The starch pattern index test identifies when an apple is ripe and ready for picking. As apples ripen the starch gradually breaks down to simple sugars, making the apple sweeter to eat. So a riper apple has less starch present. The test involves spraying the apple flesh with an iodine solution, which turns the starch black. The starch level, can be measured by comparing the test apple to images that show different levels of starch and define the ideal colour pattern.