Turning turquoise – revenge for lazy technique

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I’ve been cooking with onions and garlic my whole life, using them as flavour foundations and aroma accents in every kind of cookery, but I was not prepared for this trick.


It started with a mission to get the most out of my slow cooker with the least amount of washing up. Skipping the sauté step and doing everything in the slow cooker was recommended in my new American slow cooker book (along with generous portions of processed cheese loaf and condensed soups).

Here are two versions of what went wrong when I tried to take short cuts with slow cooker Lamb Korma



Version one

Ordinary brown and some golden fat cloves of Russian garlic form the Manjimup Farmers Market blitzed in the blender with water to form a puree. Cook gently for 30 minutes at a temperature of less than 85 0 C in the slower cooker, un-watched, un-tended and un-loved. Big mistake.


I turned the slow cooker dial to high, added some olive oil and poured in the allium* puree and let it cook. The goal was a golden, sweet and savoury paste that would act as the foundation for the other aromatics in the korma sauce.


As I checked the pot some ten minutes later, the alchemy happened right before my eyes. Just like one of those magic painting books from my childhood (the 1970s were fab) the green-blue hue flashed over the contents of the slow cooker. I howled.


Version two

When first peeping in to the world of Food Science Research at University, one book in particular caught my eye. Nestled amongst titles like Peasron’s Chemical Analysis of Foods and Unit Operations in Food Processing was Garlic and Other Alliums: The Lore and the Science by Eric Block.


I could not make time to read it back then. Of course, it was Eric Block I typed into Google Scholar to get some explanation of the chemical reactions that had sabotaged my supper.


The turning turquoise phenomenon was unexplained by science until the mid 20th century, and that explanation was pretty complicated when it arrived, even for Professor Block.



Thiosulfate ion

Thiosulfate ion


To put it very simply, Alliums are full of sulfur compounds called thiosulfinates. These provide the peppery taste to Alliums and contribute to antioxidant properties. If the conditions are right when they are released from the cell walls they get mixed up with enzymes and form thiocarbonyl compounds. These condense with amino acids to form nitrogen-rich pigment compounds called pyrroles. Three pyrroles in a compound gives you blue, four gives you green, et viola – turquoise. **


Pyrrole compound

Pyrrole compound



That would explain what happened, but how can I be sure I don’t let it happen again?


First mistake was physical: Breaking down the cell walls so violently was just plain rude. I messed with the rheology of the allium, or the way its enzymes and chemicals flow out of it cells.


The second was staging a type of kinetic reaction, the slow heating coupled with the pasting set everything up for the sulfinates-to-pyrroles reaction.


And the third was to do with my own integrity –  I just got lazy. Indian cooks do not pound their garlic and onion mixtures prior to sautéing. They chop, they dice, they mince.


Lesson learned – don’t take shortcuts to fit in with your electrical equipment. Remember that almost all the kitchen gadgets you can buy on late night tv are imitating traditional techniques, not improving them.


Question – what have you learned the hard way in your cooking adventures? Leave a comment below.


Music for this post: Betty Davis Big Freak – the only song I know with turquoise in the lyrics.






*  Allium is the genus, Allium cepa =  onions,  Allium sativum = garlic

* * Garlic and other Allium: the science and the lore Erick Block, p211


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