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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 2
Proper storage of food Store food in the right place at the right temperature 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 crosscontamination 3
Proper storage of food Store food in the right place at the right temperature Store unopened cans, jars, bottles and packets in a cool dry storage cupboard 4
Proper storage of food Store food for the correct time Check the expiry date marked on any packaged food before using 5
Proper storage of food What s the difference between Use by date and Best before date? 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 Yoghurt Cheese Milk 6 Fresh orange juice
Proper storage of food What s the difference between Use by date and Best before date? 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 7
Proper storage of food What s the difference between Use by date and Best before date? 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 8
Personal hygiene What should we do before handling food? Hair: wear a hairnet or tie up the hair Clothing: put on apron before starting to prepare food Fingernails: always keep them short and clean Cuts: cover any cuts with clean waterproof plasters 9
Personal hygiene Wash hands thoroughly before handling food and between handling different types of food 10 Source: http://www.chp.gov.hk/en/exhibition_details/2867/0.html
Ways to handle food properly and hygienically Use proper ways to thaw frozen foods Freezing prevents microbial growth in foods, it will not destroy all microorganisms 11
Ways to handle food properly and hygienically 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 Improper thawing Bacteria A piece of meat 12
Ways to handle food properly and hygienically Use proper ways to thaw frozen foods 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 13
Ways to handle food properly and hygienically Always wash food well before cooking it 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 Wash vegetables with water 14
Ways to handle food properly and hygienically Use separate equipment for raw and cooked food For example, use separate containers and chopping boards for raw and cooked foods Use chopping boards of different colours to handle raw and cooked food 15
Ways to handle food properly and hygienically Cook food properly and thoroughly 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 16
Ways to handle food properly and hygienically Clean properly Clean equipment properly in hot soapy water, then rinse and dry thoroughly Keep food cupboards and refrigerators clean Keep pets out of the kitchen (e.g. by using fences) Fence prevents the entrance of pets into the kitchen 17
Preservation of foods Micro-organisms need food, warmth, moisture and time to multiply. If one of these conditions is removed, the food is preserved and could be kept for a longer time. 18
What are the purposes of preserving foods? Cut down on wastage -Preserve the food before they become spoiled e.g. make seasonal fruits into jam 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 Benefits of preserving food 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 19
Summary of food preservation methods Principle Preservation method Examples Living organisms need water to live Temperature affects growth and action of living organisms Dehydration Storage in strong solutions of salt and sugar Heating (Pasteurisation, sterilisation, Ultra Heat Treatment) Chilling and freezing Freeze drying Dried fruit Salted fish, jams Milk, canned foods Vegetables, meat products Coffee granules, mushrooms, prawns 20
Summary of food preservation methods Principle Preservation method Examples Living organisms can be destroyed by chemical action Living organisms are inactivated by radiation Living organisms need oxygen Acids Irradiation Vacuum packing Air tight seals Pickled fruits and vegetables Prawns, fruits and vegetables Bacon, ham Canning and bottling fruit juice 21
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 22
Dehydration (drying) Colour, texture, flavour and nutritional content of foods maybe affected Comparison between fresh mango and dried mango 100g dried mango 100g raw and peeled mango Nutrition label of 100g dried mango Nutrition information of 100g dried mango Information derived from: 100g of raw, peeled mango, Food Nutrient Calculator from Centre for Food Safety http://www.cfs.gov.hk/english/nutrient/fc-introduction.php 23
Dehydration (drying): Drying under sunshine (sun-drying) Water (moisture) evaporates slowly Use open-air conditions with little hygienic control Sun-dried vegetables Sun-dried seafood 24
Dehydration (drying): Spray drying Hot air is used to remove moisture from food Suitable for foods that maybe damaged by excessive heating Dry powder is produced from liquid Spray-dried milk powder 25
