Harvesting the grapes
The winemaker’s first and possibly most important decision is when to pick. He should have been monitoring the sugar and acid levels in the grapes and their general harvest date.
Decisions on harvest date need to be taken in conjunction with the weather forecast.
If, for example, the grapes are not quite ripe enough for the wine he wants to make but rain is predicted, he will have to calculate whether to leave the grapes on the vine and then hope that there will be sufficient warm, dry weather afterwards for them to ripen fully. Some varieties are much more sensitive than others to the exact date of harvest. Syrah and Merlot, for example, can easily lose quality – a certain liveliness in the wine – if kept too long on the vine, whereas Cabernet Sauvignon is much more tolerant of a few extra days. If they are already suffering from fungal disease , the rain will exacerbate this so the best, regretful decision may be to pick the grapes just slightly less ripe than ideal. White wine is much more forgiving of a few rotten grapes than red in which the colour is rapidly lost and the wine tainted by a mouldy taste.