By Ardee Napolitano

ROUBAIX, France (Reuters) - A French brewer has started using algae with a naturally-occurring pigment to turn their beer blue.

The beer, with the brand name Line, is the result of a tie-up between a firm that wants to popularise the algae as a dietary supplement, and a nearby craft brewery that was looking for a way to make its beverages more distinctive.

The beer is selling well, said Sebastien Verbeke, an employee of Hoppy Urban Brew, which makes the drink. It's getting an enormous amount of interest and curiosity on the part of the public, he said.

The blue tint comes from spirulina, an algae that is grown in basins by a company called Etika Spirulina in northern France. The component of the spirulina that gives the blue colour, called phycocyanin, is then added to the beer during the brewing process.

Tasting a freshly produced bottle of the beer, brewery employee Mathilde Vanmansart described it as hoppy, light, and with fruity notes, while the only evidence of the added algae was the distinctive colour.

Xavier Delannoy, whose farm provides the spirulina, said after several test batches, the brewery had found a blend that appealed to customers.

He said 1,500 bottles of the blue beer were sold between October and December last year, and the brewery is now preparing to ramp up production to meet demand.

(Writing by Christian Lowe. Editing by Jane Merriman)