Determining Proper Yeast Pitch Rates

By Erik Fowler, Education & Engagement Curator at White Labs

Yeast starters are used to increase cell counts from an initial lab-grown pitch, and if done properly, may result in double the growth in 24 hours. A wonderful feature of White Labs pitchable yeast is that the volume of yeast in their PurePitch® and vial packages can ferment up to 5 gallons (18.9 L) of wort at 1.048 or lower specific gravity without the need for a starter.

The general rule of thumb for pitch rates is 1 million cells per milliliter of wort per degree Plato of original extract. These rates are based on re-pitching and assume the yeast has already experienced the stressful conditions of fermentation. Lab-grown yeast is of much higher quality than the yeast at the bottom of a fermenter and, therefore, fewer cells are needed to ferment your wort. Here are a few attributes that contribute to the high quality of lab-grown yeast:

Grown in the presence of oxygen: Yeast needs oxygen to grow efficiently and produce additional cells with strong cell walls. These cell walls help keep yeast stress-tolerant, which is key for fermentation success. An oxygen-rich environment produces healthy and happy yeast.

Get Free Yeast!

Join or renew your AHA membership in October and we’ll mail you a coupon for a free packet of White Labs yeast when you use offer code WHITELABS.

Redeem the coupon at your local homebrew retailer and get your brew on with one of White Labs’ Core Strains or try a speciality strain from one of the Vault Seasonal Releases.

Redeem Offer

Low-alcohol environment: Believe it or not, yeast prefers to be in a low- or no-alcohol environment. High levels of ethanol can be toxic to brewer’s yeast, which is why monitoring levels of ethanol production during lab propagation is important.

Pure culture: The more a yeast is handled, the higher the risk of contamination. This means non-sterile storage and propagation can lead to contamination and off-flavors in your finished beer. Lab-grown yeast benefits from being grown and handled in clean rooms, free from contaminating microorganisms.

High viability (95%+): Viability measures the fraction of live cells present in a given population. It is calculated by dividing the number of live cells by the total number of cells. Low viability can result in incomplete fermentation (or a stuck fermentation) and off-flavor production, including high levels of fusel alcohols, diacetyl, and acetaldehyde. Yeast with high viability is important to ensure a clean fermentation, correct attenuation, and proper flocculation. It is always important to check best-by dates to ensure your yeast is within the manufacturer’s suggested use-by date.

A starter may be appropriate for larger batch volumes, higher original gravities, or lager beers. For lagers, it is generally suggested that the pitch rate be multiplied by 1.5 or 2 times the pitch rate for an ale of the same original gravity. To avoid making a starter or pitching more yeast, some homebrewers pitch at a warmer initial temperature (62–68°F) and hold for 24 hours before cooling to the optimal fermentation temperature.

Below, you’ll find a chart of suggested pitch rate volumes based on starting gravity:

For Batch Size:  up to 1.048 SG 1.050-1.065 SG Over 1.065 SG
5 gallons (20 L) 1 package, no starter 1 package, 1 L starter 1 package, 2 L starter
10 gallons (40 L) 2 packages, no starter 1 package, 2 L starter 1-2 packages, 4 L starter
15 gallons (60 L) 3 packages, no starter 1 package, 3 L starter 2 packages, 6 L starter

There are many things to consider when pitching yeast, and while preparing a starter can be helpful for higher gravity beers, it may be unnecessary for average-strength wort.

Homebrewers Association
Homebrewers Association

Homebrew for the holidays. Free gift with an AHA membership gift card!