I am no expert, but this is my interpretation of the way to prune and maintain grapes. The first thing to know is that grapes are vigorous and forgiving so any mistakes will be able to be corrected next year.
Grapes bear fruit on the green shoots that grow from one-year-old canes. The old canes that produced fruit this season will not produce again. In your case, yours have not produced fruit, but it is still an established vine.
There are a couple of ways to prune established grapevines. Cane pruning is the usual system. For this, you establish a permanent trunk, and every year new canes are selected from the head of the vine, where the trunk and wire or trellis intersect. Choose one or two canes on either side, each 8-10 buds long, and tie them to the wire, and cut all other canes out. Choose canes about the thickness of your little finger and come out as close to the head as possible, with buds fairly close together. Avoid large thick canes with buds spaced far apart. Also leave one or two spur canes, cut to two buds each. These are for additional canes to choose from for the next year's pruning.
The kniffen pruning system is similar to cane pruning, except the main trunk has two levels, one at a lower wire height, another about 30" above it. Often though, the upper level shoots are so vigorous that they shade out the lower level, not allowing the fruit to develop, so the kniffen system is not ideal.
Grape vines are vigorous and produce too many shoots. Some shoot thinning is usually needed to take out unproductive shoots without fruit clusters, and those that are too close together. The goal is to balance the productivity of the vine with the amount of growth.
Each grape shoot needs several well exposed leaves to properly ripen a grape cluster. If too many shoots are crowded together, they do not get enough light for photosynthesis. Thinning grape shoots eliminates unproductive shoots and provides light and space for productive ones.
Start thinning shoots as soon as possible -in June or as soon as clusters appear. Shoots are soft and can easily be removed by hand. If there is more than one fruit cluster per shoot, the lowest one (closest to the old cane) will usually ripen earliest. It is best to thin down to one cluster per shoot.
Training and tying the shoots up on the trellis should begin early, to maintain spacing and keep shoots from trailing on the ground or breaking off. Later, if shoots are long and vigorous, they can be cut back on the ends to prevent shading the lower vine. New shoots can emerge where a leaf joins the main shoot. These side shoots should be removed.
Just before harvest the lower leaves surrounding the grape bunches can be removed to provide better exposure to the sun to ripen them.
Hope this is clear enough and not too long winded!
Don't do this major pruning until fall though, as you will cause the grapes to bleed and possible shock. Hope you see tons of grapes next year!!
VAL (Grandpa's Rose)