E924 - Potassium bromate
What it is and how it is used
Potassium bromate is a flour treatment agent — an oxidising agent added to bread flour to strengthen the gluten network so a loaf rises higher, holds a finer crumb and tolerates industrial handling. It works exceptionally well, which is why it was used for most of the twentieth century and is still used in some countries today.
The theory was that bromate would be entirely consumed during baking, converting to harmless bromide. In practice, residues survive when doses are high, baking is short, or the loaf is underbaked — and it was that residue that ended its use in Europe.
Foods commonly containing it
None in Great Britain. UK bread has been bromate-free since 1990. It remains in use in some countries outside Europe, so it is worth knowing as a label term if you buy imported baked goods.
Safety summary
Potassium bromate is banned for food use in Great Britain and does not appear in the FSA Register of Food Additive Authorisations. The UK prohibited it in flour from 1 April 1990, in step with the European ban.
The International Agency for Research on Cancer classified potassium bromate as Group 2B — possibly carcinogenic to humans in Monographs Volume 73 (1999), on the basis of sufficient evidence of carcinogenicity in experimental animals and inadequate evidence in humans. In rats it produced renal tubular tumours and thyroid follicular tumours in both sexes, and peritoneal mesotheliomas in males.
The flour treatment agents that are permitted in Great Britain are ascorbic acid (E 300), used to strengthen dough, and L-cysteine (E 920), used to relax it. Between them they do the job bromate used to do.
Known concerns
IARC Group 2B, possibly carcinogenic to humans (Monographs Vol. 73, 1999): renal tubular and thyroid follicular tumours in rats of both sexes, and peritoneal mesotheliomas in males. Residues can survive baking when doses are high or baking is incomplete — which is what drove the ban.