Exploring Brettanomyces in Mixed Fermentation

Discover how Brettanomyces transforms mixed fermentation beers with unique flavors and aromas. Learn techniques for working with Brett strains, managing fermentation, and creating complex craft brews from expert fermentation specialist Lisa Fermenta with practical tips for both beginners and advanced brewers.

Have you ever tasted a beer with intriguing notes of pineapple, horse blanket, farmhouse funk, or aged leather? If so, you’ve likely encountered the fascinating work of Brettanomyces in mixed fermentation. Once considered solely a beer spoilage organism, this wild yeast has emerged as a prized ingredient in craft brewing, particularly in farmhouse ales, sour beers, and other complex fermentations.

As homebrewers push boundaries and seek to recreate historic styles or innovate new flavor profiles, understanding how to work with Brettanomyces (commonly called “Brett”) has become an essential skill. This comprehensive guide will explore the world of Brett in mixed fermentation, from the science behind these unique organisms to practical brewing applications that will help you create beers with extraordinary depth and character.

Understanding Brettanomyces: The Wild Card of Brewing

Brettanomyces is a genus of yeast that differs significantly from the Saccharomyces cerevisiae strains typically used in brewing. While conventional brewing yeasts are domesticated and predictable, Brett represents the wild side of fermentation – untamed, complex, and full of surprises.

The name Brettanomyces comes from the Greek words for “British fungus,” as it was first classified in British brewing environments. However, these yeasts exist naturally in various environments worldwide, from fruit skins to oak bark and traditional farmhouse brewing equipment.

Unlike Saccharomyces, which primarily consumes simple sugars, Brett has an impressive enzymatic toolkit that allows it to break down and ferment complex carbohydrates that conventional yeasts leave behind. This ability to ferment dextrins and other complex sugars makes Brett particularly useful in creating bone-dry beers with unique flavor profiles.

Brett Species and Their Flavor Contributions

Several species of Brettanomyces are relevant to brewing, each offering distinct characteristics:

Brettanomyces bruxellensis: The most common species in brewing, B. bruxellensis contributes classic “horse blanket,” “barnyard,” and “funk” characteristics along with potential for fruitiness. This species is found in traditional Belgian lambics and many American wild ales.
Brettanomyces anomalus: Often produces intense tropical fruit notes (pineapple, mango) with less intensive funk than B. bruxellensis. Some strains create wonderful stone fruit characteristics.
Brettanomyces clausenii: Generally considered the “cleaner” Brett species, offering subtle funk with pleasant fruitiness and leather notes. This strain works well for brewers seeking more approachable Brett character.
Brettanomyces lambicus: Despite its name (which comes from its presence in lambic beers), this is actually a strain of B. bruxellensis. It typically produces intense cherry pie, pie crust, and medicinal phenolic notes.

Each Brett strain creates its distinctive flavor profile through the production of compounds such as esters, phenols, and fatty acids. The specific environmental conditions during fermentation significantly influence which compounds predominate, giving brewers some control over the final flavor profile.

Mixed Fermentation: A Symphony of Microbes

Mixed fermentation involves using multiple microorganisms – often a combination of conventional brewing yeast, Brettanomyces, lactic acid bacteria, and sometimes other wild yeasts – to create complex beer profiles that evolve over time. This approach mirrors traditional brewing methods used for centuries before pure yeast culturing became available.

In a typical mixed fermentation beer, Saccharomyces does the initial heavy lifting, fermenting most simple sugars and creating alcohol. Brett then takes over, slowly working on the remaining complex sugars and continuing to develop flavors over weeks, months, or even years. When lactic acid bacteria like Lactobacillus or Pediococcus are included, they contribute acidity that complements Brett’s funk and fruitiness.

Common Mixed Fermentation Approaches

Several strategies exist for incorporating Brett into your brewing process:

1. Brett as a Primary Fermenter

Using Brett from the start of fermentation creates a different profile than adding it later. Research by Chad Yakobson has shown that Brett in primary fermentation often produces cleaner, more fruit-forward beers with restrained funk, particularly when using certain strains like B. clausenii.

