I think it's the other way around. Youtube knows I'm a sucker for news segments and documentaries about airline catering. From what I've seen in those videos, it seems like the food is usually blast chilled after cooking rather than frozen. When I was an airline employee from 1995-2004, I placed catering orders for my station. All the meals were delivered chilled. I understand it is now more common for some airlines to bulk order meals from commercial kitchens that don't exclusively prepare food for airline customers. In these cases, the food is delivered to airline catering facilities frozen. It's not clear to me whether it is thawed before delivery to the aircraft. I learned from this thread that United may do this sometimes, so it might be true for them. I'm not sure how much of that is guessing vs. actual knowledge. Some have said that the formerly ubiquitous grain salads were delivered frozen. You could certainly see other meals, like enchiladas, arriving frozen.