From
http://www.brewsupply.com/Newsletter/0606.html:
Spotlight on Technique: Optimum Yeast Pitching Rates
We often have beginning brewers coming to us wanting to make strong beers like IPA, or even Barleywines, who are surprised when we recommend that they make a lower gravity beer instead. The reason is simple; while the various yeast companies make excellent products, commercial reality is that they can't provide a package that contains the optimum yeast count for a low gravity batch of beer, much less something stronger. The result is that most homebrewers are chronically underpitching their yeast.
Recommended yeast pitching rates for a ale is about 1 million yeast cells for every milliliter of wort, for every degree Plato. ( Double that for lagers.). Doing the math for a 5 gallon batch of 1.044 degree wort (6 lbs of malt extract) works out to: 209 billion yeast cells. For a 5 gallon batch at 1.064 (9 lbs of extract), you'll need 304 billion cells, for a batch at 1.088 (12 lbs of extract) you'll need 418 billion cells.
According to Wyeast and White Labs, the liquid yeast packages we're currently selling contain about 100 billion cells each. So to reach the ideal pitching rate, you'd have to buy 2 packages of yeast for a recipe using 6 pounds of extract, 3 packages for a typical IPA recipe and 4 packages for a Barleywine. That's a lot of money! Dry yeast is a little better, with an 11 gm package containing over 200 billion cells. But dry yeast is available for relatively few styles, so it's not always a good solution.
A better solution is to make a yeast starter a couple of days before you brew. But even then, you may be underpitching. While a 1 pint starter will increase your yeast cell count to the point where it's closer to an optimum count, it won't get you all the way there.
So how big a starter do you need? According a Wyeast microbiologist:
1 quart starter = 150 billion cells within 24 hours
2 quart starter = 200 billion cells within 24 hours
1 quart starter pitched into a 4 quart starter = 400 billion cells
Of course, while it's fine to pour all of a smaller starter directly into your batch, a 5 quart starter would affect your finished beer, since starters are usually made from unhopped, low gravity wort. A better approach for a big starter is to make your starter 4-5 days in advance, so it will ferment completely and the yeast will settle out. Then pour off the spent wort and pitch only the yeast slurry at the bottom.
Luckily, it's easy to make a starter. Simply boil a quart or two of water, depending on how big a starter you think you'll need. Then add either 3 oz. (~1/2 cup) of DME for a 1 quart starter or 6 oz. (~1 cup) DME for a 2 quart starter. It's also good to add 1⁄4 tsp. of yeast nutrient, at this point. Boil it for 5-10 minutes, cool it, then pour it into a sanitized jug that's big enough to hold the starter and provide space for any krausen that develops. Or boil it in an Erlenmeyer flask and skip the sanitizing. Shake well to aerate it or, if you have it, use oxygen. Then pitch your yeast, cap with an airlock let the yeast go to work. The result will be better, more consistent beers!
The data used in this article (and much more) may be found here and is used courtesy of Jamil Zainasheff, who knows something about making better, more consistent beers.
