Brettanomyces

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Brettanomyces

Brettanomyces, also known as brett or bretta, is a yeast that was originally thought of as a spoilage yeast. The genus name Dekkera is used interchangeably with Brettanomyces, as it describes the teleomorph or spore forming form of the yeast [1]. Known for it's barnyard, fecal, horsey, metallic or Band-Aid flavors, brett was unwelcome in most breweries. However, in some styles like Saison and Lambic these flavors add a layer of complexity to the beer. See Lactobacillus, Pediococcus, Saccharomyces, and Mixed Cultures charts for other commercially available cultures.

Brettanomyces Metabolism

Carbohydrate Metabolism

Brettanomyces strains may possess both alpha and beta glucosidases. These enzymes allow Brettanomyces strains to break down longer chain carbohydrate molecules and to liberate glycosidically bound sugars which are unfermentable to Saccharomyces yeasts.

Glycosides are sugar molecules connected to other organic compounds such as acids, alcohols, and aldehydes which are flavor and aroma inactive due to the sugar molecule attached. By cleaving off the sugar molecule through glucosidase activity, Brettanomyces species can liberate these compounds (called aglycones) into their aroma-active and flavor-active states, or states that may become flavor and aroma active through further modification[2]. Therefore Brettanomyces strains are able to produce novel flavors and aromas from hops, fruits, and fruit pits that Saccharomyces yeasts cannot produce. In addition, the liberated aroma and flavor active compounds may be further processed by Brettanomyces through ester production or destruction pathways.

Ester Production and Destruction

Brettanomyces is capable of forming several ethyl esters (derived from ethanol and fatty acids). Among these are ethyl acetate, ethyl lactate and phenethyl acetate, along with the hydrolysis of isoamyl acetate. During non-mixed fermentations where lactic acid and acetic acid are minimal to none, these esters are produced in smaller quantities [3].

Ester Precursors Flavor/Odor Threshold Notes
Ethyl acetate (fruity, solventy) Acetic Acid 33ppm (odor), 100ppm (flavor) High flavor threshold; pear-like in low amounts and nail polish in high amounts. Increases production with higher temperatures and oxygen
Ethyl lactate (fruity, buttery) Lactic Acid 0.2 ppm-1.66 ppm (odor) [4] Increases production with higher amounts of Lactic Acid
Phenethyl acetate (sweet, honey, rose flower like) Acetyl-CoA, 2-phenylethanol 3-5ppm (odor), 5-10ppm (flavor) [5] [6]
Ethyl butyrate (pineapple, mango [7]) Butyric Acid 0.4ppm (flavor) [8] Low levels of production by some species of Brettanomyces; production decreases with higher acidity [9]
Ethyl Decanoate (brandy, fruity, oily, grape) Capric Acid (Decanoic acid) and ethanol [10] Also known as Ethyl caprate, Ethyl caprinate, and Capric acid ethyl ester [11]
Ethyl caproate (sweet, fruity, pineapple, banana, apple or aniseed) Caproic acid [12] 0.2ppm (flavor) [13] Also known as Ethyl hexanoate, Ethyl butyl acetate, and butylacetate [14]
Isoamyl Acetate (banana) Acetic acid, Isoamyl alcohol 1.1ppm (flavor) [15] Produced by certain Saccharomyces strains but concentrations are generally reduced by Brettanomyces. [16]

Phenol Production

Phenols such as 4-vinylphenol (4VP, barnyard, medicinal) and 4-vinylguaiacol (4-VG, clove) can be produced in beer by the decarboxylation of hydoxycinnamic acids, which are found in malt. While both Saccharomyces and Brettanomyces strains are capable of converting hydroxycinnamic acids to their vinyl derivatives, Brettanomyces is also able to reduce these vinyl derivatives to ethyl derivatives. These vinyl derivatives have similar tastes to the ethyl derivatives but have lower flavor thresholds.

Phenol Phenol Type Precursors
4-vinylphenol (Barnyard, Medicinal, Band-aid, Plastic) Vinyl phenol P-Courmaric Acid
4-vinylguiacol (Clove) Vinyl phenol Ferulic Acid
Vinyl catechol (Plastic, Bitter, Smokey) Vinyl phenol Caffeic Acid
4-ethylphenol (Barnyard, Spicy, Smoky) Ethyl phenol 4-vinylphenol
4-ethylguiacol (Smokey, Spicy, Clove) Ethyl phenol 4-vinylguiacol
Ethyl catechol (Band‐aide, Medicinal, Barnyard) Ethyl phenol Vinyl catechol
[17] [18]

Acid Production

In the presence of oxygen, Brettanomyces strains are capable of producing acetic acid. Depending on the brewer's palate and the degree of acetic production, this can be a desirable or undesirable trait. The degree of acetic acid production varies among different brett strains. Acetic acid produced by Brettanomyces may also be used in the synthesis of acetate esters such as ethyl acetate. Brett has been shown to produce enough fatty acids in anaerobic fermentation to drop the pH to 4.0, which can also be esterified (see the ester table above) [9]. Many of these acids can have an unpleasant rancid odor and/or taste, which may be noticeable in young Brettanomyces beers before these acids are esterified.

