Proof of Principle for In Vitro Burger Professor Mark Post of Maastricht University in the Netherlands served a hamburger last week in London that was cultured entirely in a lab. The ground beef was the product of growing 20,000 small strips of muscle tissue from four cows – two of which were organically raised. The project has been ongoing for five years and the burger was produced in three months. According to Professor Post, the burger is a "proof of principle" for such lab-produced foods. He predicted retail availability in 20 years. Animal welfare groups reacted with joy from the People for the Ethical Treatment of Animals (PETA) to the Humane Society of the United States (HSUS) which hailed what it called "slaughter-free meat tha...