Imagine my surprise when I went to the fridge to get my jar of pickled garlic, only to discover many of the cloves had turned a very interesting shade of blue/green. I admit my first thought was ‘botulism’, so I had a quick look on the interwebzone to see if this stuff was still edible – it is!

It turns out a wonderful chemical reaction takes place in the garlic. Here comes the science part:

There is an odourless sulfur compound in garlic called alliin. There is also an enzyme called alliinase. When a bulb or clove is intact these two little guys have no contact but if you slice or crush the garlic, the alliin and alliinase are mixed and the result is a compound called allicin. (This is what gives garlic its smell and taste). 

Now, when you mix garlic with an acid like vinegar, for example, the allicin reacts with amino acids in the garlic to produce lovely little rings of carbon-nitrogen called pyrroles. Four pyrroles clustered together create green. If you have 3 of these pyrroles linked together they make a lovely blue colour.

And the good news is it’s perfectly safe to eat – in fact, in China it is made on purpose as part of the Laba Festival!

Here’s what mine looked like:

So if your garlic turns blue, don’t panic, celebrate – and eat it!