WINETECH Technical Yearbook 2020

Schizosaccharomyces pombe yeast and its role in winemaking

produce more than 1 g/L of volatile acidity (Benito et al ., 2014). This yeast has also been characterised as a high H 2 S producer compared to S. cerevisiae and produces on average 1 g higher glycerol than S. cerevi- siae. Some strains of S. pombe were shown to produce up to 10 g/L glycerol in synthetic grape juice with 222 g/L (glucose + fructose) initial sugar concentration (Benito et al ., 2014). Only 5% of the studied strains present an appropriate industrial profile, based on classic parameters, such as correct sugar con- sumption, moderate acetic acid production, complete malic acid degradation, glycerol production, and the correct sensory profile of the wines produced with these strains (Benito et al ., 2016). • Mixed culture fermentations Schizosaccharomyces pombe has been eval- uated for its use in co-fermentation with S. cerevisiae , as well as other non- Saccharo- myces yeasts, such as Lachancea thermo- tolerans and Torulaspora delbrueckii. The combined use of S. pombe with strains of these species has been shown to moderate its undesirable and quality-detrimental vin-

Loira et al ., 2018). Sexual reproduction results in the formation of two to four haploid ascospores. NITROGEN METABOLISM Schizosaccharomyces pombe has low nitrogen requirement. Strains of this species show preferential consumption of ammonia over primary amino nitrogen. Moreover, compared to Saccharomyces species, this yeast displayed lower growth rates and minimal requirements for primary amino nitrogen (Benito et al ., 2012). TECHNICAL CHARACTERISTICS Schizosaccharomyces pombe is an osmotolerant yeast capable of growth in the presence of 500 g/L glucose. It ferments optimally at temperatures between 24 and 30°C. It is a facultative anaerobe and possesses a high fermentative power similar to Saccharomyces cerevisiae , producing 11-13% alcohol in anaerobic conditions and 14-15% with slight aeration (Benito et al ., 2016). Schizosaccharomyces pombe is more resistant to SO 2 than most S. cerevisiae strains. It can remain active at SO 2 levels up to 300 ppm which is approximately 148 ppm free SO 2 (Yang, 1975). • Glycerol, VA, SO 2 and H 2 S production Schizosaccharomyces pombe can ferment to dryness in monoculture. However, the fermentations are typically slow and generate excessive amounts of acetic acid. Most strains

OCTOBER 2020

EVODIA SETATI: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch KEYWORDS: non- Saccharomyces yeast, autolysis, fission yeast, wine acidity

WHERE IT IS FOUND Schizosaccharomyces pombe strains have been isolated from fermented drinks or derived products (grapes, must, wine, beer and kombucha tea) and in high sugar substrates, such as honey, sweets, molasses and dried fruit (Benito et al ., 2016; Loira et al ., 2018). WHAT IT LOOKS LIKE Schizosaccharomyces pombe is known as the fission yeast due to its peculiar asexual reproduction by binary fission rather than budding which is common among yeasts. It forms rod-shaped cells varying between 3-5 x 5-24 µm commonly appearing as single cells or in pairs (Benito et al ., 2016;

This yeast is the most recommended of the non- Saccharomyces species to de-acidify excessively acidic wines from cool areas. CURRENT AND PREVIOUS NAMES Schizosaccharomyces pombe has previous- ly been designated several species names based on classical yeast taxonomy methods; amongst its synonyms are S. vordermani , S. mellacei , S. fermosensis , S. santawensis , S. pinan , S. taito , S. liquefaciens , S. acidov- orans , S. malidevorans and S. kambucha (Vaughan-Martini & Martini, 2011) . How- ever, these synonyms became obsolete once the genus was reduced to three species fol- lowing reclassification based on molecular DNA-based techniques.

egar character (Benito et al ., 2019). EFFECT ON MALOLACTIC FERMENTATION

Schizosaccharomyces pombe has a high capacity to metabolise malic acid into ethanol and CO 2 during anaerobic fermentation processes. Consequently, it

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