Arielle Johnson, the head of research for MAD, in Copenhagen, has a Ph.D. in flavor chemistry from UC Davis. Every other Monday, she’ll be writing this advice column—think of it as office hours with a professor of food, science, and flavor. Send her a message at [email protected] or tweet @ariellejjohnson and she will do science at you.
Yo Dr. Flavor-
What’s the deal with black garlic? Is it fermented?
Inaki the Noma intern
Black garlic is what you get when you heat whole garlic cloves at about 60ºC for around forty days in a relatively humid environment. The garlic turns black (or very dark brown) and becomes sweeter and more acidic, pliable, and sticky. It also loses the pungency of fresh garlic, allowing you to use those fruity, roasty, caramelized flavors in places where popping in a whole clove of garlic would be not so nice.
The punchy “HEY IT’S GARLIC” smell you get from fresh garlic comes from a molecule called allicin, which is created by the garlic plant for the sole purpose of making you cry. It’s part of the plant’s defense system against herbivorous predators; when you cut (or bite) into a garlic clove, tiny bags of molecules inside the garlic cells are ruptured, and an enzyme called alliinase meets the molecules of alliin (which has no smell) and converts them into volatile, tear-inducing (“lachrymatory”) molecules of allicin. This doesn’t really happen in black garlic, which suggests that the alliinase enzyme is denatured—or in other words, thermally inactivated—by sitting around at 60ºC for so long.
But a lot of other molecules form during this heated period: that famous cascade of non-enzymatic browning reactions called the Maillard reaction—you’ll know it from baked bread, roasted or seared meat, and coffee, among many other things—creates black garlic’s toasty, caramelized, roasty aromas. I know what you’re thinking: But it usually takes much higher heat to get these Maillard flavors—higher than the boiling point of water, which is one of the reasons that boiled things don’t brown! Well, the chemical reactions that make these flavors can actually happen at lower temperatures, just very slowly. What takes an hour at 200ºC takes more than a month at 60ºC.
I still haven’t answered your question. Is black garlic fermented? Well, while you’ll often see it referred to as “fermented black garlic,” and while I can’t actually find any studies on its microbiology, I feel confident saying that black garlic is the result of non-microbial chemical and biochemical transformations rather than a true fermentation.
So what does that mean? If we’re being biochemical strict constructionists, fermentation is a cellular process that converts sugars into alcohol, organic acids, or gases, in the absence of oxygen. This includes alcoholic fermentation and lactic fermentation, where single-celled organisms (yeasts and lactic-acid bacteria) feed on sugars for energy and produce alcohol and lactic acid without using oxygen. This definition would exclude vinegar, koji, and molded cheeses, which are definitely transformed by microbes, but ones that do use oxygen in their metabolisms. It would also exclude slow enzymatic and non-enzymatic processes that don’t involve living microbes, like garum/fish sauce/nam pla/ishiri and black garlic. But, more colloquially, it’s pretty accepted to use the word “fermentation” to mean “transformation of ingredients by microbes,” and you’ll often see pretty technical people—for example, vinegar scientists—talk about “acetic fermentation” even though the microbial transformation of alcohol into vinegar requires oxygen. So, as a reward for reading this talmudic discussion, I give you permission to call vinegar and molded ingredients “fermented,” but let’s file black-garlic-making in our mental culinary toolbox of “cool slow processes that aren’t technically fermentation but which we can still use to transform ingredients.”