Onion Storage Tecnology involves: The processes of drying onions, and storing Onions.
Inside an onion storage facility the onions pass through 3 main processes:
- The drying process.
- The storing process.
- The cooling-down and warming-up processes.
The process of drying onions.
The objectives of the drying process of onions are:
Well dried onions. You notice the crispiness of the sealed skins.
- Remove all superficial humidity.
- Dry the out 3 to 4 layers of the skin of the onion in effect sealing the onion from the outside.
- Dry the stem so the onion is also through here is sealed from the outside. (Remember the stem is a wound, which you want as dry as possible.)
The drying process should, preferably, be done between 25 to 30 °Celsius.
The Onion Drying program of the MULTI-SERVER will make the turbines work the maximum number of hours to extract as quickly as possible the moisture and humidity from the onions, but safe guarding a temperature range of 25 to 30° Celsius and a relative humidity range around 75%. We don’t want to dehydrate the onions, only the outer skin has to be dried and sealed in the process.
This process is completely controlled by the MULTI SERVER, which is constantly looking for the air mixture with the highest drying capacity (See DEW POINT Calculator, manipulating the hedges, turbines, heaters and condensers.
Raising and lowering the temperature of the onions.
Changes of temperature should be very slow and controlled not to destroy the inside of the cells of the bulb.
There for the MULTI-SERVER have two extra programs: One to decrease the temperature of the onions and the other one to increase the temperature of the onions at a rate of about2°Celsius per day. This is the generally advised temperature change rate by onion storage specialists.
This slow rate of temperature change has serious consequences planning possible sales from the storage.
Imagine the onions are stored at 2 °Celsius.
The destination where the onions go has a temperature of 25° Celsius and y Relative Humidity of 85%, which means a Local Dew Point of 22.3 °Celsius. Therefore the onions have to be raised to a temperature of at least 22.3° Celsius. If not they will become soaking wet due to condensation. Increasing the temperature from 2° Celsius to 22.3°Celsius will take at least 10 days.
These 10 days have to be taken into the planning for the delivery of the onions!
The process of storing onions.
A well dried and stored onion has a dry and crispy skin, but is juicy at the inside!
To be able to successfully store onions the following criteria must be met:
- The onion must be of a variety that is fit to store.
- Should have been harvested when physiologically, completely mature.
- The bulb must be firm and compact.
- The skin must be b.
- The bulb should have a low water content.
- Cultivated with Good Agricultural Practices.
- Nitrogen should not be used as a fertilizer during the last 6 weeks of cultivation.
- Sufficient amounts of lime should have been applied.
Onions can be stored at two temperatures (ranges):
- Around 2°Celsius. This is the optimal storage temperature, under which good storable onions (see above) can be stored up till 12 months. The major disadvantage of this temperature is the long period necessary to raise the temperature above the Local Dew Point. If this is not done correctly, the whole batch of onions will become completely wet and great losses will be incurred.
- A good alternative temperature range, especially when storage time does not exceed 3 to 4 months, is from 25 °Celsius to 32 ° Celsius. In this temperature range the bulb, which is still a living organism, hardly has any respiration and will, therefore, hardly lose any weight.
In both cases: Relative Humidity has to be maintained between 75% and 80%.
Note: The onion bulb will lose serious amount of weight while stored at temperatures between 5 to 25°Celsius, through respiration and the temperature range between 20 to 25°Celsius is especially dangerous because of the activity of certain bacteria and fungi.
During the storage process the ventilation will be minimal. Because DRY is DRY and we don’t want to lose unnecessary weight through respiration, (despite the fact that at the storage temperature levels the expiration is close to zero). The only reason for the ventilation is to avoid the build-up of the CO2 in between the onions.