Grapes grown on Takanobu Watanabe's farm in Tomi, Nagano Prefecture, are still chartreuse this time of the year, as the summer heat boosts the berries' sugar content before veraison, the onset of ripening.

"It gets chilly during the night in this region. But the harsh change of temperature is what makes the grapes become sweeter," Watanabe explained.

The 54-year-old is a rare breed of domestic farmer who is looking forward to Japan joining the Trans-Pacific Partnership negotiations and expanding free-trade pacts. Most of his colleagues feel threatened by the idea of having to face overseas competitors.