Garlic Turning Blue/Green ?

[churchill]

Probably been asked before but I noticed garlic turning blue/green when fried and understand that this is a reaction to copper in the tap water ...or anything else ... ??

Is it safe ..

[Sheryl]

new one to me, never seen it happen and no idea....

[katana]

Never seen it before when cooking but there are lots of hits on Google for it.

Apparently it seems to be harmless and is called 'greening'. There seem to be varied explanations. Some sites say it's due to copper sulphate formation, others due to eg pyrrole formation in the garlic under acidic Ph conditions, these pyrrole compounds being coloured.

eg

This discoloration is the result of some complicated chemistry involving the garlic's flavour compounds. The phenomenon is confusingly called "greening", and the food industry has encountered enough accidentally coloured batches of processed garlic for it to have generated some interest.

In the traditional Chinese pickle of garlic cloves in vinegar known as Laba garlic, the coloration is intentional. Chemists have speculated on its cause since at least the 1940s, and in the last few years Chinese and Japanese researchers have worked out what is going on.

The flavour of garlic is generated when an enzyme called alliinase acts on stable, odourless precursors. These are normally in separate compartments in the cell but can combine if there is damage, including that caused by vinegar. The major flavour precursor in garlic is alliin (S-2-propenyl cysteine sulphoxide) while a minor one is isoalliin ((E)-S-1-propenyl cysteine sulphoxide).

Key to the colour change is a product of these reactions called di-1-propenyl thiosulphinate. It can react at slightly acid pH with amino acids from the ruptured cells to form pyrrole compounds, which are then linked together by di-2-propenyl thiosulphinates to form dipyrroles. These are reddish purple, but as the cross-linking continues, molecules with deeper and bluer hues are formed. Among these are compounds called phycocyanins, which are related to chlorophylls and are found in some algae that are used as blue colouring by the food industry.

Keeping garlic somewhere cool increases the amount of isoalliin present, which is why the best Laba garlic is produced several months after harvest. It probably also explains the blue garlic halves in your questioner's salad dressing taken from the fridge.

Isoalliin is also the major flavour precursor in onions. They smell different from garlic because they lack alliin and have a second enzyme that intercepts the product of the alliinase reaction to form onions' characteristic tear-producing molecules. Onions do not turn blue because this second reaction leaves less thiosulphinate to be converted to coloured compounds. This explains why onions undergo "pinking" instead.

Meriel G. Jones

School of Biological Sciences

University of Liverpool, UK

http://www.last-word.com/content_handling/show_tree/tree_id/4567.html

Edited December 14, 2011 by katana

[sinbin]

It's perfectly normal. I pickled some garlic and they also went blue. No worries you can still eat them. http://sallystrove.hubpages.com/hub/Why-Does-Garlic-Turn-Blue-and-Is-Blue-Garlic-Safe-To-Eat

[gennisis]

It's perfectly normal. I pickled some garlic and they also went blue. No worries you can still eat them. http://sallystrove.h...lic-Safe-To-Eat

Wish I knew this before I had pickled some garlic in a mild vinegar and dill liquid....they all turned blue/green...so I threw them out.

Incidentaly when I was working in Russia some years ago I had pickled garlic for the first time...very very tasty and non of the typical smell or taste of raw garlic. I have tried to duplicate the style but have never succeeded.

[katana]

Strange phenomenon. Can understand why you'd be wary to eat it!

[sinbin]

It's perfectly normal. I pickled some garlic and they also went blue. No worries you can still eat them. http://sallystrove.h...lic-Safe-To-Eat

Wish I knew this before I had pickled some garlic in a mild vinegar and dill liquid....they all turned blue/green...so I threw them out.

Incidentaly when I was working in Russia some years ago I had pickled garlic for the first time...very very tasty and non of the typical smell or taste of raw garlic. I have tried to duplicate the style but have never succeeded.

Did you cook them in vinegar first ? I never realised you boiled them prior to putting them in a jar. http://kathrynvercillo.hubpages.com/hub/How_to_Pickle_Garlic