FND300 - Freezing Technology

Three Advantages of Freezing

extends food shelflife, slow down chemical/biochemical rxns, and rapid freezing helps with retention of texture and nutrition

How does Rapid Freezing help with retention of Temp and Nutrition

smaller crystals cause less damage to cell walls/membrane and disruption of turgor pressure

How Does Freezing Slow Down Chemical/Biochemical Rxns

by decreasing water activity

How Does Freezing Extend Shelf Life

By reducing microbial growth due to lowered temperature and lower water activity

Five Adverse Effects of Freezing

Physicochemical Changes, Freezer Burn, Destabilization of Emulsion, Large Ice Crystal Growth, and Chemical Changes

Physicochemical Changes Associated with Freezing

9% volume expansion of pure water, higher concentration of non-aqueous constituents (salt, sugar, acids, nutrients) in unfrozen water

How does higher concentration of non-aqueous constituents (salt, sugar, acids, nutrients) in unfrozen water cause Protein Denaturation

the solvent volume is reduced to only unfrozen water which becomes more concentrated with solutes leaving more destabilizing environment for proteins

Freezer Burn

associated with sublimation (ice on surface of foods changes to gas)

Prevention of Freezer Burn

transfer food to impermeable packaging that reduces air and water exposure, cool before freezing and freeze at a consistent temp

Destabilization of Emulsion

an adverse consequence of freezing

How Does Freezing Destabilize an Emulsion

the water in the emulsion freezes into ice crystals which push the oil droplets closer together

Chemical Changes Associated with Freezing

oxidation of flavours, pigments and vitamins A & C & E

Freezing Point of Food

-20 celcius or below

Steps in Freezing Process (list two phases of the second step)

(1) Supercooling ; (2) Crystallization which happens in two phases - nucleation and crystal growth)

Supercooling

the cooling of water to below freezing without growth of ice crystals

Nucleation Definition

the arrangement of water crystals into an ordered particle which can serve as nucleus for crystal growth

Three Defining Characteristics of Nucleation

rate limiting step, occurs at 10 degrees celcius below freezing point, does not happen readily

Crystal Growth Definition

the organized addition of water molecules onto preformed nuclei

Two Defining Characteristics of Crystal Growth

occurs at temps just below 0 and happens readily

Two Factors Governing the Rate of Crystallization

the rate of heat transfer and the initial temperature of supercooling (how far below 0 degrees celcius it is)

Slow Freezing Supercooling Requirements

Between -10 C and -20 C

Dominant Process During Slow Freezing

Crystal Growth > Nucleation

Result of Slow Freezing

fewer, but large ice crystals

Fast Freezing Supercooling Requirements

-20 C or below

Dominant Process during Fast Freezing

Nucleation > Crystal Growth

Result of Fast Freezing

many small ice crystals

General Definition of Recrystallization

The process in which ice crystals change in size, shape, orientation or stability while remaining frozen

Types of Recrystallization

Isomass, migratory, and accretive

Definition of Isomass Recrystallization

Any change in shape or internal structure of an individual ice crystal

Mechanism of Isomass Recrystallization

The mass and # of water molecules in ice crystals do not change

Example of Isomass

snowflake

Definition of Migratory Recrystallization

The tendency for large ice crystals to growth at the expense of smaller ice crystals

Mechanism of Migratory Recrystallization

The movement of water molecules from small ice crystals to large ice crystals; Increase in crystal size and decrease in crystal number

Example of Migratory

grainy and icy icecream

Definition of Accretive Recrystallization

Contacting crystals joining together to increase crystal size and decrease crystal number

Example of Accretive

glacier

Air Freezing Definition and What Types of Foods Use This

Freezing food using cold air at temperaturess between -18 C and -40 C; can be used in packaged or unpackaged foods

Sharp Freezing

A type of air freezing with that involves no circulation of air and slow freezing

Usage for Sharp Freezing

In household freezers (not used commercially)

Types of Air Freezing

Sharp freezing and Air-blast freezing

Types of Airblast Freezing

Co-current Freezing, Contercurrent Freezing and Fluidized Bed Freezing

Airblast Freezing definition and what does it involve

A type of air freezing that uses air circulation involving refrigeration units and fans

Co-current Freezing

A method of air blast freezing where food on the conveyor belt moves in the same direction as the air blows

Counter-current Freezing

A method of air blast freezing where food on the conveyor belt moves in the opposite direction as the air blows

Fluidized Bed Freezing (mention the process and the tool used)

A type of modified Air Blast freezing that involves cold air being blown up from below food on a mesh conveyor belt, lifting and separating individual food pieces

Product of Fluidized Bed Freezing

Individually Quick Frozen Products

Two Ways IQF Products can be made

Fluidized Bed Freezing and Cyrogenic freezing

Plate Freezing

Involves freezing food between two refrigerated plates

Three Defining Characteristics of Plate Freezing

Produces a rapidly frozen product with a uniform shape; can be packaged

Examples of a Plate Frozen Product

TV dinners and icecream

Cyrogenic Freezing

Involves exposing food to an extremely cold medium that is undergoing a change in state (sublimation or evaporarion)

Mediums used for Cyrogenic Freezing

Liquid CO2, Solid CO2, Liquid nitrogen

Usages for Cyrogenic Freezing

• High value foods with delicate structures (tomatoes, mushrooms, bananas)

• Dippin Dots

• Research lab materials (sperm and eggs)

Two Cyrogenic Freezing Process

1. Conveyor belt spraying down liquid nitrogen within an insulated conveyor belt tunnel

2. The product can be immersed and dipped into liquid nitrogen and moved out for packaging (common in berries)