There is no denying the popularity of the new wave of “wild” brews. These cutting-edge, contemporary versions are variously inspired by the aged sour, earthy and musty brews of Belgium and Germany and old stock ales of Britain. European brewers use both anachronistic and more modern techniques today to get that natural, primitive personality, but all are firmly grounded in historical, regional brews, those made well before the true understanding of microbiology.

North American brewers, ever intrigued by experimentation and new frontiers, are increasingly integrating the methods and catalysts of yore into avant-garde wild brews. Insatiable consumers, exploring their own boundaries and dimensions, drive this movement just as fervently. Extensive cellaring, elaborate barreling and maturation schedules and the introduction of “wild” organisms all figure into this unconventional and fashionable approach.

If wild brews are in your wheelhouse, then take a shot at brewing one. Start with a simple strategy and low-risk method that leaves nothing to chance. And, if you love the earthy, musty notes mentioned above, then a beer accented with a Bretta­nomyces yeast strain should more than scratch your itch. It will unveil a novel, intriguing realm of brewing and offer a solid foundation for more complicated adventures.

What is Brettanomyces?

Brettanomyces—known in beer circles as Brett—yeasts were crucial to imparting mature flavors of many old styles of beer and ale. British stock ale, aged in wood, was coveted for its “aged” profile, a condition absent in fresh brews. It required a year minimum for flavors and aromas to develop. Stock porters and stouts were also prized for this tangy, seasoned quality.

Brett lurks in the microscopic grottoes of the cask and prefers the sleepy, sedate ambience of the maturation period, laboring well after rowdy Saccharomyces has partied out and gone to rest. It is able to ferment sugars and other carbohydrates left behind by primary fermentation and can actually metabolize some components of the wood itself.

The ubiquitous Brett is also a key contributor to the old styles of Flanders sour reds and browns and lambics. Those fermentation and aging casks played host to Brett, but also a diverse population of other organisms that contribute to the complex, assertive byproducts associated with those brews. Of course, lambic is famously inoculated in true wild fashion by the bugs, including Brettanomyces, that waft in from the surrounding fields and orchards through the open louvers of the brewery or simply reside inside the brewery itself.

The first Brettanomyces strain identified was isolated from an English stock ale cask by Danish biochemist Niels Hjelte Claussen in 1903. He dubbed it genus Brettanomyces (British fungus) and species claussenii. Further investigation unearthed strains specific to other regions and thus, types of beer. Brettanomyces bruxellensis is common to beers of Brussels and Brettanomyces lambicus, to the lambic family and Flanders sours. They are fairly similar in some regards, yet different and versatile enough to add a funky edge to a multitude of homebrews. A fourth strain, Brettanomyces bruxellensis trios, has become popular as a primary strain in the U.S.

Using Brettanomyces

Brett can be used quite effectively in a range of traditional or experimental brews and are marvelously symbiotic with many top-fermenting Saccharomyces strains. Yeast suppliers offer them in either smack packs or pitchable tubes.

Using Brett for aging and maturation is no more complicated than adding the culture after primary fermentation has finished. A fully activated Wyeast smack pack or White Labs pitchable tube is sufficient to inoculate 5 or 10 gallons of beer and can be added to primed beer ready for bottles or bulk-aging containers.

If you are concerned about cross-contamination in future brews, consider purchasing an extra bottling bucket, filling wand, siphon, carboy or corny keg for wild use. Brett’s unmistakable footprint may become aggravatingly noticeable over time in aged beer if it lingers from poor sanitizing practices.

Brett strains are high attenuators, so prime with slightly less sugar than normal. The volumes of carbon dioxide produced will vary based on residuals from the primary fermentation, original recipe and primary yeast.

Brett prefers higher temperatures than Saccharomyces. Optimal working range is roughly 70 to 75ºF, but a few degrees lower will suffice.

Brett takes a long time to work its magic. A minimum of three months is recommended under ideal circumstances by yeast suppliers, but it may take a year or more for peak character development. Sample after three months to check the progress from a sensory perspective, but also to monitor conditioning and carbon dioxide production.

Carefully consider your selection of primary yeast, especially as to how it will coexist with Brett and contribute to the overall profile. This is highly subjective and part of the personalization and experimentation process. Remember, the recipe and mash conditions will contribute crucial residuals for Brett to forage upon.

For primary fermentation with Brett, or 100 percent Brett beer, make a starter as you normally would with any other yeast. The starter may seem passive and take a few days before it is ready to pitch. Higher pitching rates are a good idea, so treat Brett as you would a bottom-fermenter, with either a larger starter or a second feeding. If the prospect of contamination makes you uneasy, use dedicated wild fermenters.

Fermentation will create a pellicle, a whitish, lumpy film on the top of the fermenter if it is used for primary fermentation, and possibly a noticeable, but lesser one in bottles of Brett-aged beer. This is normal.

Selecting the Strain

B. lambicus is the most potently funky of the lot, known for an intense barnyard, sweaty, spicy funk. It is found among the menagerie of organisms used to make Flanders sours and lambic (and their ilk) where it toils with other yeasts and bacteria, including Saccharomyces, Pediococcus and Lactobacillus. It is most effectively used in conjunction with those other bugs, but can produce a fine aged finish if used alone.

I’ve found the pure strain of B. lambicus (White Labs WLP653 and Wyeast 5526) to be a nice complement to Belgian ales made with dark and toasted malts and dark sugar. The tart “cherry pie” esters and intense earthy notes that are produced marry perfectly with those deeper-hued beers. Porter is also a good option. Be mindful that it is very attenuative and assertive, as any lover of lambic will attest.

Brettanomyces bruxellensis is the more mellow of the Belgian strains. It is also found among the microflora of lambic and Flemish sours, but less noticeable than the emphatic B. lambicus. B. bruxellensis (Wyeast 5112 or White Labs WLP650) is perfectly suited for developing reserved earthy, woody, musty character.

It performs nicely in conjunction with a number of Belgian and French Saccharomyces strains, including farmhouse, Trappist and generic top-fermenting varieties. Saison, witbier, blonde, strong golden, German gose and essentially any dark abbey, dubbel or quadrupel would be excellent candidates for a dose of B. bruxellensis. American pale or IPA could also handle a dose of this outstanding ripening strain.

Brettanomyces claussenii is also rather tame. It is available only from White Labs (WLP645), and is described as having a fruity, pineapple ester character along with a mild funk. It may also be referred to B. anomalus in some texts.

Since it was isolated from a British cask, try using it in any number of traditional British ales, such as IPA, Burton, brown, old or barley wine, or your favorite porter or stout. Earthy, herbal English hops are a must in those. The character is also a superb complement to American brews, especially those hopped with cultivars exhibiting tropical fruit or citrus notes.

Toasted oak and B. claussenii are a match made in heaven. Try oak chips that can be purchased at your local homebrew shop, or take a stab at toasting your own. One to 2 ounces per 5 gallons is the usual dose, added to the secondary or aging stage along with the Brett.

Should 100 percent Brett beer be on your radar, the recommended strains are B. claussenii and B. bruxellensis trois (White Labs WLP644). B. bruxellensis trois primary-fermented beer finished with claussenii or bruxellensis is a combination that would favor IPA quite nicely.

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This column appears in the September 2014 issue of All About Beer Magazine. Click here for a free trial of our next issue.