Microbial spoilage

Due to its high levels of alcohol and acidity, the only microorganisms that can survive in wine are:

  • Yeasts
  • Lactic bacteria
  • Acetic bacteria

However, wine can also suffer from taints brought on by moulds on poorly-cleaned winery surfaces, particularly the insides of barrels.

The factors that affect the growth of micro-organisms in wine are:

  • Acidity - the lower the pH, the more difficult it is for microorganisms to survive
  • Alcohol - inhibits most microbes, including yeasts if above 15 –18%.
  • Temperature – growth is usually fastest at 20-35°C and only slow at cellar temperatures (10-15°C)
  • Sulphur dioxide – a concentration of 20 mg/l free will inhibit microorganisms from growing.
  • Residual sugar – existence of fermentable sugars facilitates the risk of spoilage – specifically by yeast.
  • Growth factors – e.g. nutrients such as amino acids and vitamins
  • Air (Oxygen) – essential for the growth of aerobic acetic bacteria
  • Winery hygiene

The presence of microorganisms in wine can be determined by microscopy or agar plating techniques. Stability tests, when the wine is kept in an incubator at 20 - 25ºC for 48 hours, can also be useful.

The most important feature of microbial spoilage is that it is much easier to prevent the development of microorganisms in the wine than to remove the effects of spoilage once it has occurred.