Yeast Substitution & Conversion Calculator

Yeast Guide

What should I know about Yeast Type Conversions?

Instant (fast-action) yeast: the reference point. Can be added directly to dry ingredients without proofing. Smallest granules, most active. Active dry yeast: approximately 1.25× the amount of instant. Larger granules — should be dissolved in warm water (40-45°C) for 5-10 minutes before use. Fresh yeast (compressed cake): approximately 3× the amount of instant. Soft, crumbly cake. Needs refrigeration. Short shelf life (2-3 weeks). Preferred by professional bakers — very fast and reliable. Sourdough starter is a different approach entirely, relying on wild yeast and bacteria rather than a single cultivated commercial strain.

What's the key thing to understand about Temperature and Yeast Activity?

Yeast activity varies dramatically with temperature: 0-10°C: dormant — fridge retard. 18-22°C: slow fermentation — good for flavour development. 25-28°C: optimal activity — standard room temperature bake. 30-35°C: fast fermentation — can over-proof quickly. 40°C+: yeast dies. Using temperature to control timing: for a long, overnight bulk fermentation: reduce yeast to 0.1-0.3% of flour weight and ferment at 18-20°C. For a quick 1-hour rise: use full amount (1-2% of flour) at 28-30°C. The longer, cooler fermentation develops noticeably more complex flavour than the fast, warm version, even though both use the same total amount of yeast.

What should I know about Preferments?

Preferments are small batches of dough fermented overnight, then incorporated into the main dough. They add flavour without the complexity of maintaining a sourdough starter. Poolish: equal weights flour and water (100% hydration). 0.1-0.3% yeast of poolish flour weight. Ferment 12-16 hours at room temperature. Produces open, flavourful bread (baguettes, pizza). Biga: firm preferment, 45-60% hydration. 0.1-1% yeast. Lower hydration = slower fermentation, more complex flavour. Traditional Italian breads and pizza doughs often use a biga specifically for the complex, slightly tangy flavour it develops over its slow fermentation.

What's the difference between Sourdough Starter and Commercial Yeast?

Commercial yeast advantages: predictable timing. Simple to use. Long shelf life (instant yeast: 2 years). Consistent results. Sourdough starter advantages: complex lactic and acetic acid flavour (sour notes). Lactic acid bacteria produce enzymes that improve digestibility. Lower phytic acid (antinutrient) — improves mineral absorption. Longer shelf life of the finished bread. Transferable skill — a healthy starter is for life. Sourdough disadvantages: requires 4-12 hours of fermentation, compared to 1-2 hours for commercial yeast, meaning sourdough demands considerably more advance planning for the same loaf.

What should I know about Converting Commercial Yeast to Sourdough Starter?

The ys_sourdough_out figure this calculator provides is necessarily an approximation, because commercial yeast and sourdough starter aren't really interchangeable in a strict mathematical sense — commercial yeast is a single, highly concentrated, fast-acting strain, while sourdough starter is a much more dilute community of wild yeasts and lactic acid bacteria that ferments far more slowly and produces a meaningfully different flavor profile. A commonly used practical approach when substituting starter for commercial yeast is to use a substantial proportion of mature, active starter relative to the recipe's total flour (commonly in a similar range to the inoculation percentages used in dedicated sourdough recipes), while also extending the fermentation time considerably — often from a couple of hours with commercial yeast to several hours or even an overnight rise with starter — since the wild yeast population in a starter is simply less concentrated and vigorous than a packet of commercial yeast. This conversion should be treated as a reasonable starting point for experimentation rather than a guaranteed drop-in replacement, since starter activity varies considerably between individual starters depending on their age, feeding schedule, and ambient temperature.

What should I know about Preferments (Poolish, Biga, Sponge)?

