16 Storing Roasted Coffee

Freshly roasted coffee contains approximately 2% carbon dioxide and other gases by weight. Pressure within the beans causes the gases to desorb (i.e., to be released) slowly, over many weeks’ time after roasting. During the first 12 hours or so after roasting, the internal bean pressure is high enough to prevent significant amounts of oxygen from entering a bean’s structure. Thereafter, oxidation causes staling of the coffee and degradation of its flavor.

A bean’s gas content, internal pressure, and rate of outgassing are all affected by the roast method. Roasting hotter or darker produces more gas, greater internal bean pressure, and a more expanded cell structure, with larger pores. These factors lead to faster gas desorption and accelerated staling after roasting. While I don’t think one should change roasting styles simply to increase roasted coffee’s shelf life, it’s useful to understand that darker roasts degas and stale more quickly than lighter roasts.

Roast development also affects the rate of degassing. If a bean is underdeveloped, parts of its cellulose structure will remain tough and nonporous, trapping gases in its inner chambers. A noticeable lack of outgassing in bagged, roasted coffee may indicate underdevelopment.

Several options exist for storing roasted beans, and each has unique pros and cons:

Unsealed containers

Valve bags

V acuum-sealed valve bags

N itrogen-flushed valve bags

A irtight bags

N itrogen-flushed, pressurized containers

F reezing

Unsealed containers: Beans stored in an unsealed bag or other air-filled container (such as a bucket with a lid) stale quickly. Ideally, consume such coffee within 2-3 days of roasting.

Valve bags: Bags with one-way valves are the standard in the specialty-coffee industry. Such bags allow gas to escape but generally prevent new air from entering. Coffee held in such bags will taste fresh for a couple of weeks. The most noticeable change in the coffee after a few weeks in a valve bag is loss of carbon dioxide and aroma. The CO₂ loss will be especially noticeable during espresso extraction as a lack of crema.

Vacuum-sealed valve bags: Vacuum sealing greatly limits oxidation of coffee in a valve bag, slowing its flavor degradation.

An upstart roastery’s coffee in a valve bag

Nitrogen-flushed valve bags: Flushing a valve bag with nitrogen decreases potential oxidation to almost nil. Valve bagging limits coffee’s oxidation but has minimal effect on the loss of internal, pressurized gases. Upon opening a valve bag after several days or weeks of storage, the beans stale much faster than fresh, just-roasted coffee would, because they lack gas pressure to repel oxygen. For example, coffee stored in a valve bag for 1 week will taste fresh upon opening the bag but within a day will degrade almost as much as it would have had it spent the week in an unsealed bag.

Airtight bags: Few roasters use airtight bags anymore. Such bags limit oxidation, but bean outgassing causes the bags to puff up, making their storage and handling inconvenient.

Nitrogen-flushed, pressurized containers: This is the most effective packaging option. Nitrogen flushing prevents oxidation, and pressurizing the container (usually a can) prevents outgassing. Storing the container at a cool temperature (the cooler, the better) slows staling, allowing a coffee to taste fresh for months after roasting.

Freezing: Although it still has its skeptics, freezing has proven itself to be very effective for long-term coffee storage. Freezing decreases oxidation rates by more than 90% and slows the movement of volatiles.³⁴ There is no need to worry about the moisture in freshly roasted coffee actually freezing, as it is bound to the cellulose matrix, which makes it nonfreezable.³⁵ The best way to freeze beans is to put a single serving (whether for a pot or a cup) into an airtight package, such as a Ziploc^® bag. Remove the package from the freezer and allow the beans to warm to room temperature before opening the package and grinding the beans.