FSM 3001

FREEZING

Historical Perspective

• 1875 - first mechanical ammonia refrigeration system invented

• 1920’s - Clarence Birdseye initiated frozen food packaging

Clarence BirdseyeClarence Birdseye was born in Brooklyn, NY, on December 9, 1886, and attended Amherst College, majoring in biology. He pursued a career as a field naturalist for the United States government. The job took him near the Arctic, where Clarence made a chilling discovery that changed the history of the food industry.

Birdseye’s Discovery

He found that freshly caught fish, when placed onto the Arctic ice and exposed to the icy wind and frigid temperatures, froze solid almost immediately. He also learned that the fish, when thawed and eaten, still had all its fresh characteristics. He concluded that quick freezing of certain items kept large crystals from forming, preventing damage to their cellular structure.

Storage Temperature

• Cool storage: 16 to -2oC (60 to 28oF)• Refrigerators: 4.5 to 7oC (40 to 45oF)• Frozen storage: 0 to -18oC (32 to 0oF)

Microbial Growth

• Best above 10oC (50oF)• Some growth at sub-freezing temps as

long as water is available• Little growth below -9.5oC (15 oF)

RefrigeratedStorage

BirdseyeFreezer

Cool Storage Is:

• Gentlest method of food preservation• Few adverse effects on:

• Taste• Texture• Nutritive value• Color

• Short time preservation

Timeliness of Refrigeration

• ASAP after harvest/slaughter• Remove heat rapidly through use of:

• Moving air• Hydrocooling• Vacuum cooling• Liquid nitrogen

Requirement ofRefrigerated Storage

• Low temperatures• Air circulation• Humidity control (80 to

95%)• Modified gas

atmospheres

Factors AffectingCooling Requirements

• Cold storage room insulation• Frequency of door opening• Heat load of food product• Quantity of hot product loaded daily• Respiration rate of food product C6H12O6+6O2 ⇒ 6CO2 + 6H2O + heat

Controlled Atmosphere Storage

• Standard cold storage temperatures & humidity

• Reduced O2 levels• Elevated CO2 levels• Why?

Types of ControlledAtmosphere Storage

• Drive-in cold storage rooms• Packaged:

– Fruits– Vegetables– Meats

• Hypobaric (reduced pressure) storage– Reduces air (and O2) availability

Changes in Food During Refrigerated Storage

• Chill injury• Flavor/odor absorption• Loss of:

– Firmness– Color– Flavor– Sugar/acid

Frozen Storage

Initial Freezing Point

• Pure water freezes at 0oC (32oF)• With dissolved salt, sugar or other

components, water would freeze at• higher temperatures? or• lower temperatures?

QUESTION

• Why is salt added to ice in a ice cream freezer?

• How cold is ice when it begins to freeze?• How cold will ice get?

A Freezing Curve

Freezing Curve

Changes During Freezing

• Concentration effects–precipitation, salting-out, dehydration

• Ice crystal damage– cell rupture, emulsion disruption

• Slow freeze = large ice crystals• Want a rapid freeze to -18oC (0oF)

Intermittent Thawing

• Increases ice crystal size• Damaged cell very susceptible to

enzymatic degradation

Frozen Foods

• Raw• Blanched• Heat and Serve• Cook and Serve• Thaw and Serve• Ready to Eat

Frozen Raw foods

• Meat• Poultry• Fish• Fruits

StorageLifeOfFrozenFoods

Shelf-life in Refrigeration

1-7 days1-20 days1 week to year

Fruits (most)

1-3 days1-7 days3-20 daysLeafy veggies

4-6 hours8 hours14-21 daysMilk

5-6 hours1 day2-5 daysFish

8 hours1 day7-10 daysMeat

35-38°C20-22°C0-5°C

TemperatureCommodity

Blanching

Vegetables - to inactivate enzymes– Peas, beans, spinach– Corn, BroccoliVegetables - to reduce volume

leafy vegetablesFruits -to inactivate browning enzymes

Blanching

• A mild heat treatment designed to inactivate enzymes that may cause deterioration during storage

• Primary concerns are browning and off flavor production

• Blanching treatments vary substantially from product to product

Blanching

• Hot Water– Might be added to water and pumped through a pipe

similar to HTST– Might use a system like our chip fryer

SteamMoved quickly through a zone of steam

Heat and Serve

• Fully Cooked and need only be reheated to be servedThese products are identified by short reheating times

and already developed quality characteristicsSome fried shrimp, some French friesTV dinnersSome baked goods

Cook and Serve

• Frozen, partially cooked products that require cooking to produce quality attributes– Frozen vegetables– Some baked goods– Some French Fries– Pasteurized and frozen Eggs

Manufacturer and Exporter of Frozen RotiCanai, Croissant, Pancake, Pau (Steam Buns), Fried Curry Puff, Donuts, Frozen Pizza and Other Frozen Pastry Products

PROCESSFLOWCHARTFREEZINGOFDURIAN

Thaw and Serve

• Ready to Eat when thawed– Frozen Roti Canai or Murtabak– frozen pastry products– Cakes– Cheese cakes– Mousses

Eat Frozen

• Ice cream• Sherbet• Pop sickles (ice cream Malaysia)

Freezing Equipment

• Blast Freezer aka “Hardening room”• Plate freezer

– Clarence Birdseye

Cryogenic Freezer IQF Individually quick frozen

Freezing Rate Important

• Fast freezing creates small ice crystals– Less damage to cell tissue – like fruits and

vegetables

What makes a frozen product safe?

• Pre-freezing processing• Only safe while remaining in a frozen state

Problems With Cold – Packaging

–Sealed packaging allows buildup of gasses

•Ethylene and ripening

•Carbon dioxide and cell death

Problems With Refrigeration

•Odd chemical reactions — Starch conversion to sugar in potatoes

•Loss of water

Freezer-burn

Even at frozen temperatures, water can vaporize

The water collects on package and refreezes

Particularly a problem with “frost-free” freezer storage Remaining material is dehydrated, and may have protein related toughening effects

Types of Freezing

Quiescently – slow and large ice crystals form

Blast freezing – high volume of air aids in heat transfer

IQF (individually quick frozen) very low temperatures (sometimes as low as –198°C using liquid nitrogen)

Freezing MethodsFreezing in air–Still-air sharp freezer–Blast freezer–Fluidized-bed freezer

Tunnel Freezer

TUNNELFREEZER

Fluidized Bed

SPIRALFREEZER

Freezing Methods

Indirect contact freezing– Single plate– Double plate– Pressure plate– Slush freezer

(In all cases, food or food packages are in direct contact with a surface that is cooled by a refrigerant)

Freezing Methods

Immersion freezing–Heat exchange fluid–Compressed gas–Refrigerant spray

Very fast freezing using liquid nitrogen IQF = Individually Quick Frozen

Liquid Nitrogen Spray Freezing Unit

Eutectic Point

Cost Comparison of Air-blast andLiquid-nitrogen Freezing

Items Air-blast freezing

Liquid-nitrogen freezing

Total cost of equipment installed

$131,400 $59,000Annual Cost:Operation and maintenance 8,240 1,200Liquid nitrogen --- 150,000.Fixed costs(17 % of equipment cost)

22,300 10,000

Product losses (at 46 cents a pound)

46,000 23.000

Total: 76.540 184,200Cost per pound $0.0153 $0.0368

Packaging

• Protect against dehydration• Strong & flexible• Protect against light & air• Liquid tight