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Maybe this is a silly question, but I'm not quite sure.

Consider a solid yogurt. Can we assign a specific state of matter to it?

I mean, it behaves like solid. However, if we "mix" it with a spoon, it becomes liquid, or at least in the usual sense. It is also quite plastic, which complicates.

My current guess is that it is either a glass or a gel, but I'm quite unsure about it.

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up vote 6 down vote accepted

The thickness of yoghurt is due to bacteria producing lactic acid and flocculating the casein molecules. There's an excellent article on this here.

We normally reserve the word gel for systems that display a yield stress. There are set yoghurts that would be described as a gel, but the more liquid yoghurts are just a non-Newtonian fluid.

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