Test a minimum of 10 fruits per block, preferably 20. Growers should develop scales of their own for their varieties and growing conditions. This publication contains a Generic Starch-Iodine Index chart that is an excellent picture guide for making starch index determinations. Seed color, fruit color, and fruit texture Seed color can also be used in a general way to determine maturity. The test probably works best for early-maturing varieties.
Flesh color can help determine the amount of chlorophyll still present in the apple.
If, as you chew the fruit, the flesh tends to wad up or seem cottony, the apple has not reached an ideal stage for harvest. This is a subjective test and probably no two people will always agree. Remember, harvesting fruit at its best requires skill and experience. Do not rely on just one maturity test, but try to use several different tests each year.