Few things disappoint as much as brewing a cup of coffee only to discover the beans are bad. Thankfully, there are a few quick actions you can take before brewing to assess a bean freshness: smell, look, touch, and test.
Smell the beans. Fresh beans produce a wonderful, powerful coffee scent. As the beans stale, the scent diminishes. If your beans give off a very weak smell, no smell, or smell like cardboard, they are likely stale.
Look at the oil sheen on your beans. Coffee produces natural oils during the roasting process. If the oil has disappeared from the beans, it is a good indication that the beans have staled. Light roast coffees, which are roasted for less time than dark roast coffees, produce less oil. If you are a light roast drinker, look for at least a light sheen on the bean and avoid beans that look dry. Another good sight check is to place a few beans in an unwaxed paper bag and see if the beans leave a slight residue. If they do, they are fresh.
Touch the beans. As previously mentioned, fresh beans produce an oil strong enough to leave a slight residue on paper — the residue is also strong enough to rub off on your hands. Feel the beans, if your fingers feel a little oily after you put the beans down, they are fresh. If you drink dark roasts, check to see if the beans are sticky; if they are, the beans are past their prime.
Assess and test the beans. Coffee beans develop natural CO2 during the roasting process. This CO2 must be at least partially released before brewing or the coffee will taste ripe / sour. Beans that have lost all their CO2 are considered stale. The first step in assessing your beans’ CO2 level is to look at the bag holding your beans. If the bag has a valve seal, that means CO2 is slowly being released. Once the beans reach their optimal CO2 level, they remain good for approximately one week if exposed to oxygen. Storing the beans in a valve-sealed bag* extends their life by allowing the CO2 to slowly release while preventing oxygen from entering the bag. To test the CO2 content of your beans, place a handful of beans in a plastic ziplock bag and let them rest for at least eight hours. If the bag is inflated at the end of the eight hours, the beans are still releasing CO2 and are fresh. If the bag is deflated, the beans are no longer releasing CO2 and are stale.
For tips on how to store and troubleshoot your coffee, please visit the following blogs:
*Transferring the beans to an air-tight container after opening the bag also preserves freshness.