Wednesday, March 30, 2011

Botrytis & berry breakdown - UPDATE 30/3/2011

Some vineyards are starting to have berry skin breakdown and shrivel. This seems to be due to wet conditions that the vines have experienced. For these vineyards the end of the season has come and we expect them to only further worsen and have more skin breakdown.

Above - Berry skin breakdown with some botrytis.

One of the challenges this berry breakdown causes is the effect of managing the fungus Botrytis cinerea. When the Botrytis fungus infects red grapes it produces the laccase enzyme.

Why is Laccase a problem?

It is a problem when the grapes are made into red wine. The Laccase enzyme degrades the lignin and oxidizes the red pigments. In wine, this enzyme causes a reaction that turns the wine brown and detrimentally affects it smell and taste. Browning of the red pigments is caused by an oxidation reaction, which laccase ‘catalyses’ or speeds up.

Laccase is a difficult problem for wine makers to manage as the enzyme can survive the fermentation process, has low sensitivity to sulphur dioxide (this is added to many wines as a preservative) and thrives in the natural pH of wine. This means the laccase enzyme will be present in the wine end product. Consumers would not like this as the flavour and colour is not what they expect, like or paid for (no one wants a brown wine!). And because oxygen is required for the laccase reaction, the consumer doesn’t know the wine is bad until the bottle is opened.

The laccase enzyme targets ‘phenolics’. Phenolics are the coloured compounds or pigments in grapes. These are found in the skins (the most common pigments are anthocyanins). When laccase and the phenolics come into contact, an oxidiation reaction occurs.

Red wine turns brown!

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