Sime42,
In so far as I have observed, vines fruit on the new seasons growth. And hard pruning should not, as far as I know, be a problem, if one observs how hard commercially planted vines are kept pruned.
My pruning is almost random, verging on the chaotic, and was quite ruthless a couple of years back, when I identified what I imagined were the best strongest stems coming from the root, and kept them, while getting rid of the others, all while attempting to get them trained away from the light to the front, and round onto the warmer back wall.
I would need to tober the stuff that is growing quite madly up under the heat of the roof(a full unreachable without a ladder, 2 stories up)
Cheers
P.S.
Anyone know how they are pollinated? Obviously self pollinating since we only have the 1 vine, but what is the mechanism? Not wind, and no flying insect life in our porch.