* Chemical Composition Changes: Bacteria in yogurt introduce lactic acid bacteria (LAB) which break down lactose (milk sugar) into lactic acid. This changes the chemical composition of the milk, resulting in a new substance with different properties.
* Irreversible Change: The process is irreversible; you can't easily get milk back from yogurt.
* New Properties: Yogurt has a different taste, texture, and pH compared to milk. This is due to the chemical changes that have occurred.
While some physical changes might happen during the process, like the milk thickening, these are secondary to the underlying chemical transformation.
