The Apartment Homebrewer

Pitching rate is an important factor in the brewing process. Although not the only variable in clean fermentation, pitching rate plays a key role in lag-time, attenuation, and yeast-derived flavor production. From the brewing literature, “rule-of-thumb” pitching rates are tailored for harvested and re-pitched yeast on the commercial scale. However, when using lab-grown, propagated yeast cultures, often sold in liquid form to homebrewing consumers, these pitching rates are less clear and can be better qualified for small batch brewers. In this series of Small Batch Brewing, I attempt to provide clarity on pitching rates for lab-grade yeast. In particular, I hope to answer this important question: What is a good pitch rate for healthy, lab-grown yeast when pitched directly into wort without a starter? In Part 1 (linked here), I provide a short introduction to pitching rate, lab-grade yeast cultures, and their effect on fermentation. In Part 2 (linked here), I review the literature and yeast manufacturers guidelines, narrowing in on a good pitch rate for lab-grown yeast. In Part 3 (this post), I explore the considerations of these pitching rates for small batch brewing; in particular, brewers looking to direct pitch liquid, lab-grade cultures. Lastly, in Part 4 (later post), I clarify any remaining questions. As always, cheers, and happy brewing!

Saccharomyces cerevisiae (image credit: wikimedia commons)

Is one package of liquid yeast enough for a small batch even when using a lab-grade pitch rate?
Short answer: Not necessarily! As a homebrewer, you may have heard this statement before: if it’s enough yeast for a 5 gallon batch, then you should have plenty of yeast for a small batch, right? Again, perhaps. Ultimately, before you pitch, it’s best to estimate the yeast necessary to prevent under pitching. Thus, in answering this question, I’ll calculate general ranges for when direct pitching is appropriate based on several brewing variables.

How much lab-grade yeast is necessary to appropriately direct pitch into a small batch?
Unfortunately, there isn’t one simple answer. Each batch requires a tailored amount of yeast necessary for adequate fermentation. There are five main factors to estimate the necessary yeast cell count: pitch rate, batch volume, original gravity, pitching temperature, and culture viability (the last one being very important!).

Liquid yeast viability
I started with this first because the age of the yeast culture can have a big impact even in small batches (as will be seen in the tables below). Though lab-grade liquid yeast are great products and sold to contain ~100 billion viable cells at packaging, cell viability drops at a rate anywhere from 0.7% to 1% per day compounded after packaging. This calculates to ~80% viability only after one month even with proper care and refrigeration (seriously bummer!). Worst yet, after 6 months, viability drops below 30%. Further confirmation comes from White Labs. From there website:

The longer we can make the yeast last in the vial, the better shape it will be in for fermentation. After 30 days in the vial, the viability of our yeast is 75-85%, which is very high for liquid yeast. Yeast that is harvested after a brewery fermentation will typically have a viability of less then 50% after 30 days. Our high viability is due to the health of the yeast and nutrient content of our liquid at packaging.  After 6 weeks, lag time before active fermentation is usually between 15-20 hours.  The shelf life for White Labs Yeast is four months.  Yeast used after this point is usually fine, but lag times will be longer. There will be living yeast in most vials for 6-12 months, so if a starter is made to activate the yeast, successful fermentations can be carried out with aged yeast.

Overall, when considering direct pitching a lab-grade culture, packaging date is a seriously key factor.

Lab-grade yeast pitch rate
This was answered in considerable detail in Part 2 (linked here). In summary, lab-grade cultures require up to 50% less yeast than a re-pitched cultures. As such, a pitching rate of 0.5 million cells/ml/°P for warm-pitched ales and lagers and 1.0 million cells/ml/°P for cold-pitched ales and lagers is adequate for most beer styles when using lab-grown yeast. Since we intend to direct pitch liquid yeast cultures, we’ll stick with these pitching rates.

The rest of the variables?
These are essentially folded into the necessary yeast cell count calculated via pitch rate. Pitching temperature determines whether to use the warm-pitch or cold-pitch rates (with the dividing line being ~65F). Batch volume and original gravity are the two multiplicative factors to produce the yeast cell count using the temperature-decided pitch rate. Along with the viability estimate, this accounts for all the key variables, and thus onward to the final calculation. At this point, if you’re a bit confused, no worries! Check out Part 1 (linked here) for a pitch rate summary and example calculation.

