Yeast conversion
Convert between fresh, active dried and instant yeast — as a range, because the ratio everyone quotes is a convention rather than a measurement.
What it answers
My recipe specifies a different form of yeast from the one I have. How much do I use?
What it assumes
- The conventional relative weights are fresh : active dry : instant = 3 : 1.2 : 1. THIS IS A CONVENTION, not a measured constant, and it is applied here as one.
- A ±15% range is shown around the conventional figure, because published conventions differ by roughly that much between sources.
- The mechanism behind the convention IS solid: fresh yeast is largely water and dried yeasts are not, so equal weights do not contain equal quantities of organism.
- Your packet is a better authority than this tool. Manufacturers publish usage levels for their own products and generally do not publish cross-product equivalences at all.
Read this before the number. The ratio between yeast forms is a widely used convention, not a measured constant. BakeHQ looked for an authoritative source and did not find one: Lesaffre’s own technical page for one of the world’s most-used instant yeasts states a usage level and no equivalence with fresh or active dry yeast at all. Your packet is a better authority than any website, including this one.
What you have and what you need
The answer, as a range
6–8 g
Dried yeasts contain far less water, so you need much less by weight. If you are moving to active dry, check whether your product asks to be rehydrated first.
The conventional figure is 7 g. The range is shown because published conventions differ by roughly this much between sources — a single figure would look more certain than the evidence is.
Check it against flour weight
Professional formulas express yeast as a percentage of flour, and this is the one figure here with a manufacturer statement behind it.
The working
How this was calculated
Conventional relative weights
- Formula
fresh : active dry : instant = 3 : 1.2 : 1- With your numbers
r(fresh) = 3, r(instant) = 1- Result
- convention, not a measured constant
Conversion
- Formula
W(to) = W(from) × r(to) ÷ r(from)- With your numbers
W(to) = 21 × 1 ÷ 3- Result
- 7 g
Range, because the convention is not agreed to a decimal place
- Formula
±15% around the conventional figure- With your numbers
7 × 0.85 to 7 × 1.15- Result
- 5.95–8.05 g
What the symbols mean
- W(from) — weight of the yeast form the recipe specifies
- W(to) — weight of the form you actually have
- r(form) — the conventional relative weight for that form
The three forms
Fresh (compressed) yeast
Sold as a moist block. Mostly water, so it weighs the most for the same leavening power, and it keeps for days rather than months.
Conventional relative weight: 3
Active dry yeast
Dried into larger granules. Conventionally rehydrated in warm liquid before use, though many modern products no longer require it.
Conventional relative weight: 1.2
Instant yeast
Dried into finer particles that disperse directly into flour. Needs no rehydration, and is what most 'easy bake' and 'fast action' packets contain.
Conventional relative weight: 1
Why the mechanism is solid and the number is not
Fresh yeast is largely water and dried yeasts are not, so equal weights do not contain equal quantities of living organism. That much is uncontroversial.
What is not established is a single ratio holding across manufacturers, strains and formulations. Products differ, and manufacturers publish usage levels rather than cross-product equivalences.
Fresh yeast weakens within days. An old block underperforms whatever any conversion says, and no arithmetic can detect that.
Some active dry products still ask to be rehydrated in warm liquid before use. Skipping that step changes the outcome more than a few tenths of a gram would.
What it cannot tell you
A STANDARD SACHET IS NOT A UNIVERSAL UNIT, though it is close. Sachets of instant or active dry yeast are commonly sold at 7 g, and a level teaspoon of instant yeast is roughly 3 g — so a sachet is about two and a bit teaspoons. Both figures vary by product and by how the spoon is filled, and the packet is a better authority than either. BakeHQ publishes no conversion chart because a chart implies a precision these numbers do not have.
NO AUTHORITATIVE SOURCE FOR THE RATIO WAS FOUND. Lesaffre’s technical page for one of the world’s most-used instant yeasts states a usage level of 1–3% on flour weight and no equivalence with fresh or active dry yeast whatsoever. The sites that do state a ratio are recipe publishers, which is not evidence.
Equivalence varies with formulation, strain and manufacturer. A single number that holds across all three is not established.
Fresh yeast weakens within days. An old block underperforms whatever the arithmetic says, and no conversion can detect that.
Some active dry products still require rehydration in warm liquid. Skipping that changes the result more than a few tenths of a gram would.
It says nothing about timing. Converting the weight correctly still leaves fermentation time to be judged by the dough.