Details on the Starch-Iodine staining test
A solution comprising 1% iodine and 4% potassium iodide is required. Local chemists no longer provide this solution as it is classified as hazardous under the COSHH regulations. These require precautions in the preparation of the mixture and its subsequent handling and use.
Iodine is harmful by inhalation and in contact with skin and potassium iodide may cause sensitization by inhalation and skin contact and is irritating to eyes and skin and may cause harm to an unborn child. It is advisable to wear suitable protective clothing, gloves and eye/face protection.
In the case of an accident or if you feel unwell, seek medical advice immediately. In the case of contact with eyes, rinse immediately with plenty of water and seek medical advice.
The solution should be applied to a freshly cut fruit surface. Although the pattern of staining may be apparent soon after application it is preferable to leave the stained sections for up to an hour in order to obtain a more reliable assessment.
A number of interpretation guides (CTIFL, Cornell University) exist for starch clearance patterns for apple and pear. Methods to quantify starch iodine patterns in apple have been automated. Isolcell (Italy) have developed the Amilon device for measuring starch clearance.