[bhirsch]

I had a strange thing happen the other day. I was frying some onions and garlic which had been pureed in a food processor, and they turned bright green! The pan was copper and my first thought was that the tinning was bad, but I checked and the tin was fine. Using a different batch of onions, bought at a different time and store, I repeated the process with another copper pan and the same thing happened. The tin was good here, too. I put some of the onions in a stainless steel pan and again, they turned green. Does anybody know what was going on? Thanks.

[shel]

Onion & garlic turn green when sautéed!? - Home Cooking - Chowhound

Hope this helps,


scb

[Luc_H]

Although I cannot find the reference at this time...
The process is a chemical reaction between heavy metals (usually found in the onion or garlic depending on soil conditions) and natural sulphurous compounds that the bulb makes.
As for the heavy metals, the usual suspect are copper, zinc, iron, manganese.

I have observed that Spanish white onions often do that when sweating.

Growers believe that adding copper to the soil makes for better onions as per article alludes: COPPER REQUIREMENTS FOR ONIONS GROWN ON ORGANIC SOILS IN NEW YORK.
Zinc addition apparently helps according to this article: Effect of sulpur and zinc application on onion yield and sulpur and zinc uptake in three soil orders

Maybe some farmers are overdoing it with the metallic ions!

Luc H.