It is very important NOT to wait until the background color is yellow to start harvesting ‘Ambrosia’ that will go into storage. When the background color is yellow, the fruit will be over-mature and more prone to internal browning and splitting. ‘Ambrosia’ background color should show more green than yellow at harvest time for good storability.
The starch index can be an overall useful indicator of ‘Ambrosia’ fruit maturity. Starch values of 2.5 to 4.0 at harvest time are optimal for fruit storage. ‘Ambrosia’ with starch values above 4 should not be stored for long periods of time, as these will be prone to internal browning and splitting.
‘Ambrosia’ produces very little ethylene during maturation on the tree. As starch is degraded and color changes, there continues to be only trace amounts of internal ethylene present (<1 ppm). This makes internal ethylene a poor indicator of fruit maturity for ‘Ambrosia’.
IAD readings from a delta absorbance (DA) meter can be useful for accessing fruit maturity in ‘Ambrosia’. It has been suggested that ‘Ambrosia’ should be harvested when IAD readings average 0.7 to 0.6 for storage. Fruit with values near 0.5 and below should not be stored for extended periods, while those with less than 0.3 should be marketed as soon as possible. Be sure to take DA meter readings on the margin between the blush and non-blush areas, and not directly on the blush or shade sides of the fruit.
Optimum harvest of ‘Ambrosia’ for storage tends to be around the same time as ‘Empire’. ‘Ambrosia’ in Norfolk County (ON) at optimum maturity have measured <1 ppm internal ethylene concentration, fruit firmness ~18-20 lb, starch index ~2 to 4, and background color yellow 2 to 3 on the BC color chart (Figures 1 and 2). Apples harvested later tended to become mealy and soften more rapidly, as well as develop more disorders and greasiness during storage.