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.
The winemaker, in conjunction with whomever is in charge of labour, also has to decide at what time of day to pick. In hot climates grapes are generally picked either at night (easier by machine with big spotlights) or very early in the morning in order to deliver the grapes to the winery as cool as possible. In the old days grapes would be thrown into the back of trucks and sit in the sun, often squashed and increasingly oxidized, so that they arrived at the winery having lost a substantial proportion of their primary fruit flavor. Nowadays any winemaker with pretensions to quality will insist that grapes arrive as cool as possible in small stable units, typically little plastic, stackable boxes which keep the bunches whole (although whole bunches are an impossibility if the grapes are picked by machine since they operate by literally shaking the grapes off the vine).
Machines are used increasingly in the vineyard, not just for picking but for pruning and lifting wires and therefore the canopy during and lifting wires and therefore the canopy during the growing season. But the greatest wines in the would are still picking by hand, no matter how expensive and elusive the pickers, because they can not only snip whole bunches off the vine but also make intelligent decisions about which fruit to pick.