Wind.

Wyeth, Apples, Study before Picking, 1942

To appreciate the wild and sharp flavors of these October fruits, it is necessary that you be breathing the sharp October or November air.  What is sour in the house a bracing walk makes sweet.  Some of these apples might be labeled, “To be eaten in the wind.” It takes a savage or wild taste to appreciate a wild fruit.  The era of the Wild Apple will soon be past.  It is a fruit which will probably become extinct in New England.  I fear that he who walks over these fields a century hence will not know the pleasure of knocking off wild apples.  Ah, poor soul, there are many pleasures which you will not know!  The end of it all will be that we shall be compelled to look for our apples in a barrel.

Henry David Thoreau