Apple Ripeness Tests

October 12, 2010

In yesterday’s posting, I mentioned I had picked some green apples unintentionally, and so I didn’t process them right away but instead waited a week, knowing full and well that these apples would not make the best cider.

Between this and the green Gravensteins, I was determined not to allow something like this to happen where I waste time and money picking green, unripe apples. I needed some way to test the apples while in the orchard. There are two tests for that: a refractometer, and an iodine starch test.


A refracometer needs just a little tiny bit of juice to accomplish what a hydrometer can do, which is to test the amount of sugar in the juice to figure out how much potential alcohol the juice could ferment. With a little bit of juice in the refractometer, it is then viewed at though light and a reading is taken by how much the light bends when it passes though the juice. Winemakers use them all the time to deterime if grapes are ready to be harvested. My husband has been wanting to buy a refractometer for his brewing as they are not as tempature sensitive as a hydrometer is. However, a refactometer is expensive, and it only tells me how much sugar there is, not how ripe the apple is.

An iodine starch test, on the other hand, can tell me how ripe the apple is buy showing me how much starch is in an apple. Iodine turns blue when it comes into contact with starch. Green apples are full of unfermentable starch, bus as they ripen, they convert the starch into fermentable sugar, so a ripe apple will not have much of a reaction with iodine and I will know that it is ripe. Once I crush and press the ripe apples, I can then use my much cheaper and already purchased hydrometer to determine the actual sugar content.

Apple Ripeness by Iodine Starch Test

However, it turns out getting a hold of iodine is not as easy as it once was. In theory, it should have been as easy as going to a pharmacy and finding it in the first aid isle. However, the first aid industry is moving away for iodine, and in talking to the pharmacists, there is little home use demand for it and there are also some concerns about using it in meth production. However, all the pharmacies I talked to were quite willing to order it for me and promised it would be there the next day. I ended up ordering around 1 pint of iodine, and it cost me a little over $20. I then used a sponge paint brush to apply the iodine to a cut apple.

My apples failing a iodine starch test. They are unripe.

The good news is that two weeks after I did this test on that batch of apples, I tried it again and found that they had ripened on their own in my garage, though I’m sure the sugar content was less than if they had stayed on the tree, so it was still not an ideal situation.

One other word of warning – iodine stains very easily. In the picture, I’m actually using a black plate, but I recommend wearing an apon and doing the test outside due to the staining power of iodine.


4 Responses to “Apple Ripeness Tests”

  1. […] But in cider making, I said that I avoided starch because it doesn’t ferment, and I use an iodine test to make sure an apple is ripe and has therefore converted the starch to sugar.  Well, in beer making, they encourage the grain to start to sprout, which then allows an enzyme […]

  2. […] a day I posted. They were mostly reading the homepage for that day, My Italian Apple Grinder,  and Apple Ripeness Test.  The previous one day record was set in 2011 regarding liquor sales laws here in in […]

  3. Jeremy Says:

    well I’m searching around and have yet to find any one questioning the question that I have. If one has a schedule that does not permit harvesting apples when they are ripe, then could one pick said apples early… really at any point when their are starches present in the apples… crush apples to extract juice… then add amylase enzyme or a similar enzyme that converts starch to sugar to juice when pitching yeast and expect all starches to then be converted to fermentable sugars???? Does any one have any experience in this area???

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