Consumer watchdog Stiftung Warentest issues ratings on a huge range of products - their conclusions are well-respected by the public and thus and sought after by companies.
A Stiftung Warentest spokeswoman told the internet platform "populeaks.org" that companies, such as detergent producers, changed their formulas back after the results of the tests were published.
Holger Brackemann, director of the organisation's analysis division, said the testing of orange juice had also been a cause for concern and that since post-testing alterations had been noticed, they had become more careful about giving companies notice of upcoming tests. The consumer group's board of trustees, which sponsors the testing, will now only mention that they are preparing to test juices, and not specify which kind.
"There is a high level of interest from business to find out what we'll be testing in advance," Brackemann said.
The Federation of German Consumer Organisations has called for more frequent testing and random sampling of products, to preserve the reputation of the Stiftung Warentest's ratings.
Many producers still cite their ratings from tests in 2008, which is too far back to be accurate, say industry experts.
Nutrition consultant Jutta Jaksche at the Federation of German Consumer Organisations said a reasonable time lag from the testing and marketing should be controlled.
"Otherwise the value of the test loses credibility, and it is a tremendous asset for marketing," she said.