Converting between instant, active dry, and fresh yeast
The three common yeasts are the same organism at different moisture levels and cell viability, so swapping one for another is a question of weight, not a different recipe. Instant yeast is the most concentrated and the baseline here at a ratio of 1.0. Active dry needs about 25% more by weight (ratio 1.25) because a fraction of its cells are dormant and some never wake up. Fresh, or cake, yeast is mostly water, so you need roughly three times the weight (ratio 3.0) to match instant.
Put concretely: 10 g of instant yeast is replaced by 12.5 g of active dry or 30 g of fresh. These ratios follow the King Arthur and Lesaffre guidelines and are close enough for everyday baking; yeast is forgiving, and fermentation time absorbs small differences. If a substituted dough rises noticeably faster or slower than you expect, adjust the proof time rather than second-guessing the weights.
The other practical difference is how each yeast goes into the dough. Instant can be mixed straight into the flour. Active dry traditionally gets bloomed in warm water first, though modern active dry tolerates being added dry. Fresh yeast should be crumbled and dissolved into the liquid. The conversion handles the weight; the handling is up to you. Older equivalence charts sometimes quote a 1.33 factor for active dry — the 1.25 used here reflects current manufacturer data.
Freshness changes the picture too. Fresh yeast lasts only a couple of weeks refrigerated, while instant and active dry keep for months sealed and even longer in the freezer. If a dry yeast is near or past its date, proof a pinch in warm water with a little sugar first: if it foams within ten minutes it's alive, and if it doesn't, no conversion will save the loaf.
Worked example
A recipe lists 8 g of instant yeast, but you only have fresh (cake) yeast.
- Fresh = instant × 3.0 = 8 g × 3.0
- Fresh = 24 g
→ Use 24 g of fresh yeast, crumbled and dissolved into the recipe's liquid.