Buy Right ~ It is wise to purchase coffee in amounts proportionate to how quickly it will used. Coffee begins to lose its freshness almost immediately after roasting so it is far better to purchase it in smaller quantities. Purchase freshly roasted coffee frequently and buy only what you will use in the next 1 or 2 weeks. And because exposure to air is your coffee’s worst enemy, it is a good idea to divide your coffee supply into several smaller portions, keeping the larger, unused portion in an air-tight container.
Source: National Coffee Association USA