Blanching is a heat treatment used prior to freezing, canning, or drying foods. It inactivates enzymes that cause quality degradation, softens texture, and improves appearance. Blanching is done using hot water, steam, or gas at temperatures between 70-100°C for 1-15 minutes depending on the food. It helps preserve color, flavor, and nutrients but some water-soluble vitamins and minerals are lost through leaching. Individual quick blanching systems improve quality by providing uniform, quick heating of individual pieces.

1. BLANCHING PROCESS

2. Heat Processing Overview
• Heat processing using steam or water
• – Blanching | Pasteurization | Heat sterilization
• Heat processing using hot air
• – Dehydration | Baking and roasting
• Heat processing using hot oils
• – Frying
• Heat processing by direct and radiated energy
• – Dielectric | Ohmic | Infrared
• Processing by The Removal of Heat
• – Chilling | Controlled- or modified-atmosphere storage and packaging |
Freezing | Freeze drying

3. WHAT IS BLANCHING ??
* Blanching is a unit operation prior to freezing, canning, or drying in which
fruits or vegetables are heated for the purpose of inactivating enzymes;
modifying texture; preserving color, flavor, and nutritional value; and
removing trapped air.
* For a given product, typically mass flow rate is fixed, temperature is
measured, and heating media flow rate is adjusted to ensure that the
temperature is kept at the set point.
* Processing conditions are usually set up to inactivate enzymes, but other
quality parameters also , such as color and texture, are commonly monitored.

4. Blanching
• Blanching is used to – lower enzymatic activity in vegetables and
fruits
• Not final method of preservation but as a pre- treatment, – between
the preparation of the raw material and further processing steps
• Combined with peeling and/or cleaning
• Some vegetables are not blanched – specific location of the enzymes

5. Enzymes inactivated with blanching
• Foods are blanched to inactivate enzymes, prior to other preservative
– freezing, drying, canning
• Effectiveness of blanching. (marker enzymes ) – Absence of
peroxidase enzyme after blanching – Peroxidase is the most widely
distributed heat resistant enzyme
• Enzymes which causes undesirable changes in fruits & vegetables
• – Lipoxygenase
• – Polyphenol oxidase
• – Polygalactouranase
• – Chlorophyllase

6. Mechanism of blanching
• Plant cells are discrete membrane-bound structures contained within semirigid cell walls.
The outer or cytoplasmic membrane acts as a skin, maintaining turgor pressure within the
cell.
• Loss of turgor pressure leads to softening of the tissue.
• Within the cell are a number of organelles, including the nucleus, vacuole, chloroplasts,
chromoplasts and mitochondria.
• This compartmentalisation is essential to the various biochemical and physical functions.
• Blanching causes cell death and physical and metabolic chaos within the cells.
• The heating effect leads to enzyme destruction as well as damage to the cytoplasmic and
other membranes, which become permeable to water and solutes.
• An immediate effect is the loss of turgor pressure.
• Water and solutes may pass into and out of the cells, a major consequence being nutrient
loss from the tissue.
• Also cell constituents, which had previously been compartmentalized in sub cellular
organelles, become free to move and interact within the cell.

7. Factors are affecting blanching time
• The type of fruit or vegetable.
• The size of the pieces of food.
• The blanching temperature and
• The method of heating

8. Objective of Blanching
• to inactivate enzymes, which would otherwise lead to quality
reduction in the processed product.
• To soften the tissue to facilitate packaging.
• To avoid damage to the product.
• To eliminate air form the product.
• To preserve the natural colour.
• To destroy or retard certain undesirable enzymes.
• To help preserve natural flavour.

9. Processing Conditions for Blanching
• Fruit or vegetable properties, especially thermal conductivity, which
will be determined by type, cultivar, degree of maturity etc
• Overall blanching effect required for the processed product, which
could be expressed in many ways including: achieving a specified
central temperature, achieving a specified level of peroxidase
inactivation, retaining a specified proportion of vitamin C.
• Size and shape of food pieces
• Method of heating and temperature of blanching medium
• Time/temperature combinations vary very widely for different foods
and different processes and must be determined specifically for any
situation. Holding times of 1–15 minutes at 70–100 ºC are normal.

10. PRINCILPLES & EQUIPMENTS
• The design of blanching systems depends on the product, the process
following it, and the final use of the product. Blanching is carried out as a pre-
treatment for freezing, canning, and drying.
• Most vegetables are blanched prior to freezing to inactivate enzymes that
cause the development of off flavours and off-colors during frozen storage.
• Blanching facilitates peeling and dicing, and is also accompanied by
microbial load reduction. Fruits are usually not blanched, or blanched under
mild (low temperature) conditions prior to freeze.
TYPES OF BLANCHERS USED IN FOOD INDUSTRY :-
• Water Blanching
• Steam
• Gas
• Microwave

11. Hot WATER BLANCHER
• Is performed in hot water at temperatures ranging typically from 70˚C to 100˚C.
• However, low temperature long-time (LTLT) blanching and combinations of LTLT with
high-temperature short-time (HTST) blanching have also been used in blanching.
• Development of hot water blanchers , based on IQB PRINCIPLES. For example , the
blancher cooler have three section :a pre heating, blanching stage, & cooling stage
• A mass of product blanched is 16.7 – 20 kg per kg of steam
• Water blanching usually results in a more uniform treatment, allowing processing at
lower temperatures.
• There are water blanchers that use a screw or a chain conveyor to transport the product
inside the tank, where hot water is added.
• Water is usually heated indirectly with steam in a heat exchanger; therefore steam
quality does not need to be ‘‘food-grade.’’
• Blanching requires longer processing times, results in increased leaching of minerals and
nutrients such as vitamins, and produces effluents with large biological oxygen demand
(BOD).

