After roasting, coffee beans start to slowly release CO2. This off-gassing keeps oxygen from getting inside the beans and breaking down flavor compounds. However, once the coffee is ground, the CO2 is released all at once, and there is no longer any protection against oxygen damage. Add to that the increased surface area of ground coffee and you have a recipe for bad coffee in very short order. This is why it is so crucial to grind the coffee just before brewing. In fact, I would argue that buying good coffee, if preground, is a waste of money. Some large coffee manufacturers go to great lengths to convince consumers that buying ground coffee is okay. They sell their coffee in high-tech packaging designed to preserve the coffees’ natural flavors. The problem is that even if these approaches worked perfectly, which they don’t, the coffee is still exposed to a fresh dose of air every time you open the package to make a pot of coffee.

Ultimately, the only way to get the most of freshly roasted coffee, is to grind it right before use. While I recommend buying a cheap grinder rather than no grinder, if you are investing any money in coffee making equipment, the priority should be the grinder. But be ready to spend $100 or more. Inexpensive burr grinders are not a good value. They don’t work well or for very long.