It is generally not advised that you store opened packages of coffee in the freezer. Instead, I suggest buying coffee when you need it or storing coffee in a dark pantry away from light, heat, moisture and odors.
However, there is some controversy surrounding the claim that coffee should not be stored in a freezer, as outlined in the more in-depth (paraphrased) reader question below:
Question: A lot of coffee sites say that it's not good to store coffee in the freezer. I disagree with several common claims:
- "The freezer is a moist place." The air in the freezer is dry. The vapor pressure of water or ice is much lower at -20C than at all warmer temps. It may be that letting the cold coffee sit open on the kitchen may allow some condensation into the coffee to occur, but that may be prevented.
- "Freezers hold odors." Freezers, because of the low temperatures and therefore low vapor pressures of the smelly substances, generally dont smell much (unlike refrigerators). Still, the freezer is an enclosed space and the coffee should be stored in a sealed container.
- "Freezing and thawing damages volatile oils essential to the coffee flavor." Storing at -20 deg C should both retain the essential volatile oils in the coffee, rather than letting them evaporate, and the low temperature should suppress the rate of the oxidation reactions that destroy those molecules essential for the flavor.
Answer: You've raised some great points! To the best of my knowledge, here is why many coffee sites make these claims about storing coffee in the freezer:
- Freezers are not always moist, but they can get moist.
Although stand-alone freezers do not hold moisture, most refrigerator-freezers have air transfers between the freezer and the refrigerator. Although the air will generally be at the appropriate temperature to prevent vapor from forming, opening and closing the freezer door (especially for longer periods of time when you're reaching for that bag of summer berries in the very, very back) introduces vapor and changes the temperature, as does the air transfer between the fridge and the freezer (albeit to a lesser extent).
If you'd like more detail on this, About.com Housewares guide Mariette Mifflin pointed out a specific mention of issues surrounding freezer air transfers on Whirlpool's site. Mariette added, "The freezer’s interior air temperature and humidity level will be different depending on the type of freezer, design and efficiency."
When freezers get moist and the coffee is not tightly sealed, the beans will suck up the moisture readily, as they are hydrophilic (water-loving). When they do this, they can also suck up odors because...
- Freezers do hold odors.
The distinctive odor of "freezer burn" is a prime example of a freezer adding odor to a frozen food. As the Whirlpool site points out, "food in the refrigerator and freezer can lose its flavor and even take on the flavors of other food being stored, such as fish and onions. You may have to thoroughly clean both food compartments to eliminate unwanted odors. Be sure to wrap or store odor-causing foods in tightly sealed containers to control recurring odors."
Mariette added, "When it comes to storing food in a freezer (chest or upright), even when food is sealed well, I’ve always noticed odors and can sometimes associate it with a particular frozen food. For instance, when I make my annual meat pies, they are sealed very well in Ziploc bags but anytime I open the door, I can smell those spices right away... until the pies are all gone."
- Freezing and thawing coffee may damage the essential oils.
I have no scientific evidence for this claim, but I do know that freezing and thawing foods multiple times is almost never a good idea, as it can impact the flavor and aroma (as well as the texture, although that bears little relation to this discussion!).
Also, heating and cooling foods repeatedly tends to introduce moisture into the food and then allow it to condense or evaporate, depending on the temperature. In pu-erh tea the shift between hot and cool is desirable, as it causes a natural fermentation that adds depth to the tea's flavor. That's not the same thing, as the temperature range doesn't usually include freezing, but it is an example of how shifting temperatures can change the flavor and aroma of a food or beverage.
I would imagine (though I have no proof!) that freezing and thawing coffee would cause substantial shifts in the placement of oils and water in the coffee, and may encourage oils to move to the surface of the bean during freezing, and then dissipate when the coffee is thawed.
However, my primary concern in freezing and thawing coffee is that coffee beans are highly porous and that the change in temperature may redistribute moisture from the inside of the bag into the beans themselves, adding unwanted odors.