During the wine manufacturing process, there are two steps of fermentation, alcoholic fermentation then malolactic fermentation. During alcoholic fermentation, yeast transforms sugar into alcohol. Before fermentation, Saccharomyces is present in the grape juice, as well as other yeasts such as Brettanomyces bruxellensis, commonly known as Brett. After alcoholic fermentation, B. bruxellensis can still be present in the matrix.

The presence of B. bruxellensis is an important issue, as it has been shown that its growth is linked to the concentration of 4-ethylphenol, which imparts a strong off-taste, leading to consumer rejection of the wine. To avoid wine spoilage by B. bruxellensis, some preventative actions can be taken such as racking, clarification, and sulfiting. However, if Brett spoilage has already begun, the winemaker must undertake additional remedial steps such as filtration or heat treatment, increasing production cost. If the concentration of ethylphenol is too high, the lot may have to be destroyed.