Influence of Zygosaccharomyces and Brettanomyces on Wine Quality and their Control During Vinification
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Yeast contamination during winemaking, particularly by Brettanomyces bruxellensis or Zygosaccharomyces bailii, can have a detrimental impact on wine quality if growth is not controlled. Nevertheless, speculation exists that some Z. bailii strains could be beneficial during vinification, particularly for stuck fermentations. Therefore red wines adjusted to 13, 15, or 17% v/v ethanol and containing 40 or 60 g/l fructose were inoculated with Z. bailii. However, a Saccharomyces wine strain was more effective at removing the residual sugar and produced less volatile acidity. Consequently, antimicrobial technologies to limit undesirable yeast growth were also evaluated. The efficacy of 200 mg/l dimethyl dicarbonate (DMDC) was determined against yeasts originally isolated from regional vineyards, including Candida oleophila, Candida californica, Metschnikowia pulcherrima, Meyerozyma caribbica, Meyerozyma guilliermondii, and Wickerhamomyces anomalus, inoculated into grape must. Following treatment to 10^4 or 10^6 cfu/ml of each yeast, populations initially declined several logs but within several days increased to >10^6 cfu/ml, regardless of inocula or strain. When DMDC was added to grape must with Z. bailii, 10^3 cfu/ml populations were not detected following treatment, although 10^6 cfu/ml did grow. Conversely, when DMDC was added to wines with 10^6 cfu/ml Z. bailii, growth was limited for >85 days. Growth of B. bruxellensis in wines at populations 10^4 cfu/ml was generally limited by DMDC, although sensitivity was dependent upon strain. However, 4-ethylphenol and 4-ethylguiacol production was limited in wine for several years. Alternatively, a factorial experiment using wines inoculated with B. bruxellensis evaluated storage temperature (22°, 18°, 15°, or 10°C) and molecular SO2 (mSO2) addition (about 0.0, 0.2, 0.5, or 1.1 mg/l) and determined that while some strains could grow at either 10°C or with about 0.5 mg/l mSO2; conditions of <15°C and >0.40 mg/l mSO2 synergistically limited growth. The cumulative results demonstrated that while commercial application of Z. bailii during vinification may not be practical, reliance on DMDC or the interactive impacts of SO2 and temperature could limit a variety yeasts associated with wine spoilage including Z. bailii and B. bruxellensis.