Why yeast conversions matter
Recipes rarely agree on which yeast to use. One bread book calls for 21 grams of fresh yeast, a blog post swears by 2 teaspoons of instant, and the packet in your cupboard is active dry. They are all the same organism — Saccharomyces cerevisiae — just packaged with different amounts of water, so the trick is converting by weight rather than by spoonful. Get the conversion wrong and your dough either crawls along for six hours or explodes out of the bowl in forty minutes. The good news: the ratios between the three common yeast types are simple, stable, and easy to memorise once you understand what each product actually is.
The three yeasts, explained
Fresh yeast, also called compressed or cake yeast, is live yeast pressed into soft blocks with about 70% moisture. It is beloved by professional bakeries because it wakes up fast and gives a mild, creamy flavour, but it only keeps one to two weeks in the fridge. Active dry yeast is fresh yeast that has been dried into granules with roughly 8% moisture; the drying kills a fraction of the cells, which is why packets tell you to dissolve it in warm water first — the "proofing" step revives the survivors. Instant yeast (often sold as rapid-rise or bread-machine yeast) is dried even more aggressively into fine particles with added ascorbic acid, so it can be mixed straight into flour and works about 10% faster than active dry.
| Yeast type | Moisture | Needs proofing? | Relative strength |
|---|---|---|---|
| Fresh / compressed | ~70% | No — crumble into dough | Baseline |
| Active dry | ~8% | Yes — dissolve in warm water | ~3× fresh by weight |
| Instant / rapid-rise | ~5% | No — mix into flour | ~10% stronger than active dry |
The yeast conversion chart
The universally accepted ratios are: fresh yeast = active dry × 3, and instant yeast = active dry × 0.9 (equivalently, active dry = instant × 1.1). So one standard 7 g sachet of active dry yeast equals 21 g of fresh yeast or about 6.3 g of instant yeast. Here is a ready reckoner for the amounts home bakers use most:
| Active dry | Instant | Fresh | Typical use |
|---|---|---|---|
| 3.5 g (½ sachet) | 3.2 g | 10.5 g | Slow overnight dough, ~500 g flour |
| 7 g (1 sachet) | 6.3 g | 21 g | Standard loaf, ~500 g flour |
| 10.5 g | 9.5 g | 31.5 g | Enriched doughs (brioche, buns) |
| 14 g (2 sachets) | 12.6 g | 42 g | Two loaves or 1 kg flour |
How to substitute, step by step
First, weigh — do not scoop. Yeast density varies between brands, and a "teaspoon" can be off by 30%. A cheap digital scale that reads to 0.1 g is the single best upgrade a home baker can buy. Second, apply the ratio: multiply or divide using the chart above. Third, adjust your method: if the recipe was written for active dry and you are switching to instant, skip the proofing step and mix the yeast directly with the flour; if you are going the other way (instant to active dry), dissolve the active dry in a portion of the recipe's lukewarm water with a pinch of sugar and wait 5–10 minutes for foam. Fourth, keep everything else identical — water temperature, salt timing, and kneading — because only the yeast form changed.
A note on salt and sugar
Salt slows yeast and sugar feeds it, but neither changes the conversion ratio. Add salt after the flour and yeast are roughly combined so it does not sit in direct contact with dry yeast granules for long. In very sweet doughs (more than about 10% sugar by flour weight), consider osmotolerant instant yeast, sold as "for sweet doughs", which is bred to survive sugary environments.
Proofing temperatures and timing
Yeast is happiest between 24°C and 27°C (75–80°F). Below 20°C it works sluggishly; above 40°C it starts dying. As a rule of thumb, dough at 24°C with 1% instant yeast (by flour weight) roughly doubles in 60–90 minutes. Cooler doughs ferment slower but develop noticeably better flavour — many award-winning loaves ferment overnight in the fridge at 4°C for 12–16 hours with just 0.3–0.5% yeast. If your kitchen is cold, proof the dough in the oven with only the light on, which typically holds 26–28°C. Never rush with hot water: liquid above 50°C kills yeast outright.
