Pitching yeast requires accurate measurements in order to quantify how many yeast cells are introduced into a batch for fermentation. This is commonly referred to as the pitch rate. A pitch rate should be treated as any other type of ingredient measurement; i.e. grist percentages, hop additions, water volumes. Accurate rates are key for consistent fermentation performance and flavor.
Though, the initial pitch rate does not equal the total cell population that will be fermenting your batch of beer. It’s important to understand that yeast will grow after pitching, so be sure to pay attention to the levers that control that growth like oxygen, temperature, and nutrients. Accurate, and consistent pitching and yeast growth will allow you to nail the recipe every time.
Reference pitching rates are common depending on the:
Ale yeast fermented in the 66-72℉ (18-22℃) with standard original gravities between 10P (1.040) and 18P (1.072) often get a 0.75 million cell/mL/P or 7.5 million cells/mL pitching rate recommendation. If you bump up that original gravity about 18P (1.072), the recommendation is bumped up as well to nearly double the recommended rate, 1.5 million cells/mL/P or 15 million cells/mL.
Lager yeast fermented in the 48-55℉ (9-12℃) range requires a larger pitch rate due to less growth from the cooler temperatures. Expect recommendations similar to high gravity ales, 1.5 million cells/mL or 15 million cells/mL.
Read below to learn more about pitching rates and where common mistakes may occur when dialing in these measurements in your brewery!
Though the referenced recommendations above are great starting points for determining a target pitch rate, it’s important that brewers continue tweaking and perfecting this measurement and the parameters that control yeast growth for every recipe. Each beer is unique and an assumption of a “one size fits all” ingredient recommendation simply will not make the best tasting and performing batch.
A common mistake to avoid is simply pitching and forgetting. It is important to continue fine-tuning and adjusting this part of the brewing process until you nail the exact flavor profile for the style.
Another mistake to avoid is underpitching high gravity worts, which may happen even if unintentionally. Due to the increased requirement of yeast to properly ferment these beers, breweries often use methods to grow yeast cultures in-house rather than purchasing fresh pitches directly from a supplier. This can be done by propping the yeast in smaller batches, or simply fermenting a different lower gravity beer and using the harvest to supply yeast for this high-gravity batch.
Data collection and tracking in the form of cell counting and viability is key here and can often be overlooked. It’s important to ensure the culture is healthy and has actually grown to the extent intended.
A common mistake seen here is a lack of data to inform the brewer that the culture is actually not sufficient for a high-gravity fermentation, and upon pitching displays severe under-pitching side-affects such as stalled or sluggish fermentation, unintended flavor profile, and under attenuation. The high osmotic pressure from this dense, sugary wort along with the high ethanol stress lead to a greater demand for an increased total cell population, yet growth is hindered by these stressors.
Be sure to pitch enough yeast to ensure this total cell population is reached.
On the other side of underpitching comes the negative effects of overpitching.
A mistake commonly seen when transferring yeast cone to cone, or simply harvesting a brink full of yeast and pitching the entire culture regardless of cell counts.
Yeast that is overpitched multiple generations will lead to a slurry of older yeast cells. In these conditions, cells divide less due to the excess population. As cells divide less, older cells remain from generation to generation causing the culture to age quicker and reduce the amount of use achievable.
This over-pitching will also suppress ester production due to the hindered yeast metabolism and lack of growth. If you may suspect this to be an issue, look out for poor flocculation or a thinner mouthfeel in the beer.
Viability and vitality are absolutely critical to consider when determining how much yeast is required for the next fermentation.
Viability is a measurement of the amount of living yeast cells in a culture. This can be determined by staining yeast cells and identifying how many are unable to expel a dye from the cell. Those that can not are considered dead. The reason viability is so important for pitching rates is because the amount of yeast capable of fermentation for an 80% viable versus 90% viable culture will be greatly different.
Vitality describes the health or fitness of a yeast cell. These cells can be viable, or living, but display poor fitness and cause issues in subsequent fermentations. It is a bit more difficult to measure vitality in comparison to viability. A recommended method that generally supports a culture’s fitness is evaluation of the prior fermentation.
Consistent, quick gravity and pH drops in the first 48-72 hours of fermentation signals a healthy culture. As long as the rest of the fermentation progresses as intended and the yeast is not negatively affected by harvest or storage, the fitness should carry on to the next fermentation.
It is not recommended to adjust pitch rates for an unhealthy culture if the fermentation performed poorly, rather simply restart with a fresh culture for the next fermentation.
If you suspect any of these common mistakes may be occurring in your brewhouse, don’t fret! A few quick adjustments will ensure you are back on the right track. Follow this checklist for dialing in your pitch rate and ensuring you are hitting that measurement every time: