The taro skin contains tannin substances, tannin substances encounter iron that becomes black, so this is the tannin substances in the taro and iron pot chemical reaction.

Also known as ellagic acid substances, is a plant component with tanning properties, complex structure, tanning effect of the main body is polyvalent phenol. Generally has an astringent flavor, can make proteins, alkaloids precipitation.

Extended information

Shopping tips

Often the appearance of taro will look extra rough, it looks like there are a lot of hairs on the top, which should be pinched, to see if there are some bad symptoms exist, such as too hard or have a strange flavor out.

Observe the freshness, new good taro are just out of the soil, this is to see whether fresh. Like the old old taro appearance looks very stale, there is no kind of just dug out of the soil out of the breath.

Baidu Encyclopedia - Tannin

Baidu Encyclopedia - Taro