This approach typically requires:

Higher pitch rates (similar to Saccharomyces ales)
Patience (Brett fermentations often start slower)
Temperatures around 68-75°F (20-24°C)
Consideration of oxygen needs (Brett benefits from slightly higher oxygen than conventional brewing yeast)

2. Secondary Brett Addition

The more traditional approach involves fermenting with conventional yeast first, then adding Brett for secondary fermentation. This method:

Creates more classic “funky” Brett character
Allows for longer aging to develop complexity
Often results in very dry, highly attenuated beers
Requires extended aging (typically 3-12 months)

3. Mixed Culture Fermentation

For the most complex expression, many brewers use custom blends containing:

Saccharomyces strains (often Belgian varieties)
Multiple Brett strains
Lactic acid bacteria (Lactobacillus and/or Pediococcus)
Sometimes environmental microbes from spontaneous inoculation

This approach creates the most complex and unpredictable results, with flavors developing and changing for months or years. It’s how traditional lambics, American coolship ales, and many farmhouse ales are produced.

Practical Techniques for Brett Brewing

Successfully brewing with Brett requires adjusting typical brewing practices. Here are key considerations for creating exceptional mixed fermentation beers:

Designing Your Recipe

When creating recipes for Brett beers, consider these factors:

Malt Selection

Base Malts: Pilsner malt provides a clean canvas for Brett expression. Pale ale malt works well too.
Specialty Malts: Use restraint with crystal malts, as residual sweetness competes with Brett character. Small amounts of wheat, rye, or oats can provide complexity.
Raw Grains: Unmalted wheat, spelt, or other grains can provide complex carbohydrates that Brett will slowly transform, creating evolving flavors.

Hop Selection

Traditional European Varieties: Noble hops like Saaz, Hallertau, and Tettnang complement Brett character.
New World Varieties: Citrusy American or Southern Hemisphere hops can enhance Brett’s tropical fruit notes.
Aged Hops: For traditional lambic-inspired beers, consider aging some hops for months before use to reduce bitterness while retaining antimicrobial properties.

Water Chemistry

Mineral Content: Moderate mineral content is typically best. Excessive sulfate can clash with Brett phenolics.
pH Considerations: Brett tolerates lower pH than conventional brewing yeast, making it ideal for mixed fermentations with lactic acid bacteria.

Fermentation Management

Successful Brett fermentation requires careful management of several variables:

Temperature Control

Primary Phase: For Brett-only fermentations, start around 68°F (20°C) and allow to rise naturally to the mid-70s°F (mid-20s°C).
Secondary Phase: Brett character develops well at cellar temperatures (55-65°F/13-18°C) during extended aging.
Temperature Cycling: Some brewers employ periodic temperature increases during long aging to reactivate Brett metabolism.

Oxygen Management

Initial Oxygenation: Brett benefits from good initial oxygenation, similar to or slightly higher than conventional brewing yeast.
Aging Phase: Once fermentation is underway, minimize oxygen exposure to prevent undesirable acetic acid production.

Patience Requirements

Brett works slowly. Expect:

2-4 weeks for primary fermentation
3-12 months for full character development in secondary
Potential continued evolution for years in the bottle

Equipment Considerations

Working with Brett requires special attention to equipment:

Separate Equipment

Many brewers maintain separate equipment for wild fermentations, including:

Dedicated plastic fermenters (Brett can penetrate microscopic scratches in plastic)
Separate siphons, tubing, and bottling equipment
Dedicated aging vessels

If dedicated equipment isn’t possible, rigorous cleaning and sanitizing protocols are essential. Oxygen-based cleaners followed by acid sanitizers provide the best defense against cross-contamination.

Aging Vessels

Brett develops different characteristics depending on the aging vessel:

Glass: Neutral and impermeable, allowing pure expression of Brett character
Stainless Steel: Similar to glass but with minimal oxygen permeability
Oak: Contributes its own flavors and microoxygenation that enhances Brett character
PET Carboys: Affordable but allow some oxygen ingress over extended aging

Brettanomyces Strain Selection

The specific Brett strain(s) you choose dramatically impacts your beer’s character. Commercial options include:

Commercial Strain Options

Wyeast 5112 (Brettanomyces bruxellensis): Classic horse blanket, barnyard funk with moderate fruitiness
White Labs WLP650 (B. bruxellensis): Intense earthy, leathery notes with moderate acidity
White Labs WLP648 (B. bruxellensis Trois): Tropical fruit-forward with mild funk
GigaYeast GB144 (B. bruxellensis): Restrained funk with cherry and stone fruit notes
The Yeast Bay Melange blend: A mix of Brett strains for complex character
Bootleg Biology Mixed Fermentation Blends: Custom blends of Brett, Saccharomyces, and bacteria

Harvesting Wild Strains

Advanced brewers sometimes harvest their own Brett strains from:

Local fruit (especially cherries and berries)
Spontaneous fermentations
Bottle dregs from commercial wild ales

Michael Tonsmeire, author of “American Sour Beers,” suggests starting with commercial strains before venturing into harvesting wild Brett to develop a baseline understanding of Brett character.

