Bacteria in wine

Bacteria are both the friend and foe of the winemaker and organisms that winemakers must control to prevent wine spoilage. While the bacterial malolactic fermentation is a friend of the winemaker, there are a range bacteria that can cause wine spoilage that winemakers must content with and control.

Acetobacter are responsible for converting acetaldehyde to vinegar in the presence of oxygen which can soil wine, ullage control and free SO2 are critical for control. Acetobacter can soil grapes that have been damaged by birds in the vineyard even before the grapes make it to the winery making bird control an important part of viticulture.

Brettanomyces is a spoilage yeast that can produce the classic band-aid, and barnyard characters in red wines by feeding on residual sugar while the wines are aging in the cellar. Molecular SO2, temperature, barrel sanitation and filtration are critical controls to limit Brettanomyces growth and wine spoilage.

Surface yeast, while rare can also spoil wine by production of acetaldehyde but are generally easily preventable with ullage control and topping of barrels or tanks. Of course in the rare case of sherry, the flor, which is a particular surface yeast, is a vital part in producing the wines of Jerez.