Meat grown in laboratories, some think, might be able to feed the earth's carnivorous hordes without exploiting animals. Grazing land for livestock is running out and farmed animals generate more greenhouse gases than the entire transport industry, so such meat offers many benefits.
Meat is made up of animal muscle. Cultured stem cells can be stimulated to form muscle; this makes lab-grown meat possible.

I recently asked guests at a dinner party for their views. One vegetarian hoped that it wouldn't taste of meat. She was reassured on that count by a French guest for whom meat serves only as a vehicle to consume blood and by another who believes that the joy of pork is all in the crackling.

Consider, too, that a pound of muscle cells requires more than £30,000 worth of nutrient-containing media, including the animal-derived growth factors needed to cajole the stem cells to form muscle. The cheapest source of these growth factors is serum, usually from foetal calves, several of which would have to be slaughtered to provide enough serum to grow less than a calf's worth of meat.

Genetically engineered growth factors might replace serum, but at a higher cost. I wouldn't rule out sausages made of lab-grown muscle, mixed with herbs and flour, in a few years, but the notion of such meat feeding the world remains, for now, a fantasy.