Yeast Pitching Rate Experiment

Most homebrewers, once they get seriously involved in the hobby, will make starters for their beers. While the commercial yeast products are advertised as being “pitchable”, their cells counts don’t allow brewers to inoculate a 5-gallon batch of ale at the industry standard rate of about 0.75 billion/L-°P. And the true cell counts may be substantially lower.

This has always puzzled me. Wouldn’t it be in Wyeast and White Labs’ interests to advise pitching two – or more – of their products? Regardless, are they correct in their recommendations, or should homebrewers pitch the same amount of yeast as professionals? What are the effects of varying the pitching rate, and how noticeable are they?

Based on a rather heated discussion in the Northern Brewer forums, there is both a great deal of interest in these questions, and no consensus on the answers. A recent collaboration between Basic Brewing Radio and BYO attempted to address these issues, but was limited in both the number of participants, and the applicability of their results (since each brewed different beers). To get around these logistical shortcomings, I propose the standard engineering solution: let’s throw money at the problem.

Briefly, what I plan to do is brew a batch of beer (a tentative recipe is below), split it into two fermenters, and pitch one at the standard rate, and the other at the rate that would result from pitching a vial or pouch of commercial yeast (about 0.3 billion/L-°P). I’ll then ship three samples, identified only as A, B, and C, to as many tasters as possible. Each can then do a blind triangle test, fill out a standard survey form (also below), and return it. Ideally there will be enough respondents to be able to perform statistical analyses on the data.

If you want to get involved, it isn’t too late. Either sign up via the NB forum topic, or Contact Me directly.
 
 
Update: 03 March 2010

The test beers were brewed today. I began by building up the starters from 10 mL of slurry that was 52 days old (approx. 25 billion cells). The slurry was pitched into 500 mL of starter wort (~50B); after 24 hours this was split evenly between 400 mL (~50B) and 2.4 L (~125B) starters. These were allowed to ferment to completion, while being shaken as often as possible, then placed in a refrigerator 16 hours before pitching. All propagations were conducted in wort that was 8-9°P, with about two-thirds of the gravity coming from a mash of Castle Pilsen malt, supplemented with Briess Pilsen DME.

The actual brewing session was uneventful, although I underestimated the mash efficiency slightly. The wort was chilled to 17°C (63°F) and split between two 6.5 gallon plastic bucket fermenters. Each ended up with just over three gallons of 14.6°P (1.059) wort. They were aerated for 10 minutes with an aquarium pump and stone, then the decanted starters pitched and the fermenters placed in a room with a steady ambient temperature of 62°F.

The resulting pitching rates are 0.29 and 0.73 billion/L-°P, although the second significant digit is obviously not justified.
 
 
Update: 16 May 2010

Results, including the observations of 37 independent tasters, have been posted: Yeast Pitching Rate Results
 
 
Downloads:
Caramel Camel Amber Ale (PDF) | Sensory Evaluation Form (PDF)