THE world's first test-tube hamburger made out of meat grown from artificially cultured cells could be just a year away, scientists have said.  The burger will be grown from 10,000 stem cells extracted from cattle and then multiplied a billion times to produce muscle cells similar to those found in natural beef.  "We're trying to prove to the world we can make a product out of this," said Mark Post, professor of physiology at Maastricht University in Holland, who is behind the project. Some of his colleagues have already succeeded in producing strips of "meat" using the technique. Post said he thought he could make the first burger in 12 months.  He is one of a growing band of scientists who believe that the world's surging population is leading towards a food crisis that could see billions facing shortages as it rises from 7billion to about 10 billion by 2040. "In vitro meat will be the only choice left," Post told Scientific american magazine. "I don't see any way you could rely on old-fashioned livestock in the coming decades."  Livestock farming accounts for about 18% of the world's greenhouse gas emissions, and global meat consumption is predicted almost to double by 2050. The test-tube burger is seen by scientists as the first stage: eventually tissue engineering would be used to manufacture a wide range of meat products. Livestock would still be needed but it would mean that the current practice of slaughtering millions of farm animals every year would cease.  The first step would be for technicians to extract stem cells from a cow, pig, chicken or other suitable animal. Stem cells are a primitive form of cell that have the power to grow and divide into almost any other form of cell.  Post believes the cells could be manipulated using chemicals, electrical stimulation and other techniques to divide and grow into replicas of the muscle cells. The final stage would be to "bulk up" the cells by stimulating them in the same way that animals build muscles by exercising.  about a decade ago Morris Benjaminson grew fish fillets in a laboratory. The