Black garlic is “hot fermented” fresh garlic (Allium sativum) has been produced in several Asian cultures for centuries.  Full bulb garlic is kept at a controlled high temperature (60–90°C | 140-195°F) and high humidity (80–90%) for a week to several months.  A Maillard reaction (browning) turns the garlic its black color.  Natural biota (bacteria and yeasts) capable of growth at these high fermentation temperatures contribute to some chemical changes, while the heat of the process results in other chemical changes.  In the end, the garlic is sweeter, lacks allicin (sulfur bitterness), and is umami-rich.  Unfortunately, there is little research-based information on the “fermentation” characteristics of black garlic.

Food Safety | The “fermentation” temperature MUST be at 57°C (135°F) or above.  Failing to maintain this temperature control could lead to foodborne illness.  Foodborne illness bacteria will begin to grow at temperatures just under 57°C (135°F) including Clostridium perfringens and Clostridium botulinum.  The toxin produced by C. botulinum is the most potent and deadly toxin known to man.  For that reason a temperature datalogger is recommended.  This tool will monitor temperature for many weeks.  The data can be downloaded to a computer file.  It is advised to place the datalogger unit outside the fermentation chamber and the probe inside.  Prolonged exposure to the warm temperatures and high humidity can shorten the life of the datalogger unit.

The black garlic fermentation is quite different than a traditional vegetable fermentation like sauerkraut (cabbage) or pickles (cucumbers).   Both cabbage and cucumbers have natural (biota) lactic acid bacteria that rapidly ferment the vegetable sugars in a salt brine at ambient temperatures.  This rapid fermentation inhibits the growth of pathogens like C. botulinum.  Once the brine reaches an acidity pH of 4.6 or less, C. botulinum cannot grow.  The black garlic fermentation may or may not result in an acid fermentation.

The post-fermentation properties of the black garlic determine how it must be stored for safety (ambient or refrigerated).

• If the pH is ≤ 4.2; the black garlic may be packaged for ambient (room temperature) sale.
• If the pH is > 4.2; the black garlic must be refrigerated or,
• If the pH is > 4.2; and the Aw (water activity) is ≤ 0.85, the black garlic may be packaged for ambient (room temperature) sale.
  Note that water activity meters are expensive (> $2,000).  Some food testing labs will test a sample for Aw at $10-$30 each.