Which yeast should I use, and how do they differ?

Recipes call for whichever yeast the author uses and rarely explain the substitution. The three types do the same job at different concentrations and with different handling requirements.

Step by step

1. Identify instant yeast.Also called fast action, easy bake or bread machine yeast. Fine granules, sold in sachets or tubs. Goes straight into the dry flour with no activation.
2. Identify active dried yeast.Larger granules, often sold in tins. It must be rehydrated in warm liquid with a pinch of sugar for 10 to 15 minutes until foaming, before it goes into the flour.
3. Identify fresh yeast.A soft beige block, sold at bakery counters and some supermarkets. Crumbled into warm liquid and dissolved. It keeps only two weeks in the fridge but freezes in portions.
4. Learn the conversion.1g instant equals about 1.25g active dried equals about 3g fresh. So 7g instant — one standard sachet — is about 9g active dried or 21g fresh.
5. Use liquid at the right temperature.Around 35 to 40°C for activating dried or dissolving fresh — warm to the touch, not hot. Above about 50°C starts killing the yeast.
6. Keep salt away from yeast initially.Direct contact between undissolved salt and yeast damages it. Put them on opposite sides of the bowl and mix the flour in between.
7. Adjust the quantity to the schedule, not the recipe.Less yeast for a long slow prove, more for a quick one. A loaf proved overnight in the fridge needs perhaps a quarter of what a two-hour recipe uses, and tastes better for it.
8. Test old yeast before committing.A teaspoon in warm water with a pinch of sugar should foam within ten minutes. If it does not, the yeast is dead and the loaf will not rise.
9. Store it properly.Unopened sachets keep in the cupboard. Once opened, dried yeast goes in an airtight jar in the fridge and stays good for months, or the freezer for longer.
10. Do not substitute bicarbonate or baking powder.They are chemical raising agents that act fast and produce a different structure. They cannot replace yeast in bread and yeast cannot replace them in a cake.

Tips

• 1 : 1.25 : 3 — instant, active dried, fresh. That single ratio covers every substitution.
• Warm to the touch, never hot. Above 50°C the yeast starts to die.
• Less yeast and more time makes better bread than more yeast and less time.

Common mistakes

• Using active dried yeast straight in the flour — It has a coating of dead cells that needs dissolving before the live yeast underneath can work. Added dry, a large part of it never activates and the dough rises slowly or not at all.
• Activating yeast in hot water — Yeast is killed above roughly 50°C, and water that feels hot to a finger is often above that. The mixture never foams and the loaf never rises, and the yeast usually gets the blame for being old.

If it doesn't work

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