Microbiological problems can occur at any time during the winemaking process. During grape harvest acetic acid bacteria and various moulds may grow on damaged fruit. The fermentation and maturation process may introduce undesirable yeast or bacteria if inadequate precautions are taken. Faulty or inadequate filtration or insufficient preservative addition during packaging of the finished product may also allow the growth of a variety of yeast and bacteria.
To assess the extent of a microbiological problem it is necessary to determine the identity of the microorganisms involved and ascertain numbers of viable and non-viable organisms present. In the winery this is done primarily in two ways: phase-contrast light microscopy and viable plating. Phase-contrast microscopy is the most rapid technique by which to examine any microbiological deposit; minimal preparation is required and little delay is experienced before the results are visualised. However reliance on microscopic techniques alone is insufficient for determining the nature of the instability.
The aim of this section of the Solutions website is to provide winemakers with information about the range of microorganisms that can grow in wine, as well as details on how to investigate and avoid microbiological instabilities.
A glossary of microbiological terms is also included to aid in the understanding of this and any other microbiological references.