In a case involving the secret formula used to make the sweetener for Coke Zero, the manufacturer of the sweetener sought to patent the formula after first selling the artificial sweetener to Coca-Cola. While the manufacturer always kept the exact formula a secret, the Federal Circuit still said the sale of the end product (Ace-K sweetener) to Coca-Cola meant that the invention was being sold “publicly”. Thus, the manufacturer's patent was invalidated because the sweetener was sold publicly before the manufacturer applied for the patent. Some argue this is the wrong result because the manufacturer never disclosed the formula publicly. But that misses the point. The patent system is designed to give an inventor a maximum of 20 years of patent protection, and if you allow someone to first sell the product and then seek a patent later, that person has artificially extended the length of his patent monopoly.