(Bloomberg) -- Wearing a white tank top inside a foggy greenhouse at his farm in Otofuke on the island of Hokkaido in Japan, Hiroyuki Nakagawa plucks ripened mangoes ready to be packed and shipped. Outside the temperature is a freezing -8C on a clear December day, but inside the greenhouse the thermometer clocks in around 36C.

Nakagawa has been growing mangoes in the snowy Tokachi region of Japan’s northernmost island since 2011. He sells them for as much as $230 each. He never thought an experiment in sustainable farming would one day yield the world’s most expensive mangoes.

“At first no one took me seriously,” says the 62-year-old Nakagawa, who had previously run a petroleum company. “From here in Hokkaido, I wanted to create something natural out of nature.”

Nakagawa switched to mango cultivation following years in the oil business, where surging prices convinced him of the need to look beyond fossil fuels. Under the guidance of another mango farmer from the southern prefecture of Miyazaki, who claimed it was feasible to grow the fruit in winter months, Nakagawa founded his farm and established his startup Noraworks Japan. A few years later he trademarked his mango brand as Hakugin no Taiyo, which translates to “Sun in the Snow.”

Nakagawa’s secret is using the two natural resources his homeland of Hokkaido is famous for—snow and onsen hot springs. He stores snow from the winter months and uses it in the summer to cool his greenhouses, tricking the fruits into delaying blooming. Then in the winter he uses natural hot springs to warm the greenhouse and harvest roughly 5,000 mangoes out of season.

The process allows the mangoes to ripen during the cooler months when few insects are around, which means no use of pesticides. Hokkaido’s low-humidity climate also reduces the need for mold-removing chemicals. Plus, harvesting in the winter—when farmers have less work—allows better access to labor at a time when Japan faces a worker shortage, particularly in rural areas.

The sustainable approach is just an added bonus to the taste, which Nakagawa claims is much sweeter than normal mangoes with a higher sugar content of about 15 degrees brix, and his fruit boasts a buttery smooth texture devoid of stringiness.

The novelty factor of how they’re produced has intrigued customers and retailers alike. In 2014 the department store Isetan displayed one of his mangoes at its Shinjuku location in Tokyo, and it later sold for almost $400. The eye-popping price for a single mango made headlines, garnering more attention and making it a hard-to-get item. On the official website where customers can place orders, they’re often greeted with the words “SOLD OUT” in a big, bold red font.

Nakagawa’s clients include restaurateurs such as Asia’s Best Female Chef 2022 Natsuko Shoji, who uses the fruit in her mango flower cakes. He also has customers overseas and ships his mangoes abroad to high-end retailers, such as City’super in Hong Kong.

Since then, Nakagawa has discovered more unexpected benefits of farming in winter. “Because we don’t use pesticides, tea company Lupicia has approached me about using our leaves for mango tea,” he says, gently patting a tree.

Nakagawa isn’t satisfied yet. He aims to raise other tropical produce using the same method to turn Tokachi into a fruit production hub in winter and give the local economy a boost. Next he’s eyeing another juicy fruit known for thriving in warmer climates: peaches.

“I like mangoes, but oh boy, I like peaches even more.”

©2023 Bloomberg L.P.