Until fairly recently, the only tomatoes sold in supermarkets were pale red spheres bred for their ability not to squash easily - growers didn't take flavour or texture into consideration. Now, supermarkets offer a wide variety of tomatoes grown in different parts of the world, but while many might look like perfect specimens - deep red and still on the vine - most are still pretty tasteless.

Enter heirloom tomatoes. Contrary to popular belief, "heirloom" is not the name given to one specific type of tomato; instead, it's a name used by foodies, chefs and farmers to differentiate traditional varieties of tomatoes from the tasteless fruit grown by agri-businesses.

Heirloom varieties are not necessarily red and they're not necessarily round, but they do have flavour. Some heirloom tomatoes are green even when fully ripe, and others are purple, orange, yellow or variegated. Their taste and texture are also varied.

The colours and flavours are generally best appreciated raw or slightly cooked (as in the tomato tart recipe on page 85), but some of the tomatoes can be simmered into delicious sauces.

When buying heirloom tomatoes, look for those that feel substantial. They are much more delicate than supermarket varieties, so don't stack them in your shopping bag.

They should be eaten soon after purchase because heirloom tomatoes don't keep well. However, don't refrigerate them because that mutes their flavour. Instead, store them stem-side down on paper towels or newspaper in a cool, shady place.