To the great annoyance of its rival Pepsi, Coke is one of the most well-known words in the world.

But both drinks make use of a little known ingredient found in Africa – and in particular in Sudan.

Gum arabic, which comes from some types of acacia trees, puts the fizz in your drink, carries flavour in foods, and can even be used as a lickable adhesive for postage stamps.

For years Sudan had a virtual monopoly on it; now the authorities are trying to revitalise an industry hundreds of thousands of Sudanese depend on.

To get gum arabic you have to head out into the central belt of this great agricultural country, in inhospitable land on the edge of the desert.