The challenge for natural sweetener stevia is to convince consumers, but for now volumes are tiny, industry expert Simon Bentley, a consultant with UK consultancy LMC International, said.

The plant, whose full name is stevia rebaudiana bertoni, belongs to the chrysanthemum family, originating in South America, in Paraguay and Brazil.

Stevia has a long history of being used by the indigenous population of that region as a "sweet herb" in local brews.

China dominates world production, with smaller volumes in Brazil, Paraguay and India.

Bentley told the F.O. Licht World Sugar conference that the biggest obstacle for stevia was consumer perception.

Although industry leaders such as Coca Cola, Pepsi and Cargill have started buying it, it is still largely unproven in the market place.

Pure Circle and GLG farm stevia, which may be combined with other sweeteners in blends.

"The real test will be how consumers take to it," Bentley said in a presentation.

He later told Reuters that refining production capacity was a few thousand metric tonnes a year.

"At present supply of the leaves is limited mainly to small holder farms in China and refining tends to take place elsewhere," Bentley said, without giving further details.

Stevia has a low caloric value, and is suitable for diabetics because it does not raise blood sugar levels. However, less refined products have more "off tastes."

The two-day F.O. Licht World Sugar conference ended on Wednesday.

www.reuters.com/article/healthNews/idUSTRE55G4P720090617