The flesh varies from a golden brown to a dark brown or almost black, depending on the variety of apple and the circumstances of freezing and thawing. They are somewhat sunken and soft toward the center and have a dull-brown or slate color over most or all of the center. Freezing injury may occur when temperatures drop below the freezing point of the fruits. The freezing points for all major apple varieties have been determined experimentally. When an apple freezes, ice crystals form between the cells.
Small crystals form at temperatures slightly below the freezing point of the fruit.
A further decrease in temperature will result in the formation of larger crystals in the spaces between the cells as more water is withdrawn from the cells. Injury occurs from the physical forces exerted on cells by the ice crystals, and from chemical reactions within cells from which excessive amounts of water have been removed. The injuries result in the death of the cells. Generally the cells in the vascular tissues are somewhat more sensitive to injury than those in other tissues, and the first symptoms are most likely to appear in the vascular tissues. Little can be done to prevent the freezing that occurs on late maturing varieties in the orchard, but damage can be minimized by waiting until the fruits have thawed before picking or handling them.