The Coffee Haus

I roast my own beans . I get them green from Africa usually because Africa and India has the best coffee in my opinion.
 
To answer your question about what caffeine does in the plant . Caffeine is the plants natural insecticide. That ingredient deters and even kills the critters that try to eat the leaves. So in effect, we are drinking an insecticide.

I'll throw in another factoid along with this answer. 
 
When you go much past medium roast it cooks the oils and some of the natural taste out of the bean. What people taste when they drink dark roast is the slight or even more severe effect of either beginning to burn or actually burning completely the coffee bean. What you end up with depending on the degree the beans are burned is very little natural taste of the bean along with a charcoal or burned taste. Hence the term "dark roast'. Medium roasted beans are a soft brown color.
 
Starbucks are known for beans that have a slight dark roast quality to them. Not quite medium but slightly over that line. I personally don't care for Starbucks for this reason. I think they tend to over roast their coffee.Lots people like it though. Mesh, sounds like you might like it.
 
To answer your question  most any dark roasted arabica bean will make a decent  dark roast because a lot of the actual taste is derived from the over roasting process. In fact you loose a lot of the of the taste. Probably more important for dark roasts or any coffee is freshness. Most coffee sold in grocery stores is old when it hits the shelf.
Don't let the "sell by" date be confused with the "roast date". The sell by date only means it won't be so bad by then you can't stand to drink it. If you go by the roast date, then you don't want to drink ground coffee much more than a few weeks past that date. This if if you keep it in an airtight specially made container. Most people have never tasted truly fresh coffee. To get that you need to probably go to a micro roaster locally or have it shipped 2nd day after the roast.
 

one thing about this thread is it brought up that I may have never truly had freshly roasted coffee .
changing that one over is going on my bucket list .
 
Kenny

Arabic coffee is interesting, made from beans that are pretty much green, perhaps with some cardamom added and drunk from very small cups. Sometimes it deadens your mouth if you get a rough one.

In social events its served alternately with glasses of strong sweet tea late into the evening. No sleep for hours after that.

I quite like Viennese coffee roasted with fig for a change.

I've never been to Vietnam, but I've had Vietnamese coffee. They seriously love their caffeine - gave me the jitters.
 
I have had fresh-roasted coffee from/in the Philippines. It is a different experience, for sure. We ground it by hand with a mortar and brewed it in a camp-style percolator. Sounds primitive, but right now I am feeling nostalgic about sitting outside in the morning before sunrise (and it's already warm out) with warm pandesal (little semi-sweet bread rolls)...can't wait to go back.
 
Another place they really like their coffee is Montreal. I went to a coffee shop there that was like Baskin-Robbins 31 Flavors, but for coffee. Ground to order and served in a French press. Yum. I was up all night.
 
Unfortunately, I drink way too much of the stuff to afford to be picky. My primary selection criterion these days is "what's on sale?".