Freshness is a major determinant of roasted coffee quality and consumer satisfaction. The rate of coffee staling will depend upon the amount of contact with oxygen. Conditions of heat and added moisture will accelerate staling. Moisture-resistant sealed packaging with a minimum of oxygen content is the key to coffee shelf life.
Staling of coffee occurs gradually as the result of numerous chemical processes affecting the coffee at different rates. The actual amount of time in which these processes take place will depend upon the state of the coffee (whole bean or ground) and conditions of storage (amount of oxygen contact, heat, moisture, and light).
Two basic processes take place during staling:
- The coffee loses desirable flavors
- The coffee gains undesirable flavors
In the graph below, downward lines represent the flavors that are being lost, while upward lines represent undesirable stale flavors. The time indicated is under normal ambient conditions:
- Oxygen at 20%
- Temperature at 20-25° C
- Moisture content not more than 2.5% and water activity at about 0.3
- Sample not exposed to excessive light
Types of Packaging and Shelf Life
One-way Valve Bag
Any amount of oxygen absorbed by coffee eventually leads to staleness. However, as the result of sugar browning reactions during roasting, freshly roasted coffee exudes carbon dioxide for up to a week in its whole bean form. For this reason, the highest quality coffees are typically packaged as soon as possible after roasting in a moisture-proof laminated bag containing a one-way valve. This valve allows the carbon dioxide to escape without “ballooning” or rupturing the bag, but does not allow oxygen to enter.
Other Valve Type Bags
Other types of valves allow carbon dioxide to be expelled through a plastic covered pinhole. This prevents carbon dioxide buildup within the package, but once the carbon dioxide is no longer creating a positive pressure on the coffee side, oxygen can leak into the bag. This is a good solution if the product will move through a system quickly.
If the coffee is to be packaged using no valves (including fractionally packaged ground coffee), the coffee must rest (“degas”) before it is packaged. It will pick up some oxygen during the degassing process which will limit shelf life, but otherwise the bag will balloon and possibly rupture, exposing the coffee to ambient levels of oxygen.
Packaging material: Coffee is packaged in materials ranging from paper bags to heavy foil laminates and cans. The packaging type also plays a marketing role. In terms of coffee shelf life, the type should be sealed easily (usually by heat) and moisture-proof.
Oxygen content of no more than 3% in the package is suggested. To ensure freshness at the brew stage, a “use by” date printed on the bags as well as the Julian calendar number printed on the case for the benefit of the retailer might be desirable. If ground coffee is packaged for an individual serving, the weight of coffee per package can be measured (see “Water to Coffee Ratio” in the “Brewing” section following). The actual “use-by” date depends upon the standards of the manufacturer.