Ikeda's MSG was a huge commercial success, but some scientists did not believe umami was really a fifth taste. They continued to believe that there were only four tastes. Then, in 2000, almost 100 years after Ikeda's discovery, scientists found physical proof. The human tongue contains contains tiny receptors,or taste buds, which allow us to tall the difference between tastes. Scientists found that these receptors responded to glutamate in a special way. In fact,they found that the receptors responded in that way only to glutamate, and not to any of the other four tastes.