system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can the shape, size and material of a cup, glass or container make such a significant impact on the taste of the beverage within?

To clarify with an example: I make a pot of coffee, pour it in two cups of different size and shape, and it always tastes better in my favourite cup (a very plain, 'boring', white porcelain mug). Why is that?
gpt
It depends, really.

Sometimes, you don't wash your cups well enough. The flavor from whatever was in there before stays in there and flavors the next glass. Over time and with many drinks, that can really add up and change the flavor. And if you use a certain cup a lot, it probably has been washed more, which in turn means that it has had more chances to get little nicks, pores, and scratches from cleaning that can trap flavor molecules. That doesn't necessarily mean the glass is covered in bacteria, though. Bacteria needs the right amount of food, acidity, time, temperature, oxygen, and moisture to really thrive, which aren't likely to be found in just the tiny, tiny amounts of drink left behind after an average cleaning.

Sometimes, the shape of a glass matters. The shape of the glass can determine how much you drink at once. There is a big difference in taste when you sip something and guzzle it. Smaller openings mean you drink less. If a glass is bigger or heavier, you are more likely to tilt it back a bit further when drinking from it. The shape also affects how much air is getting into the drink and how much gas is getting out of it. A soda drunk from a saucer will get flat much faster than one drunk from a bottle - there's just more surface area for the gas to escape from. And with hot or cold drinks, if more of it touches the air, it gets closer to room temperature that much faster.

Sometimes, like you noticed, the material matters. A tin cup is probably the best example of this - tin leaves a much stronger taste than most other materials we use for our cups and glasses. But whether you're drinking from glass, porcelain, plastic, styrofoam, wood, or something else, the material affects how porous the cup is (which affects how much flavor can remain trapped between cleanings), how much heat it retains (which affects how quickly it takes for the drink to reach room temperature), and what flavors the cup itself will offer.

And sometimes, it really is just in your head. That's not just a dismissive answer, though. The way you think about what you eat or drink DEFINITELY affects how you taste it. Don't believe me? Think about a child vomiting up their dinner because they've convinced themselves so strongly that they will hate it. Think about how different the exact same dish can taste when you are eating it when it was made by a loved one versus when you make it for yourself or have it at a restaurant. Think about blind taste tests, and how two items that normally taste quite different, like apples and potatoes, can be confused when you don't get to see what you're eating. Think about how a good memory can suddenly change a dish, even if you've had it many times before (and if your favorite cup doesn't give you good memories, it probably isn't much of a favorite cup).