Evaluating Maturity of Empire, Idared and Spartan Apples
Table of Contents
The starch-iodine test is one of several methods used to determine apple fruit maturity. The procedure for this test can be simply performed in the field.
Always use a freshly prepared solution at the beginning of every season. This solution is sensitive to light and should be stored in a dark container. A dark-coloured bottle or a glass jar wrapped in aluminum foil will serve the purpose. Chemicals needed for this test are potassium iodide and iodine crystals. A pharmacist or a chemist can use the following recipe to make up the iodine solution.
Iodine is a very poisonous chemical. The iodine solution should be properly labeled and kept away from children and pets. Do not feed apples used in the test to any animals or used in composting. Do not allow pets to lick the fruit after testing. In case of ingestion of either iodine, or iodine treated apples, induce vomiting and consult a physician immediately.
It is very important to select representative samples for testing. Sample at least 3 trees of each cultivar in each orchard in order to give reliable results. Sample 10-20 apples from various parts of each apple tree.
In order to perform the test properly, the following requirements must be met:
Apples will show the starch-iodine test scores starting from 1 and ending at 9 over several weeks during the fall season. How to decide "What score indicates the proper harvest date for each grower's orchard?" depends mainly on when the apples will be marketed and what type of storage is used. Apples destined for long-term controlled atmosphere (CA) storage have to be picked early and therefore require a lower starch-iodine test score. Apples destined for immediate fresh market and processing plant can be picked later and therefore require a higher starch-iodine test score. The selection of the proper score largely depends on each individual operation. No single fixed score can be recommended to guide the whole industry.
In general, apples with starch-iodine test scores of 1, 2, and 3 are considered immature. Apples with scores of 4, 5, and 6 are considered mature. Apples with scores of 7, 8, and 9 are considered overmature. Normally, apples with a starch-iodine test score of 3 or 4 are good for long-term CA storage.
Figure 1. Rating Chart for Empire
Figure 2. Rating Chart for Idared
Figure 3. Rating Chart for Spartan
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