Why has my garlic gone blue?

January 11, 2007 6:56 AM

Pickling garlic has turned it blue - will it be toxic?

A friend recently decided to pickle a huge amount of garlic. She put the cloves in clean jars with fresh chopped red chilles and used distilled malt vinegar with a small amount of white wine vinegar. Everything was fine for about a week, then the cloves of garlic started turning blue. They are now a very bright blue (copper sulphate solution coloured). Has anyone had this happen to them and do you know what might be causing the blue colour to appear? Is the garlic likely to be toxic?

posted by patricio to food & drink (9 answers total)

According to Gourmet Garlic Gardens:

Garlic contains sulfur compounds which can react with copper to form copper sulfate, a blue or blue-green compound. The amount of copper needed for this reaction is very small and is frequently found in normal water supplies.

Garlic Can Turn Blue
Raw garlic contains an enzyme that if not inactivated by heating reacts with sulfur (in the garlic) and copper (from water or utensils) to form blue copper sulfate. The garlic is still safe to eat.

This was the first hit for pickled garlic turned blue on Google.
posted by bcwinters at 7:00 AM on January 11, 2007

From the first Google result from garlic blue -

"The garlic flavor remains unchanged, and it totally edible without bodily harm."
posted by Devidicus at 7:11 AM on January 11, 2007

This has happened to me when cooking something that has both garlic and lemon juice, fwiw.

Blue scampi may be safe to eat, but it isn't so appetizing.
posted by staggernation at 7:25 AM on January 11, 2007

This thread is useless without pics.
posted by Faint of Butt at 7:57 AM on January 11, 2007

i have no source on this, but isn't there some sort of thing-my-mom-used-to-say-to-make-food-scary about home-pickled garlic leading to anaerobic bacterial buildup and botulism?
sorry for the crappy non-research, i'm late for work.
posted by twistofrhyme at 8:10 AM on January 11, 2007

twistofrhyme: Yeah, you can get botulism if your garlic is uncooked and preserved in olive oil.

Storing Garlic in Oil - Warning! - Not Safe.

It's important to keep food safety in mind when storing garlic in oil. Low-acid foods like garlic can be a source of Clostridium botulinum bacteria which are found in soil, water, and air. Oil's oxygen-free environment is perfect for growth of this anaerobic bacteria. Garlic in oil, therefore, must be stored correctly to prevent botulism food poisoning.

Commercial garlic-in-oil mixtures are acidified to prevent bacterial growth. These products can be stored safely at room temperature. Unfortunately, acidification of garlic in homemade oil mixtures can't be recommended because no research exists to support proper procedures. Different people recommend different methods and time to acidify and it is hard to know who is right. Instead, it's best to store these hazardous oils in the refrigerator, but for a limited time only. This conflicts with the desire for long term storage.

When raw garlic is stored in oil, Clostridium botulinum bacteria can grow. These mixtures must be refrigerated to slow bacterial growth. After 3 weeks of refrigeration, the increased number of bacteria will become a food safety hazard. Therefore, these mixtures should not be refrigerated longer than 3 weeks.

When garlic is immediately removed after flavoring oil, the bacteria will not have a "food source" for growth. The flavored oil can be stored safely at room temperature.

When vegetables or herbs are dried, water will not be available for bacterial growth. Therefore, DRIED vegetables or dried herbs (including garlic) in oil can be stored safely at room temperature. Note. Tomatoes are high in acid. Therefore, plain dried tomatoes in oil can be safely stored at room temperature.
posted by SpecialK at 8:14 AM on January 11, 2007

thanks bcwinters. I am guilty as charged and suitably ashamed as I'm always cross when other askers don't do their google homework.
posted by patricio at 8:23 AM on January 11, 2007

I didn't mean that to seem like a "shaming"...sorry if it came across that way. I just thought "hey, I used some good terms to get the Google Fu, might as well share 'em." For all I knew, you might have tried "vinegar garlic discoloration" or "garlic and malt vinegar reaction" or heaven knows what :)
posted by bcwinters at 10:41 AM on January 11, 2007

Harold McGee, who wrote the book on science and cooking, recently wrote an article that goes into detail on why this happens:

Two recent reports from the House Foods Corporation in Japan detail exactly how the garlic and garlic-onion pigments develop. Their creators are the same handful of sulfur compounds and enzymes that give the allium family its unique pungent flavors. Under the right conditions these chemicals react with each other and with common amino acids to make pyrroles, clusters of carbon-nitrogen rings. These rings can be linked together into multipyrrole molecules.

The ring structures absorb particular wavelengths of light, and thus appear colored. The two-pyrrole molecule looks red, the three-pyrrole molecule looks blue and the four-pyrrole molecule looks green, as does its cousin tetrapyrrole, the chlorophyll molecule. Like chlorophyll, all the pyrrole pigments are perfectly safe to eat.

A mixture of onion and garlic favors a blue hue. All the pigments result from a combination of enzyme activity and simple chemical reactions, so you get the most intense color by puréeing the garlic and onion to mix enzymes thoroughly with their targets, then holding the purée on low heat to speed the enzymes without denaturing them, and finally heating it to a simmer to speed the nonenzymatic reactions.

He also has a follow-up on his blog with more detail and references. I recommend both his book and his blog for anyone interested in the science of food!
posted by icathing at 1:16 PM on January 11, 2007