Japanese whisky is world-famous, often eye-wateringly expensive, and from Monday will be more strictly defined in an industry push to deter foreign-made imposters.

Overseas demand has soared in recent years for the country's acclaimed whiskies, sending prices sky-high, especially for the rarer aged varieties.

But concern and confusion have also grown among producers and customers as beverages made elsewhere — and sometimes not even whisky — are marketed as "Japanese whisky."

As a result, the Japan Spirits and Liqueurs Makers Association has brought in a new definition for the spirit, officially in use from Monday following a three-year grace period.

To call their products Japanese whisky, makers must now use water sourced in Japan, and their whisky barrels must be stored in Japan for at least three years, among other rules.

Although violators will not face sanctions, manufacturers have hailed the new industry standard as a way to safeguard the image of their tipples worldwide.

"We believe this will further improve the reputation (of Japanese whisky) because it makes it easier for our international customers to distinguish it from other products," major producer Suntory said.

Experts say Japan has around 100 distilleries, whose whisky has commanded increasing global respect since the early 2000s.

Annual exports of Japanese whisky were worth ¥56 billion ($370 million) in 2022 — 14 times more than a decade earlier. In 2023, this figure eased to ¥50 billion.

Brands such as Nikka Whisky's Yoichi 10 and Yamazaki 12 have scooped prestigious international awards, and distillers now plan production decades in advance to cope with demand.

Suntory's Hibiki 17 played a starring role in the hit 2003 movie "Lost in Translation," in which the character played by Bill Murray promoted the drink with the line: "For relaxing times, make it Suntory time."