Etiket Arşivleri: Freezers

Freezing

• Examples of freezing in daily life

• Purpose of freezing

• Stages of freezing

• Effect of freezing on properties

• Types of freezers

• Freezing medium

• Shelf life and quality of frozen foods

• Equipment to characterize freezing

• Effect of solids on freezing point of solution

• Determination of freezing time

Examples in Daily Life

• Ice rink
– 9,000 gallons of ‐9 °C brine
– 5 miles of pipes
– 270 tons of cooling (1 ton of refrigerant = 3516.8 W)
– Humidity and temperature control needed
– Ice hockey versus ice skating (Load, impact)

• Earth’s surface
– 10.4 % is covered with ice
– 20% is permanently frozen
– Thickness of ice covering Antarctica (avg. temp. ~ ‐37 °C)

• Average: 2164 m; Max: 4785 m (> 10 times height of Sears tower)

• ~61 m rise in ocean level if all ice melted; add ~ 7 m for Greenland; not much in arctic

• Does the water inside animals living in extreme cold, freeze?

• Do hot water pipes burst before cold water pipes in winter?

• Can the engine coolant or fuel in our car freeze?

• Does Niagara Falls freeze?

• How does an ice maker work?

• How does a frost‐free freezer work?

• How does a snow‐maker at a ski slope work?

• How does a de‐icer (for cars and planes) work?

• Ice as an insulator
– Igloo
– Freezing of pond (do fishes survive? What does wind do?)

• Depression in freezing point
– Salting of roads during winter

• Freezing foods
– Blue ice, gel pack, dry ice, liquid nitrogen
– How is a popsicle made?

• Safety of using liquid nitrogen (in a room or car)
– 10 liter dewar spilt in a 17 x 17 x 8 room

• Reduces oxygen level to < 19.5% (need to use respirator)

• Freeze drying of milk/coffee powder
– Lower the temperature and use vacuum to sublimate ice

Freezing

• Purpose of freezing of foods

– To slow down rates of detrimental reactions by lowering temperature and water activity (aw)

• Microbial spoilage

• Enzyme activity

• Nutrient loss

• Sensorial changes
– Prolongs shelf life beyond that of refrigerated foods

Kaynak: https://projects.ncsu.edu/project/foodengineer/231/notes/freezing/Freezing-ppt.pdf

The Basics of Freezers and Freezing Food

The Basics of Freezers and Freezing Food

IS A FREEZER A LUXURY – Freezing versus Canning

Freezing

• Easy and fast

• Holds color, flavor and nutrients

• Suited to more foods than canning

• Safe and convenient

• Cost of freezer is an initial high cost, plus electricity to run
• Cost of materials for freezing food can be low especially plastic zip-loc are used versus rigid containers

• No additives required

• Freeze leftovers, extra baked goods, casseroles

• Take advantage of meat and vegetable specials and bulk buying, resulting in considerable cost saving

• Wild game storage (eg. ducks, geese, deer, caribou, moose, elk) are hunted in the fall. Freezing of this ensures a food supply for the rest of the year. Same goes for wild berries

Canning

• More technical knowledge

• Takes time

• Discoloration, alteration in flavor and nutrients can be lost if canning liquids not utilized in soups and or gravy

• Manitobans like our dill pickles and canned tomatoes, jellies and relishes

• Can be unsafe if proper processing/canning procedures aren’t followed

• Cost of initial canning equipment is costly, especially pressure cooker, but last a long time
• Jars and lids have to be replaced

• Canned goods require salt and/or sugar, vinegar which is especially important to avoid for individuals on special diets

• Not possible with canning

• Limited to mainly vegetables

• Meat would have to be pressure cooked and therefore is not usually recommended

Freezers can be very cost-saving as it allows bulk and special sales buying. Ensures storage of extra food to
maintain food source during storm days. Canned goods are costly to ship as you are paying for tin and liquid the product is stored in. Frozen products are usually just in light weight plastic type bags or containers. Store bought or home preserved frozen or canned produce are preserved using prime quality produce. A problem with buying fresh produce especially in northern communities is that the quality has deteriorated with long distance shipping. Just a few days in transit causes “fresh” produce to lose significant amounts of all important nutrients. What this means, is that frozen vegetables can be superior (especially in winter) to many of the fresh produce we buy as well as a great cost saving. Good comparisons are broccoli, cauliflower, green beans and strawberries.