The recent spikes in the price of food, which have acted as a catalyst to protests across the developing world, are a short-term manifestation of a long-term trend: That of high and rising agricultural commodity prices. But getting investment exposure to this long-term upswing in prices, without falling foul of the inevitable short-term volatility, is a conundrum that is proving hard to unravel.

Against a backdrop of tightening supply, investors have started to think about agriculture and food-commodity stocks in the same way they once considered energy investments. Jim Rogers, co-founder of the Quantum Fund with George Soros, says the world is on a knife edge. "Some governments have started hoarding stocks which will drive up prices. But will be blaming it on speculators like me," he says.