A German environmental group says it has found traces of the widely used weed-killer ingredient glyphosate in Germany's 14 most popular beers, a potential blow to the country's reputation for "pure" brewing.
Industry and government immediately sought to play down Thursday's report from the Munich Environmental Institute.
The Brauer-Bund beer association said the findings, which were based on a small number of samples, were not credible.
Germany's Federal Institute for Risk assessment said the levels did not pose a risk to consumers' health.
"An adult would have to drink around 1,000 litres of beer a day to ingest enough quantities to be harmful for health," it said in a statement.
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Under the "Reinheitsgebot", or Germany's 500-year-old purity law - one of the world's oldest food safety laws - brewers have to produce beer using only malt, hops, yeast and water.
Glyphosate was brought into global use by Monsanto in the 1970s and is used in its top-selling product Roundup as well as many other herbicides around the world.
The environmental group, an investigative body, said it had tested Germany's 14 top-selling beer brands and said all showed traces above the 0.1 microgram limit allowed in drinking water.
It added that no general conclusions about the contamination of certain brands of beer could be made.
Brauer-Bund said there were government controls in place in breweries to ensure that no harmful substances made their way into the production process. Its own monitoring system for malt has never detected levels of glyphosate that were above the permitted maximum limits, it added.
Hasseroeder, a beer brewed in Saxony-Anhalt in eastern Germany and owned by Anheuser-Busch Inbev, contained the highest trace of glyphosate at 29.74 micrograms per litre, the institute said.
Anheuser-Busch InBev said it questioned the scientific integrity of the tests due to the small number of samples.
It rejected the institute's allegation that brewers were not adequately monitoring raw ingredients as "absurd and completely unfounded."
