Iodine test

The iodine test is a test that is able to detect starch using iodine as a chemical indicator. Example uses include brewing beer, and determining when apples are ripe and can be harvested.

If starch is present, the iodine solution will turn dark blue/purple. If there is no starch, the iodine will stay brown.

Iodine Test Media

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  A bottle of iodine solution used on apples to determine the correct harvest time. The chart shows the level of residual starch.

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  The cut surface of an apple stained with iodine, indicating a starch level of 4–5.

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  A starch agar plate filled up with iodine. A holo is present around B. subtilis.