Potassium Bromate: The Bread Additive Banned Almost Everywhere But the US

Bread is one of humanity’s oldest foods. Getting it right has always required balancing biochemistry, economics, and scale. At industrial scale, consistency matters as much as quality.

That’s where potassium bromate came in.

What It Does to Dough

Potassium bromate is a flour maturing agent, a category of additives that condition flour by oxidizing gluten proteins. The chemistry works like this: when bromate (BrO3-) contacts wet flour, it oxidizes the sulfhydryl groups on gluten proteins, forming disulfide bonds. Those bonds create a stronger, more extensible gluten network.

The result is dough that rises higher, holds its shape better during proofing, and produces a finer, more uniform crumb. For bakeries producing thousands of loaves an hour, that consistency is worth money.

Before modern industrial baking processes, flour was aged naturally for weeks after milling. Oxidation by atmospheric oxygen accomplished some of the same thing potassium bromate does, just slowly. Potassium bromate fast-tracks the process.

Alternatives exist. Ascorbic acid (vitamin C), azodicarbonamide, and enzyme-based treatments can achieve similar dough-conditioning effects. They’re often more expensive or harder to work with at scale.

The Carcinogenicity Question

Potassium bromate itself isn’t the molecule that causes concern in the body. The bromate ion (BrO3-) is.

Animal studies found that bromate is a kidney carcinogen and thyroid carcinogen in rodents. Rats and mice given potassium bromate in their drinking water developed renal cell tumors and peritoneal mesotheliomas at relatively high doses.

The International Agency for Research on Cancer (IARC) classified potassium bromate as a Group 2B possible human carcinogen based on this animal evidence. Group 2B means the evidence is sufficient in animals but inadequate in humans to establish carcinogenicity.

For comparison: Group 1 is “known human carcinogen.” Group 2A is “probable.” Group 2B is “possible.” Coffee was briefly in Group 2B before being removed when evidence clarified. Pickled vegetables are also Group 2B. So the classification alone doesn’t tell you everything, but it does mean IARC reviewed the evidence and found it concerning enough to flag.

The “It Bakes Off” Argument

Supporters of potassium bromate make a specific technical argument: the compound is fully consumed during baking. The chemical reactions that strengthen gluten also use up the bromate. What remains in the finished bread is bromide, not bromate, and bromide is essentially harmless at dietary levels.

This argument has a real technical basis. Under ideal baking conditions, with proper temperature, time, and hydration, conversion is largely complete.

The problem: studies have found residual bromate in commercially baked bread. A UK study in the 1990s found detectable levels in supermarket loaves. Japanese researchers found similar results. The conversion isn’t guaranteed. It depends on exact baking conditions that vary between ovens, loaf sizes, and facilities.

This is why the “it bakes off” argument didn’t satisfy regulators in most of the world.

Where It’s Banned

The list of countries that have banned potassium bromate is long:

• EU (banned 1990 under Directive 90/457/EEC)
• United Kingdom
• Canada
• Japan
• China
• Brazil
• Sri Lanka
• Nigeria
• Peru
• And many more

The EU banned it more than 35 years ago. Japan and Canada followed.

The United States did not. FDA reviewed potassium bromate in the late 1990s and asked bakers to voluntarily stop using it, but never completed a formal rulemaking to ban it. Many major commercial bakers responded to that request and removed it. But it’s still legally permitted at the federal level, and still appears in some products.

California’s 2027 Phase-Out

California’s Food Safety Act (AB 418, signed September 2023) banned four food additives from food sold in the state, effective January 1, 2027: potassium bromate, brominated vegetable oil, propylparaben, and red dye No. 3. BVO and Red 3 have since been banned federally. The California law moves ahead on potassium bromate and propylparaben regardless.

This doesn’t make them federally banned. But California is such a large market that many food manufacturers reformulate nationally rather than maintain two separate supply chains. The California precedent often effectively moves the whole US market.

Practical Advice

Potassium bromate must appear on ingredient labels if it’s added to the flour. The label will say “potassium bromate” or sometimes “bromated flour.”

Most artisan breads, organic breads, and major national brands don’t use it anymore. The most likely places to find it: store-brand sandwich bread, pizza dough products, and certain commercial flour mixes.

Choosing bromate-free bread costs nothing extra and is a simple label check. Given the IARC 2B classification and the breadth of international bans, that’s a reasonable default.