or in other words, 

the process of eating is very complicated. rewarding hormons can not be easily cheated. 

e.g. during chewing the odor starts going to the nose which tells you want you eat. 
but only after swallowing when smell goes even more back/up the nose it completes the sensation. only thereafter, the food smells and tasts complete. you can try it by eating chocolate. try to spit it out. its not the same. 
whine is another good example. this is why the professional tasting of whine looks al strange