a few causes. A dense, gummy crumb usually means under-fermentation or a weak, under-ripe starter — give bulk more time and make sure your starter doubles reliably before you bake. A flat loaf that spreads instead of rising points to over-fermentation or too little dough strength, so shorten bulk or add folds. Not accounting for the flour and water in the starter throws hydration off; the calculator prevents this.

Other classics: baking without enough preheat or steam (poor spring, pale crust), scoring too shallow or with a blunt blade (bursting at the side), and trusting the clock over the dough. Weighing everything in grams, rather than measuring by volume, removes a surprising amount of variability on its own.

Beginner tips

Start simple: one strong bread flour, 68–72% hydration, 20% of a well-fed 100% starter, and 2% salt. Keep the dough warm and consistent, do three sets of folds, and bulk until it has grown by roughly a third and feels airy. Shape with a light hand, cold-proof overnight, and bake in a preheated Dutch oven. Change one variable at a time so you can learn what each does.

Above all, keep notes — dough temperature, timings and how the loaf turned out. Sourdough rewards observation, and a short baking log will teach you more than any single recipe. Expect your first few loaves to be learning loaves; they will still be delicious.

Professional techniques

Experienced bakers chase consistency through control. They target a specific dough temperature every bake using the DDT formula, build a dedicated levain (sometimes in multiple stages) sized precisely to the dough, and time bulk by temperature and feel rather than a fixed clock. Techniques like autolyse — resting flour and water before adding starter and salt — improve extensibility and shorten mixing.

Multi-stage levain builds let a baker refresh a small seed up to a large, peak-active levain with predictable timing, which matters at scale. Cold retarding is used deliberately to schedule production and sharpen flavour, and shaping is tightened to build maximum surface tension for a taller, more open loaf. The through-line is measurement: temperatures, weights and percentages, all tracked.

Recipe scaling

Because baker's percentages are pure ratios, scaling a sourdough recipe is straightforward: decide the dough weight you want per loaf, multiply by the number of loaves, and every ingredient grows in proportion while hydration, starter and salt percentages stay identical. A single 900-gram loaf and a batch of twelve share the exact same formula — only the absolute weights change.

This calculator scales from 1 to 100 loaves instantly. Set your per-loaf size or total dough weight, choose the loaf count, and it multiplies flour, water, starter and salt together, so a home bake and a market batch taste the same. When scaling up dramatically, remember that mixing, fermentation capacity and oven space become the practical limits, not the maths.

Storage

Cool a baked loaf completely on a rack before cutting — an hour or two — so the crumb finishes setting; slicing hot makes it gummy. Store cut-side down on a board, in a paper bag, or in a bread box at room temperature, where a good sourdough stays excellent for 3–4 days thanks to the acids that slow staling. Avoid the refrigerator, which speeds staling.

For longer storage, freeze. Slice the loaf first, wrap it airtight, and freeze for up to three months; toast slices straight from frozen. To revive a whole loaf, thaw it wrapped, then crisp the crust in a hot oven for a few minutes. Sourdough's natural acidity means it keeps notably better than plain yeasted bread.