Curious subject for training as a bonsai I have to say! The vinous stems would make this difficult to keep looking good.

Well, if it is indeed what you say it is, the plant is quite hardy so should stay outdoors in a sheltered spot. It needs a proper winter rest. The roots will appreciate so protection over the winter though in a shallow pot that I presume it is in? Cover or wrap with fern/bracken fronds or hessian.

I would also get in contact with a bonsai grower to give you more pointers on the necessary root pruning and top pruning that will be required.

I am amazed that they have produced a bonsai Vitis vinifera - as Fractal says it is a vine and they really like to put down huge long roots right into the subsoil... I can't imagine how it is going to cope in a small shallow container. As BS says get in touch with a bonsai grower for advice on pruning both roots and top growth.

Okay I've done a little hunt and it seems that you do get bonsai Vitis - live and learn as they say. There is lots of useful info on this site http://www.absolutebonsai.com/grape_bonsai

I agree that it an unusual plant to bonsai, Fractal. It has such a long, deep tap root that I don't see how it could be grown in a shallow container.

Cutting the tap root when the plant is young encourages lots of fiberous roots
(feeder roots) to develop which is to be desired.

Try www.bonsaitreeforums.com for helpful and friendly advice - a bit like this site, except for bonsai nuts.