Why does garlic turn green?
If the garlic is not ripe and dry fully, it can get converted into green color in the presence of sunlight. This happens because of the presence of chlorophyll compound. Plants have chlorophyll pigment in their leaves and stem which helps them in synthesizing sugars or food for the plant. The edible part of garlic is the modified leaves and stem of the garlic plant. So, these parts will consist of chlorophyll molecules. The color conversion will occur in the presence of acidic foods like vinegar, onions, lemon juice and so on. The color change also happens when the copper present in the tap water reacts with the acid. The color change occurs till the garlic is not totally mature. Once it is allowed to mature completely, the color change can be fixed. The chlorophyll is responsible for the appearance of green color to the cloves.
The chopped up garlic will turn into green slowly after sometime if they are kept like that exposed to the air. In the United States, water consists of copper. The copper reacts with the sulfur compounds in the garlic to give blue color. The vessels containing copper will also initiate change in color to the garlic. If the garlic is harvested from the field without getting matured, then they will turn into green color in the presence of acid in the lemon.
Garlic is not toxic or dangerous, if its color is changed to green. It can be eaten without any problem in spite of its changed color. If the skin on the garlic cloves is removed then the color change will occur inside the oven. If the garlic is not peeled, then the color of it starts changing to green. The dry garlic will not turn green when exposed to sunlight while the garlic that is not totally dry will turn green in sunlight.