In all foods, flavour is mostly determined by the level of sweetness and sharpness. In apples this is characterised by the balance between sugar and malic acid.
Dessert apples, or ‘eating apples’, have lower levels of acid and higher sugar content, giving them the sweet flavour that makes them delicious to eat – but also means they tend to lose their ‘appley’ flavour when cooked.
Bramley apples, however, are unique because they contain a higher acid content and lower sugar levels to produce a stronger, tangier tasting apple whose flavour is retained when cooked.