But what they also found is that companies don't get into too much trouble for it!
If someone finds something nasty, like a rodent, in their food they can take the food company to court.
However, the food makers usually defend themselves by saying they took "all reasonable steps" to stick to food safety laws. It's called the "due diligence" defence.
But Which? say it's not good enough.
Keep your eyes peeled!
They advise the public on how to get the best on what they buy.
And now they're asking for stricter laws so that companies take more responsibility for hygiene and standards.
A spokesperson for the Food Standards Agency said there were no plans to review the "due diligence" defence though, so keep your eyes peeled when eating!