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Most of our bread flour is milled using high-speed, fluted steel rollers. Modern roller milling is ruthlessly efficient at stripping away the nutrient-rich germ and fibrous outer layers of cereal grains, separating them into many different fractions and leaving behind a white powder that’s not much more than starch and gluten. Millers in the UK are required by law to add certain minerals and vitamins (namely calcium, iron and vitamins B1 and B3) to all white bread flour, however it has been produced. Similar additions are required in other countries.