The Science of Freezing: History, Techniques, and Tips

1. Freezing Food

2. History • The frozen food industry was born in the 1920’s • Clarence Birdseye produced the first frozen fish

3. History • The industry continued to grow and develop with the growth of such technology as fast-freezing equipment, home freezers, and the microwave oven • The 1950’s brought on the TV dinner revolution

4. The Science of Freezing • It preserves food by slowing the action of enzymes rather than destroying them

5. The Science of Freezing • Foods that are free of microorganisms when frozen will remain so, since most microorganisms can’t grow at such a low temperature

6. Freezer Burn • Caused by the loss of moisture from food when the food is exposed to air • Culprit: Loose packaging, fluctuation in freezer temperature

7. Freezer Burn • If not packaged properly, even foods that do freeze well can experience a damaging effect • Foods that are freezer burnt often have a brown or grayish color, look very dry, and have a fuzzy gray or white spots that look like icy mold

8. Commercial Freezing • Rapid Freezing Process – Limited changes in color, texture, size and flavor • Also, helps foods resist freezer burn • Ice crystals are smaller causing less damage to food cells

9. Commercial Freezing • Freezing in air is the oldest and still the most common method of freezing food, and also the one used in home freezing • Indirect-contact freezing is food that is placed on belts or trays. A refrigerant circulates through the wall beside the food and it chills quickly and freezes

10. Commercial FreezingCont… • Immersion freezing food is submerged directly in non-toxic refrigerant to cause quick freezing • Most packaging is opaque because many foods lose flavor when exposed to light

11. Home Freezing • Storage containers and wraps used for frozen foods at home must be moisture proof and airtight to maintain quality

12. Home Freezing • Even if it is properly maintained it has a 6-12 month period before it starts to deteriorate

13. Home Freezing • Foods with high water content, including grapes, pears, salad greens, lose shape and texture when frozen • Be sure to label and date all packages!!

14. Freeze-drying • Is a commercial process that combines freezing and drying to preserve foods. • First food is frozen; then its treated to remove the solvent from dispersed or dissolved solids. • In most food, this means removing the water. • Technical name: lyophilisation.

15. Sublimation • During freeze-drying, water in the form of ice is removed through sublimation – occurs on the surface and continues inward. • Wet clothes on the line during winter example. • By the time the ice at the very center has sublimed, up to 99% of the food’s moisture has been removed. • The result is dried food.

16. Sublimation • Flash frozen or frozen very quickly – a special, low-pressure chamber. It is then held at or below freezing temperature. • The low temperature keeps the water frozen, and the low pressure speeds the rate at which ice crystals in the food escapes as water vapor.

17. Using Freeze Dried Foods • Foods could be stored for months even years • Must be protected in airtight packaging • Examples are fruit in cereal and chicken in instant soup • Makes foods extremely light – should be reconstituted.

20. Packaging Food • Suitable containers • Safety – needs to be non-toxic and provide a sanitary, protected environment • Food quality – must provide protection from light, odors • Convenience – open easily, resealable, and able to pour easily are a + • Expense – lower packaging means lower cost for manufacturers and the result is a lower cost to consumers! • Environmentally safe – recyclable containers! • Marketing appeal – attractive to the consumer!

21. Packaging Food • Modified-atmosphere packaging • Called MAP – This process creates a specific gaseous environment for a food product to lengthen shelf life. • Used mainly for ready-to-eat products with extended shelf lives. • Bags of lettuce, baby spinach, and baby carrots use this technology in stores!

22. Packaging Food • Aseptic packaging • Used for beverages and liquids that have been aseptically treated – extremely high temperatures and contain several layers of material. • Containers are not recyclable. • Example: Drink boxes!

23. Packaging Food • Edible films/wraps • Additional film added to apples - Wax • Trends in packaging • Edible films • “Smart” packaging that tells the consumer a number of things – if the temperature has ever risen enough above the proper temperature the the contents of the package may be unsafe to consume • “Intelligent” packaging that tells the consumer whether or not the contents are spoiled and may not be safe to eat. Ex. A dot that may change colors

24. Irradiation • One third of the world’s food supply is still degraded or destroyed by pests, bacteria, and the resulting spoilage. • Irradiation – food is exposed to a controlled amount of radiation (transfer of energy in the form of waves) for a specific time to destroy organisms that would cause spoilage.

25. Irradiation • Radura Symbol – Page 462 • The FDA (Food and Drug Administration) regulates irradiation as an additive. • Delaney Clause – states that no substance shown to cause cancer in humans or animals may be added to food in any amount. • The FDA approves food for irradiation on a case-by-case basis.

26. Radura Symbol