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Questions & Answers - Blue or Green Garlic

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Question:

  1. I have a recipe for cooking with herbs and wine. It requires that one prepare a wine/herb mixture in advance. I mixed garlic and herbs with wine in a bottle and allowed it to sit for a long time, as instructed. It appears that the garlic has turned blue inside the bottle. I am concerned about poisoning my guests. Do you have any insight? Thank you for your consideration. - Ron & Vanessa
     

  2. Linda, I have almost the same problem with my garlic changing color, only mine turned sort of green when I placed it in white vinegar. Used to put it in oil but that got messy sometimes and I thought I would give vinegar a shot. Did I goof up or is it like the wine deal? - Bob W.
     

  3. I just made my first herbed vinegar, using chives, garlic chives, pineapple sage, rosemary and garlic. It looked great last night, I got up this morning and the garlic has turned a shade of blue/green or green/blue. Did it mold? The vinegar is in old wine bottles (cleaned and heated in boiling water on the stove eye like canning jars) with cork stoppers and wax helping to hold the stoppers down. I did heat the vinegar in a metal pan. Is that the reason? The only thing heated was the vinegar and then poured over the herbs in the wine jars. OK now, can you tell me what I did wrong, or if I can use this when it is ready? I was going to give it to friends, but I don't want to make them sick! That was a lot of work and now I just feel sick. Thanks, I will await your reply. - Gail W.
     

  4. My daughter made me a bottle of flavored vinegar a couple of days ago for Christmas, and was so disappointed that the garlic had discolored.  It looks like only the cloves touching the glass turned blue, but we haven’t opened the bottle to confirm.  Can you tell us what may have caused this?  Other than the blue garlic(!), the vinegar smells wonderful. Thank you so much any ideas you can provide!  Have a Wonderful New Year! - Claire
     



Answers:

Check out my article on Garlic.

 



Garlic Turning Blue or Green


Latest Findings:

International Journal of Food Science & Technology, Identification of Two Novel Pigment Precursors and a Reddish-Purple Pigment Involved in the Blue-Green Discoloration of Onion and Garlic, written by Shinsuke Imai,* Kaori Akita, Muneaki Tomotake, and Hiroshi Sawada, Received for review August 12, 2005. Revised manuscript received December 5, 2005. Accepted December 10, 2005.

Abstract:

By using a model reaction system representing blue-green discoloration that occurs when purees of onion (Allium cepa L.) and garlic (Allium sativum L.) are mixed, we isolated two pigment precursors (PPs) and a reddish-purple pigment (PUR-1) and determined their chemical structures. PPs were isolated from a heat-treated solution containing color developer (CD) and either L-valine or L-alanine, and their structures were determined as 2-(3,4-dimethylpyrrolyl)-3-methylbutanoic acid (PP-Val), and 2-(3,4-dimethyl-1H-pyrrolyl) propanoic acid (PP-Ala), respectively. Next, PUR-1 was isolated from a heat-treated solution containing PP-Val and allicin, and its structure was determined as (1E)-1-(1-((1S)-1-carboxy-2-methylpropyl)-3,4-dimethyl-1H-pyrrol-2-yl)-prop-1-enylene-3-(1-((1S)-1-carboxy-2-methylpropyl)-3,4-dimethyl-1H-pyrrol-2-ylidenium). The structure of PUR-1 suggested that PP molecules containing a 3,4-dimethyl pyrrole ring had been cross-linked by an allyl group of allicin to form conjugated pigments. While PUR-1 is a dipyrrole compound exhibiting a reddish-purple color, a color shift toward blue to green can be expected as the cross-linking reaction continues to form, for example, tri- or tetrapyrrole compounds.

What the above means:

The discoloration is due to pigments that form between sulfur compounds in garlic and amino acids. When the garlic tissue is disrupted, as happens in processing, an enzyme is liberated and reacts with it to form thiosulfinates compounds that then react with the natural amino acids in the garlic to form blue pigments. The age of garlic determines how much isoalliin there is in the first place, and the nature of the processing determines how much enzyme is liberated.
 



Original thoughts and ideas:

Garlic is known to contain sulfur compounds which can react with minute traces of 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. 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.

If fresh garlic is picked before it is fully mature and hasn't been properly dried, it can turn and iridescent blue or green color when in the presence of an acid. It may be caused by an allinin derivative.

A reaction between garlic's natural sulfur content and any copper in your water supply, or in the cooking utensils your are using (such as cast iron, tin, or aluminum) can sometimes change the color of garlic.

The other sources of copper might be butter, lemon juice, or vinegar.

Garlic will also turn green (develop chlorophyll) if exposed to an temperature change or is exposed to sunlight. Some people say it can be stored for 32 days at or above 70 - 80° F to prevent greening (but I'm not yet sure that is true).

Are you using table salt instead of kosher or canning salt? That can cause the garlic to turn blue or green. Table salt contains iodine, which discolors whatever you're pickling. Use kosher or pickling salt.
 

Different varieties or growing conditions can actually produce garlic with an excess natural bluish/green pigmentation (anthocyanins*) made more visible after pickling.

* Any of various water-soluble pigments that impart to flowers and other plant parts colors ranging from violet and blue to most shades of red. This pigment is produced after chlorophyll is destroyed due to environmental changes. This is a variable phenomenon that is more pronounced for immature garlic but can differ among cloves within a single head of garlic. If you grow your own garlic, be sure to mature it at room temperature for a couple of weeks before using it.

 

Don't worry, greenish-blue color changes aren't harmful and your garlic is still safe to eat. (unless you see other signs of spoilage).