The color of garlic

Harold McGee has a new occasional column in the New York Times, called The Curious Cook, and dedicated to the chemical properties of food and how cooking works. McGee, of course, wrote the essential book on food chemistry, On Food and Cooking. In today's column, in addition to recounting his personal history of how he got into writing about food science, and noting some interesting new theories about smell, he tackles the interesting colors of garlic and onions.

Now that grocery stores have started selling containers of whole peeled garlic cloves, I've been buying them, thankful for the end of the tedious chore of peeling off the skins. But a container of garlic in the fridge, uh, "ripens" rather quickly. After a couple of weeks in a closed container, the moisture causes the garlic to become pungent, its odor permeating through the rest of the fridge. Storage in an open container is hardly better. So I started looking into preserving garlic. First idea: store in olive oil! Bad idea! Dangerous! It turns out (as I learned through Google research, not through personal experience, thankfully), garlic in olive oil is a prime way to grow Salmonella bacteria in your own home! The oil seals out air, while the garlic has the optimal pH to grow the toxic anaerobic cultures. So don't do that. Instead, to preserve garlic, you have to soak it in an acidic solution, like a 1:1 vinegar/water mixture. This is safe and lasts for a long time. To use preserved garlic, just rinse it, dry it off, and mince normally; it has a higher liquid content then dried garlic, but seems to taste similarly.

But, the garlic sitting in the vinegar sometimes turns blue. And that's what McGee wrote about today:

I hear every year from cooks who have been alarmed at seeing normally pale garlic turn bright green and even blue, sometimes when the cloves are pickled whole, sometimes when they’re chopped and cooked with other ingredients. I’d often been puzzled by little blue-green specks when I made garlic bread with loaves of sourdough, but I was really rattled the first time I puréed raw garlic, onion and ginger together in a blender to make chicken in yogurt from Madhur Jaffrey’s “Invitation to Indian Cooking.” When I fried the purée the entire mass turned turquoise blue.

...a strong green color develops in [Chinese preserved] garlic only with acetic acid, the main acid in vinegar (also found in sourdough), because it’s especially effective at breaching internal membranes and mixing the cell chemicals that react together to create the green pigment. The pigment itself turns out to be a close chemical relative of chlorophyll, which gives all green leaves their color.

Interesting, I just went to look at my blue garlic, and the color has faded! McGee doesn't talk about it, but perhaps the "multipyrrole" molecules he talks about that give the color are unstable. In any case, I am relieved to know that the blue and green chemicals are perfectly safe to eat.