> ...gravity pushing that food down isn't really the main driving force. What does most of that job is layers of smooth muscle, that contracts and pushes things along without you even being conscious of it.

For anyone who wants to know more, this process is known as peristalsis.

Certain neurological conditions (e.g. Paralytic Ileus) can impact it and the results of this certainly prove that gravity doesn't play much of a part in the movement of food through the gut.

The problem with aircraft is that the cabin air is very dry, (bleed air from the engines that has been run through airconditioning packs and is at least partly recycled). This dries out the mucous membranes in the nose, which in turn dulls your sense of smell.

Your sense of taste isn't standalone - it depends heavily on your sense of smell. So with that missing/impaired, food will taste bland or even entirely different to how it does on the ground.

Come to think of it, this may also be a factor in the ISS as well as the congestion problems they have. It would be interesting to know if they have humidifiers on board up there.

::Edit:: Yes they do, sort of! it's the Temperature and Humidity Control (THC) subsystem of the Environmental Control and Life Support System (ECLSS).