Acids Produced Precursors Notes
Acetic Acid (Vinegar, hard boiled egg) Oxygen Increased production with higher levels of oxygen exposure [9].
Isovaleric Acid (Feety, parmesian) [19][20] Leucine Commonly described as a "spoilage" acid produced by Brettanomyces in wine, but also appears in beer.
Caproic acid (Fatty, cheesy, waxy, barnyardy) [9] Fatty acid.
Enanthic acid (Rancid odor) [9] Fatty acid.
Caprylic acid (Rancid-like smell and taste [9] Fatty acid. Also found in milk. Gives a waxy/oily mouthfeel. Flavor is more intense at low pH levels. Also called octanoic acid.[21]
Pelargonic acid (Rancid odor) [9] Fatty acid.
Capric acid (Barnyard animal odor/taste) [9] Fatty acid. Also found in milk, coconut oil, and seed oils [22].
Undecylic acid [9] Fatty acid.
Lauric acid (faint odor of bay oil or soap) [9] Fatty acid.

Other Compounds

Compound Produced Precursors Threshold Notes
Tetrahydropyridine (cheerios, mousy, urine, cracker biscuit) L-Lysine, ethanol, and oxygen See the Tetrahydropyridine page for more details. Classified as a ketone [23].

Brett Strains

Isolates

In cooperation with Funk Factory

Common Name Species Name Synonym (Strain) Name Lab/Package Flavor/Aroma Source Note
Anomala Dekkera anomala B. intermedius ECY-04 strong ester profile with some light funk and acidity beer - Adelaide, Australia
Anomalus Dekkera anomala B. anomalus Wyeast bottled stout - Burton on Trent, England
Bruxellensis Dekkera bruxellensis B. bruxellensis BSI Same as White Labs Pro-Brewers only.
Bruxellensis Dekkera bruxellensis B. bruxellensis WLP650 Barnyard Not the same as WY's Brux
Bruxellensis Dekkera bruxellensis B. bruxellensis Wyeast 5112 "sweaty horse blanket" Not the same as WL's Brux
Bruxellensis Dekkera bruxellensis B. bruxellensis ECY-05 funky with barnyard notes accompanied by some fruit isolated from Belgian stout
Bruxellensis Dekkera bruxellensis B. bruxellensis RVA 502 A medium-intensity Brettanomyces yeast strain. Will add a bit of funk when added during the secondary. Typically used in Belgian-style beers, especially lambic. A famous Trappist brewery produces its unique beer with this yeast during secondary fermentation. RVA Yeast Labs
Bruxellensis Dekkera bruxellensis B. bruxellensis GB144 Produces a sweet, slightly fruity profile with just a hint of barnyard and spicy phenolics GigaYeast
Claussenii Dekkera anomala B. claussenii BSI Same as White Labs Pro-Brewers only.
Claussenii Dekkera anomala B. claussenii WLP645 Fruity, pineapple
Claussenii Dekkera anomala B. claussenii RVA 501 A low-intensity strain. Contributions from this strain are mostly aromas of pineapple and fruit. This strain prefers higher temperatures (85º F), but will produce nice aroma and subtle flavor at normal ale fermentation termperatures (68-72º F). RVA Yeast Labs
CMY1 Dekkera bruxellensis B. bruxellensis CMY1 BSI Chad Yakobson's mutation of BSI Drie
Custersianus Dekkera custersiana B. custersianus ECY-19 light fruit and hay Bantu beer brewery, South Africa
Drie Dekkera bruxellensis B. drei BSI "highly aromatic" Isolate from Drie Fonteinen; Pro-Brewers only.
Farmhouse ? B. fantome ECY-03 Fruity and funky profile with some acidity gradually increasing over time. Aeration has more of a muted effect Isolate from Fantome
Lambicus Dekkera bruxellensis B. lambicus BSI Same as White Labs Pro-Brewers only.
Lambicus Dekkera bruxellensis B. lambicus WLP653 Horsey, Smoky, Spicy Different from WY's "lambicus"
Lambicus Dekkera bruxellensis B. lambicus Wyeast 5526 Pie-cherry Different from WL's "lambicus"
Lambicus Dekkera bruxellensis B. lambicus RVA 503 High-intensity “Brett” strain. Very spicey with “smoky” and “horseblanket” flavors and aromas. This strain is used mostly in Lambics and Flanders sour beers. RVA Yeast Labs
Naardenensis Dekkera naardenensis B. naardenensis ECY-30 strawberry, honey, ripe fruit with a tart, citrusy acidity after 6mo of aging Isolated from Dr. Pepper
Nanus Eeniella nana B. nanus ECY-24 spicy, saison-like profile bottled beer - Kalmar, Sweden
Trois Dekkera bruxellensis B. trois WLP644 Mango, Pineapple Isolate from Drie Fonteinen, DISCOVERED NOT TO BE BRETT ON 12/10/2014
Unknown Unknown Unknown RVA 804 Produces some amazing aromas of pears, and other fruit esters. We highly recommend this strain for Belgian Dubbels. This strain also makes a very nice cider. A highly flocculating, medium-high attenuating strain adds nice complexity to stouts, and Belgian Ales and Specialty Belgian Ales. Flocculation: Medium, Attenuation: 78-85%, Suggested Temp Range: 65-72°F, Alcohol Tolerance: 14%. This strain originates from local fruit trees.

