A crab apple (Malus domestica, which includes all apples) is one of two things. To many, it is thought of as a wilding apple (like the roadside trees that are a forager’s delight, grown from pips of cores tossed out car windows, one likes to think). They are crabs because in the random dice throw of apples from seed, they are typically too tart to be thought of as much of an eating apple (though the random exceptions are one of the reasons that there are so many hundreds of different named apple varieties). The other interpretation is that they are the small-fruited ornamental varieties which, selected for appearance rather than taste, also almost invariably revert back to the native apple tartness.
The glory of the ornamental small fruited crabs is that their main purpose in life is to be bedecked in countless spring flowers; and then be bedecked in just as many fruit (which stay for a long time on the tree showing off (like Seville oranges)) through late summer and autumn. Being viewed as a looker rather than a cooker, and a great looker at that, people often don’t realise that they are perfectly edible. They put out a lot of fruit, so much so that all but the stingiest gardeners would probably let you pick your fill, and they actually have some great virtues as cooking apples. The rich ruby skins make for rich ruby pulp and juice and the tartness comes with a high pectin, high acid zing. It makes them kind of like quinces, but with the ruby colour that quinces somehow alchemically create being there even before cooking.
For our crab apple jelly, from the garden of my family’s place in New Zealand, the recipe is simple: