Homebrewing Pitch Rates
In my opinion, one of the simplest things you can do to improve your homebrew is to pitch the proper amount of yeast. Most beginner homebrew kits come with a small packet of dry yeast which the instructions tell new brewers to sprinkle over their cooled wort with no explanation or justification. As such, when brewers take the next step they grab a packet of dry yeast, or a pack/vial of liquid yeast, and call it good. After all, that's how they learned. Unfortunately, over/under-pitching is a common reason for off-flavors in homebrew, and by addressing the pitch rate you can quickly improve your beer!
Why should I pitch a certain amount of yeast?
Long story short, you want to pitch enough yeast to avoid two problems: under pitching and over pitching. Under pitching, or not pitching enough yeast, can lead to problems such as under-attenuation, stressed yeast, and off-flavors (such as increased ester production, DMS production, and "hot" alcoholic qualities). Over pitching is much harder to do, and it's debated what exactly constitutes "over pitching" on the homebrew scale. That said, over pitching can lead to decreased ester production. Personally, I think that pitching the right amount of yeast is important because of consistency. The difference, in my opinion, between a good brewer and a great brewer is consistency. Can you make the same beer twice? Are you consistently making great beer? Aiming for specific numbers helps you stay consistent, and the pitch rate is no different. Something to keep in mind is that the importance of pitching rates is somewhat debated. Some sources say that under-pitching may not be as big a deal as we think it is, while other swear by it. There are also discussions going on (fueled by this excellent article from Brulosophy) whether we should also be addressing vitality in this discussion. As with all things brewing, take notes and figure out what works for your system. Be open to change.
What are the pitching rates?
Pitching rates are determined by batch volume, gravity, and type of yeast. Lagers have different pitching rates than ales, and a high gravity beer needs more yeast than a low gravity beer. The formula for pitching rates is:
# of cells needed per mL of wort per degree Plato
Based on the beer you are making, you will adjust the # of cells needed, multiply it by the batch size in mL, and then multiply that by the OG in Plato.
Ale Pitching Rate The standard ale pitching rate formula is:
.75 million cells per mL of wort per degree Plato
Not too much to discuss with this rate, it is the standard baseline for ales.
Lager Pitching Rate
The standard lager pitching rate formula is:
1.5 million cells per mL of wort per degree Plato
Lagers are heralded for their clean, ester free aroma and crisp malt character. Lagers are also often fermented at a lower temperature than ales, hence the pitching rate. On one hand, you have more cells for the initial growth phase, where many esters are formed, and more cells with help you reduce ester production in your finished product. At the same time, the lower temperatures means that the yeast will not reproduce as quickly, and so the increased number also helps keep the growth phase short.
Note that this rate is also the rate you may want to use for 100% Brett Fermentations, according to this interview with Michael Tonsmeire, the Mad Fermentationist! For more information on this subject, check out his book American Sour Beers.
Hybrid Pitching Rate
The standard hybrid pitching rate formula is:
1 million cells per mL of wort per degree Plato
I often call the hybrid pitching rate formula the "high gravity" pitching rate. One of the reasons we discussed to pitch the proper amount of yeast is to decrease yeast stress. Because of the high ABV, there is additional osmotic pressure and stress on the yeast. High gravity beers are also notorious for having attenuation issues. By pitching a higher number of cells, you're ensuring that there is less stress on the yeast and that the beer is attenuated.
For anything 8% ABV or over, I'd consider using a hybrid pitching rate.
By pitching enough yeast, you're one step closer to providing the optimal circumstances for consistently great beer. Keep track of your pitching rates, take notes, and dial in your system. Happy homebrewing!