There's a good chance your tin of coffee contains ground-up cockroaches

Some people can't start a day without a coffee - and a lot of people might change their coffee habit for good after this.

For most of us who can't afford a coffee shop-like monster machine to use whole beans, we often reach for big tins and jars of pre-ground beans to keep going for a couple of weeks at least.

A few people oddly develop an allergic reaction to this widely consumed type of coffee. Sucks for them but innocent enough, right?

Wrong. The reason why they start to experience this allergy will make your skin crawl.

That's because if you're drinking coffee made from pre-ground beans, there's also a pretty high chance you're swigging down ground-up cockroaches.

University of Montana biology professor Douglas Emlen first spilled the beans on the gross finding in a 2009 interview about his research into dung beetles, as reported by news.com.au .

Dr Emlen described how, as a student, he drove across the country with his professor who was 'fiercely addicted to caffeine' and often made them drive up to 45 minutes off route to find somewhere that served whole bean fresh ground coffee.

"I remember giving him a really hard time because we were wasting a lot of travel time trying to feed his addiction because he needed a coffee every couple of hours," said Dr Emlen.

"And he finally explained to me he had to drink only whole bean fresh ground coffee — and it was because of cockroaches."

After years of teaching entomology, the study of insects and their relationships with humans, the professor became badly allergic to cockroaches from handling them so often.

He couldn't touch a cockroach without getting a reaction and suffered similarly when he drank coffee made from pre-ground beans.

When the professor looked into it he found pre-ground coffee is all processed from huge stockpiles that get infested with cockroaches.

He explained that little can be done to filter out the creatures, so they all get ground up along with the beans. Feeling ill yet? Here's a little more.

Dr Emlen said at the time US defect standards allowed coffee beans to contain as much as 10 percent' insect filth and insects'.