How much yeast per batch of flour
For a same-day loaf, use about 1% instant yeast, 1.2% active dry, or 3% fresh yeast relative to flour weight — so 500 g of flour wants roughly 5 g instant, 6 g active dry, or 15 g fresh. For overnight cold ferments, halve those amounts. For pizza dough fermented 24–72 hours in the fridge, 0.2–0.5% instant yeast is plenty. More yeast is not better: excess yeast makes dough rise fast but taste flat and yeasty, and the crumb turns coarse.
Storage and shelf life
| Type | Unopened | Opened |
|---|---|---|
| Fresh yeast | 1–2 weeks refrigerated | Use within days; freeze up to 3 months |
| Active dry | 6–12 months in a cool cupboard | 4 months refrigerated, airtight |
| Instant | 12+ months in a cool cupboard | 4–6 months refrigerated, airtight |
To test old yeast, stir a teaspoon into 60 ml of lukewarm water with a pinch of sugar. If it is not foamy within 10 minutes, it is dead — replace it rather than doubling the dose.
Troubleshooting
- Dough won't rise: dead yeast, water too hot, or too much salt in direct contact. Test the yeast and check temperatures.
- Rose too fast then collapsed: too much yeast or too warm a spot. Halve the yeast next time.
- Alcoholic smell: over-fermented. Punch down, reshape, and shorten the next rise.
- Dense crumb: under-proofed — the shaped loaf did not get its final rise. Use the poke test: a dent that springs back slowly means ready.
Master the simple 3-to-1 and 0.9 ratios, weigh everything, and you can confidently bake from any recipe in the world regardless of which yeast it was written for.
Yeast in preferments: biga, poolish and levain
Advanced bakers rarely add all their yeast straight to the final dough. A preferment — a small pre-mixed portion of flour, water and a pinch of yeast fermented for 12–16 hours — builds flavour that straight doughs cannot match. A poolish (equal weights flour and water, 0.1% yeast) adds extensibility and a nutty aroma; a biga (stiffer, 50–60% hydration) adds strength for airy ciabatta-style crumb. The conversion ratios still apply: if a formula calls for 2 g of fresh yeast in the preferment and you only have instant, use 0.6 g. Because preferments ferment so long, tiny yeast amounts are normal — this is where a 0.1 g scale earns its keep.
Measuring yeast without a scale
A scale is best, but in a pinch: one 7 g sachet of active dry yeast is about 2¼ teaspoons; 1 teaspoon of instant yeast weighs roughly 3.1 g; 1 teaspoon of active dry about 3.4 g (the granules are denser). Fresh yeast is easiest — just cut the block by weight fractions. These are approximations, so when a recipe is yeast-sensitive (long cold ferments), borrow a scale rather than trusting spoons.
Does yeast expire?
Unopened dry yeast lasts well past its printed date if kept cool — often a year or more. Opened packets decline over months, losing roughly 10–20% of their vigour in the fridge. Fresh yeast is the fragile one: once it darkens, smells strongly of alcohol or crumbles dry, it is past saving. The foam test never lies: lukewarm water, a pinch of sugar, ten minutes. No foam, no bake — buy fresh.
High-altitude baking: adjusting yeast
Above roughly 1,000 m (3,300 ft), lower air pressure lets dough expand faster while giving it less structural support, so sea-level yeast amounts over-proof quickly. Reduce total yeast by 15–25% and start checking the dough about a quarter earlier than the recipe says — at altitude, the poke test matters more than the clock. The conversion ratios between yeast types do not change; only the total amount does.
A worked example: converting a full recipe
Take a recipe calling for 500 g flour, 21 g fresh yeast, 10 g salt and 320 ml water, and you only have instant yeast. Convert the yeast: 21 g fresh ÷ 3 = 7 g active-dry equivalent, × 0.9 = 6.3 g instant. Skip the recipe's proofing step and mix the instant yeast directly into the flour. Keep water temperature (24–27°C) and all timings identical, because the amount of leavening is now the same — only the form changed. Weigh the 6.3 g on a 0.1 g scale: eyeballing small yeast quantities is where most conversions quietly fail.