When is the best time to harvest yeast from the tank?

Harvesting yeast at the point when attenuation is three-quarters of the way to final gravity is optimal because the yeast has had sufficient time to consume fermentable sugars and is typically in a healthy and viable state. At this stage, the yeast is actively flocculating and settling, making it easier to collect without significantly impacting the beer or introducing off-flavors.

Harvesting too early, such as at the very beginning of fermentation or when attenuation is only halfway to final gravity, results in recovering yeast that may not be fully active or may still be in a stressed state due to higher levels of residual sugars and higher fermentation by-products. Additionally, yeast harvested after fermentation is completed may not yield as robust a culture, as some of the yeast may have been stressed or may already be starting to autolyze, impacting its health and viability for future pitches.

Collecting yeast at this optimal point helps ensure that the yeast is in prime condition for future uses, contributing to consistent fermentation and quality in future brewing batches.