If long-term storage is anticipated, fruit should be harvested in the higher firmness range. This index, even when used independently, is of value in determining when apples are too soft or ripe for storage. It is important to remember that firmness varies from season to season and factors other than maturity can affect firmness. For example, fruit on the outside of the tree may have a higher pressure rating than fruit on the inside. Fruit size will also influence firmness readings.
Large fruit is usually softer.
Soluble solids content Sugar content of the juice increases as the apple matures. Soluble solids of apples, which are highly correlated with sugar content of apples, are measured with a hand refractometer. The accuracy of this index varies from year to year and from tree to tree, depending upon the leaf-fruit ratio. Percentage of soluble solids for commercial harvest depends on variety. Starch content Starch content gradually decreases as the apple matures.