E-numbers / Other additives / E925
also: Cl2 · Chlorine gas
A gas once used to bleach and treat flour, now banned in the UK and EU. Still used in the US. Look for it in imported baked goods.
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Chlorinating flour creates trace organochlorine compounds in the finished food.
Why it’s worth knowing. Chlorinating flour creates trace organochlorine compounds in the finished food. Some of these byproducts, including the mutagen 3-MCPD precursors and related compounds, have shown DNA-damaging effects in laboratory studies. It is not on the UK list of approved food additives, so you will not normally see this E number on a UK label.
Chlorine gas (Cl2), the same element used in water treatment and bleaching, applied to flour as a processing treatment. In food contexts it acts both as a bleaching agent (whitening the natural yellow pigments in flour) and as a flour improver that changes the gluten and starch structure to produce softer cake textures.
When chlorine gas contacts flour, it oxidises the carotenoid pigments that give flour its natural cream colour, producing a white appearance. It also partially depolymerises starch granules and modifies proteins, which reduces the strength of gluten and makes the flour absorb fat more readily. This gives high-ratio cake batters (those with more sugar than flour by weight) a finer, more tender crumb. The treatment leaves no residual chlorine gas in the flour, but it does produce a range of chlorinated organic compounds as reaction byproducts.
E925 was used almost exclusively in soft wheat flour destined for high-ratio cakes, particularly fine-crumbed layer cakes and American-style sponges. It was never widely used in bread. Since the EU and UK ban, it no longer appears in domestically produced flour or baked goods. It may appear in baked goods or cake mixes imported from the United States, where chlorinated flour remains legal, though US exporters increasingly avoid it for international compliance. On a UK label it would appear as "E925" or "chlorine" in the ingredients list, but you are unlikely to encounter it on any UK-sold product today.
Chlorine does not remain in flour as free gas, but the reaction with flour lipids, starch and proteins generates a range of chlorinated organic compounds. These include chlorinated fatty acids, chlorinated furanones and precursors to 3-monochloropropane-1,2-diol (3-MCPD). The profile and quantities of these compounds depend on treatment dose and flour composition. Their presence is the primary reason regulators in Europe moved to ban the treatment.
Chlorine treatment of cake flour generates chlorinated lipid derivatives and other organochlorine compounds as reaction products detectable in the finished flour.
3-MCPD, a compound whose precursors can be generated during chlorination of flour lipids, is classified as possibly carcinogenic to humans (Group 2B) by IARC.
Some chlorinated furanone compounds that can arise from chlorine reactions with organic matter are genotoxic mutagens in laboratory tests. The most studied is MX (3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone), established in water chlorination research. Whether flour chlorination generates meaningful quantities is less well characterised, but the structural class raises a legitimate genotoxicity signal.
MX, a chlorinated furanone, is a potent mutagen in the Ames test and has shown carcinogenic activity in animal studies at high doses.
A 2025 review of flour bleaching history identified genotoxic potential of organochlorine byproducts and nutritional losses (vitamins E and carotenoids) as the principal drivers of European regulatory prohibition.
Chlorine treatment destroys naturally occurring vitamin E (tocopherols) and carotenoids in flour. These are not major contributors to overall intake from flour, but the destruction is complete and irreversible. UK and EU regulators noted this as an additional reason to prohibit the treatment when alternatives exist.
Chlorination of soft wheat flour substantially reduces tocopherol content compared to untreated flour.
Because E925 is banned in the UK and EU, the practical exposure route is through imported US baked goods or cake mixes. Anyone wishing to avoid chlorinated flour byproducts should check the country of origin on imported cakes and mixes, and look for flour labelled unbleached. There is no specific at-risk group defined under UK law because the additive is not authorised here.
E925 does not appear in UK or EU food because it is prohibited, so the question of everyday exposure does not arise for domestic products. The genuine scientific uncertainty is about how much organochlorine material flour chlorination actually deposits in the final baked product and whether those quantities carry any real-world biological risk at typical consumption levels. Studies showing genotoxicity of related chlorinated furanones come primarily from water-chlorination research where concentrations and compound profiles differ. The EU and UK regulators concluded that the absence of adequate safety data, combined with the availability of non-chemical alternatives for achieving similar baking results, justified the ban. No one has formally set an ADI. The US FDA has not prohibited it. The science remains incomplete rather than settled.
Yes. Chlorine is not listed as a permitted food additive in the UK's assimilated version of EU Regulation 1333/2008, and the UK Bread and Flour Regulations 1998 explicitly prohibit bleaching agents in flour. No UK or EU manufacturer is legally permitted to use E925 in food.
Exposure is possible through imported products, primarily from the United States where chlorinated cake flour remains permitted. US-origin cake mixes, pre-made layer cakes, or baked goods exported to the UK could be made with chlorinated flour. Check the country of manufacture on the label.
In the UK and EU, no legally produced food contains E925. Historically it was used almost exclusively in soft wheat flour for high-ratio cakes (layer cakes, fine sponges). In the US it is still permitted in soft wheat cake flour at up to 2000 mg/kg of flour.
Yes, chlorine gas is not derived from animal sources. Its vegan status is not the relevant consideration for E925; its regulatory status is.
Last reviewed: 20 June 2026
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