Ethylene
Also known as: ethene, C₂H₄, ripening gas
Short definitionA colourless gas (C₂H₄) that fruit and vegetables give off by themselves; it triggers ripening and ageing. Even a very small amount, such as one part per million, is enough. It is dosed on purpose in ripening rooms and removed in other stores.
When a mixed-produce store is drawn, the first question is which product will stand next to which. Bananas, apples, pears, avocados, kiwifruit, tomatoes and melons release ethylene as they ripen; the gas ripens the fruit beside them too, and the process speeds up as a chain. In sensitive produce the result is waste: lettuce spots, broccoli yellows, carrots turn bitter, potatoes sprout and cut flowers wilt early. Exhaust from LPG and diesel forklifts and rotting waste are also sources of ethylene.
Prevention starts in the room layout. Products that give off ethylene and products harmed by it go into separate rooms; the ripening room door does not face the corridor where sensitive goods wait. The cheapest way to get rid of the gas is fresh air, but it increases the cooling load. Potassium permanganate filters and catalytic converters are the other options. In ripening, 100–150 ppm is dosed. Because ethylene is explosive above 2.7% in air, a generator or a diluted mixture is chosen over a pure cylinder.