Yeast Harvesting and Reuse

Why Reuse Yeast

Yeast is a renewable resource. Harvesting yeast from one batch and pitching it into the next saves money (no new yeast purchase), provides a strong pitch of healthy, acclimated cells, and can improve beer consistency over multiple generations.

Methods of Harvesting

Slurry collection (bottom cropping): After primary fermentation, rack the beer off the yeast cake at the bottom of the fermenter. Collect the slurry in a sanitized jar. This is the simplest method but collects a mixture of yeast, trub, and hop debris.

Top cropping: During the peak of fermentation, some ale strains rise to the surface in a thick krausen. Skim this foam with a sanitized spoon and collect it. Top-cropped yeast is cleaner and more vital than bottom-harvested slurry because it contains the most active, flocculant cells.

Decanting from a starter: If you made a yeast starter, chill it in the refrigerator for 24 hours. The yeast settles to the bottom. Pour off (decant) the spent starter liquid and pitch the concentrated yeast cake.

Yeast Washing

Yeast washing separates yeast from trub (hop debris, protein, dead cells). The process:

1. Collect the slurry in a sanitized jar
2. Add sterile (boiled and cooled) water — about 3x the slurry volume
3. Shake and let settle for 20-30 minutes
4. The heavier trub settles first; yeast remains in suspension
5. Pour the milky yeast suspension into a new sanitized jar, leaving trub behind
6. Repeat if needed for cleaner yeast
7. Refrigerate and use within 2-4 weeks

How Many Generations

Yeast can be repitched for 5-10 generations without significant drift, provided sanitation is impeccable and the yeast is stored properly. Professional breweries routinely repitch for dozens of generations.

Over many generations, yeast populations can shift: mutation, selection pressure, and contamination accumulate. Periodically starting from a fresh culture ensures genetic fidelity to the original strain.

Storage

Short-term (1-4 weeks): Refrigerate harvested yeast in a sanitized, sealed jar. Use within a month for best viability.

Medium-term (1-6 months): Store in the refrigerator with a layer of sterile wort on top (the liquid protects cells from oxygen). Make a starter before pitching to assess viability and grow the cell count.

Long-term (6+ months): Freeze yeast with glycerol as a cryoprotectant (15% glycerol solution, stored at -4 F). Or maintain a yeast bank on agar slants/plates. Advanced techniques that require sterile lab practices.

Practical Tips

Harvest from lower-gravity, lightly hopped batches — these provide the cleanest, healthiest yeast. Avoid harvesting from heavily dry-hopped, high-gravity, or spiced beers. Label every jar with strain name, harvest date, and parent batch.

The Economics

A single liquid yeast package costs $7-12. Harvesting provides free yeast for multiple subsequent batches. Over a year of regular brewing, yeast reuse can save $100+.