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On a farm in central Kenya a group of guests pick purple tea leaves.

They've travelled from Nairobi, part of a tea tour that launched last October.

It's a sign of how a rapidly growing base of consumers, like Bella Gwada, are flocking to the health benefits of specialty teas.

"It's palatable, like you don’t even need to add sugar, it's easily digestible, milder than black tea and it's just an experience."

Kenya is the world's biggest exporter of black tea and the crop is one of the East African nation's top hard currency earners.

The government says new varieties could cushion farmers from oversupply of black tea and low prices.

Karanja Kinyanjui is a purple tea pioneer. His farm, which runs the Gatura Greens tour, started growing the crop in 2009.

"Purple tea is twice the price of green tea. When we are buying from the farmers, we buy at 100 shillings while normally they get 50 shillings for the same kilogram of tea. And when we process ourselves, we sell this one double the price of green tea."

Experts, such as Samson Kamunya of the Kenya Tea Research Institute, say substances in the purple pigment have several health benefits.

"So very strong anti-inflammatory effects, antimicrobial, anti-ageing."

The tea is also produced in China and Japan and Kinyanjui has 20 acres of the purple variety alongside 100 acres of the usual variety.

The farm processes its own purple tea which is sold directly to Chinese buyers.

The business also has clients in Canada, Sweden, the United Kingdom and the United States.