Tannic acid is tannic acid extracted from gallnut. Yellow or light brown light amorphous powder or scale; No peculiar smell, slightly special smell and extremely astringent taste. Soluble in water and ethanol, soluble in glycerol, almost insoluble in ether, chloroform or benzene.

Its aqueous solution will turn blue-black when it meets iron salt solution, and adding sodium sulfite can delay the discoloration. In industry, tannic acid is widely used in tanning and making blue ink. Tannic acid can condense protein. People use tannic acid to chemically treat pigskin and rawhide, and tannic acid can solidify the soluble protein in rawhide.

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Properties of tannic acid

Pure tannic acid is light yellow powder, which is easily soluble in water. Persimmons sold in the market are generally soaked in lime in advance or covered with lime. Because lime can solidify tannic acid and make it insoluble in water, tannic acid will never find trouble with the tongue again, and persimmons will not be astringent. Heating can also cure tannic acid.

So some people like to soak persimmons in hot water, one is to remove astringency, and the other is to remove bacteria. Sometimes, even if you don't use an iron knife to cut pears and persimmons, there will be some black spots on your skin. This is another chemical change. Because tannic acid contains a large number of phenolic hydroxyl groups, it is very sensitive to light and is easily oxidized and turned into a black oxide.

Another name for tannic acid is tannic acid. Tannic acid can be found everywhere in nature, and many barks contain tannic acid. In the areas of Sichuan and Yunnan in China, there is a gallnut tree (also known as Rhus chinensis) with some tumors, which contains a lot of tannic acid.

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