Black garlic is made when heads of garlic are aged under specialized conditions of heat and humidity. Bulbs are kept in a humidity-controlled environment at temperatures that range from 60 to 77 °C (140 to 170 °F) for 60 to 90 days. There are no additives, preservatives, or burning of any kind. The enzymes that give fresh garlic its sharpness break down. Those conditions are thought to facilitate the Maillard reaction, the chemical process that produces new flavour compounds responsible for the deep taste of seared meat and fried onions. The cloves turn black and develop a sticky date-like texture.
Bacterial endophytes capable of fermentation and with a strong ability of heat resistance have been identified in common garlic and black garlic. These may have relevance to black garlic production.