How fast does yeast viability decline?

Liquid yeast loses roughly 21% viability per month when stored at 2-4°C. Dry yeast retains viability much longer — 1-2 years when sealed.

Can old yeast still be used?

Yes, but you need a larger starter to grow enough cells. Yeast under 6 months old can usually be revived with a proper starter.

How should I store yeast?

Refrigerate at 2-4°C. Do not freeze liquid yeast. Keep sealed until use. Store dry yeast in a cool, dry place.

Does storage temperature affect viability?

Yes, significantly. Yeast stored at the recommended 2-4°C loses viability much slower than yeast stored at room temperature. Never freeze liquid yeast as ice crystals damage cell walls. Keep yeast refrigerated from purchase until use.

Is dry yeast viability the same as liquid?

No, dry yeast retains viability much longer. Properly sealed dry yeast can last 1-2 years at room temperature and even longer refrigerated. This calculator uses liquid yeast decay rates. For dry yeast, viability loss is negligible within the expiry date.

BrewCalcs

Yeast Viability Calculator

Estimate yeast viability based on production date and storage.

Age

Age of the yeast packet since manufacture

Initial Cell Count

Cell count stated on the packet

How We Calculate This

Viability Decay

Viability decreases exponentially over time using the Zainasheff model: Viability = 100 × decayRate^months. The default decay rate of 0.79 represents approximately 21% loss per month. A storage temperature factor greater than 1.0 simulates warmer conditions (accelerated decay); less than 1.0 simulates colder-than-ideal refrigeration.

Frequently Asked Questions

Related Calculators

Yeast Starter Calculator

Calculate starter size and steps to grow enough yeast cells.

Pitch Rate Calculator

Calculate optimal yeast pitch rate for ales and lagers.

Fermentation Temperature Calculator

Find optimal fermentation temperature ranges for different yeast strains.

Yeast Cell Count Calculator

Calculate total yeast cells needed from OG, volume and pitch rate.

Yeast Propagation Calculator

Plan multi-step propagation to build yeast from a small culture.

Last updated: 2025-02-20

All calculations are estimates. Always verify values and adjust based on your equipment and ingredients.