Brettanomyces and Saccharomyces Co-fermentation

Funky mixed fermentations, for the purposes of this article, refer to fermentations that contain Saccharomyces and Brettanomyces. They do not contain lactic acid bacteria such as Lactobacillus and Pediococcus. As such, these beers may have a lightly tart flavor, but are not described as being sour (see the Mixed Fermentation page). The flavor of funky beers is often dominated by the array of flavor compounds produced by Brettanomyces (see Brettanomyces metabolism). Generically speaking, these flavors range from tropical fruits, stone fruits, smoke, barnyard animal funk, bitterness that lingers on the palate longer than hop bitterness and is accompanied by undertones of fruit, horse blanket, sweat, body odor, etc.

Brewing Methods

Conceptual graph of dynamics of funk expression and inoculation timing of Brettanomyces. Y-axis for each microbe group depicts relative activity which combines in a conceptual sense: growth, attenuation and production of flavor compounds. Plot drawn by Drew Wham based on concepts discussed in American Sour Beer

Technique	More Funk	Less Funk	Note
Inoculation timing	After Saccharomyces has finished fermentation	At the start of Fermentation	See figure 1
Brettanomyces Inoculation cell count	Lower cell count or higher cell count	Higher cell count or lower cell count	Pitching rate of Brettanomyces in secondary appears to have no measured impact on beer flavor. See Brettanomyces secondary fermentation experiment.
Strain of Saccharomyces	Phenol positive strain	Phenol negative strain	Pof+ strains of S. cerevisiae form 4-vinylguaiacol by enzymatic decarboxylation of ferulic acid
Ferulic Acid	More Ferulic Acid	Less Ferulic Acid	A precursor of 4-vinylguaiacol
Time since Inoculation	Aged Beer	Young Beer

Finishing Funky Mixed Fermentations

Bottling and Kegging

See the Packaging page.

Dosing Clean Beer with Brettanomyces At Bottling

One method that some brewers attempt is adding a small pitch of Brettanomyces to a clean beer at bottling time. This can be done either in the bottling bucket/tank, or added to each bottle individually. If adding Brettanomyces to each bottle individually, a 1 mL dosage of Brettanomyces from a starter should be enough since pitching rate seems to have little impact on the beer . Some brewers believe that adding the Brettanomyces at bottling time results in a more complex beer. It is speculated that the extra stress of pressure within the bottles helps to create this complexity.

One challenge with this approach is that it is difficult to predict how much Brettanomyces will further attenuate the beer once in the bottle. Over-carbonation and bottle bombs can easily be an issue with this method if the brewer is not careful. Each degree Plato adds ~2 volumes of CO2 . Daniel Addey-Jibb, co-owner and brewer at Le Castor near Montreal, Quebec advises that the approach that his brewery takes is to ferment their saison wort down to 1°P. Once at 1°P , the beer is cold crashed, fined, and then bottled with Brettanomyces. The beer is then stored at room temperature for three months to condition naturally in the bottle. During bottling conditioning, their Brettanomyces culture takes the beer down below 0°P, and their desired level of carbonation is reached. This process took Addey-Jibb's team dozens of trials to perfect using their specific wort recipe, saison yeast, and Brettanomyces strain. Different species or strains of Brettanomyces might ferment differently, and different wort compositions might also ferment differently. For example, Addey-Jibb's saison is mashed with malted barley, wheat, and rye at a low temperature so there are not many higher chain sugars, allowing the beer to dry out quickly . Other wort compositions that include higher chain sugars from specialty malts and/or higher mashing temperatures might ferment much slower, and thus knowing what the final gravity will be once Brettanomyces is added is difficult to know without running trials on that specific fermentation profile.

A "forced fermentation test" might help to determine the final gravity of a given Brettanomyces strain or blend of strains. Use the same wort composition as the beer in question, and pitch a large cell count of Brettanomyces. Use a stirplate if possible, and an airlock to keep oxygen out (some Brettanomyces strains can attenuate further when fermented aerobically and thus will not give an accurate final gravity reading when fermented aerobically). Keep the temperature around 80-85°F for a month or two, and then measure the gravity. Each gravity point gives produces about 0.5 volumes of CO2. Adjust the priming sugar for the rest of the batch accordingly. Use bottles that are rated for higher pressures, such as Belgian bottles or sparkling wine bottles .

For more information on bottling sour and funky beer in general, see the Packaging page.

See Also

Additional Articles on MTF Wiki

• Brettanomyces
• Saccharomyces
• Mixed Cultures
• Brettanomyces secondary fermentation experiment