i have a fun experiment for you coffee lovers.
Find a high quality single source bean that isn't oily and lightly roasted. Compare the flavors and nuances of that lighter roasted bean that lacks an oily surface to the darker roasted oily beans that have been Italian/espress roasted which Starbucks has made so common. And tell me which you think have nuanced flavors pop out. It's why I like to mix beans of different kinds as they each round out one another's flavors. It tastes some getting used to ever since Starbucks made really good beans and darker roasts more common.
Some fun reading about coffee beans and roasts.
http://rougeroastery.blogspot.com/2008/02/science-of-oily-beans.html
Thanks for the information.
Here are a couple of opinions on oily beans, "I have had beans that were oily and were good, but in my experience oily beans are one indication of over-roasting, poor storage, or age.
Beans stored in a hot roastery, shipped in the back of a hot truck, and stored n a hot storage room at a coffee shop will also become oily far faster than beans stored in a cool place.
Low quality beans are often over-roasted to a dark, oily state because it is the only way to burn off their natural flavor so that they become drinkable (Vietnamese Robusta comes to mind- there you get your choice of a rubber taste, or a burnt rubber taste).
So, generally, both of your sources are generally correct, but you cannot take "oily is bad" as a rule much like the "Golden Rule," it is a guideline." "Beans get oily when they have been roasted beyond the point where the cell walls rupture and the oils stored inside the cell wall vacuoles are released. This stage, while roasting, is roughly marked by a crackling noise called the 2nd crack (the first crack happens at a lower temperature when the water turns to steam).
If the roast is very dark, so the beans are a dark chocolate color or darker, the oil will be on the bean from the day of the roast and stay there until it is about 3 to 4 weeks old, at which point it will all have evaporated. The sight of beans this color without oil is a warning that the coffee is stale. If the roast is a bit lighter, milk chocolate color, the oil will take about 3 days to a week to appear on the bean surface. In some parts of Europe, which like this level of roast, the saying is that a bean without oil is either too old or too young. Beans lighter than milk chocolate have intact cell walls and will never get oily, and that will not be a clue about freshness or otherwise.
So much for the facts, what about the taste?
Advocates of lighter, oil-free roasts claim oily beans taste rancid. Advocates of oiled roasts say that without them appearing through roasting, the oils cannot get into the cup, since grinding alone leaves most cell walls intact. There is a bit of truth to both these statements, and in terms of the flavors in the coffee oils, a medium, milk chocolate roast, fairly new, and just showing a few spots of oil, will taste the best.
However, not all things are equal. The darker one roasts, the more one roasts out the fruit and floral flavors in the coffee. On the other hand, very dark roasts have spice and smoke flavors that many people enjoy. These flavors have nothing to do with the oils.
Finally, among people who make a hobby of espresso, you will probably find nobody who will willingly drink a coffee whose beans are so oily that they foul the grinder. I hesitate to say that roasts this dark are the Thunderbird or peppermint schnaps of coffee, but it wouldn't be an entirely unfair statement."
These are the driest beans I have had, La Columbe Italian roma espresso beans. Tasted like your classic Italian espresso.
