This growing season and vintage has been marked by some challenging conditions. Wines made from grapes affected by Botrytis cinerea may contain laccase, an enzyme which, due to its relative stability in wine, is capable of causing serious oxidative damage. A fact sheet detailing information about managing botrytis infected fruit can be found here.
Managing Botrytis infected fruit fact sheet ( click here)
The main concerns regarding laccase are:
- Browning and premature ageing is likely maintaining anaerobic conditions at all times is important. Where fruit has been harvested and rot is present (even at low levels), winemakers be prudent regarding residual laccase activity both before and after primary fermentation. Unlike other enzymes which occur naturally, laccase can continue to be active post-fermentation, causing browning and premature ageing. Under these conditions, the use of sulfur dioxide even at elevated levels, or intervention by normally accepted winemaking techniques, will prove ineffective. Oxidation of wine due to laccase activity will only occur in the presence of oxygen, therefore maintaining anaerobic conditions at all times during the winemaking process is of paramount importance.
- Pasteurisation might be required. Careful sensory appraisal should also be made at the post-primary ferment stage to ensure that wines meet winemaking quality standards and are fit for purpose. In the event of a positive laccase result, the only advisable solution is to pasteurise at a temperature of 65C for a minimum of 40 seconds. Recheck presence of laccase activity post-pasteurisation.
- Monitoring is essential. Laccase activity can be monitored either qualitatively following the method listed in the above link or by using one of several commercially available quantitative test kits. There are a number of laboratories that offer testing including the AWRI Commercial Services.
- Laccase test kits. In the case of juice samples, in particular red juice, there have been observations that laccase test kits may underestimate potential laccase activity in wine. Therefore, it is essential that laccase tests are repeated when botrytis-affected fruit is fermented into wine, especially if a negative, or a low positive, result is obtained at the juice stage.
- Minimise air contact post-fermentation. Once primary fermentation has completed, rack immediately off yeast lees, store in full (i.e. no ullage) tanks and exclude contact with air as much as possible. Wine should only be transferred into oak when the wine has been tested and no laccase activity is detected.
Should you require further assistance, please call the AWRI’s Winemaking and Extension Services team on 08 8313 6600 or contact us by email.