The Japan Wine Competition, which takes place every year in Yamanashi, within sight of Mount Fuji, grows bigger each year – as indeed, does the number of Japanese wines and wineries. This year, there were close on 800 Japanese wines to be judged by the five panels of tasters, with cooler regions such as Nagano, Yamagata and the northerly island of Hokkaido being given a particularly good showing.

The Yamanashi region remains the hub of the growing Japanese wine universe. The reason? It is by far the biggest producer of wines made from koshu, Japan's own distinct native grape.

Koshu is like pinotage and zinfandel in a way, in that it has been around forever, but only recently has anyone shone an illuminating light on it. In Japan the light-shiner is Grace Winery's Shigekazu Misawa, who decided that if koshu were given the respect it deserved, in the vineyard and the cellar, it could become a queen in its own right.

Koshu's problems have been twofold. Firstly, it's weighed down by a 100-year history as a grape that makes table wine. At the end of the 19th century, a fledgling wine industry began to take notice of it but the traditional system of growing koshu remains mostly as it was back then: massive Jack and the Beanstalk–like vines produce vast quantities of pink-skinned bunches of grapes hanging down from a high trellis; which makes it quite difficult to work with. Secondly, Japan's high rainfall and humidity makes getting the best out of koshu, or any grape for that matter, a labour-intensive operation.

Mr Misawa is on a mission to improve matters. He bought a vineyard, Akeno, and planted the vigorous koshu in a European-style vertical trellis to reduce yield and increase quality. While some pooh-poohed his efforts, he and his wine- maker daughter Ayana, were vindicated when, this year, the 2013 Akeno Koshu won the first ever international gold medal for koshu wine at the Decanter World Wine Awards. It is a wonder of delicacy and concentration, the only bad news being that it's made in quantities too small for export. His other four 2013 koshus should soon be on the water however, and they are excellent.

Despite the fact that most koshu is still grown in the traditional way, and therefore tends to dilution and simplicity, I can vouch for the fact, having tasted the six gold medal-winning koshu in Japan, that it is possible to produce beautiful dry whites of delicacy and concentration. Imports of koshu in the UK are still at an early stage, but if you want an introduction to the grape, albeit without the complexity it's capable of, Marks & Spencer has brought in the 2013 Sol Lucet Koshu from Kurambon, £12.99, a fragrant, light and delicate summer refresher.