Calcium and phosphate minerals combine to keep bones strong and rigid. Soaking chicken bones in vinegar for several days leaves bones soft and rubbery. The acid component of vinegar reacts with calcium compounds in bones, making the calcium soluble so that the water component of vinegar can then dissolve the calcium from the bones, leaving the bone less rigid and able to bend.
Chemical Reaction With Bone and Acid
The acetic acid in vinegar and calcium carbonate in chicken bones react together to produce calcium acetate -- a calcium salt that is soluble in water -- and carbonic acid. When calcium acetate is formed, it diffuses out of the bones and into the water component of the vinegar. Carbonic acid is not stable at room temperature, and it immediately breaks down into water and carbon dioxide gas, which is released as small bubbles that can be seen if the bones are watched closely over time.