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Why Does Garlic Turn Blue and Is It Safe to Eat?

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This garlic turned blue in the home kitchen during a pickling process.

This garlic turned blue in the home kitchen during a pickling process.

The Blue Garlic Surprise

Perhaps you, like I, have been cooking with garlic for years, expecting garlic to remain a kind of off-white, uninteresting color throughout the cooking process. Then one day, the garlic turns a bright blue-green, even an aquamarine or turquoise color, transforming a familiar dish into an odd concoction of color accents that undermine the familiar tones we expect.

The visual impact of this changed dish can be likened to the colors of trees in autumn, with their red, gold, green, and dun colors, suddenly being splashed with fluorescent hues of blue and green reminiscent of the op art of the 60s. Autumn colors aren’t supposed to display this jarring contrast, nor is food. It’s unsettling.

If one day your garlic turns a shocking shade of blue, making your homemade pickles, pork roast, or pot of cabbage and kielbasa look strange and even poisonous, be assured that no matter how strange it looks, it hurts only your eyes, not your body.

My Blue Garlic Experience

This past Thanksgiving, I volunteered to bring our family's traditional Polish kielbasa and cabbage dish to the holiday dinner. Ours is a simple recipe consisting of traditional Eastern European ingredients, including onion, garlic, cabbage, sausage, black pepper, and apple. Our version of this dish is mild-tasting and slightly sweet, and we all love the recipe just as it is. But this year, I decided to charge up the flavor a bit by adding sauerkraut to the cabbage, something I had never done before.

By early evening on Wednesday, my kitchen smelled heavenly from the onions, cabbage, apple, and kraut slowly simmering on the stovetop, from the freshly pressed whole head of garlic waiting to go into the pot, and from the thinly sliced kielbasa resting on the cutting board. It was a peaceful moment, leaving me with the feeling that all was well with the world.

An hour before the pot was finished, I added the pressed garlic and sliced kielbasa and folded them in. Immediately, I began to see a few bright blue-green bits of color in the pot. As I stirred the pot, more began to appear. Soon, the pot contents were lavishly sprinkled with shocking, almost neon-like, blue-green, confetti-looking bits. I started picking them out and putting them in a small dish but soon gave up. It seemed the more I removed, the more it appeared.

This copper sulfate is about 20 years old and just about a perfect color match to my blue garlic.

This copper sulfate is about 20 years old and just about a perfect color match to my blue garlic.

It took a few minutes for me to realize that the garish blue-green material was pressed garlic that had gone through a color transformation. Suddenly, a long-forgotten memory began to surface about making copper sulfate crystals in my high school chemistry class. The color sprinkled around the cabbage and kraut in the pot looked somewhat like the color of those crystals, only a bit more green, in fact, much the color of the corrosion that can appear at the junction of a car battery and its terminal.

Never in my cooking life had garlic turned blue-green, but never had I cooked my family’s original kielbasa and cabbage dish with sauerkraut, either. I suspected the color change had something to do with the acid in the kraut and whatever chemicals were in the garlic.

Garlic Turning Blue Is Sometimes Called "Greening"

This term is a misnomer because multipyrrole production in garlic, the process that turns garlic shades of blue and green, has nothing to do with restoring freshness, aligning with principles of the Green Movement, or exposing garlic to light.

If you would like more in-depth information on the chemistry behind garlic turning blue, read the excellent article written by The New York Times columnist Harold McGee When Science Sniffs around the Kitchen. Scroll down to about the last third of the page.

How Does Garlic Turn Blue?

Studies prompted by the food industry as a result of increasingly occurring batches of accidentally colored garlic have begun to unlock the mystery of why garlic turns blue. These studies have found a number of complicated chemical processes responsible for garlic turning shades of blue, green, and even pink under certain conditions.

The colors occur when enzymes and amino acids present in garlic react with the sulfur compounds responsible for garlic’s pungent smell. The reaction causes different multipyrrole molecules to form. Different types of multipyrrole molecules are responsible for the different pigments. The multipyrrole molecule most familiar to us is chlorophyll, produced by plants in the presence of light; however, chlorophyll is not produced by the cooking or pickling processes that turn garlic blue.

Variables Involved in Garlic Turning Blue

Here are some of the factors that have an influence on garlic changing color:

  • Age of the garlic: Some sources say that newly harvested, unaged garlic (meaning garlic with a high water content) is more prone to turning color; other sources say the opposite.
  • Added presence of acid: It seems clear that the presence of acids such as lemon juice or vinegar can cause a color change, although not always.
  • Temperature: Garlic that is pre-heated may or may not react with acid to change color.
  • Color of garlic bulbs: Some garlic is pure white, and some have tinges of purple or red; the colored garlic may be more prone to turning blue-green.
  • There is at least one place in the world where garlic is deliberately turned into a jade-green color. For centuries the Chinese have produced Laba garlic, a jade-green pickled garlic that is an important food accompaniment to celebrating the harvest festival of Laba. If the Chinese can perfect this color change in garlic, why do we have only “accidents”?

If your garlic turned blue by surprise, you may have already researched this accident and found discussions about sulfur compounds in garlic reacting with copper present in water supplies, utensils, or copper-rich foods. There may be validity to this explanation, in which case the blue color indicates the presence of copper sulfate, not the presence of multipyrrole pigments.

Blue Garlic Facts for the Home Kitchen

Until more research is completed, here’s some helpful information to have when your garlic turns blue in your kitchen:

  • Absent any sign of spoilage, such as foul smell or mold, your blue garlic is safe to eat.
  • There are so many variables causing accidental garlic color change that it may be impossible for you to duplicate this surprising event in your home kitchen.
  • No one has yet discovered how to turn blue garlic back to white, although continuing to heat the turquoise garlic may dull it down to a pinkish-brown.
  • When serving your dish that contains aquamarine bits of color, say nothing. Most folks, if they notice this color at all, will never ask, knowing that whatever you bring to the table is good to eat because you brought it. If someone does happen to ask why there are bright blue-green flecks of color in the dish, take them aside and tell them your secret and that you expect them to keep it: “The dish needed some color.”

© 2011 Sherri