Sometimes I hear something that is different from my long-held perceptions, and want to find out the real story. This time the issue was coffee storage. The KCRW Good Food program of October 15, 2005 had a visit from their supermarket guru, Phil Lempert to talk about supermarket coffee. He said that putting coffee in the freezer is a very bad idea (the reasoning is provided below). I had always thought that freezing coffee might help reduce the degradation, so decided to determine the expert consensus.
First, some words about the basics of coffee roasting and the subsequent degradation. A green (unroasted) bean has a very long shelf life—months or even years (many large coffee producers have huge warehouses to store green beans until the market is most favorable for their sale). When the bean is roasted, it undergoes many changes—the so called browning reactions that convert the carbohydrates and proteins into a multitude of flavorful and aromatic compounds. These compounds are vulnerable to deterioration through volatilization, oxidation and rancidification via exposure to oxygen, light, heat and moisture. In addition, carbon dioxide—which provides body and bouquet to coffee–dissipates. Grinding breaks the cells of the coffee bean, thus releasing encapsulated aromatic compounds and exposing essential oils to oxygen.
I consulted a few sources on coffee storage, and there is significant disagreement whether coffee should be kept in the freezer or at room temperature. There is agreement, however, that coffee should be protected from moisture, light, heat and air. In addition, the experts agree that storing beans in the refrigerator has negative consequences because the beans can pick up unwanted flavors from neighboring food and drink (or ex-food!).
Several sources recommended putting coffee in the freezer for storage because the low temperatures slow down the degradation process. However, this method creates the possibility that moisture will condense on the beans when the container is opened (think of the water that condenses on a glass of iced tea on a hot day), thus harming those that are put back into the freezer. To prevent condensation, beans could be frozen in small containers and allowed to warm to room temperature before the container is opened. In other words, when you buy a pound of coffee, pack it into small packages that contain the amount that you grind at one time.
In The New Kitchen Science, Howard Hillman writes “If you must store your coffee bean supply for more than two weeks, freeze it in a well-sealed moisture-proof container. Beans can go directly from freezer to grinder to coffee maker.”
Corby Kummer’s conclusion in The Joy of Coffee is that “refrigeration virtually guarantees off-flavors in brewed coffee, and that coffee never tastes quite the same after it has been frozen–even if freezing is far better than refrigerating. But if you can’t use up your beans within two weeks or so, settle for putting them into the freezer, whole and tightly sealed, in either a glass jar or plastic container.”
A final note about the nearly fraudulent labeling “vacuum packed for freshness”: After roasting, beans start to release carbon dioxide (CO2), with a released volume that is about 3 times the volume of beans. If beans were canned or bagged immediately after roasting, the release of CO2 could damage the can or bag. Consequently, most packers let beans sit for 12 hours or several days to allow the off-gassing process to go to completion (or just a few hours for ground coffee) before packing into the “vacuum sealed for freshness” packages. In other words, the packers allow the coffee to go stale before packing it!
- Detail of an advertisement for Postum in St. Nicholas magazine, May 1905, Volume XXXII, Number 7 from the Internet Archive (found in their Flickr Commons collection). Full text of ad: “It’s easy to win back a strong heart, stomach and nerves, and easy to ‘best’ the Coffee habit, when you quit it entirely and use well-made Postum…There’s a reason.” (public domain)
- Advertisement for White House Coffee in The Mirror, a publication of Waltham High School, June 1916 from the Internet Archive (found in their Flickr Commons collection). (public domain)