Proper storage of food -...

Proper storage of food

• Store foods correctly:

– In the correct place, e.g. store raw and cooked foods separately in the refrigerator

– At the correct temperature, e.g. leftover foods should be kept in the refrigerator at 4°C or below

– For the correct time, e.g. never leave food, raw or cooked, at room temperature for more than 2 hours

– In suitable containers or packaging

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• Store fresh foods in a cool dry place, in a refrigerator or freezer

• Store food in the right positions in a refrigerator, e.g.

– store raw and cooked foods separately in the refrigerator (cooked food in the upper shelf and raw food in the lower shelf) to avoid cross-contamination

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Store food in the right place at the right temperature

• Store unopened cans, jars, bottles and packets in a cool dry storage cupboard


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Store food in the right place at the right temperature


• Check the expiry date marked on any packaged food before using

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Store food for the correct time

• “Use by date” for high risk foods. After this date the food may not look or taste different, but it will be unsafe to eat and should be thrown away

What’s the difference between “Use by date” and “Best before date”?

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Yoghurt Cheese Milk Fresh orange juice


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• “Best before date” for low-risk foods, e.g. biscuits or food with long shelf life e.g. UHT milk. After this date the food will start to deteriorate in terms of flavour, colour, texture or taste

Mango juice drink Oatmeal Packaged chocolate


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• What are “high-risk foods”?

– Foods which are the ideal medium for the growth of bacteria or micro-organisms, e.g.

• milk, yoghurt and fresh juice

• What are “low-risk foods”?

– Foods which have a long shelf life, such as dried foods

Personal hygiene

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Hair: wear a hairnet or tie up the hair

Cuts: cover any cuts with clean waterproof plasters

What should we do before handling food?

Fingernails:always keep them short and clean

Clothing: put on apron before starting to prepare food

Personal hygiene

• Wash hands thoroughly before handling food and between handling different types of food

10Source: http://www.chp.gov.hk/en/exhibition_details/2867/0.html

http://www.chp.gov.hk/en/exhibition_details/2867/0.html

• Freezing prevents microbial growth in foods, it will not destroy all micro-organisms

Ways to handle food properly and hygienically

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Use proper ways to thaw frozen foods


• Improper thawing provides an opportunity for bacteria that may have been present before freezing to multiply to harmful numbers

A piece of meat

Improper thawing

Bacteria

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• Frozen food should be completely thawed before cooking

• Refrigerator (chilling compartment), cool running water, or a microwave oven can be used to defrost frozen food

• Food must be cooked immediately after defrosting to prevent bacterial growth


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• Vegetables can be washed:– under clean running

water– by soaking in water

for one hour and then rinse (vitamins and minerals will leach out into water if vegetables are being soaked)

– by blanching the vegetables in boiling water for one minute

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Always wash food well before cooking it

Wash vegetables with water

• For example, use separate containers and chopping boards for raw and cooked foods


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Use separate equipment for raw and cooked food

Use chopping boards of different colours to handle raw and cooked food


• Cook food thoroughly to the right temperature before consumption, and check food’s internal temperature with a food thermometer when necessary.

• Keep hot food hot and reheat leftover food thoroughly before serving

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Cook food properly and thoroughly

• Clean equipment properly inhot soapy water, then rinseand dry thoroughly

• Keep food cupboards andrefrigerators clean

• Keep pets out of the kitchen(e.g. by using fences)

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Clean properly

Fence prevents the entrance of pets into the kitchen

Preservation of foods

• Micro-organisms need food, warmth, moisture and timeto multiply.

• If one of these conditions is removed, the food is preserved and could be kept for a longer time.

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What are the purposes of preserving foods?

Benefits of preserving food

Cut down on wastage-Preserve the food before they become spoiled e.g.

• make seasonal fruits into jam

Add variety to our diet-Increase the range of food available, e.g.

• canned and frozen foods make our meals more varied

• can buy products that are not in season

To ease the work of meal preparation-Preserved food cut down the time of preparation and cooking, e.g.

• canned food for emergency and in bad weather

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Summary of food preservation methods

Principle Preservation method Examples

Living organisms need water to live

• Dehydration• Storage in strong

solutions of salt and sugar

• Dried fruit• Salted fish, jams

Temperature affects growth and action ofliving organisms

• Heating (Pasteurisation,sterilisation, Ultra Heat Treatment)

• Chilling and freezing• Freeze drying

• Milk, canned foods

• Vegetables, meat products

• Coffee granules, mushrooms, prawns

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Principle Preservation method Examples

Living organisms can be destroyed by chemical action

• Acids • Pickled fruits and vegetables

Living organisms are inactivated by radiation

• Irradiation • Prawns, fruits and vegetables

Living organisms need oxygen

• Vacuum packing

• Air tight seals

• Bacon, ham• Canning and

bottling fruit juice

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Summary of food preservation methods

Dehydration (drying)

• All micro-organisms need water to survive and multiply

• Dehydration is the removal of water from food

• Many micro-organisms are killed by removing water from them

• Drying of food also prevents some chemical reactions from taking place inside the food

