The reaction of phosphoric acid to proteins in the milk – they are cut and causes a substance to be deposited in solid form from a solution.
It is a reaction of the Phosphoric Acid contained in the soft drink to the milk. Phosphoric Acid molecules attach to the milk giving them more density and separate out while the remaining liquid that makes up the milk and soft drink now being lighter floats on top. The solid matter is basically milk that has been curdled by the addition of the more acidic soda.
Both items are acidic but soft drink more so. In general, most soft drinks has a higher pH because of the Phosphoric Acid content where milk has a normal pH
There are some studies to suggest that because of the high Phosphoric Acid content in most soft drinks that they can help to increase the likelihood that a person will develop Osteoporosis if they aren’t getting enough Calcium in their diet.
According to WebMD, there has been an observed connection between high soda intake and increased risk of bone fractures, but it wasn’t until recently that theories about why this might happen have surfaced. The article mentions that the increased occurrence of osteoporosis in frequent soda drinkers was previously attributed to those people consuming soft drinks instead of calcium-rich beverages like milk or orange juice.