# Why does milk turn yellow in a silver glass?

I boiled some milk and started to poured it in a silver cup by mistake. There was just some drops in it. The glass was clean and nothing was added to it.

But after an hour, I found that the milk turned bright yellow. Never seen milk in that color. What happened? Is something wrong with the silver cup or milk?

• Are you sure that the glass is actually silver metal and not another metal like aluminium?
– bob1
Commented Jan 27, 2020 at 8:42
• I bought it from a "Silver shop" and it was sold based on weight as silver is sold. I have no way to verify if its actually silver. Does it turn yellow if its aluminium? Commented Jan 27, 2020 at 9:22
• Regarding the silver - I was merely asking as different metals may interact with the milk in different manners. You could do a density test to distinguish between aluminum and silver. Measure the volume of the cup (not how much it holds) by displacement (use a measuring cylinder if you have one) and then weigh it. Mass/volume = density, Al=2.7g/cm^2, silver=10.49 g/cm^2. Boiled milk often has a yellowish tinge to it, and milk that evaporates water and dries out is yellowish, so it could just be that you are seeing.
– bob1
Commented Jan 27, 2020 at 20:08