system
Given the following post, respond as if you're commenting on Reddit:
human
How do 'after-tastes' work? Why do we get a different taste only after the food has been swallowed?
gpt
When you put food in your mouth, the 'taste' you experience, besides its physical characteristics, is a combination of the basic flavors identified by your tongue, such as sweet, sour, etc. and the scent, which is actually picked up by your nose. Your sense of smell is such a major component of the smell of "taste" that if you block it, you'll have enormous trouble telling foods apart. The scents don't have to be inhaled either: your mouth hole and nostrils are actually internally connected roughly at the point where you swallow, so smells from the food you're eating will travel upwards from there.

So having explained that, the reason why sometimes you will experience an aftertaste will be more understandable to you: because the food that has sat in or passed through your mouth is considerably different from the one that you first experienced when it went in. You chewed through it, exposing its inner parts, and then mixed it with your saliva which is packed with enzymes that we have *specifically evolved for their ability to chemically break down the foods we stuff in our mouths*. This breaking-down mush then stays on your tongue, in your teeth, and in spots on your mucous membrane, and the smell makes it up to your nose. And it's changed because you changed it.