Staling of Roasted Coffee

Coffee stales much faster than it is commonly perceived.  An extreme example is noted in "Coffee Technology"by Michael Sivetz where he mentions that moisture absorption from the air or due to water quenching need only to be 1% to noticeably stale coffee within the hour.  This represents 30 cc (1 fluid ounce ) per 3 kg ( 6.6 lb ) batch which,  considering that the beans lost 12 to 20 times that much moisture when roasting, is quite significant.  Advocates of water quenching claim that all the water evaporates as it hits the bean.  I am not so certain that this is so because after roasting the bean is very porous which means that the water will quickly cool the outside layer the bean will then have difficulty conducting the heat to the surface to evaporate 100% of the moisture.  The increased porosity will help draw the moisture inside.

Each opening of the container allows more moist air to reach the roasted coffee.   Sivetz writes that the beans are "moderately stale" within a week, more stale within two weeks and stale in three weeks.  Greater surface area i.e. ground beans significantly increases the absorption of air and moisture.

Vacuum packaging does remove most of the air but if it is done within a few hours of roasting it can create problems because of the high pressure CO2 will be released from the beans and inflate the bag.  If the coffee is ground the CO2 will be mostly released within the hour.

In theory the Valve on the Bag permits a longer storage time but I am sceptical about that valve working perfectly.  The changes in air pressure are small and applied over long periods of time as the barometric pressure changes which causes the bag to breathe.  The valves are attached to a bag that is filled with coffee beans which is not a flat surface hence I am thinking that it leaks and that it's purpose is to prevent the bag from bursting from C02 pressure.  Before going further that has to be tested.  I reiterate that the only safe bet is buy Freshly Roasted coffee.