• Dried food have a relatively long shelf life if stored properly

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Dehydration (drying) • Colour, texture, flavour and nutritional content of foods

maybe affected

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100g raw and peeled mango100g dried mango

Information derived from: 100g of raw, peeled mango, Food Nutrient Calculator from Centre for Food Safetyhttp://www.cfs.gov.hk/english/nutrient/fc-introduction.php

Nutrition label of 100g dried mangoNutrition information of 100g dried mango

Comparison between fresh mango and dried mango

http://www.cfs.gov.hk/english/nutrient/fc-introduction.php

• Water (moisture) evaporates slowly

• Use open-air conditions with little hygienic control

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Dehydration (drying): Drying under sunshine (sun-drying)

Sun-dried vegetables Sun-dried seafood

• Hot air is used to remove moisture from food

• Suitable for foods that maybe damaged by excessive heating

• Dry powder is produced from liquid

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Dehydration (drying): Spray drying

Spray-dried milk powder

• A combination of freezing and drying

• Food is quick-frozen then dried in vacuum (withoutair) under reduced pressure

• The heat vaporises the ice, which turns to steam(without going through the liquid state) and leavesthe food dry

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Dehydration (drying):Accelerated freeze-drying

Illustration of freeze-drying

Dehydration (drying):Accelerated freeze-drying

• There is only little change to the colour, flavour, texture and nutritive value

• Freeze-dried food mix with water again easily

• Examples of freeze-dried foods:

27Freeze-dried coffee Freeze-dried vegetables and cuttlefish in cup noodles

Dried cuttlefish

Dried corn

Dehydration (drying): Storage in strong solutions of salt and sugar

• Salt and sugar are natural preservatives

• Both high concentration of salt and sugar cause the loss of water from the micro-organisms through its cell membrane into the solution by osmosis

• The micro-organisms become dehydrated and die

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• What is concentration?

– Concentration is the quantity of a substance in a particular volume of mixture

– High concentration of salt: 15-20%

– High concentration of sugar: 65% or above

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High LowConcentration of colour

High LowConcentration of salt

Salt


• What is osmosis?

– Osmosis is the net movement of water molecules through a selective permeable membrane into a region of high solute (e.g. salt/ sugar) concentration

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• Examples of food preserved by salt

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Bacon Ham

Fish in brine (salt and water)


• Examples of food preserved by sugar

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Marmalades Jam Crystallised ginger

Ingredients:Plum, white sugar, salt, greengage juice, sweeteners (E951, E955)


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• Examples of food preserved by salt and sugar

Preserved plums Dried mangoes

Ingredients:Mangoes, sugar, salt, preservative (E223)

High-temperature methods

• Warmth helps enzymes to become active and micro-organisms to multiply rapidly

• High temperature stops the action of enzymes and kills the micro-organisms in food

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High-temperature methods: Pasteurisation

• Pasteurisation is a heat treatment (temperature below 100°C) used to kill some micro-organisms in food

• Minimal damage to flavour, texture, and nutritional quality of food

• Storage of food is extended for several days

• Other preservation method, e.g. refrigeration must be used to keep the pasteurised food

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Examples of foods preserved by pasteurisation

Pasteurised eggs

Milk

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High-temperature methods: Sterilisation

• Sterilisation is a heat treatment (temperature at 100°C or above) used to kill most micro-organisms in food

• All micro-organisms and enzymes are destroyed

• Sterilised food have a long shelf life

• Used for milk and fruit juices

• Milk is changed to a creamy colour, with a slight caramelisation of the milk sugar content, giving a “cooked” flavour

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Sterilisation: Ultra Heat Treatment (UHT)

• UHT is a sterilisation method using a high temperature within a short period of time

• Food is heated to very high temperature, up to 130°C for 1-5 seconds, and then cooled rapidly

• All bacteria are destroyed

• Only little colour change, slight change of taste and little loss of nutrient content

• Often packed in airtight cartons made of layers of plastic and aluminium coated paperboard

• UHT and sterilised milk have an extended shelf-life while unopened, but must be refrigerated once opened

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Examples of foods preserved by UHT

39UHT treated milk and soymilk

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Examples of foods preserved by UHT

Whipping cream

Fruit juices e.g. lemon tea

Sterilisation: Canning and bottling

• Canning and bottling are 2 forms of sterilisation

• Food can be:

– Packed in cans/heat-proof glass containers and then sterilised, or

– Sterilised and then packed into sterilised cans/bottle

• Both canned and bottled foods have a long shelf life

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• Once canned and bottled foods are opened, they should be treated as fresh foods

– Remove foods from the cans/bottles after opening, put them in a covered container and store in the refrigerator

42Canned pineapple

Store in a cool dry place.Refrigerate any unused portion in a separate covered container

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Bottled prune drinkCanned condensed milk

Consume within 5 days ofopening. Keep refrigerated.

