What causes the different flavors between apple varieties?

Many varieties of apples are hybrids or cross breeds of two or more varieties of apples so you get the difference in appearance, taste, texture and even smell that way.

Also many apple trees need specific sets of environmental traits to survive...Pink Lady apple trees probably grow better in Australia and other places with similar climate, seasonal cycles and soil properties and Galas probably grow better elsewhere. The soil and climates can vary greatly and this will also cause differences in the fruit that the trees bear.

Finally, some growing seasons are better than others for the same fruit. One year, the tomatoes may be particularly better than any other year (Jersey tomatoes are excellent this year). This happens when growing conditions get closer to the perfect conditions needed by a particular crop.

Apples are bred the same way dogs are bred. They take a variety of mutations and combine the best traits from two different plants. Becouse apple trees are typically as old as Humans this process takes generations.

Also climate has a lot to do with sweetness and crispness. An apple needs a frost to develop properly. Unlike most other fruits the cold helps an apple stay crisp and sweet.

My current favorite is a little apple called a Jazz apple. Nice and crisp with a great sweetnes.