I recently switched from percolator coffee to espresso. The taste is noticeably better. I feel as if it is common knowledge that espresso coffee is superior to percolator coffee. Why is it different? What are the scientific reasons for this?
Espresso tastes different than percolator coffee, but not necessarily better. Espresso extraction produces a more concentrated drink with a different set of compounds that you would get with percolator extraction. With a shorter extraction time and higher pressure, espresso will have a slightly different set of compounds than you would get from the same coffee with percolation.
Some people prefer a more concentrated taste, however, some do not (many people think espresso is "too strong" when drank straight, thus the popularity here in the US of mixed espresso drinks). This doesn't mean it's necessarily better. Some types of beans are not well suited to espresso extraction and will actually produce a better cup when brewed with other methods.
All coffee can be benefited or hindered by brew/prep method, but the quality of the bean and it's roast have quite a bit of influence in the matter. Badly grown, processed and roasted coffee will not magically be made better by espresso extraction. It might actually end up worse because concentrating it can highlight it's flaws.
In essence it's pressure, temperature and how coffee is generally ground for the method that make the difference.
Espresso forces water at high pressure (generally about 250PSI) and a specific temperature (generally between 92 and 94 degrees Celcius) through ground coffee. Percolator coffee relies on gravity to move water that's generally boiling (100 degrees) through coffee. The water temperature does make a significant difference because it is possible to burn coffee with water - which is one of the reasons that to many espresso drinkers filter coffee tastes burnt.
Grind makes a significant difference as well, Espresso coffee is generally ground finer than drip filter coffee which makes for a more intense taste for the volume of liquid. As per Chris' post, roast and been quality makes a difference - although I'd slightly disagree with Chris and say that it's more than a hindrance. The same bean ground for espresso and produced by an espresso machine and then ground for and produced by a drip filter will taste much different - and he's right in saying that it will highlight a really bad bean. It is also part of the skill of good baristas though that they know how to grind and extract almost any bean to get the best out of it, I know baristas who adjust for humidity though too so how far you can go is a guess for me.
To me, espresso has a much better taste. I learned this overseas, where, in many countries, they make traditional, straight espresso. I know the modern American preference is coffee with lots of sugar and cream, but not for me.
I've used a cone filter at home with boiling water, to try to make espresso, but it tastes nothing like real espresso from a machine. That's why I just ordered two espresso makers, one for work and one for home.
The second answer seems to give a good reason for the difference. The high temperature must cause the burned taste.