If you watch any television food programs, you see some uncommon, unusual ingredients used by chefs. On one recent show, the chefs used black vinegar. So what is this type of vinegar?
Most black vinegar is made in China and is a dark, fragrant vinegar. It is made from sticky white rice, water and salt. Some brands may also use millet, whet, sorghum or soybeans.
For more flavor, they are aged to get a sweet, smoky, earthy flavor. It is not the same as soy sauce.
Connoisseurs of black vinegar claim the best black vinegars are made in the province of Chinkiang (a.k.a. Zhenjiang.)
Source: https://www.cooksinfo.com/black-rice-vinegar and https://bit.ly/2p5ov1D