When you julienne any firm fruit or vegetable, including apples or carrots, it simply means slicing them into small, square strips. Julienning makes evenly sized sticks of food, not only for appearances, but also so they will cook evenly. By learning to julienne apples, you will be improving your knife skills. It takes some practice, but it doesn't take long to learn the technique.
Remove the center of the apple with an apple corer. Make sure you have removed all seeds and seed pods. Peel the apple to remove the skin.
Cut off all rounded edges. Use a sharp knife to make each piece into a rectangle. Cut off as little of the apple as possible during this process.
Cut the rectangular pieces of the apple into slices that are approximately 1/8-inch thick. Try to keep the slices as even as possible, for the best appearance and for cooking each piece evenly. If the slices of the apple are of uneven widths, they will cook at different rates.
Turn the slices so that the widest part is flat against the cutting board. You may place another slice of apple on top of the first slice, but generally do not try to cut more than two pieces at a time. Cut these slices into 1/8-inch strips. These strips should now be approximately 1/8 inch square.