Freshly milled flour is oxidised before use in order to improve its gluten-forming properties. This was traditionally achieved by storing flour and exposing it to air for a period of time. Chemical oxidation or bleaching of flour was introduced in the early 20th century in order to speed up oxidation, saving time and money.

Chemicals such as nitrogen peroxide, potassium bromate and chlorine have been used to rapidly oxidise flour, but increased concerns about the health risks of these chemicals has led to bleaching being prohibited in many countries. In the UK, chemical bleaching was banned by the 1998 Bread and Flour Regulations. Ascorbic acid is now added to flour as a safe alternative.

Some of these chemicals also affect the colour of flour, whitening it. Other chemical bleaches that are not oxidising agents and have no effect on gluten have also been used simply to 'improve' the appearance of the product. Again, this practice is now prohibited in many countries including the UK.

Want to find out more? Look at the chapter on ingredients in the book flour and water.

Back to the glossary.