What it is
E102 (tartrazine) is a synthetic azo dye giving a bright lemon-yellow colour. Wholly synthetic from petroleum-derived intermediates.
Why it matters
Common in soft drinks, jelly, cake mixes, mustards, condiments, and some medications. Has separate (non-vegan) safety concerns — linked to hyperactivity in some children — which is why UK labels carry a mandatory warning.
What to do
Always vegan.