Why Do Foods Pick Up One Another’s Odors in the Refrigerator?

Odor comes from volatile compounds carried through the air. When an onion is cut, fish is stored, or a cheese matures, these compounds enter the air. Outdoors, they disperse and become diluted; in a small, enclosed space such as a refrigerator, they have nowhere to disperse, and in fan-assisted models, circulating air carries them to every shelf. Cold does not eliminate odors; it only slows their production. That is why an odor that seems likely to disappear in a few days can linger much longer in the refrigerator. The only way to air out the refrigerator is to open the door, which also lets the cold out.

Why odors get into some foods has to do with fat. Most odor compounds dissolve in fat rather than water; the higher a food’s fat content, the better it holds onto odors. Butter, cream, and chocolate are therefore the best odor absorbers in the refrigerator, and they can change flavor within a few hours when left uncovered. Milk and yogurt are affected for the same reason. High-water foods such as cucumbers and apples carry odors on their surfaces rather than absorbing them. Washing removes the odor from them, but butter cannot be washed and retains the odor.

Eggs are affected in a different way. Although the shell looks closed, it has thousands of pores that let both moisture and odors through. One egg taken out of its carton and left uncovered can absorb the odor of a nearby onion all the way through its shell. Cheese, bread, and cooked rice are porous in the same way. To keep any food odor-free, store it in its own covered container; plastic wrap stretched over the top is often not enough. Leaving eggs in their carton is the easiest precaution to take for these 3 foods.

The foods that release odors tend to be the same few: chopped onions and garlic, fish, aged cheeses, pickles and fermented foods, and leftover spicy dishes. They cannot be stored without releasing odors, but their odors can be contained in their own containers. A glass jar or a container with a locking lid works much better than a plate covered with plastic wrap, because the wrap can pull away where it is stretched and let air escape around the edges. Sealing hot food is not effective either; steam condenses and lifts the lid, allowing the odor to escape.

The route odors travel is also the route for preventing them. Keeping each food covered in its own container, placing odor-producing foods in the lower and back sections of the refrigerator, and moving fatty dairy products to a shelf away from them solves the problem by itself in many homes. You cannot stop air from circulating in the refrigerator, but containing the molecules at their source works every time. Once an odor has penetrated butter or cream, it cannot be restored, so prevention costs less than cleaning up afterward. Instead of trying to rescue a product that has picked up an odor, it is easier to separate its container from the start.