This is part 2 of the From Plant to Bottle series. If you are just joining me, you may want to start from the beginning of this series.
The next very important part of grape growing is the proper trellising and pruning of the vines. Most of my experience is with a trellising system called VSP or vertical shoot positioning, which, I believe, is the most common trellising arrangement in the United States. With this method the plant’s trunk (stem) is brought from the ground to a wire and two canes are trained onto the wire, one to the left and one to the right. The shoots then grow out of these canes and are trained straight up into the other wires, thus “vertical shoot positioning”. Not all shoots are kept and there is some spacing between them so that there will be air flow and minimal crossover, keeping the shoots growing in an upright fashion as nicely as possible and not all tangling together.
Grapes are pruned several times during the season for various reasons. The old growth from the previous year must be removed because the vines would become huge and unwieldy if they kept growing from the last year’s growth. In addition, the only fruitful part of the plant is the new growth. This pruning is done starting from the very first year after planting. Then, at various times there must be thinning (cutting off) of unwanted shoots and clusters (or potential clusters) of grapes to keep the crop low. This is critical because over cropped vines (that is, vines with too many grapes on them) produce thin wine with not much character and red wines that are more like rosés. You want only about 3 to 4 tons of grapes per acre for fine quality wine from vinifera grapes. Other species can tolerate a heavier load and retain quality. I will discuss that in more detail later. Sometimes it is difficult to assess the appropriate amount of fruit to leave on each vine, but, if you leave only one cluster per shoot, you are certain to have some good grapes (assuming the weather co-operates with lots of sunshine and very little rain). It is also preferable to not have clusters of grapes touching each other as this harbors moisture and can cause the skins to break down and rot more easily. If not thinned, the crop can be 8 or more tons to the acre, depending on the variety. Pruning these grapes can be a difficult task in that you have to be heartless, so to speak – it is very difficult to cut off beautiful clusters of grapes, tons of them, and see them just lying on the ground. I want to cry for them every time I look at all those beautiful bunches, so consequently, I don’t help with this process. Thank goodness someone does it, though, or the quality of the wine would suffer.
I have actually seen a situation where there were so many grapes on the vines in a specific vineyard that the weight of those grapes caused the trellis to collapse, thus ruining some of the plants and many of the grapes, to say nothing of the damage to the posts and wires. The grapes were probably not very good quality so they were not as much of a loss as the cost of fixing and replacing posts, wires, and vines. With overloaded vines, one light wind shear coming through the vineyard can cause an incredible amount of damage.
Grape varieties ripen at different times, much like apples, and are harvested between the months of August and November in the United States…earlier in warm climates and later in cooler climates. As you may imagine, it is a good thing that they don’t all ripen at the same time as this gives the winemaker the opportunity to work at a steady pace on the incoming grapes. The earliest stage of ripening, when the grape berries stop growing and start to ripen, is known as veraison. This is easy to detect in red grape varieties as it is when they start to turn red. White wine varieties go from a darker greenish color to a more golden or golden green color, some with a light blush of pink in the skins. This is also the time that the grapes begin to slowly soften. It is also very important to have good air flow through the grape vines so the grapes remain dry, and have exposure to the sun. This helps prevent the various molds and fungi from finding a hospitable environment in which to grow. Hedging off some of the overgrowth that is hanging down and covering the grapes is a good idea. Some people go as far as taking some of the leaves off from around each bunch of grapes...labor intensive but very beneficial.
Next Week: To Pick or not To Pick