Why Does Garlic Sometimes Turn Blue?

I've noticed sometimes when I cook garlic in butter that the garlic will turn blue after a while, and I had to ask myself why this happens.  After finding out that it is safe and poses no loss of taste, I sighed and continued reading.  It seems to be due to the presence of sulfates within the garlic, a component of what gives it such a pungent smell.  What happens is that the sulfates combine with the copper ions present in the butter, water, or cooking equipment to create something known as Copper (II) sulfate, or CuSO₄. This new compound is what gives off that bright blue colour.

So you may ask now if there are any precautions to be taken to avoid receiving this colour.  Luckily science has gained us much information about this process.  The main component of this phenomena is an enzyme present within the garlic that catalyzes this reaction, and can be deactivated simply by heating at high temperatures, or by letting the garlic age.

Egyptian Blue: Calcium Copper Silicate

In a recent article by Scientific American, a story is told of Calcium Copper Silicate (Egyptian Blue) being the first artificial pigment made by humans, and soon to be utilized, once again, as a nano ink for biomedical imaging.  I'm not going to go over the details of the article, but I will present some background information of this soft blue colour.

Being the first recorded synthetic pigment, you may ask how it was originally synthesized.  The first procedures, in 3000 B.C., involves the heating of sand, calcium carbonate, copper, and an alkali substance to obtain this blue pigment having a composition of CaCuSi₄O₁₀.  The reaction below is a general understanding of the reaction, where the molecules can be variable in a number of different ways.

Cu₂CO₃(OH)₂ + 8SiO₂ + 2CaCO₃ → 2CaCuSi₄O₁₀ + 3CO₂ + H₂O

The blue colour comes from the absorption of the copper, which can range from the blue, seen above, to a much darker blue, depending on how pure the mixture is. But what wasn't known at that time, was that when irradiated with visible light, the compound emits IR photons, which is the property that will conduct the imaging technologies.

References:
Via: Scientific American
Wikipedia