Natural fruit ripening begins after the fruit has completed its growth. Basically, ripening is a metabolic process in which the ingredients of a fruit change. Fundamentally, starch is converted into fructose by hydrolysis. The fruit then develops its typical taste and becomes edible. On top of this, the ripening process also changes the consistency and appearance of the fruit: bananas turn yellow, tomatoes red, avocados soft, and so on. 

Only Climacteric Fruits Ripen after Picking

Fruits are generally distinguished according to whether or not they have a climacteric phase after harvesting. The climacteric phase is the stage of the metabolic process in which the harvested fruit absorbs oxygen and releases carbon dioxide through cellular respiration. Just like during ripening on the tree or plant, the starch components of the fruit are converted into sugars – the fruit ripens. At the same time, the ripening hormone ethylene (C2H4) is released; this in turn stimulates other climacteric fruits to ripen.

• Climacteric fruits (e.g., apples, bananas, mangoes or tomatoes) can be harvested at an early stage – after achieving minimum maturity. After harvesting, the fruits are stored in ripening chambers where they ripen to maturity for consumption.
   
• Non-climacteric fruits (e.g., citrus fruits, pineapples, blueberries) do not ripen after picking. They must mature on the plant before they are harvested.

To ensure that the fruit does not reach its ideal degree of ripeness until it reaches the supermarket shelf, it is essential to control the ripening process. This is done in ripening chambers, where the fruit is stored in the transport box on pallets or shelves under controlled conditions. Ripening of the fruit can be slowed down or accelerated by adjusting the temperature and humidity as well as by providing a targeted supply of ethylene gas and regulating the CO2 concentration. 

Bananas, for example, typically reach maturity for eating within 4 to 8 days in ripening chambers. For this, they require temperatures between 14 °C and 23 °C (57,2 °F and 73,4 °F) and a high humidity of >90 % RH. To ensure that all fruits ripen evenly and there is no harmful accumulation of CO2 in the ripening chamber, a uniform air circulation and fresh air supply must also be ensured.

Technical Equipment of Ripening Chambers

To control the relevant climatic parameters and gas composition of the storage atmosphere, modern ripening chambers are equipped with the right choice of technical equipment:

• Cooling systems and humidifiers for temperature and humidity control 
• Fans and ventilators for sufficient ventilation and fresh air supply
• Systems for controlling (feeding and discharging) ethylene, CO2 and nitrogen

In addition, sensors are needed to measure the humidity and temperature, the CO2 and oxygen levels, and the ethylene concentration. They form the basis for optimal control of the ripening process. The reliability and measurement accuracy of the deployed sensors therefore have a direct influence on the ripening process and on the quality of the stored fruit.