Isn't it against the teachings in our din to critique food? They should be grateful for it instead.

Yeah this is a great point so we should always be grateful for any food that is present. Many people nowadays all over the world are having difficulty struggling for food. However we know that the Prophet sallallahu alayhi wa sallam for example is mentioned when he was presented with certain foods sometimes he would avoid them and the reason he would avoid them is because it wasn't his liking in terms of his taste and that's normal every human will have a different taste and so on. If you are doing it for a specific purpose let's say you're doing it to guide others as to what may be good or what may not be good for example so you're doing it for a specific reason then that's fine that's more of an exception. The general principle the underlying principle is that yes we should avoid saying bad things about food but for a specific reason such as you know you're advising others then no issue with that inshallah.