What it is
E270 is lactic acid. The name suggests dairy ("lac"), but modern industrial production is by microbial fermentation of plant sugars (corn, sugar beet, cassava). Animal-derived lactic acid is virtually non-existent in modern food production.
Why it matters
Used as an acidity regulator in dressings, yoghurt alternatives, pickled vegetables, fermented soy products, and baked goods.
What to do
Vegan in modern production. The closely-related lactates (E325 sodium lactate, E326 potassium lactate, E327 calcium lactate) are likewise plant-fermented and vegan.