Managing Mixed Fermentation Characteristics

Creating exceptional mixed fermentation beers requires balancing several sensory aspects:

Acidity Development

When combining Brett with lactic acid bacteria:

Timing Matters: Adding bacteria after primary fermentation reduces acidity
Temperature Control: Higher temperatures accelerate acid production
Grain Selection: Highly modified malts provide less food for bacteria

Aging and Maturation

Brett character evolves dramatically over time:

Young Brett Beer: Often displays sharp fruitiness and harsh phenolics
3-6 Month Mark: Funk begins to develop and integrate
1-2 Year Mark: Complex layers of aroma and flavor emerge
Extended Aging: Continued evolution, particularly in bottles or oak

Blending Strategies

Many commercial producers of mixed fermentation beers rely heavily on blending:

Maintaining barrels of different ages
Blending young beer with mature stock
Adjusting acidity and funk levels through careful mixing
Creating consistent house character despite batch variation

Taming Brett: Safe Practices for Homebrewers

If you’re concerned about Brett “infecting” your clean beers, follow these practices:

Scheduling Strategy: Brew Brett beers after clean beers, not before
Cleaning Protocol: Use percarbonate cleaners followed by acid-based sanitizers
Replace Soft Parts: Tubing, gaskets, and plastic parts that contact Brett beers should be replaced or dedicated
Sanitization Timing: Sanitize immediately before use, not days ahead
Positive Pressure: Keep fermentation vessels under airlock to prevent airborne contamination

Tasting and Evaluating Brett Beers

Developing your palate for Brett character helps you refine your brewing approach:

Key Flavor Compounds

Ethyl Acetate: Presents as pineapple, tropical fruit
4-Ethylguaiacol: Creates smoke, clove, or bacon notes
4-Ethylphenol: Responsible for bandaid, barnyard, horse blanket aromas
Isovaleric Acid: Parmesan cheese or sweaty notes (often decreases with age)
Tetrahydropyridines: Mousy or cracker-like flavors in aged Brett beers

Evolution Timeline

Track how your Brett beers change to inform future brewing:

Note flavors at bottling/kegging
Sample periodically (every 2-3 months)
Document when peak drinking window occurs
Consider vertical tastings of different ages of the same beer

Commercial Examples to Study

To understand Brett character, seek out these commercial examples:

Orval Trappist Ale: Belgian Trappist with Brett in the bottle
Brasserie de la Senne Taras Boulba: Delicate Brett character
Allagash Interlude: Wine barrel-aged farmhouse with Brett
The Bruery Terreux Saison Rue: Brett farmhouse ale
Cantillon Classic Gueuze: Traditional lambic with pronounced Brett
Russian River Sanctification: 100% Brett fermented American wild ale
Crooked Stave Surette: Mixed culture saison with moderate acidity
Jester King Atrial Rubicite: Fruit refermented mixed culture beer

Brettanomyces represents one of brewing’s most fascinating frontiers. Working with this wild yeast requires patience, flexibility, and a willingness to surrender some control to biological processes that unfold over months or years. The reward, however, is beer with unparalleled complexity and a genuine connection to brewing traditions that stretch back centuries.

As you begin your journey with Brett brewing, remember that every batch is an opportunity to learn. Take detailed notes, be patient with the process, and develop your palate for the unique characters that only Brettanomyces can provide. The complex flavors created through mixed fermentation represent brewing at its most artisanal and expressive.

Whether you’re creating a subtle Brett-finished Belgian pale or a complex coolship-cooled spontaneous fermentation, the world of mixed fermentation offers endless possibilities for creativity and expression. The next time you open a well-aged bottle of your own Brett beer and experience how it has transformed over time, you’ll understand why so many brewers have fallen under the spell of this remarkable microorganism.

About the Author:

Lisa Fermenta is a certified nutritionist and fermentation expert who explores the health benefits of probiotic beverages. Her journey began in her grandmother’s kitchen, where she learned traditional fermentation techniques that have been passed down for generations. Lisa has studied with fermentation masters across Asia and Europe, bringing global perspectives to her brewing approach. She regularly conducts workshops on complex fermentations, emphasizing both flavor development and the science behind mixed-culture brewing. Her extensive collection of cultures includes rare Brettanomyces strains sourced from traditional farmhouse breweries across Europe.

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