Botrytis infection

Botrytis infection

The fungus botrytis cineria can attack the grape berry and introduce the oxidative enzyme called laccase into the berry and hence grape juice.
Laccase exists in solution and can NOT be removed through clarification as is the case with the grape derived enzyme tyrosinase.
Laccase has a much lower sensitivity to sulphur dioxide (SO₂) compared to that of tyrosinase.
Laccase persists through to the wine, unlike the grape derived oxidative enzyme (tyrosinase). This is because wine pH values are closer to the optimum for laccase and less likely to be denatured (inhibited).
Laccase targets phenolics such as the red colour compounds in red wine and oxidises them to brown coloured compounds (see red wine oxidation).
Because adequate levels of FSO₂ are difficult to achieve in red wine (see SO2 and red wine), red wines made from botrytised infected grapes are problematic.

Botrytis cineria attacks the skin of the grape berry.
A severe attack will result in rot.

That is a loss of skin integrity, followed by microbial attack and spoilage.
Given misty mornings for the growth of botrytis cineria and sunny days to arrest and control its growth can be beneficial in the production of sweet white wines.
In the sittuation where botrytis cineria does not result in the loss of skin integrity, the grapes shrivel and are clad in a mantel of fungul spores and then the infection is refered to as nobel rot
Wines produced from grapes affected by botrytis can result in sweeter, more complex and luscious wines.
This is due to the loss of water through the very small infecting tube of the fungus, concentrating the sugars, acids and flavours present.
Luckily, the chemistry that occurs due to the fungul infection sees acid levels reduced, extra desirable flavours introduced and an increase in the level of the sweeter alcohol, glycerol.