Calculating amount of yeast required

[atrljoe]

I want to start experimenting with some small one gallon batches of beer. I am starting out with a Russian Imperial Stout. I am using a Wyeast liquid starter, and from what I have read they usually have 70-140 billion cells in them. That is quite a variance. How do I adequately calculate how much yeast to use? If you use a starter how do you know how many cells you created? I know if you dont pitch yeast, the fermentation wont happen, but what happens if you pitch to much?

 

[flars]

I just use a starter/pitch rate calculator. These are two good ones.
http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/
http://www.homebrewdad.com/yeast_calculator.php

Play with different volumes and OGs to get used to how they work.

Other good information on these sites also.

 

[flars]

Drastically over pitching may cause the loss of flavor development certain strains of yeast would produce. Pitching 5 times the yeast needed is getting into the drastic territory.

 

[schokie]

Even with a 3 gal batch you'll need a starter for a RIS. A 1L starter with a recently manufactured yeast package should be ok for you. Or just buy two packets.

Don't worry about pitching too much. Unless you're reusing an entire yeast cake that's not going to happen. The far more common problem is pitching too much. Even a slight under pitch will cause off flavors and problems with your yeast. As flars said, it takes a very large over pitch before you have problems.

 

[WoodlandBrew]

One of the more common methods for assessing cell count is by using a hemocytometer, although you could also use a cell density meter.

Under pitching generally results in more esters. Over pitching generally results in lower IBUs. There are several good research papers on pitch rates including this one from the MBAA:
http://www.mbaa.com/publications/tq/tqPastIssues/1996/Abstracts/tq96ab09.htm

The abstract has quite a bit of detailed information:

It was ... found that higher pitching rates led to lower bitterness unit levels in the resulting beers ... Lower pitching rates were found to result in higher intensities of the overall aroma and of hoppy and fruity aroma

 

[atrljoe]

Thanks guys, great informatio thanks flars for the links.