Fresh, instant dry or active dry yeast for pizza

The short answer

Pizza yeast is a microscopic fungus, Saccharomyces cerevisiae. It comes in three forms: fresh, instant dry and active dry. They are the same cells with more or less water removed, which is why the amount changes. I work with fresh yeast; to replace it, I divide the amount by 2 to 3 for instant dry and by 2 for active dry. The yeast converter does the maths for you.

What yeast does in the dough

Yeast feeds on the simple sugars in flour and turns them into three things:

1. carbon dioxide, the gas that inflates the dough;
2. ethanol;
3. acids and by-products, which partly evaporate during baking and give the crust its flavour and aroma.

That is alcoholic fermentation. But yeast does more than raise the dough: through those by-products it also takes part in maturation, the development of flavour. Fermentation and maturation move forward together, as I explain in fermentation and maturation.

The three forms of yeast

Fresh yeast

My favourite. It is sold in blocks and, when it is really fresh, it crumbles easily between your fingers. In my recipes I dissolve it in the water before adding the flour, or crumble it straight into the mixer bowl.

Instant dry yeast

It comes as small, slightly elongated granules. Its dose sits between half and a third of the fresh amount. As a practical benchmark I use 3 g fresh = 1.2 g dry, which is a division by 2.5.

Active dry yeast

Its cells are alive but dormant: drying has put them to sleep. Before use, wake them up for 10 to 15 minutes in water between 30 and 43 °C (86–109 °F). The dose is generally half the fresh amount.

Activity and temperature

Yeast activity follows temperature: the warmer the dough, the faster the yeast works.

• At 4 °C (39 °F) and below, fermentation activity is zero. A fridge that is too cold stops the dough instead of slowing it.
• Between 6 and 8 °C (43–46 °F), the ideal range for a fridge rest, fermentation carries on, slowly.
• At room temperature, it speeds up, all the more so in a warm kitchen.

That is why temperature, far more than the amount of yeast, is what drives the dough. I cover this in temperature drives the dough. It is also why a dough heading for the fridge needs a pause at room temperature first: without it, fermentation may never get going.

Why the dose depends on the fermentation you want

Yeast drives gas production throughout the whole process. The right dose therefore depends first on how much fermentation your pizza needs, then on the time and temperature the dough has to get there.

These are the fresh yeast doses in my recipes:

For the same recipe, the season matters too: when it is cold I add a little more yeast, when it is hot I use less.

The yeast amount calculator gives you that starting point, fridge hours included.

Yeast and salt

Salt slows yeast activity: that is one of its four jobs in the dough. People often say it "kills" yeast. In practice, if you add the salt at the end of kneading, or mix everything together straight away, it has no effect on the rise. In my recipes the yeast goes in with the flour and the first part of the water, and the salt only comes later, dissolved in a little water. More in salt, water, malt and oil.

Storing fresh yeast

Fresh yeast is alive and perishable:

• in the fridge, in an airtight container, it keeps one week to 10 days;
• in the freezer, crumbled first into a container, it lasts several months, so you always have some to hand.

Active dry yeast keeps for several months in a cool place such as the fridge. Respect its use-by date and throw it away once that has passed.