When Will Apples be Ready to Pick?

Will wet soils bring the crop on sooner? What effect will cloudy skies have on maturity? Are we ahead or behind last year? One way to monitor the maturity development and answer these questions is using the starch-iodine test.

What you need: Assemble a testing kit to carry with you to evaluate your apples. You will need:

• A shallow dish to hold the iodine solution

• A sharp knife to cut apples

• A squirt bottle of water to rinse off treated apples

• Starch-sugar conversion charts for each cultivar (see below)

• Paper towels and garbage bag

• Paper & pen to record dates and results

Prepare the iodine solution: Contact your pharmacy to prepare a fresh batch - it’s best to make fresh solution each harvest season. Store the solution in a dark coloured (or foil-wrapped) bottle, away from light.

Caution: Remember that iodine is poisonous. Correctly label the bottle and keep away from children and pets. Consider treated apples poisonous - do not feed to animals or use in composting. Prevent pets from licking the treated fruit. 

Here’s the recipe to give to the pharmacist:

1. Dissolve 8.8 grams of potassium iodide in approximately 30 ml of warm water. Gently stir the solution until the potassium iodide is dissolved.

2. When it is properly dissolved, add 2.2 grams of iodine crystals. Shake the mixture until the crystals are thoroughly dissolved.

3. Dilute this mixture with water to make 1.0 litres of test solution. Mix well. 

Starch-iodine charts: Here are several online sources of maturity charts:

• Empire, Idared and Spartan - www.omafra.gov.on.ca/english/crops/facts/00-027.htm

• McIntosh and Red Delicious - www.omafra.gov.on.ca/english/crops/facts/00-025.htm

• Gala - www.umass.edu/fruitadvisor/clements/articles/gala.jpg

• Liberty - www.umass.edu/fruitadvisor/clements/articles/liberty.jpg

• Cortland - www.umass.edu/fruitadvisor/clements/articles/cortland.jpg

• Mutsu - www.umass.edu/fruitadvisor/clements/articles/mutsu.jpg

How to do the test: Slice apples across, dip cut edges in solution, rinse with water, and compare to the charts. A simple test to determine how much starch has changed to sugar – and if apples are ready to pick.

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