Smaller Labs

Mfg Taxonomy Notes
BKYeast Brett X1 Suspected Brettanomyces Anomalus
BKYeast Brett C1 Isolate from Cantillon Iris
BKYeast Brett C2 Isolate from Cantillon Iris
BKYeast Brett C3 Isolate from Cantillon Iris
DCYeast DCY01
Saccharolicious Brett I
Saccharolicious Brett II originates from Brasserie à Vapeur in Pipaix, Belgium, and was isolated from a bottle of Cochonne

Brett Blends

Manufacturer Common Name Notes
East Coast Yeast ECY34 Twelve (12) different isolates of Brettanomyces exhibiting high production of barnyard "funk" and esters. Dryness, ripe fruit, and acidity will be encountered over a period of months and over time (>1 yr), may display gueuze-like qualities in complexity. Contains various isolates from lambic-producers, B. bruxellensis, B. anomala, B. lambicus, and B. naardenensis. For those who want the most from Brett yeast, whether a 100% Brett fermentation is desired or adding to secondary aging projects. Suggested fermentation temperature: 60-74 F. Attenuation high.
The Yeast Bay Beersel not overly funky but there is a sweaty note hanging behind lemon and citrus fruits, nice blend of subtle funk and citrus/fruit
The Yeast Bay Brussels similar to Beersel but with more funk in aroma and less fruit, complex barnyard character
The Yeast Bay Lochristi Smells of Iris C2, probably the same, subtle blend with some delicate fruit, strawberry
The Yeast Bay Amalgamation Brett Super Blend 6 Brett blend to create a dry beer with a bright and complex fruit-forward flavor and aroma, accompanied by some funk

Using Brett

Primary versus Secondary Fermentation

Brettanomyces can be pitched into a beer at many points in the beer's fermentation life cycle. If used as the primary fermenter, the beer that is produced is often fruit forward and not very funky. A large cell count will be needed (somewhere between an ale and lager pitching rate). See the 100% Brettanomyces Fermentation page for more information. If pitched into a beer that has already been fermented by Saccharomyces, a wider range of flavors including the funkier flavors can be produced (see the Brettanomyces Metabolism section above). A small cell count of Brettanomyces is plenty for creating these flavors, and normally a starter is not necessary. See the Mixed Fermentation and Funky Mixed Fermentations pages for more information on using Brett in secondary.

Starter Information

Special thanks to Nick Impellitteri from The Yeast Bay, and Shawn Bainbridge from Milk The Funk, for guidance on this section.

When pitching just Brettanomyces from a commercial pure or blended culture and no other microbes, it is recommended to make a starter for the culture. If the Brettanomyces is being pitched into secondary, no starter is necessary unless the brewer suspects that the Brettanomyces has lost a lot of viability due to age, heat exposure, etc.

There are two concepts unique to Brettanomyces compared to Saccharomyces when considering doing a starter. First, Brettanomyces performs best in a "semi-aerobic" environment. This means that the oxygen levels are low, but also not non-existent. An initial blast of oxygen into the wort, and foil left over the top to allow the air to slowly diffuse into the starter should be enough oxygen for the starter. With too much oxygen introduction, Brettanomyces can produce a lot of acetic acid (this is species dependent). Since Brett does not flocculate very well, and cold crashing a Brett starter can lead to difficulties, limiting the acetic acid production during the starter fermentation by refraining from too much oxygen exposure is advised [24].

The second aspect of Brettanomyces cell growth is that it typically takes about 7-8 days to reach it's maximum growth [25]. Thus, each step of a starter for Brett should be 7-8 days.

A Brett starter strength and size can be accurately calculated using an online yeast calculator such as Mr. Malty or YeastCalc using the 'hybrid' yeast type setting. This will calculate a pitching rate somewhere between ale and lager pitching rates, which should be adequate for 100% Brettanomyces fermentations. Maintaining a temperature of 70°-80°F/20°-26°C should be adequate for most strains. After the 7-8 days of growth, the entire starter should be pitched into the fermenter Brettanomyces is known for not flocculating well, even if cold crashed. Cold crashing will also slow the metabolism of Brett. Therefore cold crashing is generally not advisable.

