Last year, we were fretting about melamine contamination in foods from China. Again, this week, it’s happening – melamine was put into milk by some unscrupulous vendors. The idea here is that melamine is high in nitrogen and cheap. An easy way to get an idea of how much protein is in something is to assay for nitrogen – by cutting milk with water and adding melamine, the unscrupulous can pass off watered down milk as full-strength.
There’s a very good chance it will involve cyanuric acid, which forms a water-insoluble complex with melamine, causing clouding. This same interaction has been used to test for cyanuric acid in swimming pools. Interestingly, this seems to be part of why melamine is so toxic. Melamine actually hydrolyzes to cyanurate, which leads to the insoluble melamine-cyanurate complex precipitating in the kidneys.
See also: Terra Sig on this.