Bleaching lightens or whitens a material by chemical action or by exposure to sunlight, with bleaching agents employed where needed. For example, oils are bleached with fuller’s earth, activated carbon or activated clays, which adsorb impurities — chlorophylls and carotenoid pigments among them — for removal by filtration. Heating some oils causes heat bleaching, converting pigments such as carotenoids to colourless materials. In flour milling, bleaching agents whiten the flour and modify gluten for baking performance. Each application must use only food-approved agents at permitted levels, since bleaching chemistry touches the food directly.