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The ripening process for bananas is typically as follows:<br />
Green bananas in cartons or open crates are loaded into the ripening room (fruit pulp temperature should not be lower than 14 ºC as lower temperatures can damage the fruit).
The room is closed and thermally controlled until the pulp temperature reaches 15-17oC. This temperature is controlled and maintained by a thermostat. During summer conditions or for direct field produce, a refrigeration system will cool the room to maintain the set temperature and remove the heat of respiration.
Ethylene is supplied into the room at a concentration of around 100-400ppm (0.01 - 0.04%). The room is then kept closed for 24 hours. The ethylene acts as a catalyst initiating the hormonal process of ripening.
At the end of this time the room is ventilated to clear the ethylene gas and the carbon dioxide released due to increased respiration during the initial ripening phase.
The room temperature is controlled between 17oC to 15oC over three or four days. The fruit pulp may reach a temperature of 32oC during this process and gases, including carbon dioxide, are evolved in substantial quantities. Most of these gases would normally be vented off by ripening room operators to maintain the carbon dioxide level below 1%, as carbon dioxide levels above 7% inhibits further ripening.
The room is finally ventilated and the ripe fruit removed. A common way of ventilating involves opening the doors for at least five, and usually fifteen, minutes before entry is made. Extractor fans may also be used.
N.B. The amount of ethylene gas required for a ripening room is normally calculated on the free air space after the bananas have been loaded (i.e. if bananas take up 35% of the room size, the amount of ethylene required is calculated for the remaining 65% free air space.<br />Method of introducing ethylene gas<br />Ethylene generators which use a catalytic process to produce pure ethylene gas from a solution containing mainly ethyl alcohol (ethanol) but which may have trace quantities of other ingredients (e.g. methanol). The solution (sometimes known as 'ripening fluid') is poured into a reservoir on the ethylene generator where it is slowly fed to an internal heater which vaporises the ethanol which then passes to the catalytic converter. Each litre of solution produces about 0.33-0.4 m3 of ethylene gas. <br />Hazards Involved<br />The hazards from this process fall into two main categories:<br />Fire/Explosion<br />
If the introduction of ethylene is uncontrolled there is a risk that the ethylene may reach or exceed the lower explosive limit (LEL) of 3.1% and be ignited by unprotected electrical apparatus or gas heating systems or other incendiary sources, resulting in a fire or explosion.
Formation of flammable gas/air mixtures may result from spillage of ethanol-based solution used in ethylene generators.
Toxicity and asphyxiation<br />There are also potential acute risks from oxygen depletion and from the accumulation of other gases such as carbon dioxide; these health risks are exacerbated by the enclosed nature of the process:<br />
Oxygen deficiency in the room may result from excess addition of ethylene or ethylene-nitrogen mixture from cylinders.
The evolution of carbon dioxide during the fruit ripening process may result in a toxic or asphyxiating atmosphere. For example high levels of carbon dioxide may cause loss of consciousness and death from respiratory failure. Other effects such as headache and exhaustion occur at much lower exposure levels.
Ripening rooms (5 each) for Banana, Mango, PapayaExternal Room Size (Lx B x H) 7000 x 5000 x 4000 mm ( 4 Nos.) Room temperature & RH. 10 to 15 °C /90 to 95% Ambient Temperature 2 °C (min) and 45 °C (max) Product incoming Temperature 20 °C Product Incoming Rate 10 MT per room per batch Cooling Time 24 Hrs Insulation Material PUF panels, 80 mm Door Type Lamination Manual sliding door 1500 mm x2100 mm PCGI both sides Refrigeration System Type Type of condenser Type of compressor Cooling Capacity Refrigerant Total number of units Number of evaporating units Location of condensing unit Location of evap/AH unit Humidifier Evacuation system Ethylene System Split Air Cooled Semi Hermetic 1 x 40000 Btu/hr R 404A 1 nos per room 1 Nos per room Outside near the chambers In ripening chambers suspended from ceiling. Steam type ,modulating one for each room Fan unit & damper Ethylene Generators Power Requirement 4 x 10 Kw, 3 Ph, 415 V, 50 Hz <br />
Temperature dependence of the ripening process:
Too high: irregular ripening of the fruit / poor keeping quality (> 18°C)