Black Garlic is fermented, aged garlic. The skin doesn’t black, just the inside cloves.
Black Garlic was historically made in Japan, Korea and Thailand. It was sealed in ceramic or earthenware pots and let sit in a cool area for several months to ferment naturally. It has a mellow, sweet taste, like slow-roasted garlic, with none of the acridness of regular raw garlic. Some compare the taste to liquorice or balsamic vinegar. Any garlic smell is gone. The garlic is chewy and sticky from the sugars in it. It is naturally black; no artificial colouring or flavouring is needed. The fermentation produces melanoidin, which makes it black.
Most of the Black Garlic sold in North America comes through the Black Garlic Company of Hayward, California (founded 2008 by Scott Kim and John Yi.) The company puts fresh, unpeeled garlic heads in a heat and humidity controlled patented machine to ferment for three weeks, then it is then cooled and dried for a week before being sold on. In South Korea, companies such as Ui-Seong Black Garlic use a different process: theirs is aged and fermented on trays in artificial cellars.