Fast Facts – Managing powdery mildew in the cellar

by | Feb 17, 2021 | Relevant Resources, Fact Sheets

Facts about powdery mildew

  • It is a vineyard fungal disease that can cause crop losses and affect wine quality negatively.
  • Powdery mildew affected grapes can contain higher microbial populations.
  • Fermentation duration can be increased.
  • Wines produced can have earthy, mushroom, cooked tomato and wet fur characteristics.
  • Wines can also have undesirable textural changes and increased phenolics and bitterness.
  • In addition wines can have increased titratable acidity and protein instability.
Practical advice on how to handle grapes and musts affected by powdery mildew:
  • Ideally, affected vineyards should be hand harvested in order to select for healthier bunches.
  • In case of mechanical harvesting the worst affected bunches must be removed by hand first before harvesting commences.
  • Add a high dosage of SOat crushing (60 – 100 mg/ml) depending on how severe the grapes have been affected.
  • In the case of white juice, minimise skin contact and extraction by using shorter pressing cycles.
  • Assess each press fraction for negative attributes and if present, discard or conduct fining trials (bentonite, casein or PVPP) depending on the severity of these attributes. Suppliers can advise.
  • Use additional enzymes for adequate cold settling or flotation.
  • Measure the YAN since powdery mildew infection can lower it and adjust if necessary during fermentation.
  • Inoculate with a commercial yeast to reduce the risk of undesirable microorganisms.
  • In the case of red musts avoid cold soaking and press early.
  • Avoid post fermentation maceration and ageing on lees.
  • Expect a higher bentonite requirement for white wines. Red wines might require a proteinaceous fining to achieve better balance.

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