To keep those unruly grape vines from climbing everywhere in summer a little summer pruning is necessary. Completely correctly it will not affect the size or quality of the grapes.
Using a clean pair of secateurs look at each shoot on the vine. Count three leaves from the bunch of grapes towards the growing tip and cut off the end of the shoot leaving the bunch of grapes and three leaves.
Later in summer you may need to do this again follow the same rules OR remove all the new shoots that grew after your last summer pruning leaving only one leaf on that new shoot.