If you attend homebrew club meetings, look at the results of homebrew contests or just hang out at your local homebrew shop for awhile, you know that most homebrewers use liquid yeast. The name “liquid yeast” is somewhat of a misnomer; the yeast itself is not liquid, it’s just suspended in a liquid media. As the chart on pages 32–34 shows, there are a wide variety of liquid yeast strains available to homebrewers.

The two biggest suppliers of liquid yeast to homebrewers are White Labs (of San Diego, California) and Wyeast (of Odell, Oregon). The Siebel Institute, of Chicago, Illinois, sells slants for $115. Their main customers are commercial breweries, although their strains are available to homebrewers.

White Labs packages their yeast in plastic tubes. The tubes are actually the blanks for larger plastic bottles, which is why the walls of the tubes are so thick. The 35 mL yeast vials are advertised to contain 35–50 billion cells, but about two months ago White Labs quietly upped their cell count to an average of 100 billion cells. “The actual counts now range from 70–130 billion,” says Chris White, president of White Labs.

Wyeast’s 125 mL Activator packs are advertised to contain 100 billion cells, but actually average around 120–130 billion cells, according to Les Perkins, microbiologist and quality control manager for Wyeast.

Wyeast strains come in a pouch with an interior pouch of nutrients. When “smacked,” the inside pouch ruptures, feeds to yeast in the outer pack and causes the whole package to swell. (The idea for smack packs, incidentally, came from David Logsdon, president of Wyeast who wanted a way for brewers to “feed” the yeast, without the possibility of contaminating the culture.)

“One thing many homebrewers might not realize,” says Perkins, “is that with fresh yeast you don’t have to wait for the package to swell. The cell count re-fers to how many cells are present before the inner pouch is ruptured. The cell count doesn’t increase much when the pack is activated. The nutrients just activate the yeast. If the yeast is fresh, you can pitch right from the outer pouch.”

At packaging, the yeast cells in both White Labs and Wyeast packages are 99% viable. Both companies date their packages so homebrewers can assess their freshness. And, since liquid yeast is raised under sterile conditions (and tested for purity), there are no contaminating bacteria or wild yeasts in the tubes or packs.

Your local homebrew shop should have its liquid yeast refrigerated and, if you order from a website, you should opt for cooling packs (if available) to keep the yeast cold during shipment. At home, store your liquid yeast in your refrigerator. If a liquid yeast package freezes, the yeast cells inside will rupture and die.

Before pitching liquid yeast to your wort or yeast starter, you should let the culture warm slowly by taking it out and letting it warm to room temperature. (See the sidebar for instructions on making a yeast starter.)

I spoke to Chris White about how White Labs makes their liquid yeast. (I also spoke to Les Perkins and Wyeast’s process is similar.) White Labs banks their yeast strains frozen in glycerol at-80 °C (-112 °F). Both White Labs and Wyeast house strains for their homebrewing line as well as yeast for commercial breweries. White Labs keeps over 400 strains at their facility; Wyeast keeps about 300.

Working cultures are grown on agar plates. (Agar plates are petri dishes filled with an agar “jello” containing nutrients for the yeast. The yeast grow on top of the “jello” in colonies, or in streaks.) (Wyeast uses slants — test tubes filled with agar that cooled while the tube rested at an angle. Thus, the agar “jello” slants down into the tube.)

Yeast samples are transferred from the plates to liquid culture and stepped up in volume over a couple weeks. Each step is bar coded to help them keep track of what stage various cultures are at. White says that, on an average week, White Labs has about 50 different strains in one stage or other of growth.

White Labs grows their yeast in an all-malt media. (Wyeast uses a malt-based media with added nutrients). In contrast, most yeast grown for industrial purposes is grown on molasses, made from sugar beets.

The specific gravity of the culture media is low compared to normal beers, and their media (and Wyeast’s) is continually-aerated. The temperature is kept higher than typical beer fermentations, but lower than 90 °F (32 °C), the temperature at which yeast grows the fastest. (Wyeast propagates their yeast at 68–70 °F (20–21 °C) and adjusts the pH of the culture during the process.) Chris White says, “We grow our yeast in a ‘brewing mentality.’ If you stray too far from that when growing yeast, they don’t perform well under brewing conditions.”

White Labs performs a variety of tests on their yeasts including examining stained cells under a microscope for viability, plating cells on various differential media for the presence of contaminating bacteria and wild yeast and screening for mutation. Before packaging, yeast go through a “mini-starvation” stage in which the yeast cells quit budding off new cells and lay down a store of glycogen, which helps them survive the time between packaging and pitching. (Wyeast also tests their yeast, including keeping smack packs from individual lots to monitor their shelf life.)  

White Labs just obtained a gas chromatogram last year and is using it to analyze the volatile production of the yeast and use that to quantify predictive measures of yeast quality.

Because liquid yeast needs to be fresh to be useful in brewing, it is grown in much smaller quantities than dried yeast, which can be stored for much longer times (up to two years). “The cost per cell for liquid yeast is much higher than with dried yeast,” says Chris White. While dried yeast sachets cost $1.50–2.00, liquid yeast packages cost about 6 bucks.

Although smaller than dried yeast facilities, liquid yeast labs are large compared to homebrew setups. Of their over 100 fermentation tanks, White Labs biggest is 10 barrels (340 gallons/1,290 L), although they are getting several 20-barrel (680 gallons/2,570 L) tanks next year. (Wyeast’s biggest tank is 20 barrels.) The biggest fermenters are used for the final growth stage of their most popular strains — for example WLP001 (California Ale) for White Labs and 1056 (American Ale) for Wyeast. For less popular strains, smaller fermenters are used. For some commercial strains at White Labs, the final volume is only 26 gallons (100 L).

Working with multiple strains day after day allows the liquid yeast companies to get to know the quirks of individual strains. Perkins reports that Wyeast is conducting experiments and finding some interesting results. “A lot of the conventional wisdom about yeast comes from studies on lager yeast used for making Pilsners. But,” he says, “ale strains don’t always behave as conventional wisdom says they should.” Wyeast has found that pitching rate affects ester production a great deal in some strains, but others are relatively insensitive to changes in pitching rate. The pH of fermenting beer affects the flocculation characteristics of some yeast strains and others show unusual flocculation patterns at different temperatures. “Some strains will drop out at a certain temperature, but then go back into solution if you lower the temperature.” Perkins said Wyeast is going to continue their experiments and they will be releasing the results to homebrewers when the studies are complete and they can state the results with confidence.

Liquid yeast companies have brought a lot of strains to homebrewers — and they are continuing to develop more. White Labs recently introduced three Brettanomyces strains for homebrewers interested in lambics and “wild” beers. And, they have recently released a clean ale strain (WLP060) that White says works great for Kölsches. Wyeast plans to release a Bière de Garde strain (3725) and a farmhouse ale strain (3726) soon.
    
    Chris Colby thanks Dr. Chris White and Les Perkins for their help.