AHA Updates Guidelines for Yeast Handling to Enhance Repitch Quality

11 October 2026

The American Homebrewers Association (AHA) has published updated guidance on yeast handling, distinguishing between rinsing and washing and recommending the former for removing solids while the latter reduces contamination.

The AHA's article "Yeast Washing & Yeast Rinsing: What’s the Difference?" defines yeast rinsing as diluting the yeast slurry in sterile water to separate solids and dead cells, then decanting off the viable yeast to preserve a healthier, more reliable pitch for the next batch. The process can help extract and eliminate compounds that generate undesirable flavors.

"If it separates the trub, hop particles, and dead yeast from the desired yeast cells, you have probably rinsed your yeast quite well," the AHA asserts in its latest guidance.

Washing on the other hand is a preventive measure meant to reduce the risk of contamination from the repitch. The process uses food-grade phosphoric acid to target a slurry pH between 2.0 and 2.5, eliminating contaminating bacteria and killing off wild yeast.

The AHA specifies that the slurry should be chilled to between 36–40°F (2–4°C) to make it easier to control the acid, suggesting yeast washing should be done when the temperature is lower.

Rinsing and washing both aim to promote the health of the liquid yeast pitch. The AHA article recommends adding yeast nutrient and shaking or stirring the slurry to ensure the yeast is evenly dispersed.

Industry Alignment with Commercial Practices

The new AHA guidance mirrors practices reported by commercial yeast suppliers such as Berkeley Yeast and Wyeast. Berkeley Yeast strongly advises against harvesting yeast from beers with an original gravity of 18°P or higher as the high sugar content can lead to low yeast viability. Advice from Berkeley suggests the brewer should monitor the beer's alcohol content, aiming for under 6.5% ABV in the beer from which to harvest.

Wyeast also covers the temperature of the slurry: "Electrolyte is used to 'shock' the yeast, in a process similar to washing. The procedure lowers the temp of the slurry to 2 to 4 degrees Celsius to facilitate this." The chilling requirements align with Wyeast's recommendations for long-term storage, with harvested yeast kept at 34–36°F (1–2°C) for no more than two weeks.

Although Wyeast indicates that some breweries successfully repitch harvested yeast for 5–10 generations, it stresses the importance of quality control and consistency in the process to prevent off-flavors.

Operational Challenges and Best Practices

Proper sanitation is extremely crucial, according to the AHA, because contaminating microorganisms may outgrow the yeast culture. Keeping the fermentation at cool temperatures helps with yeast growth, countering stresses like heat, age, or high alcohol levels during fermentation.

In practice, beer viability will vary by batch and brewery. The AHA suggests repitching 500 ml of yeast for 1 BBL of English mild, 1.25 L for an American pale ale, and up to 2 L at high gravity. But pitch rates should be empirically determined for each individual house strain.

One practical consideration is knowing the density of the slurry, by which the brewer estimates the volume required. The standard weight for 1 L of a diluted yeast slurry with 40% yeast solids is 1.1 kg (2.4 lbs).

With the association's updated guidance, brewers at all scales now have a checklist to sustain pitch viability, limit contaminants, and avoid off-flavors. Compliance with AHA recommendations should yield a consistently better fermentation, justifying regular tests for pitch rates and verification of the generated yeast slurry.