Wine is made in the Vineyard
Before you ferment grape juice into wine, even prior to picking the grapes you have grown, much of the work takes place in the vineyard. The goal for most top wines is to achieve the ripeness in the grapes. And these take presedance long before the grapes are picked.
During the winter months, green pruning and bud thinning take place in order to decrease the amount of plant material on the vines. This is because that could hold back the grapes to be maximally exposed to the sun.
Green harvesting is simply the act of removing unripe grapes in bunches. This has to be done while the grapes are still green – green harvesting. The remaining berries (left after the green harvest) will receive more important nutrients, increase the concentration and flavor compounds needed to make great wine. A second green harvest can also be done lated during the the growing season, and removing clusters that are not ripening well will also increase number of the best grapes on the vine.
Deleafing or leaf removal is another method used in the vineyards. This removal of leaves, in order to give more exposure to sun (and at the same time this cuts the possibilty of the rot to take place) is sometimes needed.