Why Did My Garlic Turn Blue?

Published Categorized as Food
A photo of a man eating garlic on a blue backgroundufabizphoto /Depositphotos

Let’s talk about the incredible things you never knew about garlic. Like its tendency to turn blue when you kind of expect it to stay white.

Cooking is fun, but let’s face it, the prep work of peeling and slicing is usually not. That’s why I was thrilled when I found a jar of pre-peeled garlic on sale at the market.

The uses were limited only by my imagination and ingenuity! I could mix it with basil leaves to make green pesto, slice it thinly and give it a quick roast to sprinkle it over rice, soups, and sautéed vegetables, or add it to marinates to give steaks that garlic zing.

Great meals, minimal prep.

But after a week, I opened the jar and found that my treasure trove of garlic cloves had turned an unsightly shade of blue. Not even a hint of blue—but a vibrant turquoise. Say what you will, but this isn’t a color you expect to see on your food.

So why did my garlic turn blue? After a bit of research, here’s what I found out.

To put it simply, it’s a chemical reaction of the enzymes in garlic to its environments—similar to how potatoes or avocados can oxidize when exposed to air.

In this article we’ll talk about why garlic changes color, how to prevent it from turning blue, and whether and how you can use discolored garlic in cooking.

Why Does Garlic Turn Blue?

Garlic contains a sulfur compound called alliin (no, not a typo), and enzymes called alliinase.

When garlic is still whole or intact, the two chemicals are “locked” in their individual cells and don’t interact with each other. That’s why, when you give a fresh bulb of garlic a good sniff, you won’t detect any odor at all.

The moment you cut or crush the garlic, the situation changes…

The allin and alliinase mix together to create a new compound called allicin.

This is what gives garlic its very rich and pungent scent and flavor—and why the strength of the garlic flavor also depends on how you cut it (more on that, in a moment). Whole garlic is very mild, while crushed or pounded garlic seems richer.  

Normally, you only crush or cut garlic right before you cook it, so there’s no time for the garlic’s color to noticeably change.

But if you leave sliced garlic cloves in the fridge for a long period of time—and they happen to be bruised or exposed to other compounds—its natural enzymes and sulfur compounds will break down and form multi-pyrrole molecules.

Multi-pyrrole molecules sound scary, I know, but they really aren’t.

These are the molecules that create organic pigments; the same kind of pigments we put in cakes and such. One example of a very common multi-pyrrole molecule is chlorophyll, which plants make during sunlight and gives them their quintessentially green color.

Do Only Certain Kinds of Garlic Turn Blue?

Older garlic will turn blue faster than new garlic. That’s because the garlic has built up larger amounts of chemical precursors that lead to the formation of multi-pyrrole molecules. In retrospect, the market vendor probably peeled old garlic whose bulbs or skins had become dry and withered, so it would sell faster.  

Garlic bulbs with bluish tints in its skin is also more likely to discolor once its peeled. That doesn’t mean that they’re “old bulbs” though—some garlic varieties just contain more chemical precursors, because of the region or the conditions where they were grown.

Pickled garlic discolors quickly, because of the introduction of acids. The allicin in the vinegar interacts with the garlic compounds and speeds up the discoloration process.

Cooking environment can affect the garlic’s color. Sometimes, garlic turns blue because of compounds that it’s exposed to, such as trace minerals in the water or the minerals in the metal in your pan (e.g., copper, aluminum, iron and tin).  

Is Blue Garlic Still Safe to Eat?

Just like chlorophyll doesn’t make you sick, the multi-pyrrole molecules in garlic are generally harmless.

The color doesn’t affect the scent or flavor, and it won’t make you sick. And if you’re toasting the garlic, or adding a dark-colored sauce, you won’t even notice the color by the time you’re done cooking.

As a matter of fact, in some cultures, garlic turning blue is pretty much sought after.

For example, the Chinese actually pickle garlic in order to achieve a beautiful jade-green color, which they consider to be beautiful and auspicious.

This is called “laba garlic” and served during the Lunar New Year or Spring Festival. (Watch this video to see how it’s done—it even shows how using vinegar with different acidity levels can create different shades of blue.)

How to Prevent Garlic From Turning Blue

If blue garlic bothers you, there are ways to avoid discoloration during cooking.

Cook cut or grated garlic right away. Once you cut or crush garlic, the chemical reactions begin. So if you’re doing a lot of prep work, do all the other vegetables and ingredients first, and then prepare your garlic last.

Store peeled garlic in the refrigerator. If you pre-prepare garlic, keep it in the refrigerator until you’re ready to put it in the pan. However, the refrigerator can only slow down the process—after a few days, discoloration will occur (like what happened to my bag of peeled cloves).

Use young garlic if you’ll be cooking at low temperatures. Some recipes will call for sweating the garlic, or simmering it at a very low temperature for a long time. The heat can actually speed up the discoloration process, so it’s best to use fresh, young garlic cloves or varieties that aren’t already prone to turning blue.  

Cook old garlic cloves at high temperatures. If you have old garlic that’s been sitting on your counter for a long time, or pre-peeled or pre-crushed garlic from a jar, cook it quickly at a high temperature so it doesn’t have time to turn blue.

Cook onions first. Onions also contain some chemical precursors of garlic. Completely cooking down the onions before adding garlic can bind these compounds, so they don’t interact with the raw garlic and change their color.

Add acid last. Acids speed up discoloration. So if you’re making a dish that requires adding vinegar or lemon, add these after the garlic has already been cooked.

Use a stainless steel pan. This won’t react to garlic, unlike cast-iron, tin, copper or aluminum.

Words of Caution

There’s a difference between garlic that’s turned blue, especially in liquid, and garlic that’s turned moldy when left out or kept in the fridge for too long.

Moldy garlic is not safe to eat and should be disposed of immediately. Moldy garlic is also easy to tell apart because mold is fuzzy, grows in spots, and gives the bulbs a distinct peaty, slightly medicinal smell.

If you suspect that your garlic has turned moldy, err on the safe side—wrap it in plastic and throw it in the garbage. (And don’t put it off for later as others in your household can make the mistake of eating it.)

Final Words

There are worse things that can happen to a dish than blue garlic. While the color can look odd at first, it won’t affect the quality of your cooking. It will bother you more than anyone else, and if they do notice it you can impress them with your knowledge of chemistry.

By Jim Stonos

When Jim isn't in the kitchen, he is usually spending time with family and friends, and working with the HCW editorial team to answer the questions he used to ask himself back when he was learning the ropes of cooking.