An indicator of the ripeness of fruit, particularly with pome fruit, is the degree of the starch/sugar transformation.

This effect is made use of with a relatively simple ripeness test, by dyeing the proportion of starch contained and comparing the extent of the discolouration against a standardized colour chart.

In practice one uses an iodine/potassium iodide solution ( "Lugol solution" : 10 g potassium iodide, 5 g iodine crystalline filled up to 1,000 ml with distilled water; the solution is also available in pharmacies). The fruit is sliced through with a sharp knife at the level of the widest diameter; the iodine solution is then applied or sprayed onto the cross section. Since starch immediately turns brown upon contact with iodine, the degree of starch decomposition can be visually determined after 1 to 2 minutes and compared against the colour chart.

The basic conclusion holds: the lesser the discolouration, the less residual starch, and the riper the fruit.