Quick Freezing

With the increasing demand from overseas for fruits and vegetables, fresh fish of highest quality, then the expertise to preserve post harvest commodities is needed. Freezing is one of the techniques for extending shelves life of post harvest commodities, which can produce frozen commodities close to its harvest condition. However, the quality of post harvest commodity is closely dependent to the technique and duration taken to freeze the said commodity. The shorter the duration taken to frozen the commodity, the higher the quality of the post harvest commodity.

Carbon Dioxide and Nitrogen as Freezing Medium

Carbon dioxide and nitrogen is the kind of industrial gases which can be used as freezing medium. Carbon dioxide, when the volume is expanded, will form a snow at temperature -78oC, meanwhile nitrogen can be liquefied and stored at temperature -196oC. With such properties, carbon dioxide and nitrogen is a very powerful freezing agent, which could freeze post harvest commodities less than 15 minutes, much stronger than mechanical freezing which take time up to 4 to six hours.

Benefit of using CO2 and N2 as freezing Medium

	Freezing Method
	Mechanical	Cryogenic (CO₂ & N₂)
1. Duration	Long (4-6 hours)	short (5-15 minutes)
2. Cell structure	damaged	intact
3. Juice content, nutrition value, flavor	reduced and degraded (drip loss)	relatively intact (no drip loss)
4. Weight loss	up to 15%	less than 1%
5. Color	changed due to oxidation (discoloration)	unchanged
6. Investment for equipment	Expensive	Not Expensive
7. Electric consumption	Big	Small
8. Operation	Difficult	Easy

Types of quick freezing using CO2 and N2

Deep freezing

In deep freezing, all parts of post harvest commodities are frozen quickly using CO2 or N2 resulting the central temperature of the commodities to drop to -25oC

Crust freezing

In this method not the whole parts of the commodity, but only 50 to 90% is frozen by CO2 or N2, especially the surface of the commodity (surface freezing). The surface of the commodity which have been frozen is enough to protect the commodity from dehydration, oxidation, and microorganism activities. The commodity is then stored in cold storage until the whole parts is frozen. Basically, crust freezing is to minimize unwanted effects of the mechanical and cryogenic freezing.

Types of quick freezing using CO2 and N2

Quick freezing can be done continuously or intermittently with the following techniques:

Direct Spraying

Here the commodity is frozen by spraying directly with CO2 and N2. The freezing process using direct spraying can be carried out continuously in a tunnel chamber, or intermittently in the food cabinets.

Immersion freezing

Here the technique is by immersing the commodity in liquid nitrogen. This type of freezing is the quickest process, since the commodity touch the cooling media directly.

Commodities which can benefits from quick freezing:

fruits (pineapple, banana, strawberry, etc.), vegetables (broccoli, asparagus, mushroom, etc.), meats, poultry, etc. fish, shrimps, etc. processed food (bread, ice cream, cake, etc.)

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