Controlled atmosphere storage (CA)
Also known as: CA storage, CA room, ULO storage
Short definitionA cold room sealed gas-tight, with the oxygen in its air reduced and the carbon dioxide kept in check. Fruit such as apples, pears and kiwifruit waits here months longer than in an ordinary store.
A grower who wants to sell apples until summer asks for this room. The air we breathe is 21% oxygen; in a CA room that share is pulled down to 1–3%, and carbon dioxide sits at a value between 1% and 5% depending on the variety. The room is at 0–3 °C. Fruit with less oxygen respires more slowly and gives off less ethylene; it keeps its firmness and acidity. Rooms where oxygen is taken below 1.5% go by the name ULO.
The quote adds a few items to an ordinary cold room: panels with joints filled with mastic and taped, a gas-tight door, a nitrogen generator, a carbon dioxide scrubber, a gas analyser and a breather bag. Moisture loss means lost weight, so the evaporator is chosen with a large surface and a 3–5 K difference. Fruit from an opened room has to be sold within a few weeks, which is why rooms of 100–300 tonnes are built side by side. The air inside is odourless and kills in a few breaths; nobody enters until the oxygen reading is above 20%.