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Examples of foods preserved by canning

Canned tuna fish

Canned soups

Canned meat Canned baby milk powder

Examples of foods preserved by bottling

• Bottled foods are stored in heat-proof glass containers

• Bottled foods are heavy and the glass may break, they are not as common as canned foods

45Bottled honeyBottled jam Bottled waterBottled sauce

Low-temperature methods

• Low temperature slows down the speed at which bacteria reproduce but do not destroy bacteria

• Very low temperature causes bacteria to be inactive

• As the food warms up, the bacteria begin to reproduce

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Cold storage: Chilling

• The growth of micro-organisms stops if foods are kept at 4°C in the refrigerator

• Chilling is a short-term way of preserving fresh food

• Chilled foods are perishable foods, e.g. prepared salads, sandwiches and cakes

• The optimum temperature for chilled foods is below 4°C

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• Cook-chill

– A method of producing ready-made foods and meals when foods are cooked then quickly cooled to between 0°C and 3°C in 90 minutes or less

– Chilled foods are stored at low temperatures (in refrigerator) and then heated up to at least 72°C before eating

– Cook-chill products have a shelf-life of around 5days

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Cold storage: Chilling

Examples of food preserved by cook-chill method

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Fried fish ball

Pre-cooked rice

Microwave meals

• Food is stored in a freezer at a temperature around -18°C

• Food is quick frozen to prevent large ice crystals from forming inside the food as they would damage the texture of the food once it is thawed

• Only little change in nutritive value of frozen food

• Enzymes and micro-organisms become active again when the frozen foods are thawed

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Cold storage: Freezing

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Frozen fish filletFrozen scallop meatFrozen chicken wings


• Cryogenic freezing– Food is immersed or sprayed with

liquid nitrogen– Used for delicate products and

fruits, e.g.• raspberries, prawns and

strawberries

What is liquid nitrogen?– At room temperature and pressure,

nitrogen is a gas– Liquid nitrogen has a temperature of

-196°C at normal room temperature

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Liquid nitrogen is cold air at room temperature


• Cook-freeze

– Meals are prepared and then quickly frozen at -20°C

– The food can be distributed in the frozen state and heated by microwave or micro-ovens when required

54Frozen pizzaFrozen rice in lotus leaf Mini glutinous rice dumpling

Chemical methods:Use of acids

• Most bacteria cannot live in an acid environment

• Acids may be present in food naturally (e.g. malic acid in apples, citric acid in citrus fruits), or added artificially (e.g. citric acid is used to preserve certain fruits and vegetables)

• “pH” is a measure of acidity; the lower its value, the more acidic the food

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1 2 3 4 5 6 7 8 9 10 11 12 13 14pH


• Vinegar and citric acid are examples of acidic preservatives

• Vinegar

– It contains ethanoic acid and can be used in pickling to provide flavour and decrease pH

56Pickled scallion Pickled ginger

Ingredients:Scallion, sugar

and vinegar

• Citric acid

– Used for preservation of fruits and vegetables to provide flavour and decrease pH


57Pickled cucumber Pickled tuber mustardJam

Ingredients:Cucumber, water, sugar, soy sauce, salt, acidity regulator (citric acid)

Ingredients:Organic pomegranate concentrate, organic sugar, organic pomegranate

juice, apple pectin, ascorbic acid (vitamin C) & citric acid (acidity

regulators)

Ingredients:Preserved mustard, salt, flavourenhancer (E621 Monosodium

glutamate), chilli, rapseed oil, spices, white sugar, acidity regulator (E330

citric acid)

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Besides food preservation, what are the other functions of acids in food preparation?

• Vinegar is used to:

– tenderise meat, as the acid softens the meat tissues

• Lemon juice (contains citric acid) is used to:

– prevents foods, e.g. apples and bananas, from going brown after they have been cut

• Vitamin C (ascorbic acid) is used to:

– speed up the fermentation process in bread making


• The process uses radiation to kill pests, insects and some micro-organisms in food

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Food irradiation

• Irradiated food should be clearly and legibly marked with the words “IRRADIATED” or “TREATED WITH IONIZING RADIATION” in English capital lettering and “輻照食品” in Chinese characters.

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Food irradiation

Ingredients: Black tea, chrysanthemum and wolfberry (IRRADIATED)

成份: 紅茶、菊花及枸杞子 (輻照食品)

Example of food label of irradiated food in the market

Removing air

• Air is needed for some micro-organisms to multiply

• If air is removed, some micro-organisms cannot multiply

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• In canning and bottling, foods are heated and sealed in vacuum

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Removing air:Sealing in cans and bottles

Canned and vacuum packed cranberries

Removing air:Vacuum packaging

• This is done by removing air and sealing the package

• Once opened, the food has a normal shelf life

• Colour and texture are maintained

• Chemical preservatives are often added to vacuum packed foods, so they can be kept for a longer time

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Removing air:Vacuum packaging

• Examples of vacuum packed foods

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Ham Bacon Sausage Rice

Proper storage of food -...

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