Dehydration (drying): Accelerated freeze-drying A combination of freezing and drying Food is quick-frozen then dried in vacuum (without air) under reduced pressure The heat vaporises the ice, which turns to steam (without going through the liquid state) and leaves the food dry Illustration of freeze-drying 26
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: Dried cuttlefish Dried corn Freeze-dried coffee Freeze-dried vegetables and cuttlefish in cup noodles 27
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 28
Dehydration (drying): Storage in strong solutions of salt and sugar 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 High High Salt Concentration of colour Concentration of salt Low Low 29
Dehydration (drying): Storage in strong solutions of salt and sugar 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 30
Dehydration (drying): Storage in strong solutions of salt and sugar Examples of food preserved by salt Bacon Ham Fish in brine (salt and water) 31
Dehydration (drying): Storage in strong solutions of salt and sugar Examples of food preserved by sugar Jam Marmalades Crystallised ginger 32
Dehydration (drying): Storage in strong solutions of salt and sugar Examples of food preserved by salt and sugar Ingredients: Plum, white sugar, salt, greengage juice, sweeteners (E951, E955) Ingredients: Mangoes, sugar, salt, preservative (E223) Preserved plums Dried mangoes 33
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 34
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 35
Examples of foods preserved by pasteurisation Milk Pasteurised eggs 36
High-temperature methods: Sterilisation Sterilisation is a heat treatment (temperature at 100 C or above) used to kill most microorganisms 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 37
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 38
Examples of foods preserved by UHT UHT treated milk and soymilk 39
Examples of foods preserved by UHT Whipping cream Fruit juices e.g. lemon tea 40
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 41
Sterilisation: Canning and bottling 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 Canned pineapple Store in a cool dry place. Refrigerate any unused portion in a separate covered container 42
Sterilisation: Canning and bottling Consume within 5 days of opening. Keep refrigerated. Canned condensed milk Bottled prune drink 43
Examples of foods preserved by canning Canned soups Canned tuna fish Canned meat Canned baby milk powder 44
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 Bottled sauce Bottled jam Bottled honey Bottled water 45
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 46
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 47
Cold storage: Chilling 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 48
Examples of food preserved by cook-chill method Microwave meals Fried fish ball Pre-cooked rice 49
Cold storage: Freezing 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 50
Cold storage: Freezing 51
Cold storage: Freezing Frozen chicken wings Frozen scallop meat Frozen fish fillet 52
Cold storage: Freezing 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 Liquid nitrogen is cold air at room temperature 53
Cold storage: Freezing 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 Frozen rice in lotus leaf Mini glutinous rice dumpling Frozen pizza 54
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 ph 1 2 3 4 5 6 7 8 9 10 11 12 13 14 55
Chemical methods: Use of acids 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 Ingredients: Scallion, sugar and vinegar Pickled scallion Pickled ginger 56
Citric acid Chemical methods: Use of acids Used for preservation of fruits and vegetables to provide flavour and decrease ph Ingredients: Cucumber, water, sugar, soy sauce, salt, acidity regulator (citric acid) Pickled cucumber Ingredients: Organic pomegranate concentrate, organic sugar, organic pomegranate juice, apple pectin, ascorbic acid (vitamin C) & citric acid (acidity regulators) Jam Ingredients: Preserved mustard, salt, flavour enhancer (E621 Monosodium glutamate), chilli, rapseed oil, spices, white sugar, acidity regulator (E330 citric acid) 57 Pickled tuber mustard
Besides food preservation, what are the other functions of acids in food preparation? Vinegar is used to: Chemical methods: Use of acids 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 58
Food irradiation The process uses radiation to kill pests, insects and some micro-organisms in food 59
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. 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 60
Removing air Air is needed for some micro-organisms to multiply If air is removed, some micro-organisms cannot multiply 61
Removing air: Sealing in cans and bottles In canning and bottling, foods are heated and sealed in vacuum Canned and vacuum packed cranberries 62
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 63
Removing air: Vacuum packaging Examples of vacuum packed foods Ham Bacon Sausage Rice 64