But, after accidentally leaving the product in his pocket for two years, Mr Whipple decided to keep the burger for even longer to see how long it could continue looking normal.

“It wasn’t on purpose,” Mr Whipple told US television show The Doctors.

“I was showing some people how enzymes work and I thought a hamburger would be a good idea. And I used it for a month and then forgot about it.

“It ended up in a paper sack in the original sack with the receipt in my coat tossed in the back of my truck and it sat there for, I don’t know, two or three months.”