Discovery of dye stains image of Corsica's 'naturally blue' wine

Corsica's vin bleu has been a party favourite this summer, but it appears the curious blue “wine of the sea” may be less natural than it says on the box, with local authorities on Wednesday launching an investigation for dubious marking practices.

The furore began a few weeks ago when chemistry students at the University of Toulouse, keen to find out the secret identity of the ingredient responsible for turning the wine blue, instead uncovered the presence of E133 – the synthetic dye used to colour curaçao.

The discovery of E133, also known as Brilliant Blue FCF, was made in two popular blue wine labels, Imajyne and Vindigo – which is Spanish but is also sold in France.

While there's been no comment from the producers of Vindigo, the people behind Imajyne deny their product is anything less than natural.

"We do not use E133; it's not the same process as curaçao or Vindigo," says Sylvain Milanini, the CEO of the Corsican estate Pozzo di Mastri.

Milanini, whose wine has been in production since 2017, insists the blue colour is the result of a fermentation process involving salt, spirulina (a type of seaweed) and marine yeasts. The details of the process are secret and are the subject of a patent.

In their study, published in European Food Research and Technology journal, the students found average concentrations of 8.62 and 5.46 mg / L of E133 in both Vindigo and Imajyne. The wines were not found to contain spirulina, a naturally blue dye.

On the back of the study, the Ajaccio public prosecutor says it's now investigating the use of the word “wine” to market Imajyne – given that using dyes is against French wine regulations.