Craft Beer Yeast Handling (1/3) - Types of Brewery Organisms

• Brettanomyces

Figure 1 - B. bruxellenis from DME Agar at 800x Light Magnification (Bootleg Biology, 2019)

A genus of yeast which was first documented to contribute to stock ales of the 19th century, it is responsible for part of the terroir of the tertiary fermentation of Lambic and Flanders ales. The genus consists of five species with two found in the brewery, B. bruxellensis and B. anomalus. Considered a contaminant as it can contribute undesirable flavours and aromas; it has been viewed as a new type of yeast for experimentation by craft brewers (Yakobson, 2012). It can be used to increase profile complexity. Brettanomyces is an asexual budding anamorph and can ferment in aerobic and anaerobic conditions. Brettanomyces follows similar pathways to Saccharomyces; however, Brettanomyces can produce more phenolic compounds such as 4-ethylguaciacol and 4-ethylphenol and more esters such as ethyl caproate, ethyl caprylate, and ethyl decanoate (Tyrawa, 2019).

• Lactobacillus

Lactobacillus is a genus of bacteria of a group known as lactic acid bacteria (LAB). Other LAB used in food fermentation include Lactococcus, Streptococcus, Pediococcus, and Leuconostoc. The metabolic pathways for LAB are glycolysis, lipolysis, and proteolysis, which is the formation of lactic acid from sugar, fat, and protein, respectively. Other fermentation products include diacetyl, acetoin, acetaldehyde or acetic acid (Bintsis, 2018). Species of lactobacillus found in a brewery setting include L. brevis, L. lindneri, and L. delbrueckii. Lactobacillus are rod-shaped, facultatively anaerobic, and gram-positive. Lactobacillus grow best near 30°C with a pH between 4.0-5.0 (White, 2012). Considered a contaminant for brewing applications, there are several styles of beer that require Lactobacillus. Examples include Berliner Weiss, Flanders Red Ale, Oud Bruin, Lambic, Gueuze; it can contribute to Witbier and Saison; and used in styles of Gose and Litchtenhainer (Strong and England, 2015). Barley malt has populations of lactobacillus on the husks. Some brewers will use a small amount of malt to inoculate unhoped wort for souring, this can aid for mash or kettle acidification (White, 2012).

• Pediococcus

Pediococcus is a genus of coccocoidal or ovid shaped LAB. They are gram-positive, produce lactic acid from glycolysis, and grow best at a pH between 4.0-5.0 (Priest, 2012). They are non-motile and non-spore forming; typically, they do not produce carbon dioxide, ethanol, or acetic acid (Wade et al., 2018). Considered a contaminant apart from certain sour beers, as they contribute diacetyl, turbidity, and acid formation; as well as they form extracellular polysaccharides which appear as a “ropey” viscous substance (Priest, 2012). Due to the division mechanism of Pediococcus cells, they often appear to be in small clusters and are the only LAB in beer to do this, which allows identification with a microscope (Wade et al., 2018).   

• Saccharomyces

Saccharomyces is a genus of unicellular fungi known as "yeast". The most common species used can be classified as S. cerevisiae, S. pastorianus, or S. cerevisiae diastaticus. Saccharomyces perform a fermentation of short polysaccharides to produce alcohol, carbon dioxide, and flavours and aromas that are associated with beer. Strains from this genus are anamorphs, where aerobic conditions encourage cell growth, and anaerobic conditions encourage alcohol production (Van Zandycke, 2012).

• Saccharomyces Cerevisiae

S. cerevisiae is the most common species. Critical in the fermentation of beer, wine, spirits wash, sake and in the production of bread. S. cerevisiae is categorized as a "top-fermenting" yeast as it produces a thick layer of krausen during fermentation and are used primarily for ales. S. cerevisiae carries out fermentation at temperatures of 18°C-24°C. They are known for ester production that leads to a more complex profile. Over 200 different strains of S. cerevisiae are commercially available (Dunn, 2012). 

• Saccharomyces Pastorianus

S. pastorianus, or lager yeast, is a hybridization of S. cerevisiae and S. eubayanus (Libkind et al., 2011). It is physiologically different from S. cerevisiae; ferments at cooler temperatures and can process melibiose. S. pastorianus typically has a higher degree of attenuation with lower levels of ester formation, establishing the profile of lagers. S. pastorianus were selected unintentionally from brewing practises resulting from the Reinheitsgebot which restricted brewing during the summer (Sherlock, 2012).

• Saccharomyces Cerevisiae var Diastaticus

Figure 7 - S. diastaticus from DME Agar at 800x Light Magnification (Bootleg Biology, 2019)

S. diastaticus can attenuate higher than S. cerevisiae by consuming starch and dextrins. Complex polysaccharides escape digestion by S. cerevisiae, S. diastaticus produces glucoamylase. Glucoamylase cleaves the 1-4 linkages in amylose while leaving the 1-6 linkages in amylopectin (Andrews and Gilliland, 1952). Dextrins contribute to body and mouthfeel of the final beer, not consumable by S. cerevisiae, but are fermented when S. diastaticus is present. S. diastaticus cannot be identified from S. cerevisiae using plating methods; a polymerase chain reaction must be used to identify the glucoamylase genetic marker: STA1. S. diastaticus is an issue in brewing as STA1 is common with Saison-style yeasts. Sources include: an increase in craft-scale brewing, market demands increasing the variety of yeast strains, and lacking in equipment such as pasteurization units, kieselguhr-based filtration, and automated clean-in-place. Contamination of S. diastaticus can result in higher alcohol, phenolic flavours, over-carbonation, and final package failure. Cellar management that avoids cross-contamination of yeast and brewing wort with reduced levels of dextrins can be used to lower the mentioned risks (Ferguson, 2018).

• Kveik

Kveik is a Norwegian dialect word for "yeast', and in English, it refers to a mixed culture of S. cerevisiae used for hundreds of years in traditional farmhouse brewing. As a verb in Norwegian, it means to "begin life" (Geithung, 2019). Common traits among Kveik cultures are high-flocculation, low phenols, quick fermentations while being high temperature tolerant. They are a genetically distinct group of S. cerevisiae, and have direct applications to brewing, allowing for faster fermentations and lower cooling requirements. Kveik cultures also have a high degree of alcohol tolerance. Kveik cultures produce more of ethyl caproate, ethyl caprylate, ethyl decanoate, and phenethyl acetate compared to monoculture S. cerevisiae (Preiss et al., 2018).