What is roasting?
Roasting brings out the aroma and flavor that is locked inside the green coffee beans. Beans are stored green, a state in which they can be kept without loss of quality or taste. A green bean has none of the characteristics of a roasted bean -- it’s soft and spongy to the bite and smells grassy.
Roasting causes chemical changes to take place as the beans are rapidly brought to very high temperatures. When they reach the peak of perfection, they are quickly cooled to stop the process. Roasted beans smell like coffee, and weigh less because the moisture has been roasted out. They are crunchy to the bite, ready to be ground and brewed.
Types of roasts
Light roasts
Light brown in color, this roast is generally preferred for milder coffee varieties. There will be no oil on the surface of these beans because they are not roasted long enough for the oils to break through to the surface. It is usually roasted at 350-400F (180-200C). Light roasts are also known as light city, half city, or cinnamon roasts.
Medium roasts
This roast is medium brown in color with a stronger flavor and a non-oily surface. It’s also known as city roast, breakfast roast, or American roast because it is generally preferred in the United States.
Dark roasts
This roast produces shiny black beans with an oily surface and a pronounced bitterness. The darker the roast, the less acidity will be found in the coffee beverage. Dark roast coffees run from slightly dark to charred, and they are also known as high, continental, New Orleans, European, or Espresso roasts.
Learn more:
https://www.ncausa.org/About-Coffee/Coffee-Roasts-Guide
https://coffeeofthenorth.org/types-of-coffee-roasts/