The controversial chemistry of bread: Why a flour improver is banned globally

Science · Published 20 October 2026 · Updated 21 October 2026 Swipe more like this →

In short: Potassium bromate is a chemical paradox. It is a powerful oxidizing agent capable of strengthening dough and allowing bread to rise higher, yet it is also a known carcinogen. While it remains legal in much of the United States, a growing global movement is seeking to pull it from our bakeries.

Potassium bromate (KBrO3) functions as a strong oxidizing agent with an electrode potential of 1.5 volts, making it chemically similar to potassium permanganate. In the baking industry, it is used as a flour improver to strengthen dough and facilitate a higher rise. Theoretically, the chemical is reduced to bromide during the baking process; however, if the bread is underbaked or if excessive amounts are used, residual bromate can remain in the final product.

The chemical's production involves passing bromine through a hot solution of potassium hydroxide, creating potassium hypobromite, which then disproportionates into bromide and bromate. Alternatively, it can be produced via the electrolysis of potassium bromide solutions. Because it can be obtained in high purity, it is also valued in laboratories as a "primary standard" analytical reagent and a source of Br+ in organic synthesis, particularly for brominating recalcitrant aromatic substrates like nitrobenzene.

The IARC labels potassium bromate a category 2B carcinogen, notwithstanding its industrial applications. This has led to a fractured regulatory landscape. It is strictly banned in the European Union, Canada, Brazil, and several other nations. In the United States, the FDA has urged bakers to avoid it since 1991 but has not mandated a federal ban. However, California became the first U.S. state to enact a total ban on the manufacture and distribution of the substance, set to take effect in 2027.

The history of its use is marked by controversy. For example, Japanese manufacturer Yamazaki Baking resumed use of the additive in 2005, claiming new production methods minimized residue, before suspending it again in 2014 due to supply issues and resuming it once more in 2020. These fluctuations highlight the ongoing tension between industrial efficiency and public health safety.

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