The world's first lab-grown burger has been cooked and eaten at a news conference in London. Scientists took cells from a cow and, at an institute in the Netherlands, turned them into strips of muscle that they combined to make a patty. Prof Mark Post, of Maastricht University, the scientist behind the burger, remarked: It's a very good start." The professor said the meat was made up of tens of billions of lab-grown cells. Sergey Brin, co-founder of Google, has been revealed as the project's mystery backer. He funded the 215,000 ($330,000) research. Stem cells are the body's "master cells", the templates from which specialised tissue such as nerve or skin cells develop. Most institutes working in this area are trying to grow human tissue for transplantation to replace worn-out or diseased muscle, nerve cells or cartilage. Prof Post is using similar techniques to grow muscle and fat for food. He starts with stem cells extracted from cow muscle tissue. These are cultured with nutrients and growth-promoting chemicals to help them develop and multiply. Three weeks later, there are more than a million stem cells, which are put into smaller dishes where they coalesce into small strips of muscle. These strips are collected into small pellets, which are frozen. When there are enough, they are defrosted and compacted into a patty just before being cooked. At the moment, scientists can only make small pieces of meat; larger ones would require artificial circulatory systems to distribute nutrients and oxygen.