Legend: Yeast viability in one month increments from packaging date for a single package of lab-grown yeast

Calculating necessary cell count for small batches
Using the five main variables, the necessary yeast cell counts for pitching are calculated for a range of beers sweeping batch volume (from 1-5 gallons) and original gravity (from 8 to 15 °P). As stated before, the pitching rate assumes lab-grade liquid yeasts for both warm and cold-pitched beers. The yeast counts are highlighted according to packaging age in one month increments as seen in the color-coded legend (right).

In Table 1 (below), the necessary yeast cells are calculated for warm-pitched beers. At first glance, this table is quite colorful. However, upon further inspection, we find some very interesting findings. Starting with the standard 5 gallon batch, one package of lab-grade yeast in mostly insufficient for warm-pitched beers even at the reduced lab-grown pitch rate. Additionally, direct pitching into a five gallon batch is only appropriate for packages that are very fresh, less than one month old. For these reasons, yeast starters are the best way to go for a five gallon batch in order to prevent under pitching. Alternatively, two or more packages may be pitched, however, I find this method to be on the expensive side. The choice is yours!

Looking at the small batches in the 2-3 gallon range, all original gravities are fully capable of direct pitching a single package while satisfying an appropriate pitching rate for warm-pitched beers. Bigger beers require greater cells pitched and as a result require a fresher culture when direct pitching. And for the one gallon brewer, you should have plenty of yeast no matter what, even in cases where the yeast packaging date is greater than 6 months old, although, I’d still use fresher.

Table 1: Yeast cells needed for pitching in warm-pitched ales and lagers. The box color represents required package age for direct pitching. Units in billions of cells.

When considering pitching at colder temperatures, the necessary yeast cells are considerably greater, and as a result less friendly to single package direct pitching. In Table 2 (below), the calculated yeast cells are considerably in the red spectrum. Essentially, even a factory fresh pack with ~100 billion cells, most cold-pitched ales and lagers for small batches are inadequately pitched with one package directly. Some possibilities for direct pitching into small batches open for lower gravity beers in the 2-2.5 gallon range. Still, when considering direct pitching into a small batch at cold temperatures, package age is the key factor, and best done with fresh yeast no older than two months. And for the one gallon brewer, all gravities are pitchable; however, even at this small of scale, package age should be considered.

Table 2: Yeast cells needed for pitching in cold-pitched ales and lagers. The box color represents required package age for direct pitching. Units in billions of cells.

What does this mean for the small batch brewer?
Well, I think there are four take-a-ways: (1) When direct pitching at adequate lab-grade rates, the small batch brewer greatly benefits by having the ability to by-pass a starter while maintaining appropriate pitching rates (2) Direct pitching lab-grade cultures is better suited for warm-pitching rather than cold-pitching. (3) Utilize your local homebrew shop or trusted online retailer to obtain fresh, healthy lab-grown yeast cultures when considering direct pitching. (4) If the yeast cell count exceeds you package age, consider making a starter or alternatively making a smaller batch.

Next Post in Series: Part 4, Additional considerations for Small Batch Brewers
In the next part of the lab-grade pitching rate series, I discuss additional information for direct pitching, including yeast life cycle strategies and re-using yeast.

What are your thoughts on pitching rates of lab-grown yeast? Leave your brewing experiences in the comment section below. Cheers, and happy brewing!

Post Sources and Additional Links for Pitching Rate Info
Wyeast on Pitching Rates: https://www.wyeastlab.com/hb_pitchrates.cfm
White Labs of Lab-grade Pitching Rates: http://www.whitelabs.com/faq/beer-amateur/pitching-rates
Yeast: A Practical Guide to Beer Fermentation: http://www.brewerspublications.com/books/yeast-the-practical-guide-to-beer-fermentation/
Talking Yeast with Wyeast from Northern Brewer: https://www.youtube.com/watch?v=lEkwp_2Yezo&list=PLgOVeEqw5B8MkKdSZVKMHWdWpxNqn3uRv
BYO: The Latest on Liquid Yeast: https://byo.com/stories/item/1487-the-latest-on-liquid-yeast

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