Some fruits go on ripening after they are picked; these are called climacteric fruits: banana, avocado, mango, tomato, kiwifruit, pear, persimmon. These products are harvested firm and green so that they withstand transport, and are ripened somewhere close to the market. By supplying ethylene gas, the fruit’s natural ripening hormone, in a controlled dose, the ripening room ensures that the whole batch is ready on the same day, with the same colour and firmness. Non-climacteric fruits such as strawberries, grapes, cherries and citrus do not sweeten after harvest; for them the room is used for colour only.
Typical conditions vary with the product. Avocados begin to soften in 12–48 hours at 15–20 °C with 10–100 ppm (parts per million) of ethylene. Mangoes at 20–22 °C and tomatoes at 18–21 °C turn colour in 1–3 days with 100 ppm of ethylene. In citrus degreening the aim is to remove the green of the peel: 20–25 °C, 1–5 ppm of ethylene, 2–4 days. In all of them the relative humidity is held at 90–95% and the room is ventilated regularly so that the carbon dioxide built up through respiration stays below 1%. When the ethylene treatment is over the product is cooled to its own storage temperature.
The room structure resembles an ordinary cold room; the difference lies in its equipment: a system that both cools and heats, product core temperature probes, ethylene and carbon dioxide sensors, a fresh air fan and damper, a humidifier, a gas-tight door and a pressure equalising valve. The evaporator is selected with a high air flow, because the condition for even ripening is that the same amount of air passes through every carton. In the capacity calculation the product’s heat of respiration is the main item: during ripening, respiration rises to several times its level during storage, and if it is left out of the calculation the room temperature cannot be held.
Practical notes: ripening cannot be reversed, so the programme is built around the sales plan, and for batches that will come out on different days several small rooms are more useful than one large room. Ethylene-sensitive products (lettuce, cucumbers, broccoli, carrots, cut flowers) must not be kept near ripening rooms. The same name is also used in the production of cheese, sucuk and dried meat; the ripening rooms there are a different design that works not with ethylene but with a temperature of 10–15 °C, 75–90% humidity and slow air movement. For product values you can consult the food storage conditions guide.