DA readings refer to the level of chlorophyll (green color) in the fruit, just below the skin. As the fruit ripens, chlorophyll levels decline. Therefore, low DA values are indication of advanced fruit maturity. Starch index, fruit firmness, and, to some degree, Brix values are commonly used to determine the harvest date for most commercial apple varieties. Generally speaking, fruits intended for CA should be picked at starch index (3-5), firmness (> 16 lb), and DA reading (around 0.60). Fruits intended for fresh consumption should be harvested at starch index (5.5-7), firmness (13-16 lb), DA reading (0.35), and Brix (12-14%).
