The 3 : 1.5 : 1 rule
Fresh yeast is mostly water, so it's the weakest by weight; instant is the driest and strongest. As factors of fresh: active dry is about ×0.4, instant about ×0.33. To go the other way, divide. The differences come down to water content and the share of live cells.
Substitution chart, by recipe amount
| Fresh | Active dry | Instant | Typical use |
|---|---|---|---|
| 5 g | 2–2.5 g | 1.5 g | Rolls, small loaf |
| 10 g | 4–5 g | 3–3.5 g | Standard wheat loaf |
| 20 g | 8–10 g | 7–8 g | Rye loaf, enriched dough |
| 30 g | 12–15 g | 10–12 g | Large batch of dough |
Rough teaspoon guide: 1 tsp instant is about 3 g, 1 tsp active dry about 3 g, so a 7 g packet of instant replaces roughly 21 g of fresh.
What changes besides the amount
- Adjust the time, not just the weight. Swapping fresh for instant without shortening the rise leaves dough under-fermented and flat in flavour.
- Water content drives the ratio. Fresh is 70–75% water, active dry 8–12%, instant 4–7% — which is why less dry yeast does the same job.
- Heat kills yeast. Growth peaks at 32–35 C; above about 55 C the cells start to die, so keep proofing water warm, not hot.
- Test old yeast. Stir 1 g into 50 mL of warm water; lively foam within 5 to 10 minutes means it's still good.
Sourdough starter as a substitute
A live starter can stand in for commercial yeast, but its strength varies with how recently it was fed. As a starting point, replace 10 g of yeast with 40 to 80 g of active starter and expect an extra 2 to 4 hours of rising, plus a tangier flavour.
Common questions
How much active dry yeast replaces fresh yeast?
Use about 40 percent of the fresh weight. For 10 g of fresh yeast use roughly 4 g of active dry, or 3 to 3.5 g of instant.
Can I swap instant and active dry one for one?
Close enough for most doughs. Instant is a little stronger and works about 15 percent faster, so the dough may rise sooner. If timing matters, add 10 to 15 percent more active dry or allow a bit longer.
Do I need to proof the yeast first?
Active dry benefits from dissolving in warm water at around 40 to 43 C for a few minutes. Instant and fresh can go straight into the flour.
