Blanching in food industry

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1. OBJECTIVE


Blanching operations are designed to expose the entire product to high temperatures for a short period of time, by using steam heating indirectly for fruit juices and directly for vegetables. The primary function of this operation is to inactivate or retard bacterial and enzyme action, which could otherwise cause rapid degeneration of quality. Two other desirable effects of blanching include the expelling of air and gases in the product, and a reduction in the product volume (BAT in the Food, Drink and Milk Industries, June 2005).


2. FIELD OF APPLICATION


Blanching is a controlled heating process similar to pasteurization and it is used in the processing of fruit juices, fruits and green vegetables (BAT in the Food, Drink and Milk Industries, June 2005).


3. DESCRIPTION OF TECHNIQUES, METHODS AND EQUIPMENT


  • Principal of blanching
    (BAT in the Food, Drink and Milk Industries, June 2005)

Both pasteurisation and blanching are based on the use of the minimum heat requirement needed to deactivate specific micro-organisms or enzymes, thus minimising any quality changes in the foods themselves [87, Ullmann, 2001].

  • Method description
    (BAT in the Food, Drink and Milk Industries, June 2005)

Before blanching, the food is preheated. Depending on the product and/or availability of equipment, blanching may be accomplished direct or indirect heating systems. After blanching, the food is cooled using either water or air.

  • Direct heating:

Direct heating is normally made by immersion in hot water (80 to 100°C) or exposure to live steam. The operation is normally carried out in horizontal chambers. The residence time in the blancher can vary from approximately 1 minute to minutes depending on the vegetable or fruit being blanched.

  • Indirect heating:

For some products direct contact with water is to be avoided thus heat exchangers working with hot water or vapour are applied.


Blanching can be batch or continuous:

  • Batch blanching:

Typical batch blanching equipment is the drum blancher with countercurrent water cooling.

  • Continuous blanching:

Typical continuous blanching processes are steam blanching with air cooling, belt blanching with water cooling, belt blanching with air cooling.

  • Energy and water consumption within different blanching techniques
    (BAT in the Food, Drink and Milk Industries, June 2005)

The following table shows a qualitative comparison of energy and water consumption levels within the different blanching techniques: Table 1: Comparison of the energy and water consumption levels within the different blanching techniques

Blanching.jpg


4. COMPETITIVE TECHNOLOGIES AND ENERGY SAVING POTENTIALS

a) Changes in the process
  • Microwave blanching: (Northwest Food Processors Association)
When microwave blanching is performed waste water volumes and energy consumption can be reduced. Microwave blanching is used in fruit and vegetable processing (BAT in the Food, Drink and Milk Industries, June 2005).
Microwave energy is being used in some food industries as a method to blanch vegetables. In microwave technology, a form of radio waves passes through the material. The molecules in the material oscillate to align themselves with the high-frequency alternating electrical field. This causes intermolecular friction which generates heat and results in a temperature rise. Industrial ovens can be designed either for batch or continuous processing. The advantages of microwave blanching over conventional blanching are
  1. more uniform volumetric heating,
  2. minimal oven temperature gradients,
  3. no blanching residual products,
  4. reduced energy costs, and
  5. reduced processing time.
The primary barrier to implementing microwave blanching is the high cost of equipment. Microwave blanching has been used primarily in Europe and Japan, with little acceptance in the United States.


  • Belt blanching with water cooling: (BAT in the Food, Drink and Milk Industries, June 2005)
This cooling process requires the least energy comparing to other blanching techniques.


b) Changes in the energy distribution system
  • Heat recovery from the cooling system of the blanching process: (BAT in the Food, Drink and Milk Industries, June 2005)
The final stage in the process of blanching includes a cooling system for the food stream. The water from the first compartment of the cooing section which is warm is re-used in the preheating section, leading to heat recovery and a reduction in water consumption.


  • Re-use of cool streams of the process: (BAT in the Food, Drink and Milk Industries, June 2005)
If the coldest water available is used for cooling, this also reduces the energy consumption for both the cooling step after blanching and if the food is destined for low temperature storage or processing, e.g. freezing. Water from cooling cans and jars in fruit and vegetable preservation can be re-used to heat cold water for use in blanching.


c) Changes in the heat supply system
No information is available.



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