Harriet Lamb: The bitter truth about a sweet taste the world adores

Cocoa grows in hot, rainy climates mainly 20 degrees north and south of the equator. When the trees' pods are opened they contain up to 40 beans. The beans are fermented under leaves before being dried in the sun. Nearly 50 million people in some of the world's poorest countries depend on cocoa for their livelihood.

Some 70 per cent of cocoa comes from West Africa. Weighed, then sold to traders, most cocoa is exported, either as raw beans or as cocoa butter or liquor. This is where the value of cocoa is multiplied as it is then blended with milk and sugar to make chocolate.

But the real story of cocoa is the destruction of income experienced by cocoa farmers over the last 40 years. Adjusting for inflation, cocoa sold on global markets has fallen by more than half its 1970 value. Imagine living on a wage that has fallen below that level. At the same time, the cost of seeds, fertilisers, fuel and food have all shot up. Oh, and the farmers will only get a fraction of the price cocoa fetches on global markets.

No wonder most cocoa farmers do not have the money to invest to maximise their income. A technological breakthrough may help cocoa farmers. But they need an economic and social fix too. Growers in West Africa – the world's biggest cocoa-producing region – received 16 per cent of the value of a chocolate bar 20 years ago. Today the figure is around 3.5 per cent. By contrast, the manufacturers' share has risen from 56 to 70 per cent.

When I was visiting cocoa farmers in Ghana last month, I met villagers for whom schools, medical centres and even drinking water are all a long walk away. In Cote d'Ivoire, the world's biggest producer at 41 per cent of total volume, the level of illiteracy is shocking.

Yes, cocoa prices have risen globally as hedge funds on Wall Street and London bet on the latest rumour. Maybe chocolate will go up a few pence. But the key is to ensure the benefits flow back to farmers and their communities. If more big companies address this challenge, that will be a real breakthrough.

Harriet Lamb is the executive director of the Fairtrade Foundation