The ys_preferment_flour and ys_preferment_water outputs relate to a technique where a portion of a recipe's total flour and water (plus a small amount of yeast) is mixed in advance and left to ferment for several hours before being incorporated into the final dough, rather than mixing every ingredient together at once. A poolish is a high-hydration preferment, typically mixed at roughly equal parts flour and water by weight (around 100% hydration), giving a loose, batter-like consistency that ferments to a bubbly, slightly liquid texture. A biga is a stiffer, lower-hydration preferment, often mixed at only around 50–60% hydration, giving a dense, dough-like consistency that ferments more slowly and develops a different flavor character than a poolish. Both techniques work by giving enzymes and microorganisms extra time to break down starches and develop organic acids and flavor compounds before the final mix, generally producing bread with more complex flavor, better keeping quality, and improved dough extensibility compared to a straight dough made entirely in one step with all the yeast added at once.

What should I know about Substituting Yeast in Enriched Doughs (Brioche, Buns)?

Enriched doughs — those containing significant amounts of butter, sugar, and eggs, such as brioche, cinnamon buns, or sweet dinner rolls — ferment more slowly than lean bread dough even with the same amount of yeast, because the extra fat and sugar interfere with yeast activity and gluten development. Sugar in moderate amounts is actually food for yeast, but at the higher concentrations typical of enriched sweet doughs, it draws water away from the yeast cells through osmosis, slowing fermentation, which is why many enriched dough recipes specifically call for slightly more yeast than an equivalent lean dough, or allow for a noticeably longer rising time at the same yeast quantity. Fat also coats flour particles and can slow gluten development and slightly inhibit yeast activity, compounding the slower rise. When substituting yeast types in an enriched dough recipe (for example, swapping fresh for instant, or adjusting commercial yeast to a sourdough-based version), the general conversion ratios still broadly apply, but expect the overall timeline to run longer than the equivalent conversion would suggest for a lean dough, and judge readiness by the dough's appearance and the poke test rather than assuming a lean-dough timeline will transfer directly to a rich, enriched one.

Worked Example: Converting 7g of Instant Yeast

A standard sachet of instant (fast-action) yeast is 7g. Converting to active dry yeast, which needs roughly 25% more by weight because some cells are dormant and need rehydrating before they become active, gives 7g x 1.25 = 8.75g, commonly rounded to 9g. Converting to fresh (cake) yeast, which is used at roughly double to 2.5 times the weight of instant yeast because it has far higher water content and lower yeast-cell density by weight, gives roughly 7g x 2 to 7g x 2.5 = 14-17.5g, with most bakers using about 2x as a practical default. Going the other way, a recipe calling for 20g fresh yeast converts to roughly 20 / 2.5 ≈ 8g instant, or 20 / 2 ≈ 10g active dry.

Checking Yeast Is Still Active Before You Bake

Because yeast is a living organism that loses potency over time, especially after its packet is opened or once past its best-before date, a quick proofing test before committing a full batch of flour to a recipe is good practice. Dissolve about a teaspoon of sugar and the yeast being tested in roughly 100ml of warm water (around 37-43°C, warm to the touch but not hot enough to feel uncomfortable, since water much hotter than this can kill yeast), then leave it undisturbed for about 10 minutes. Yeast that is still active will produce a visible foamy, bubbling head during that time; yeast that stays flat with no bubbling is likely dead or too weak to reliably raise a dough, and is better replaced than risked in a full recipe.

Why Rise Time Changes When You Switch Yeast Types

Swapping yeast type for an equivalent weight doesn't always give an identical rise time, because the different forms don't become fully active at exactly the same rate: active dry yeast typically needs rehydrating in warm water for several minutes before use and can be marginally slower to get going than instant yeast, which can usually be mixed straight into dry ingredients, while fresh yeast, once properly incorporated, is often considered the fastest-acting of the three by experienced bakers. These are generally modest differences in practice rather than dramatic ones, but a recipe timed around instant yeast may need slightly longer proofing if switched to active dry, which is worth building in as a buffer rather than assuming the exact same schedule will hold.