【BLOG FOR WINE CONNOISSEUR】
Recently, I have been asked a lot of questions like 'What is Koshu? I am often asked this question, so let me tell you a little about Koshu. First of all, the origin of the Koshu grape is that DNA analysis in 2013 proved that the grape was introduced to Japan from the Caucasus region, where Vitis vinifera originated, crossing the Silk Road and repeated interbreeding with wild species in China. Koshu itself is characterised by its medium size, pink coloured skin, relatively low sugar content and moderate alcohol content when made into wine. When I was working in Japan in the early 2000s, it was a difficult time when Koshu wines were regarded as 'watery, bitter and mediocre wines with no character'.
In an attempt to somehow make Koshu wine better, Chateau Mercian and the late Professor Takatoshi Tominaga of the University of Bordeaux, an authority on wine aromas, began research in the early 2000s. Through their research, the team discovered that Koshu also contained 3MH(Cys-3MH and (E)-Hexen-2-al Are Not the Major Precursors), an ingredient that forms the basis of the citrus aroma shared with Sauvignon Blanc. At the time, this was after wonderful NZ Sauvignon Blanc had taken the world by storm, so the shocking news took the Japanese wine industry by surprise and gave hope to winemakers. Since then, various studies have been conducted all over Japan to bring out the best of Koshu, and as cultivation and winemaking techniques have been refined, quality has improved and styles have diversified. Recently, research into clones has progressed, and three strains with different characteristics, KW01 (fresh type), KW02 (high-yield type) and KW05 (concentrated type), have been designated as recommended strains. Due to its thick skin, Koshu is relatively disease-resistant compared to European varieties such as Chardonnay, and is well suited to Japan's hot and humid climate conditions. It was once considered a late ripening variety, but with changes in growing conditions and wine styles, such as global warming, the harvest period has changed and ranges from early September to late October. As for training, most of the grapes are traditionally Pergola training, which is rooted in Japan, where there is a lot of rainfall. The traditional Japanese practice of umbrella-hanging ‘Kasagake’, in which each bunch of grapes is covered with an umbrella paper, is also practised in Japan, where there is a lot of rainfall and damage from mildew and grey mould.
I would say that the most common modern productions are those that extract delicate citrus aromas and are as aromatic as possible, and orange wines that are produced more naturally. The key to extracting citrus aromas and 3MH from Koshu is to reduce the use of Bordeaux mixture, a pesticide containing heavy metals such as copper (as copper absorbs the aroma compounds), harvest just before ripeness when the aroma compounds are at their maximum, and use VL3 yeast, which is a good match for aroma extraction. The aroma is very sensitive to oxidation, This means that the wine is prepared under anaerobic conditions. From vineyard to vinification, thorough management is crucial and time-consuming. Chateau Mercian's Tamamoro Koshu Kiiroka, shown in the pictured below, is the result of thoroughgoing the above and skillfully expresses the delicate citrus aroma of the Koshu grape.
As you know, orange wine is also made by soaking the rind in the same way as red wine is made, and fermenting it while it is still brewing to bring out the colour and flavour of the skin. The characteristic colour, flavour and texture of the Koshu 'Gris' variety, which has traditionally been stripped away, are brought together and balanced. If you would like to try a great Japanese orange wine that combines character and finesse, such as those traditionally made in Friuli, Italy, or Brda, Slovenia(orange wine from Brda is one of those wines you must try if you can find it!), try the orange wine pictured below, made from Koshu grapes from Yamagata Prefecture, from Fukagawa Winery in downtown Tokyo.
Both express the character of Koshu in very different ways, but both are wines that give you a sense of the Koshu of today. Hiro
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