Unleashing the Potential of Brettanomyces: Unique Yeast for Unique Flavors

The short answer: Brettanomyces (“Brett”) is a wild yeast that slowly ferments sugars regular yeast leave behind, so it dries beer out and adds funky, earthy, leathery or tropical fruit flavours. Use it as the only yeast in primary for fruity, less funky beers, or add it after a normal fermentation and age for months for classic funk. It lives on in hoses, gaskets and plastic, so keep separate soft parts for Brett beers; stainless steel cleans and sanitizes normally.

How you add it	Timeline	Character
100% Brett in primary	2–6 weeks	Fruity, tropical, less funky
After primary (same fermenter, or a barrel)	3–12 months	Classic funk, very dry
At bottling	Develops in the bottle over months	Evolving dryness and funk; use strong bottles

Brett was first described in 1904 at the Carlsberg laboratory, isolated from English stock ale; the name means “British fungus”. Winemakers still treat it as a fault. In beer it’s the signature of Belgian and wild ales.

Where Brett flavours come from

You taste	What makes it	Good or bad
Barnyard, leather, horse blanket	4-ethylphenol	The classic funk; strongest when Brett follows a phenolic Belgian or saison yeast
Smoke, clove, spice	4-ethylguaiacol	Same source; pleasant in balance
Pineapple, mango, tropical fruit	Esters	Most obvious in 100% Brett beers
Vinegar, nail polish	Acetic acid and ethyl acetate	A fault: Brett makes these when it gets oxygen
Cheesy, sweaty	Isovaleric acid	A fault in anything more than a trace

Choosing a strain

Culture	Character
B. bruxellensis (WLP650, Wyeast 5112)	Classic funk: barnyard, leather, some fruit
B. claussenii (WLP645)	Mild: pineapple and fruit, little funk
B. lambicus (WLP653, Wyeast 5526)	Strong, classic lambic-style funk
Bottle dregs from unpasteurized Brett beers	Whatever survived in the bottle; grow it up in a starter first

One trap: WLP644 “Brett Trois” was later found to be a Saccharomyces strain, not Brett. It’s a fruity ale yeast and won’t give Brett funk or dryness.

Three ways to use it

100% Brett in primary

Pitch Brett as the only yeast. It grows slowly, so make a big starter and give it more time than a normal one. Ferment at ale temperatures. You get a fruity, dry, mildly funky beer in a few weeks. Good in pale ales and IPAs.

After primary

Ferment with a clean or Belgian yeast. When primary is done, add Brett to the same fermenter: no need to rack. Seal it, keep it at a steady room temperature and wait 3 to 12 months. A pellicle (a white, wrinkly or bubbly skin) may form on top: leave it alone. It forms where Brett meets a little oxygen, so keep the headspace small.

At bottling

Ferment to final gravity, then add Brett along with the priming sugar, the way Orval is made. Brett keeps eating sugars the first yeast left behind, so the carbonation keeps climbing for months. Prime at the low end, use heavy Belgian or champagne bottles, and see our bottling guide.

Keeping Brett away from your other beers

• Stainless is fine. A stainless fermenter, racking arm or fitting cleans and sanitizes fully, so a Unitank can make a Brett beer and then a clean lager. Use your normal hot clean and sanitizer. See cleaning and sanitizing a fermenter.
• Soft parts are not. Gaskets, tubing, plastic fermenters, siphons and bottling wands hold Brett in tiny scratches. Keep a separate, labelled set for Brett beers: a spare set of tri-clamp gaskets and a length of silicone tubing is enough.
• Wood stays wild. Oak cubes or barrels that held a Brett beer keep it.

Troubleshooting

Problem	Cause	Fix
Vinegar or solvent	Oxygen	Seal the fermenter, keep headspace small, purge with CO₂
Gushing or over-carbonated bottles	Brett still fermenting	Bottle only when gravity is stable over a few weeks; chill the bottles you have
Mousy, stale-cracker aftertaste you only notice after swallowing	A known fault from Brett and some bacteria	Keep oxygen out and sanitation tight; there’s no quick fix once it’s there
Little funk after months	Mild strain, or a clean first yeast that left few phenols	Use B. bruxellensis, a phenolic Belgian or saison yeast first, and more time

Frequently asked questions

Is Brett a bacteria?

No, it’s a yeast. It’s often grouped with Lactobacillus and Pediococcus because they turn up in the same beers, but those are bacteria. See lactic acid bacteria.

Does Brett make beer sour?

Not much. It makes a little acid, more with oxygen, but real sourness comes from bacteria. For a sour Brett beer, use a blend that includes bacteria.

Will Brett infect my other beers?

Only through shared soft parts or poor cleaning. Keep separate gaskets and hoses, clean stainless properly, and it stays where you put it.

When can I bottle a Brett beer?

When the gravity hasn’t moved over two or three readings a few weeks apart. Brett can keep working slowly for months, and bottling early is how bottles burst.

Related guides

Wild fermentation, lactic acid bacteria, barrel fermentation, cleaning and sanitizing a fermenter.