The Rise and Fall of Yeast and Bacteria During Fermentation: Part 2

Previously, I blogged about the The Rise and Fall of Yeast and Bacteria During Fermentation: Part 1 which summarized the type of yeasts that come in with clean fruit at harvest and their fate during primary fermentation when the wine yeast Saccharomyces becomes the dominant species. The following chart shows that once past the primary fermentation, other species of yeast and bacteria may contribute to fermentation.

The growth and decline of any particular species is influenced by a variety of conditions such as:

• Nutritional status
• pH
• Alcohol levels
• Sulfur dioxide additions
• Cellar temperature

(C) As the graph indicates, a secondary fermentation can begin if the lactic acid bacteria, Oenococcus oeni is present and the conditions are conducive for growth of O. oeni. This secondary fermentation can also occur if the winemaker inoculates the wine with O. oeni in order to facilitate the occurence of the conversion of malic acid to lactic acid, a process called malolactic fermentation (MLF).
Stages A-C illustrates the rise and fall of the various yeasts and bacteria that occur in a fermentation using clean fruit.
(D) In Stage D, the resultant wine is subject to a variety of spoilage organisms if good sanitation practices are not observed. A very good article on this topic, is written by Lisa van de Water and published in Practical Winery & Vineyard. The article is called Monitoring microbes during cellaring/bottling and is a very good reference article on all the things that can go wrong after the wine is made.
Meanwhile, we are trying to stay warm in the coldest winter this area has experienced since the winter of 2003-2004.

References:
1. Kenneth C. Fugelsang and Charles G. Edwards, Wine Microbiology, Springer Science and Business Media, LLC, 2007.
2. Lisa van de Water, Monitoring Microbes During Fermentation, Practical Winery & Vineyard Journal, September/October 2009.
3. Lisa van de Water, Monitoring microbes during cellaring/bottling, Practical Winery & Vineyard Journal, January/February 2010.