Wine Spoilage Microorganisms
Spoilage by Bacteria in Wine Prodcution
The bacteria associated with cellared and bottled wine fall into two groups, the lactic acid bacteria and the acetic acid bacteria. The three main genera of lactic acid bacteria are Lactobacillus, Pediococcus, and Oenococcus. The two genera of acetic acid bacteria that are important to the wine industry are Acetobacter and Gluconobacter.
Lactic Acid Bacteria
Lactobacillus, along with Pediococcus and Oenococcus, are referred to as lactic acid bacteria (LAB), which produce lactic acid from fermentation of glucose. Oenococcus oeni is the species most commonly used for malolactic fermentation (Chapter 7) but all three can be associated with spoilage and wine faults. The overproduction of these bacteria can lead to spoilage problems, especially in wines that contain sugar and have a pH greater than pH 3.5.
Lactobacillus
Lactobacillus have complex nutritional requirements (besides carbohydrates, they require amino acids, nucleic acids, vitamins and fatty acids). The occurrence of Lactobacillus in wine is highly pH and ethanol dependent. In high-pH wines (greater than 3.5), Lactobacillus will dominate. Ethanol tolerance varies among Lactobacillus species. Lactobacillus in wines with residual sugars can lead to the production of acetic acid and other off-odors and flavors.
Pediococcus
Similar to the other LAB, Pediococcus have complex growth-factor requirements. Pediococcus growth is encouraged in wines having a high pH (pH greater than 3.5).
Management Strategies
Many vinification practices can influence growth of LAB in a winery. Some of the important practices include: fruit condition, must treatment (adjustment), clarification, fermentation conditions, skin contact time (in case of red wine), lees contact, wine clarification, storage, and winery sanitation. Sound fruit has a low population of LAB on the surface, therefore; using clean and healthy fruit is important in reducing the number of microbes that would enter the winery at harvest.
Acetic Acid Bacteria
Acetic acid bacteria belong to the family Acetobacteraceae, commonly known as vinegar bacteria, and are often responsible for the vinegary spoilage of wines through the production of acetaldehyde and acetic acid from ethanol (and glucose). The two genera of acetic acid bacteria that are important to the wine industry are Acetobacter and Gluconobacter. Gluconobacter lives in grapes and musts, but disappears as alcoholic fermentation begins.
Management Strategies
Control of Acetobacter in wines can be initially accomplished by limiting populations entering the winery on fruit and by implementing and maintaining an adequate sanitation program. At harvest, their growth is favored as soon as skins of the berries are broken and sugars are made available. Acetobacter can be transferred by workers through direct contact or contact with contaminated equipment or tools. Acetobacter can also be transferred by fruit flies (Drosophila spp.) that are common in wineries during crush.
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