Around 90 per cent of Britain’s annual blackcurrant crop is used to make the cordial, according to the manufacturer, with the berries harvested in the summer and pressed for juice.
A new technique, developed by scientists at Leeds University, extracts natural colouring from the leftover skins of the fruit to create sustainable hair dyes.
Colour chemist Dr Richard Blackburn said: “Because of issues and concerns around conventional dyes, we wanted to develop biodegradable alternatives that minimise potential risks to health and offer consumers a different option.”
Some ingredients found in common synthetic hair dyes are known irritants and can trigger allergic reactions. There have also been concerns over whether they could cause cancer, the researchers said, while the effects of dyes on the environment are unknown.
The skins of blackcurrants contain high concentrations of pigments that provide colour to many berries, flowers, fruits and vegetables.
Dr Blackburn said: “They are non-toxic, water soluble and responsible for pink, red, purple, violet and blue colours and are widely used as natural food colourants all over the world.”
The berries “represent a sustainable supply of raw material because of how much blackcurrant cordial we drink”, he added.
The technology developed by his team enables the pigment to be extracted from blackcurrants and to provide intense red, purple, and blue colours on hair. When mixed with natural yellow, it could also produce browns.
The colours are said to last for at least 12 washes, similar to other semi-permanent dyes.
Prof Chris Rayner, an organic chemist, said: “We’ve made it possible to have great hair colour, and to get it from nature in the most sustainable way possible.”
The researchers are commercialising the technology through a Leeds University spin-out company, under the brand Dr Craft. The dyes are expected to go on sale this summer.