Advances in food processing and preservation by low temperature freezing.pptx
1. ADVANCES IN FOOD
PROCESSING AND
PRESERVATION BY LOW
TEMPERATURE:
FREEZING
Submitted to :Dr. Anil Kumar Chauhan
Submitted by: Shivam Dadwal
Subject: Emerging technologies in food processing
Subject code: FPT- 501
2. • Food freezing is a food preservation process based on exposing
food to temperatures below its freezing point, a point at which
the state of matter changes and the properties of the product
are altered, turning it into ice and solidifying all the water or
moisture contained in the food.
• The purpose of this process is to retard all activity of micro-
organisms or bacteria in the food without significantly altering
its nutritional content, and thus its spoilage.
3. • Use of low temperature is the easiest, most convenient method
of preserving food.
• Freezing does not sterilize foods or destroy the microorganisms
that cause spoilage.
• It simply slows the growth of microorganisms and the chemical
and enzymatic changes that effect the quality or cause spoilage.
• Use of freezing as a method of food preservation is that
microorganism are only deactivated and not killed.
4. •SLOW FREEZING: Slow freezing occurs when food is
directly placed in freezing rooms called “sharp freezers”
•This method involves freezing by circulation of air by
convention i.e.Through a specially insulated tunnel.
•Either naturally or with aid of fans.
•The temperature ranges from -15 to -29 degrees and
may take 3 to 72hours.
5. •QUICK FREEZING: vigorous circulation of air enables
freezing to proceed at a moderately rapid rate.
In this process the temperature is kept between -32 to-40
degrees and the food attains the stage of maximum ice
crystal formation in 30 min. or less.
6. • BATCH FREEZING: this type is mostly used for small operations.
• If a variety of products are to be frozen a batch freezer may be selected over
continuous as they are more versatile.
• This freezing system is used for products with longer freezing time.
7. • CONTINUOUS FREEZING: this process is used for production on large scale basis.
• These freezers are best suited for freezing small vegetables.
• It allows quick handling after freezing and a quick transfer to the cold store.
8. • DIRECT CONTACT FREEZING:The product to be frozen is completely surrounded
by the freezing medium i.e. the refrigerant which maximizes the efficiency of the
heat transfer.
• for example- immersion freezing, fluidized bed freezing.
9. • INDIRECT FREEZING: In this type food materials to be frozen are separated from
the refrigerant by a conducting material usually a steel plate.
• The food is indirectly exposed to the freezing medium
10. • 1.BLAST FREEZING: forced air is used
• Air is recirculated over food at between -30 to -40 degree Celsius
• In batch equipment. Food is tacked on trays in rooms or cabinets.
• Continuous equipments consists of trolleys stacked with trays of food or on
conveyor belts which carry the food through an insulated tunnel.
ADVANTAGES: can freeze irregular shaped foods including which have already
been packed.
Economical freezing method and is used on a wide range of products.
DISADVANTAGES: high manpower needed for operation
11.
12. 2.
• Plate freezers are freezers where a refrigerant is passed through hollow metal
horizontal or vertical plates that are pressed either side of the food being frozen.
• This system is ideal for freezing large blocks of food products, but cannot easily
freeze irregular shaped items
13. • By using a plate freezer, you will freeze various types of foods way faster than
traditional air blast freezers without increasing the use of energy and handling costs.
• In many industries such as the seafood processing industry, a fast-freezing plant is
completely indispensable.
• The major disadvantages of plate freezers are the high capital cost, especially if
they are automated to run continuously, and the limitation on product types that can
be handled.
14. 3.
• One recent development is the renewed interest in contact belt freezers.
• Current belt freezers generally use a disposable plastic film that acts as the
conveyor belt travelling through the freezing tunnel over refrigerated plates.
• These plates rapidly and effectively freeze the contact surface of the product,
while the tunnel environment is cooled to reduce the entire product temperature.
• these freezers are mainly designed for processing delicate, sticky and hard-to-
handle products, even liquids can be frozen with ease.
• rapid and efficient freezing, the use of flat belts delivers products free from belt
marks and wrinkles.
• Since the belt is disposable, the freezer can be quickly and efficiently cleaned at
the end of production, minimizing expensive delays.
15. • include automatic loading and unloading, low maintenance cost and
flexibility to freeze different products.
• Both packed and unpacked products with variable freezing times (10 min to
3 hr.) can be frozen in spiral belt freezers due to the flexibility of the
equipment.
• The belt speed can be varied to cope with changing production rates but care
must be taken to maintain a uniform thickness of product on the belt.
16.
17. 4.
• Vertical jets of refrigerated air are blown up through the product, causing it to
float and remain separated. This is a continuous process which may take up to 10
minutes.The products e.g. peas, beans, chopped vegetables or prawns, move
along the conveyor belts.
18. • ADVANTAGES:
• This has a faster freezing and less dewatering to result, which also leads to less
defrosting.
• The fluidized bed freezer is effective and reliable in freezing wet products.
DISADVANTAGES
Fluidized bed freezing is limited to small fine foods (peas, sweet corn kernels,
shrimps, strawberries, etc.).
19. 5.
• Liquid nitrogen or carbon dioxide is sprayed directly onto
• small food items such as soft fruit and prawns.
• Due to the liquids extremely low temperatures (-196 c)
• and (-78 c) respectively freezing is almost instant.
• The nitrogen gas is removed by fans.
20. • ADVANTAGES:
• Fast freezing rate is often seen as one of the main benefits of a cryogenic system
together with the freezers small size.
DISADVANTAGES:
• The limitation cryogenic freezer is the rate of excess cryogen residue in foods.
• Low initial investment and rather high operating costs are typical for cryogenic freezers.
21.
22. •Freezing preservation retains the quality of
agricultural products over long storage periods. As
a method of long-term preservation for fruits and
vegetables, freezing is generally regarded as
superior to canning and dehydration, with respect
to retention in sensory attributes and nutritive
properties.
