So what does it mean exactly when we talk about a light roast? In a nut shell it means the coffee beans has been roasted for less time than a medium and darker roast. Just reaching the "first crack" which is what happens when they pop and expand. That is between the temperatures of 356 to 400 degrees.
Now just because it is roasted less time doesn't mean that it is weaker. The lighter roast actually brings out fruity and vibrant flavors thanks to the higher acidity. In addition, it actually has more caffeine. Despite the widespread coffee myth of dark roast or/and espresso being more stronger. A lighter roast is a pale brown and has no oils on the surface of the bean. Therefore, perseveres more of the coffee's natural flavors. This roast is recommenced if you are looking to taste the full complexity of what the coffee bean has to offer. Great with a single origin and a pour over method.
Medium roast AKA city roast are brown in color (depending on the bean and temperature) and show some signs of oils on the surface of the bean. With this roast the bean reaches temperatures between of 400 to 430 degrees. As a medium roast it still preserves some of the natural flavors, but also develops some new flavors from the roasting process. It gives you a more balance and well rounded cup of coffee and is the most popular. Enjoyed best as a cold brew or with a french press brewing method.
Dark Roast can also be can also be referred to as Full City or Vienna. It has lower caffeine,and shiner because of the oils on the surface. It has less acidity and tends to have a bolder body. Don't let that that stop you and turn you off because, if it is roasted right you get chocolate, nutty and caramel. Great for espresso and cappuccino.