Categories of organic storage techniques
1.0 Normal Atmosphere Storage (NAS)
Definition. NAS is storing product in the normal atmospheric condition (under ambient condition) usually in household or warehouses.
2.0 Controlled Atmosphere Storage (CAS)
Definition. CAS is storing product in an atmosphere where at least one inside component is being controlled continuously throughout the storage period. Due to complexity and large investment requirement, this technique is usually recommended for quantities more than 10,000 metric Tons (MT). The operation involves utilization of air conditioning and refrigeration principles.
3.0 Modified Atmosphere Storage (MAS)
Definition. MAS is storing product in an isolated atmosphere where proportion of each internal parameter is fixed and no other control is made during storage. The primary objective of MAS is to naturally create an atmosphere that will prevent proliferation or development of internal parameters responsible for the deterioration of the commodity.
Types of MAS
3.1 Hermetic storage
This is the simplest type of MAS. The method allows the internal parameters to act and react among themselves. The final result, usually not exceeding 20 days, is a modified atmosphere where the development of some specific internal parameters are prevented or killed.
3.2 Flushed
This type of MAS is commonly used for high value, durable agricultural including dried fruits, leaves, herbs and flowers. This method of storing is also a common practice museums and libraries where artifacts, antiques and books are stored. This method operates under an atmosphere where oxygen is replaced by either carbon dioxide or nitrogen, preventing the development of insects, microbes and the oxidation process within the commodity.
The structure is equipped with airtight inlet and outlet ports. The inlet port is commonly situated near the bottom and the outlet port on top of the structure. The flushing involves opening the outlet port while flushing the carbon dioxide or nitrogen thru the inlet port. The difference in molecular weight will push the lighter gas (oxygen) upwards to escape via the outlet port. Amount of carbon dioxide or nitrogen to be flushed to obtain the required concentration, is predetermined before the operation.
3.3 Vacuum
This type of MAS is most suited for high value, non-crushable commodities. This method has the ability to control infestation in no more than five days, which is faster than simple hermetic storage.
The storage structure is equipped with a port. A vacuum pump is attached to the port. An indicator/recorder is mounted in the structure which will enable the operator to monitor the level of vacuum inside the structure. Indicators may vary from simple U-tube manometers to specialized digital indicators.
The rated capacity of the pump depends on the volume of the structure. Pump assembly should include utilization of vacuum hose and quick connect adaptors.
Materials to be used for the structure should obtain yield strengths that will overcome collapse due to the negative pressure.
3.4 Sacrificial commodity
This type of MAS sacrifices a small of the commodity with the intent of encouraging a significant increase in population insects and microbes in short time. This increase in populations will certainly deplete the oxygen content inside the structure through natural metabolism. Usually, the sacrificial commodity is wetted to entice microbes and some insects.
3.5 Oxygen absorber
Another type of MAS is the use of oxygen absorber. This type utilizes an absorber agent, usually packed in small gas permeable pouches, that absorbs the oxygen in the enclosure. The common compositions of this agent are iron powder and alkali metal salt.
3.6 Sousvide Technique
This type of MAS was developed in Europe and is now a major technique used especially in storing/packing cooked meal products. The procedure involves cooking the product at low temperature for longer periods before packing.