Before reading this you might want to have read the first part of my guide to fine chocolate for beginners. It's not strictly necessary of course, but it is a good place to start if you are new to fine chocolate..
Read it? Good. Now lets take you to the next level. As you may have guessed yourself, the taste of a chocolate-bar is not only dependent on the declared ingredients on the back, but also very much on quality differences in both the cocoa-beans themselves, and even more so by the processing they are put through. So lets get into the chocolate production process from pod to bar to give you a understanding of how it all fits together, so that finally we can explain why some chocolates are so much better than others.
First a quick recap: Chocolate production begins with harvesting ripe cacao pods which are opened and emptied to extract the seeds and pulp. This mass is then fermented for up to a week until the pulp have disappeared, leaving only the seeds which are then dried for shipment to chocolate-makers around the world. There the beans are roasted and shelled to separate out the cocoa nibs, which can then finally be milled and refined into a liquid cocoa mass, the basis of all chocolate as we know it: cocoa-liquor.
Much of this liquor is then separated into cocoa-powder and cocoa-butter for further industrial use. Cocoa-powder is commonly used as an ingredient in baking or to make hot chocolate, while cocoa-butter is amongst other things used in cosmetics and medicines. Most importantly however, some of the cocoa-butter is added back into cocoa-liquor along with sugar and other ingredients, which after another couple of days of conching, tempering and moulding finally become the fabled chocolate bars that we all love so much.
Whew, that was quick. If you couldn't follow me through all of that then have a look at how chocolate is made for additional details. Now lets dig into the details to see how all of this combines to affect the final taste of a chocolate bar.