This document discusses blanching of fruits and vegetables. It explains that blanching uses heat treatment to inactivate enzymes and describes under and over blanching. It notes the most heat resistant enzymes in vegetables and that blanching times vary based on size and other factors. Blanching is often used before freezing, canning, or dehydrating vegetables. Cooling must follow blanching to prevent over softening, and there are different methods for cooling. Reasons for blanching include slowing enzymes and preserving quality, cleansing surfaces, brightening color, retaining vitamins, and softening vegetables. The main types of blanching are hot water and steam blanching, and blanching parameters are provided for

1. Blanching of Fruits
and Vegetables
DEPARTMENT OF FOOD TECHNOLOGY, SLGTI

2. Blanching
 The special heat treatment to inactivate enzymes is known as
blanching
 Under blanching is ineffective
 Over blanching is too much damages the vegetables by excessive
cooking, especially the fresh characters of the vegetable
 Two of the more heat resistant enzymes important in vegetables
are catalase and peroxidase
 If these are destroyed then the other significant enzymes in
vegetables also will have been inactivated
DEPARTMENT OF FOOD TECHNOLOGY, SLGTI

3.  Vegetables differ in size, shape, heat conductivity,
and the natural levels of their enzymes
 blanching time and temperature have to be
established on an experimental basis
 Small vegetables may be adequately blanched in
boiling water in a minute or two minute
 Large vegetables may require several minutes.
DEPARTMENT OF FOOD TECHNOLOGY, SLGTI

4.  Blanching is often used as a pre-treatment for
freezing, canning, or dehydration
 Cooling of vegetables after blanching is performed
in order to avoid excessive softening of the tissues
and has to follow immediately after these
operations
 one exception is the case of vegetables for drying
which can be transferred directly to drying
equipment without cooling
 Cooling in water can be achieved by sprays or by
immersion
 DEPARTMENT OF FOOD TECHNOLOGY, SLGTI

5.  Vegetables have to reach a temperature value
under 37° C as soon as possible
 Too long a cooling time generates supplementary
losses in valuable water soluble substances
 In order to avoid this, the temperature of the
cooling water has to be as low as possible.
DEPARTMENT OF FOOD TECHNOLOGY, SLGTI

6. Reasons for blanching
 Slows or stops enzymatic action, preserving flavor,
color and texture
 cleanses the surface of dirt, bacteria, molds and
other organisms
 brightens the color
 helps retard loss of vitamins
 softens vegetables and makes them easier to pack
DEPARTMENT OF FOOD TECHNOLOGY, SLGTI

7. Types of blanching
Hot water blanching
Steam blanching
DEPARTMENT OF FOOD TECHNOLOGY, SLGTI

8. Hot water blanching
DEPARTMENT OF FOOD TECHNOLOGY, SLGTI

9. Steam blancher
DEPARTMENT OF FOOD TECHNOLOGY, SLGTI

10. Blanching parameters for some
vegetables
Vegetables Temperature, °C Time, min.
Peas 85-90 2-7
Green beans 90-95 2-5
Cauliflower Boiling 2
Carrots 90 3-5
Peppers 90 3
DEPARTMENT OF FOOD TECHNOLOGY, SLGTI

11. DEPARTMENT OF FOOD TECHNOLOGY, SLGTI
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