Wine´s main characters: yeast

The conditions generated in the wine fermentation supports the growth of the yeasts above other microorganisms. These conditions involve:

• High initial sugar concentration 
• Low final pH of wine  
• Presence of phenolic compounds

Moreover, as we have explained yet, the growth of yeast rapidly generate anaerobic conditions, which hampers other microbes’ growth, if possible. So, yeasts represent the most important group of microorganisms to winemakers.

Inside this group we have to underline the genera Saccharomyces. This genera allows the production of quality wine, because of its characteristics and high alcohol tolerance. Besides Saccharomyces, however there are many other genera and species present during vinification that ultimately impact quality, both positively and negatively.

Yeasts’ reproduction in winemaking

There are two forms of reproduction that we will see in wine fermentation: budding and eventually, ascopores mediated sexual reproduction.

Budding represents the most frequently form of reproduction and, in the case of wet mounts from juice or fermenting wine, the most common form that will be seen. Budding is a form of asexual reproduction. Budding of the mother cell initially yields a bud and, eventually, a daughter cell after separation.

 

Source: http://en.wikipedia.org/wiki/Yeast#/media/File:S_cerevisiae_under_DIC_microscopy.jpg

 

We can also find a sexual form of reproduction in wine yeasts. This kind of reproduction is similar to which we can observe in humans. Yeasts divide their genetic material into especial haploid cells called ascopores (which we can compere to oocyte and spermatozoid). Then, two of these ascopores mate and develop a new diploid yeast.

Yeasts species in wine

There are few yeasts genera represented in winemaking during all its process. As we learned, these yeasts vary from the grape surface, must… to the final product, wine. Here we present three of the most characteristic yeasts found in winemaking.

Candida

The anamophic genus Candida represents a very broad group with a number of species found in wines. Candida species are represented by a number of different genera including Issatchenkia, Kluyveromyces, Pichia, Metschnikowia, Saccharomyces, Torulaspora, and Zygosaccharomyces
Dekkera

Many winemakers consider Brettanomyces and its sporulating equivalent Dekkera to be a threat to wine quality. Worldwide, economic losses due to these yeasts are very high, not only from overtly spoiled and unmarketable wines but also from wines of diminished quality that do not command their expected market price

Saccharomyces

The two primary species found in wines, S. bayanus and S. cerevisiae.

References

• Kenneth C. Fugelsang, Charles G. Edwards. Wine Microbiology. Practical Applications and Procedures. 2nd Ed. Springer 2007
• Helmut König, Gottfried Unden, Jürgen Fröhlich. Biology of Microorganisms on Grape, un Must and in Wine. Springer 2009

Aitor Balmaseda