How much slurry should I harvest?

Collect 100-250ml of thick yeast slurry from the bottom of your fermenter. This typically provides enough cells for a standard ale batch without a starter.

How long can I store harvested yeast?

Stored in sanitised containers in the fridge, harvested yeast is best used within 1-2 weeks. Viability drops over time. After a month, make a starter before use.

Should I wash harvested yeast?

Yeast washing (rinsing with sterile water) separates yeast from trub and hop debris. It is recommended for cleaner repitching but not strictly necessary for immediate reuse.

Should I make a starter from harvested yeast?

If the harvested slurry is fresh (under 1-2 weeks old) and thick enough, you can pitch directly. For older slurry or thin harvests, making a starter ensures you have enough healthy, active cells. A 1-2L starter is generally sufficient to build up cell counts.

How many generations can I repitch yeast?

Most homebrewers safely repitch for 5-10 generations. Beyond that, genetic drift and mutation risk increases. Professional breweries may go further with strict quality control. Signs of degraded yeast include longer lag times, changed attenuation, and altered flavour profiles.

BrewCalcs

Yeast Harvest Calculator

Estimate yeast cell count from harvested slurry volume and density.

Slurry Volume

Volume measurement

Slurry Thickness

100% = thick cake, 25% = thin slurry

How We Calculate This

Slurry Cell Estimation

Thick yeast slurry contains approximately 2-4 billion cells per millilitre. Thin slurry has less. This calculator estimates total cells based on volume, density, and cell density factor, then applies a viability percentage to give the count of healthy, pitchable cells.

Formula: Total Cells = Volume × (Density% / 100) × Cell Density Factor

Viable Cells = Total Cells × (Viability% / 100)

Frequently Asked Questions

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Last updated: 2025-02-20

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