Botrytis cinerea: How to Manage Infected Fruit and the Tools to Reduce its Impact on Wine Quality
Due to rain and high humidity levels in parts of North America over the past weeks, some vineyards are showing signs of Botrytis infection.
Early, fast and accurate determination of infection levels can be used for effective screening of vineyards, grape lots or juice and enables winemakers to adjust the winemaking process and minimize negative effects on final wine quality.
How Botrytis cinerea contamination impacts on grape and wine quality
An infection with Botrytis cinerea negatively affects grape quality and the resulting wine:
- Botrytis affected grapes have a very high risk for enzymatic oxidation due to laccase activity.
- This fruit can have reduced sugar, acid and polyphenol levels.
- It can increase the risk of problematic alcoholic fermentations and increases levels of spoilage microbes.
A fast and accurate determination of infection levels: Gluconic Acid
Gluconic acid, one of the most important metabolites of Botrytis cinerea, is the best marker to estimate the level of infection and adapt the winemaking process. Vinquiry Laboratories by Enartis USA provides same day Gluconic Acid test results, as well as Gluconic Acid Test Kits from Vintessential Laboratories for in-house testing. Grapes considered healthy can have gluconic acid levels between 0.2- 0.3 g/L. Levels up to 1.0 g/L indicate an initial fungus infection (O.I.V reference).
Tools to reduce Botrytis impact on quality
Laccase enzyme produced by Botrytis cinerea has been shown to have very detrimental effects on color and several other grape phenolics (Dubernet 1977). Sulfite has been shown to have a limited effect on laccase activity at reasonable levels (<200 mg/L) (Dubernet 1973). However tannin has been shown to limit laccase activity (Dumeau 2004). EnartisTan Antibotrytis and EnartisTan Blanc have both been shown to significantly reduce laccase activity.
One of the best tools to utilize for machine harvested fruit with potential Botrytis infection is the antioxidant blend AST. This blend has a synergistic combination of ascorbic acid, potassium metabisulfite and gallic tannin. When added to grapes, the synergistic action of AST limits laccase activity and prevents microbial spoilage. The activity of laccase has also been shown to persist after fermentation late into the ageing process (Somers 1989). Utilizing EnartisStab Micro M or EnartisStab Micro, has been shown to reduce laccase activity in juice and wine, respectively.
Gluconic Acid Analysis: $31.00 (Sample volume: 50 mL)
Vintessential Gluconic Acid Test Kit (30 tests): $200.75
Botrytis Panel (PCR for Botrytis, gluconic acid): $75 (Sample volume: 50 mL or 5 clusters)
Tel. 707 838 6312 – www.enartis.com/en-us/
How to adjust the winemaking process: keys steps
Hand harvest and sort contaminated grapes in the vineyard:
- Utilize enological tannins such as EnartisTan Blanc or EnartisTan Antibotrytis to limit laccase activity in machine harvested and crushed fruit or use blends such as AST.
- Limit skin contact to reduce extraction of off-flavors.
- Remove any spoilage microbes as soon as possible with EnartisStab Micro M.
- In white and rosé wines, promote fast clarification to reduce off-flavors and toxins that can alter fermentation.
We recommend the use of EnartisZym Elevage, an enzyme with β-glucanase activity, to break down glucans and improve clarification and filterability, ideally in juice/must.
Protocols and resources
Botrytis winemaking protocols for white, rosé and red wines can be found in the link below along with a more indepth webinar on the topic.
Compromised Fruit: Botrytis Bunch Rot and Powdery Mildew
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