12. Hot-water blanchers
• Holds food in hot water (70-100ºC) for a specified time
• Then move to a dewatering-cooling section.
• reel blancher
• Food enters a slowly rotating cylindrical mesh drum
• partly submerged in hot water.

13. WATER BLANCHERS

15. Steam blanching
• In steam blanchers, a product is transported by a chain or belt conveyor through a chamber
where ‘‘food-grade’’ steam at approximately 100˚ C is directly injected.
• Steam blanching is usually used for cut and small products, and requires less time than water
blanching because the heat transfer coefficient of condensing steam is greater than that of hot
water
• However, because of the high-temperature gradients between the surface and the center of the
product, larger products or pieces of product can be ‘‘overblanched’’ near the surface and
‘‘underblanched’’ at the center. To increase heat transfer efficiency, forced convection
blanchers have been designed.
• Steam blanching is more energy-efficient and produces lower BOD and hydraulic loads than
water blanching. In addition, nutrient leaching is reduced compared to water blanching.

16. Stem Blanchers
• Specific for foods with a large area of cut surfaces
• leaching losses < hot-water blanchers.
• Mesh conveyor carries food, through a steam atmosphere in a tunnel
• typically 15m x 1–1.5m
• Water sprays at the inlet and outlet to condense escaping steam.
• Food enter & leave blancher through rotary valves or hydrostatic seals
• reduce steam losses
• increase energy efficiency
• steam may be re-used.

17. STEAM BLACHHERS

18. Blancher–cooler

19. Batch fluidised-bed blanchers
• Batch fluidised-bed blanchers
• – mixture of air & steam
• – fluidises & heats product simultaneously.
• Advantages:
• – faster, more uniform heating
• – good mixing of product
• – reduction of effluent volume
• – shorter processing times
• – smaller losses of vitamins & other soluble heat sensitive components

20. Pipe blanchers
• A continuous insulated metal pipe fitted with feed & discharge ports.
• Hot water is re-circulated through pipe & food
• Large capacity while occupying a small floor space.

21. • All the method of blanching has the following problems:
• The time-temperature require to ensure enzyme inactivation
• centre of the product
• Overheating of food - loss of texture and other sensorial characteristics
• To over come this problem, ---- IQB-system (individual quick
blanching)

22. IQB-system (individual quick blanching)
• In the first stage – Heating stage
• food is heated( sufficiently high temperature) in a single layer to inactivate
enzymes
• In the second stage (adiabatic holding)
• a deep bed of food is held for sufficient time
• allow the temperature at the centre of each piece
• Cooling stage
• fog spray to saturate the cold air with moisture.
• Nutrient losses during steam blanching are reduced by,
• exposing the food to warm air (65ºC)
• preliminary drying operation (‘pre-conditioning’)

24. IQB-system
• Surface moisture evaporates & surfaces then absorb condensing
steam during IQB.
• Pre-conditioning + IQB
• – reduce nutrient losses by 81% for green beans
• – 75% for Brussels sprouts
• – 61% for peas & 53% for lima beans
• no reduction in the yield of blanched food
• Complete inactivation of peroxidase & minimum loss in quality
• – retention of 76–85% of ascorbic acid.

25. MICROWAVE BLANCHING
• Microwave blanching come under the newer method of the blanching technique.
Microwave blanching is commercialy used in EUROPE & JAPAN.
• Industrial microwave can either be batch or continuous.
• Its main disadvantages is higher cost of equipments
• It is commercially used for the MUSHROOM to inactivate POLYPHENOLOXIDASE
& prevent browing .It can also be done foe sweet corn kernel , spinach , carrot , bell
pepper etc.
• Combination of hot water with microwave blanching result in complete
polyphenoloxidase inactivation in a reduced processing time.
• Microwave blanching reduced the nutrient losses as compare to water blanching

26. MICROWAVE BLANCHERS

27. GAS BLANCHING
Hot gas blanching using combustion of flue gases with addition of steam to
increase humidity and prevent product dehydration has been studied.
This type of blanching has the advantage of reducing waste production, is
comparable to conventional blanching with respect to nutrient retention, but often
results in product weight loss.
This approach is not currently used in industry and needs further research.

28. Effects on food
• Flavour
• Terture
• Colour
• Quality indiacator
• A micro-organism
• Nutrients
• Some minerals, water-soluble vitamins and other water-soluble components are lost
during blanching.
• Losses of vitamins mostly by
• – leaching, thermal destruction and oxidation.

29. Nutrition loss depends on
• Maturity and variety
• methods of preparation (cutting, slicing or dicing)
• surface-area-to-volume ratio of the pieces
• method of blanching
• time and temperature of blanching (lower vitamin losses at HTST)
• method of cooling

30. Colour and flavour
• Brightens the colour of foods
• removing air and dust on the surface
• Sodium carbonate (0.125% w/w) or calcium oxide added to blancher
water
• protect chlorophyll and retain the colour of green vegetables
• Increase in pH may increase losses of ascorbic acid
• Enzymatic browning of cut apples and potatoes is prevented
• holding the food in dilute (2% w/w) brine prior to blanching.

31. Texture
• One of the purposes of blanching is to soften the texture of
vegetables
• facilitate filling into containers
• Calcium chloride (1–2%) added to blancher water
• form insoluble calcium pectate complexes
• this is help to maintain firmness of the tissues.

33. Conclusion
• Blanching is an old and well-established practice in the food
industry.
• Early technological improvements focused on increasing product
quality.
• Targeting the right enzyme indicator would reduce blanching time
and tackle all these priorities: improving product quality (increasing
retention of nutrients and other fresh like quality attributes), reducing
energy consumption, and reducing waste production