Shopping for Flavor
How does a brewer shop for the flavors, aromas, attenuation and other yeast-derived qualities he or she wants in the finished beer? He could locate a commercial beer with the right flavor profile and grow the yeast from the living cells floating in the brew: beers that are cask- or bottle-conditioned (sometimes labeled as “on lees” or “sur lies”) still contain live yeast. Or he could let a commercial or government yeast laboratory do the hard work of isolating desirable yeast cells, growing colonies from single healthy cells, and maintaining the pure strains in good condition until needed.
These labs serve as banks to propagate and store popular commercial strains of yeast, as well as proprietary strains developed by individual breweries. A large brewery can afford its own quality control division to monitor the yeast for contamination by bacteria or wild yeast, or mutations that can start to influence beer flavor. However, smaller breweries and homebrewers will turn to commercial labs to provide the quality control and support.
David Wendell of Wyeast Laboratories in Mt. Hood, OR, is accustomed to steering brewers, and especially homebrewers, towards yeast strains that will give the desired outcome. “Often they know a commercial beer that is similar to the taste they want,” he says. “Or they are looking for a particular profile, for example, if a beer has a fruity, dry character, a signature ester profile. Or they have more technical requirements, maybe a highly flocculant yeast”—meaning a yeast that clumps together after fermentation.
Homebrewers may have misconceptions about yeast. Wendell often fields the question “How much alcohol strength can I get with this yeast?”
“The answer,” he says “is that you can make strong beer with almost any strain if you pitch properly [add enough yeast, but not too much], aerate properly, use the ideal temperature, and the yeast is unstressed [hasn’t been through a large number of cell divisions].”
It’s worth remembering, however, that alcohol may be a desirable byproduct as far as the human beer drinker is concerned, but from the yeast’s point of view, alcohol is a toxic waste, and yeast strains vary in their ability to tolerate rising levels of alcohol. High alcohol concentrations will shut down, then ultimately kill off the yeast. Brewers who are aiming for very high alcohol beers will often turn to champagne yeasts, which are more alcohol tolerant.
The yeast requirement of homebrewers and commercial brewers will be very different. Joane Carilli, with White Labs, a yeast laboratory and bank in San Diego, CA, says “Home brewers are making five gallons at a time in your house. Homebrewing is not commercial brewing.”
Homebrewers can experiment with a different yeast strain for every beer, but a commercial brewery will generally be more conservative. “One ale strain can make a good range of beers,” says Wendell. “Production breweries that are making beer day in and day out will keep one yeast they know well and use it for all their ales. They’ll need a pilsner strain as well.”
Carilli knows that, despite the high-tech capabilities of modern yeast propagation, there’s still as much art as science in brewing. “As much as brewers want to control it, yeast is a living organism, and the good brewers know all they can do is manage it. The best brewers never forget that.”