You sense sourness or salt when you eat
While umami's the flavour
The taste that you savour
When something is really a treat.
Many processed foods contain monosodium glutamate (MSG) and on the packets it is sometimes described as a flavour enhancer.As someone who trained as a chemist I knew that it was the sodium salt of glutamic acid (2-Aminopentanedioic acid if you really want to know) and is one of the amino acids that make up the proteins in our body. However I had no idea why it was added, or how it worked, so I decided to have a dig around on the web - and found an exciting story about taste which I had never learnt at school.
I was brought up to think that our taste buds could detect four different tastes - sweet, sour, bitter and salt, and this was complemented by the sense of smell. However about 100 years ago a Japanese researcher, Dr. Kikunae Ikeda, was trying to find out why a stock made from the seaweed kelp improved the taste of many other foods. He found that the stock contained glutamate and that it provided a distinct taste. This 5th taste is now known as umami, which is a Japanese word (うま味) meaning "pleasant savoury taste" and there are special receptors in the tongue that react to the presence of glutamate in the food.