Tannin are oligomeric phenolic compounds of molecular weight ranging from 500 to >20, 000. They are soluble in water except for some high molecular weight structures. They can bind to proteins to form insoluble or soluble tannin-protein complexes. Tannin are generally found in apples, grapes and many other fruits and which give 'body' to the fermented beverages. Some structures of tannin compounds found in cider apples are shown below.

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