Chilling & freezing part 2

Question 1

what are the factors we need to take into account for determining an appropriate freezing method for food

Answer 1

1 the type of freezing operation(batch or continuous)
2 The scale of production
3 the size, shape and packaging requirements of the food
4 the rate of freezing required
5 the capital and operating costs etc

Question 2

air freezing - air blast freezing

Answer 2

air blast freezing is extensively used on different food products. to can be either. batch (food stacked on trays in cabinet) or continuous in operation (conveyor belt which carry the food through an insulated tunnel)

packaged and unpackaged foods

Question 3

air freezing-fluidized bed freezing

Answer 3

fluidized bed freezing is a modified blast freezing method. this method is restricted to smaller sized foods (eg peas, sweetcorn kernels, shrimps, strawberries, French fried potatoes etc)
during fluidized bed freezing, an ice glaze is formed on the surface of food particles. The ice glaze prevents the food particles from dehydration as well as remain the separation of the food particles during freezing.

unpackaged foods
batch or continuous

Question 4

liquid immersion freezing

Answer 4

liquid immersion freezing is used for both packaged and unpackaged food products which are immersed into cold solution like brine solution, alcohol, sugar, glycol and glycerol solution with a low freezing point for freezing. As refrigerants, the cold solution must be safe for the food product’s taste, cooler, flavor and healthfulness.

packaged and unpackaged
dk whether batch or continuous?

Question 5

Indirect freezing- plate freezing

Answer 5

plate freezing is restricted to the foods that are flat and relatively thin (eg fish fillets, fish fingers, beef burgers etc)
advantage:since there is no air contact with product, hence no weight loss
disadvantage: it is a batch operation
packaged(regular geometry)

Question 6

indirect freezing- scraped surface freezing

Answer 6

draped surface freezing is used for liquid foods or semi-solid foods like ice cream mix or margarine. it has rotor which continuously turns with blades scarping the sides the chamber and the cylinder is cooled on the outside with ammonia or brine.

unpackaged?

Question 7

two phase freezing- cryogenic freezing

Answer 7

cryogenic freezing is characterized by a change of state in the refrigerants(or cryogens) as heat is absorbed from the freezing food. The heat from the food provides latent heat of vaporization or sublimation of the cryogen. The freezing rate of cryogenic method is greater than that of other freezing methods!!! the two most common refrigerants are liquid nitrogen and solid or liquid carbon dioxide which are colorless, odorless and inert.

dk whether batch or continuous?
dk need packaging or without?

Question 8

Physical spoilage of frozen foods

Answer 8

recrystallization-
during frozen storage, ice crystals change size, shape and number, which is known as ‘recrystallization’. ice recrystallization is significantly;y caused by fluctuations in the storage the,erpature, leading to quality deterioration in all frozen foods during storage and distribution. for example, if the temperature during frozen storage oil ice cream increases, some of the ice crystals next and consequently increase the amount of unfrozen water in the ice cream. when temperature decreases, the water grates to join existing crystals, rather than creating new crystals. hence, it leads to a gradual reduction in the numbers of small crystals and an increase in the size of large crystals, resulting in loss of quality similar to that observed in slow freezing.

-freezer burn
freezer burn is an undesirable phenomenon caused by sublimation from the surface of frozen foods over time during frozen storage, which leads to the toughening and discoloration of the surface of the frozen foods. for eg, beef turn from red to brown, green beans shrivel and turn from green to yellow

Question 9

is freezer-burned food safe to consume and why?

Answer 9

safe to consume from a microbial perspective but is of poor eating quality. the freezer burned area can be simply cut out before or after cooking.

Question 10

how can freezer burn be prevented

Answer 10

prevent any excess headspace by using a sealed vacuum bag or airtight container
be sure to consume the food within the recommended amount of storage time
limit the amount of time your freezer is open