It is worth noting that a "Malt Yeast Peptone Glucose" growth substrate has been shown to be a better substrate for growing an initial pitch of Brettanomyces. Specifically, when grown in wort, Brettanomyces will go through a 24 hour lag phase, a growth phase, another lag phase, and a second growth phase (all within 7-8 days). When grown in MYPG substrate, there is only a single growth phase and no lag phase, which has been reported by Yakobson to produce a larger cell count in the same amount of time [26]. Cells grown in MYPG also are better adapted to grow in wort [27]. Practical instructions for making this substrate can be found on Jason Rodriguez's blog, "Brew Science - Homebrew Blog".

Storing Brett

Store Brett at room temperature, and not refrigerated. 60-75°F/15.5-23.9°C should be acceptable (reference needed). Chad Yakobson noted that after storing Brett in a refrigerated environment, after 6 months the Brett would die. If Brett is stored cold, it will be very sluggish and slow to start fermentation. Making a starter is highly recommended if the Brett culture has been stored cold [28].

See Also

References

  1. ↑ Wikipedia. Brettanomyces. Retrieved 2/24/2015.
  2. ↑ Daenen et al., 2008. Evaluation of the glycoside hydrolase activity of a Brettanomyces strain on glycosides from sour cherry (Prunus cerasus L.) used in the production of special fruit beers. FEMS Yeast Res. 8, 1103-1114.
  3. ↑ Yakobson, Chad. Pure Culture Fermentation Characteristics of Brettanomyces Yeast Species and Their Use in the Brewing Industry. Production of Secondary Metabolites. 2011.
  4. ↑ Haz-Map, Ethyl Lactate odor threshold.
  5. ↑ Burdock, George A. Fenaroli's Handbook of Flavor Ingredients, Fifth Edition. CRC Press. 2005. pg 1521.
  6. ↑ YMDB. Phenethyl acetate.
  7. ↑ Aroxa. Ethyl butyrate. Retrieved 1/18/2015.
  8. ↑ Flavoractiv. Ethyl butyrate. Retrieved 1/18/2015.
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 Yakobson, Chad. Pure Culture Fermentation Characteristics of Brettanomyces Yeast Species and Their Use in the Brewing Industry. Pure Culture Fermentation Discussion. 2011.
  10. ↑ Wikipedia. Ethyl Decanoate. Retrieved 1/18/2015.
  11. ↑ Spedding, Gary. Flavor notes for Michigan Craft Guild Conference. 2014.
  12. ↑ Encyclopedia of Food Microbiology. Batt, Carl A. Academic Press. Sep 28, 1999. Pg 320.
  13. ↑ Aroxa. ethyl hexanoate. Retrieved 1/18/2015.
  14. ↑ Chemspider. Ethylhexanoat. Retrieved 1/18/2015.
  15. ↑ Aroxa. Isaoamyl acetate. Retrieved 1/18/2015.
  16. ↑ Spaepen and Verachtert, 1982. Esterase Activity in the Genus Brettanomyces
  17. ↑ Doss, Greg. Brettanomyces: Flavors and performance of single and multiple strain fermentations with respect to time. Presentation at 2008 NHC. pg 12.
  18. ↑ Yakobson, Chad. Brettanomyces in Brewing the horse the goat and the barnyard. 1/14/2011
  19. ↑ Botha, Janita J. Sensory, chemical and consumer analysis of Brettanomyces spoilage in South African wines. March 2010. Pg 2, 13, 17, 18
  20. ↑ Oelofse, Adriaan. Investigating the role of Brettanomyces and Dekkera during winemaking. December 2008.
  21. ↑ FlavorActV. Caprylic Acid. Retrieved 2/10/2015.
  22. ↑ "Decanoic acid". Wikipedia.
  23. ↑ Humbard, Matt. Milk The Funk Discussion. 3/10/2015.
  24. ↑ Brettanomyces bruxellensis: effect of oxygen on growth and acetic acid production. Aguilar Uscanga, Délia1, and Strehaiano. 2003.
  25. ↑ Yakobson, Chad. The Brettanomyces Project. Propagation and Batch Culture Results. Retrieved 2/17/2015
  26. ↑ Yakobson, Chad. The Brettanomyces Project. MYPG Compared to Wort as a Growth Substrate. Retrieved 2/18/2015.
  27. ↑ Yakobson, Chad. The Brettanomyces Project. Propagation and Batch Culture Discussion. Paragraph 5. Retrieved 2/18/2015.
  28. ↑ Yakobson, Chad. Presentation at 2012 Music City Brew Off. At 43:00.
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