Indigo Carmine (Indigotine)
What it does
Blue colour.
How it's made
Synthetic dye.
Indigo carmine (indigotine) is a synthetic deep-blue colour used in sweets, biscuits, ice cream and drinks, and also as a diagnostic dye in medicine. It gives a rich royal blue and can be blended to make greens and other shades.
It is made from indigo, the same blue compound historically obtained from plants but now synthesised chemically. To turn insoluble indigo into a usable food colour, it is treated with sulphuric acid (sulphonation), which attaches sulphonic-acid groups and makes the pigment dissolve in water as indigo carmine.
The sulphonated dye is neutralised, purified and standardised into a blue powder. Although the parent indigo can be plant-derived, the food colour is a defined, purified chemical, used in regulated amounts where a strong blue is needed.
Possible reactions
Occasional allergic skin reactions; rarely blood-pressure effects on injection (not food).