The apple that cried, "Gas!"
It turns out that it is true that one rotten apple can spoil the whole bunch, girl. If you have any overripe apples, throw them out immediately. The same thing goes for bananas, pears, avocados, peaches, plums & tomatoes. Kiwis, blueberries, grapes, & melons & kiwis all spoil faster when exposed to ethylene. Lettuce, spinach, broccoli, carrots & cucumbers are made more bitter by ethylene. That's because produce releases very large amounts of a ripening gas known as ethylene. Ethylene gas is a plant hormone. The word "hormone" comes from the Greek word for "hormon," which means "to set in motion." That's exactly what ethylene does; it sets in motion a large number of enzymatic processes that are generally responsible for ripening.
One such process is respiration, which is the process of deriving energy from stored sugar. These reactions lead to a breakdown of the green pigment chlorophyll & the synthesis of other pigments. Starch is converted into simple sugars like glucose or fructose, & at the same time, pectin begins to disintegrate, which softens the tissue. Pectin is the fiber that cements cell walls together. Rotting is just the end stage of ripening, with more & more ethylene being formed, some of which is released into the surrounding air. All of this stimulates the ripening of nearby fruits, setting off a chain reaction that results in the spoilage of the whole container. Ethylene moves through the air, plastic bags & even fridge drawers. Bananas soften faster, pears soften, leafy greens yellow, & berries mold sooner. Keeping your apples refrigerated, they respire more slowly than at room temperature.
Today, growers use "Controlled Atmosphere" (CA) storage, where oxygen is removed to just 2-3% (normal air contains 21%). The temperature is kept at 32-34°F (0-1°C), & they raise CO₂ levels to 1-3%. This slows ethylene production & respiration, resulting in some varieties of apples being available year-round, although they don't keep their full flavor & some varieties get mealy. The producers use activated carbon to adsorb ethylene gas, or they use zeolites, which are minerals with tiny pores that trap gases & moisture. One such zeolite is a mineral called stilbite. This was discovered by a Swedish mineralogist, Alex Frederick Cronstedt, who found that when he heated stilbite, he noticed it released a lot of steam. The name "zeolite" comes from the Greek words "zeo," meaning to boil, & "lithos," meaning stone, which translates to "boiling stone." Zeolites soak up water like a sponge & when heated, they "sweat" steam.
Japanese in Oya, a village 60 mi (100 km) north of Tokyo, discovered that Oya stone, formed from hardened lava, could be used to store produce in Oya caves for extended periods, up to a year, without it turning bad. It turns out that Oya stone is mostly composed of zeolites. The caves have been used to store apples, potatoes, carrots, onions, cabbage, root vegetables, grains, sake (rice wine) barrels, miso, pickled foods & mushrooms. They stay cool and stable all year. By the late 1800s-early 1900s, the caves were used intentionally for storage. Commercial fruit warehouses also use potassium permanganate that "eats" ethylene gas by turning it into harmless potassium or manganese oxide & COâ‚‚. Commercial apples are sometimes also treated with a chemical, methylcyclopropene (1-MCP), that blocks ethylene receptors in fruit. 1-MCP fits into receptors like a key that fits into locks, allowing storage for up to a year, though flavor fades slightly. However, the fruits remain firm & the texture is not lost. There is no health issue in eating apples treated with these chemicals.
If a fruit is mushy, remove it immediately; if it's bruised, remove it. Bruises accelerate ethylene production by 2-5x. If a fruit smells fermented, discard it. Store ethylene-producing produce separately & refrigerate. Separating produce by ethylene behavior is one of the easiest ways to extend shelf life.
