one way valve thinks with the development of society, nowadays increasing people are more willing to drink freshly ground coffee instead of instant coffee.
So how to choose the freshest coffee beans? Whether the hull has oil or not is an important standard to judge if the coffee beans are fresh when you choose them. Generally, the hulls of fresh medium roasted coffee beans should be dry without oil, and the hulls of fresh dark roasted coffee beans should be shiny. The oil spread on the hulls of coffee beans is not the crema we say traditionally, it is an kind of organic material soluble in water. So the coffee you brew will not have a layer of oily crema.
Therefore, reputable coffee roaster should be your first choice. Moreover, you can try to squeeze the coffee bag a little bit with your nose close to it to get the smell by the coffee valve. If the smell is with strong aroma, the freshness is without any problem. On the contrary, if the smell is not with strong aroma, that means the taste of coffee beans has already changed which you should avoid buying them.