Coffee Appreciation

Beans get darker and shinier as they progress in the roast. I think it goes:

green --> yellowish --> tan --> light brown --> brown --> dark brown --> almost black.

The shininess starts around the brown/dark brown part.

French roast is a good example of almost black and shiny. Taste gets stronger and more bitter as the roast goes on but caffeine content is reduced.

This is all based on me watching two roasting sessions a month or so ago. It might not be too accurate.

it's oils coming out isn't it?

Yep, both of those. The higher the roast level the more the cell structure of the bean breaks down, allowing the oils to creep to the surface and look all shiny. Oils also come to the surface as the coffee ages. Water processed decaf is black and oily even at a moderate roast level because the decaffeination process involves flushing the green coffee with hot water which causes it to become far more pourous.

A nice chestnut brown roast level with a subtle sheen is shiny because the bean has fully puffed out and reflects the light nicely, and a fully matte finish will be due to the bean still being a little bit wrinkly from a medium roast or a medium-dark on a very hard bean.