In short: To convert fresh yeast to active dry, divide by 2.5; to instant, divide by 3. Fresh yeast keeps about a month in the fridge, dry yeast up to a year sealed and about a month refrigerated once opened.
What yeast actually does
Yeast is a living micro-organism. It ferments sugars and releases carbon dioxide and aromatic compounds, which is what makes dough airy, soft and characteristically flavoured. Several types exist, and each differs in how it is stored, activated and used.
Fresh (compressed) yeast
Sold in dense blocks, usually 100–500 g. Cream-coloured, pliable and easy to crumble. Highly active, but demanding about storage: shelf life is around 30 days, refrigerated only, in tightly closed packaging. Freezing is not an option — after thawing the yeast loses activity and weeps. It is dissolved in cold or slightly warm water before being added to the dough.
Active dry yeast
Made by drying compressed yeast. It has to be activated before use: soak it in warm water or milk for 10–15 minutes. It keeps considerably longer than fresh yeast.
Instant yeast
Goes straight into the flour with no activation, and keeps up to a year in a sealed pack — about a month refrigerated once opened. Convenient, but the ordinary kind is designed for doughs without much sugar.
Osmotolerant yeast for enriched doughs
Sugar and fat bind water. In a heavily enriched dough the yeast cell has less free moisture available than in plain bread dough, so fermentation slows down. Osmotolerant strains are bred to work in exactly that environment; the manufacturer recommends them from about 5 % sugar relative to the weight of the flour.
Conversion and storage
| Type | Converting from fresh | Storage | How to add |
|---|---|---|---|
| Fresh (compressed) | — | about 30 days refrigerated, never frozen | dissolve in cold or slightly warm water |
| Active dry | divide by 2.5 | longer than fresh; refrigerate once opened | activate 10–15 min in warm liquid |
| Instant | divide by 3 | up to a year sealed, a month refrigerated once opened | straight into the flour |
| Osmotolerant | as instant | as instant | straight into the flour, for enriched doughs |
Frequently asked questions
How do I convert dry yeast to fresh
Multiply instant yeast by 3 and active dry by 2.5. Divide to go the other way, and always work by weight.
Does instant yeast need dissolving first
No, it is mixed straight into the flour. Active dry yeast does need activating in warm liquid.
Which yeast should I use for enriched dough
Osmotolerant. Ordinary yeast is inhibited by sugar, and enriched dough rises slowly on it or not at all.
Sources
- Saf-instant. The Original Gold — yeast for sweet doughs, recommended from 5 % sugar to flour weight
- Lesaffre. Saf-instant turns 50 — how instant dry yeast works and why it goes straight into the flour