Types of Blanching

1. Water Blanching:

                It is method performed in hot water at a temperature ranging from 70 to 100°C. But in this type combination of low temperature long time and high temperature short time have also been used. Water blanching usually results in a more uniform treatment than others. For automatic processing different water blanchers are developed in that basically screw or chain conveyor used to transport product inside tank where hot water is filled. Water is heated indirectly with steam in a heat exchanger so steam quality does not need to be a “food grade”. Main disadvantage of this method is it takes longer processing time so it results in increased leaching of minerals and nutrient such as vitamins and also produces large amount of effluent with large BOD.

2. Steam Blanching:

                In this type product is transported by chain or screw conveyor through chamber where a “food grade” steam is directly injected at 100°C. Steam blanching is usually used for cut and small products and it requires less time than water blanching and losses are also less. Due to temperature gradients between surface and center of food products uneven blanching takes place and which results in “overblanched” near surface and “underblanched” in center. To increase efficiency forced convection blancher has been developed. This technology allows higher product bed depths and higher product throughputs. To reduce product non-uniformities another technology is developed which is called as individual quick blanching.

3. Microwave Blanching:

                It is developed because of important findings were retention of ascorbic acid and carotene and require very short processing time compare to others. To overcome some drawbacks on disadvantages it has been combined with water blanching.

4. Gas Blanching:

                Hot gas blanching using combustion of flue gases with addition of steam to increase humidity and product dehydration has been studied. This type of blanching has the advantage of reducing waste production and retention of nutrients. But major disadvantage of this is it results in product weight loss. This approach not currently used in industry and needs further research.