Around 90 per cent of British blackcurrants are used to make the branded cordial, according to the manufacturer, with the berries harvested in the summer and pressed for juice.
A new technique, developed by scientists at the University of Leeds, extracts natural colouring from the leftover skins of the fruits 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 ingredients could cause cancer, the researchers said, while the effects of dyes on the environment are not known.
The skins of blackcurrants contain high concentrations of anthocyanins, 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.
“We knew they bound strongly with proteins - hair is a protein - so we thought if we could find an appropriate source of these natural colours, we might be able to dye hair.”
The berries “represent a sustainable supply of raw material because of how much blackcurrant cordial we drink”, he added.
The patented technology, developed by the team, enables the pigment to be extracted from blackcurrants to provide intense red, purple, and blue colours on hair.
When mixed with natural yellow, this could provide a range of colours, including browns.
According to the research, published in the Journal of Agricultural and Food Chemistry, the colours last for at least 12 washes, similar to other semi-permanent dyes on the market.
Professor 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 University of Leeds spin-out company, Keracol Limited, under the brand Dr Craft.
The blackcurrant-based dyes are expected to go on sale this summer.