Quick freezing of food

The two basic ways to achieve the freezing of foods are quick and slow freezing. The technical features of the quick freezing process are ultra rapid freezing at very low temperatures (-30 to -40 ° C) designed to bring the inside the product to a temperature of -18°C as quickly as possible. Rapidly frozen foods have a much longer storage life than foods stored in cold stores.

The products that are generally preserved by quick freezing are meat, fish, some vegetables such as peas, spinach, cauliflower, carrots, beans etc.

When the quick freezing process is used, these liquids solidify to form extremely fine crystals of ice, and the cellular structure is left intact, whereas, in the ordinary freezing process, where low temperatures are reaching more slowly, the texture of the product is altered.

In quick freezing, large quantity of food can be frozen in a short period of time.

Quick freezing is a method of increasing the shelf-life of perishable foods by subjecting them to conditions of temperature low enough to inhibit the oxidative, enzymatic and microbial changes, which are responsible for the changes in flavor and color of foods.

Quick freezing is ideal for producing good quality frozen foods. The food freezes immediately and keeps its shape and appearance.

Quick freezing is obtained by one of the following methods:
*Freezing Tunnel or Blast Freezer
*By Direct Contact with Metal Plate Surfaces maintained at Low Temperatures
*By immersion in (or by Spraying)  a Low Temperature Liquid
Quick freezing of food

High Pressure assisted Freezing (HPAF)

High pressure freezing processes operate in pressure-resistant vessels with thermally isolated thermostatic circuits to reach temperatures below 0 ° C.

Packed foods are immersed in the pressure/cooling medium and frozen.

In high pressure assisted freezing process, water solidification is produced while pressure around the product is high.  During freezing, use of high pressure facilities supercooling and promotes uniform and rapid ice nucleation throughout the product on pressure release, producing smaller ice crystals.

Phase transition occurs under constant pressure, higher than atmospheric pressure while the temperature is lowered to below the corresponding freezing point.

HPAF is based on the fact that freezing point changes with pressure and the product can be stored at normal frozen storage conditions.

High pressure assisted freezing was particularly useful for freezing large pieces of food when uniform ice crystals are requires.

In high pressure assisted freezing, product are cooled under 200 MPa to -20  ° C without ice formation, then the pressure is released and the high supercooling reached ( approx. 20 °C) promotes uniform and rapid nucleation.
High Pressure assisted Freezing (HPAF)

Microwave Processing – How it works?

Microwave Processing – How it works?
Introduction
Microwave energy, usually generated by a magnetron, occurs as alternating current at either 915 or 2450 megahertz. Both frequencies are authorized by the federal government for use with microwave ovens. Because water molecules are polar (have positive and negative ends), they tend to oscillate as they try top align themselves alternately between the positive and negative charges of the microwave energy.

Function
When the frozen foods are exposed to microwave energy, the liquid water in them (all frozen foods contain some water in the liquid stat) begin to heat due to the friction created by high speed oscillations of the water molecules. Most of the water in frozen foods is in the ice state and is not affected by the microwave energy, until heat generated by liquid water molecules is conducted to the ice, melting it, and thereby producing more liquid water to become involved in the heating process.

History
The first application of microwave energy in industry occurred during the 1070s when cooperative experiments between the Gloucester Laboratory, a USDC facility, and the Raytheon Co. resulted in the introduction of a continuous microwave tunnel in the seafood industry, for thawing or tempering of shrimp and fish blocks. In tempering, the product is not quite thawed yet lends itself to further processing such as cutting or coating with a breading. Microwave Processing – How it works?