Methods of preservation

UNDERSTANDING YOUR FOOD<br /> the ultimate educational resource<br /> TEACHER NOTES<br /> <br /> PRESERVATIVES<br /> teachers’ notes<br /> KS3<br /> science or food technology<br /> Timing - 30 mins;a possible<br /> homework exercise<br /> Two pupil activity sheets P3<br /> accompany this activity.<br /> 1<br /> Herbs and spices are the only foods<br /> which are allowed to be irradiated in<br /> bulk at the present time. In practice,<br /> however, although the technology is<br /> available, it is rarely used –<br /> presumably because it is<br /> still controversial.<br /> P3. Methods of food preservation<br /> This activity helps to summarise the main methods of food preservation.<br /> The activity includes a table of preservation methods with statements which<br /> give descriptions of how the methods prevent the spoilage of food.<br /> Pupils have to match each description with the correct method.<br /> Pupils complete the table by adding examples of foods preserved by each<br /> method. The correct matching is as follows:<br /> a. freezing<br /> e.g. a great variety of foods including meat, vegetables<br /> b. curing<br /> e.g. meat<br /> c. chemical preservatives<br /> e.g. cooked meats, wine, some cheeses<br /> d. canning/bottling<br /> e.g. fruit, vegetables<br /> e. cooking<br /> e.g. various<br /> f. jam making<br /> e.g. most fruits<br /> g. dehydration<br /> e.g. soups, vegetables, pasta<br /> h. pickling<br /> e.g. fruit, vegetables<br /> i. irradiation<br /> e.g. herbs and spices only<br /> 1<br /> j. chilling (domestic refrigeration)<br /> e.g. milk, cream, butter<br /> k. gas or vacuum packing<br /> e.g. bacon<br /> <br /> METHODS OF FOOD PRESERVATION pupil activity P3<br /> There is a need to preserve and process much of the food that is grown. Preservation<br /> of food is necessary to ensure a safe supply of nutritious food to all individuals. It is a<br /> way of preventing wastage of food when this is in quantities too great for immediate<br /> consumption. It allows foods to be eaten out of season and gives variety and<br /> nutritional quality to our diets all year round.<br /> Many foods must be processed before they are fit for us to eat. Processing often<br /> involves making the food easier to digest, preserving it, improving its flavour and its<br /> texture.<br /> Methods of processing vary from being simple, such as cooking raw vegetables at<br /> home, to extremely complicated. Processing can be a great art as shown by the<br /> blending of many ingredients to create superb dishes by skilled chefs. It can be on a<br /> huge industrial scale such as the commercial baking of bread.<br /> As soon as food is harvested (picked or slaughtered) the organisms of decay begin<br /> breaking it down. This leads to unacceptable deterioration and the possible<br /> production of dangerous substances. Preserving food must try to stop or greatly slow<br /> down this natural process.<br /> The skill in preserving and processing food is to get the best quality of product that is<br /> possible. The aim is to produce the best colour, texture and flavour but without<br /> reducing the nutritive value of the food. Processing must not introduce toxic material<br /> and must be done at a cost that is acceptable to the consumer.<br /> For you to do<br /> The table, on the next page, shows the main methods of food preservation. Below it<br /> are descriptions of how the methods of preservation are able to stop the spoilageof<br /> food.<br /> Match the method of preservation with how it works. The first is done for you.<br /> In the final column of the table add the names of foods that can be preserved by<br /> each method.<br /> <br /> pupil activity P3 METHODS OF FOOD PRESERVATION<br /> Method How does it work?Examples of foods<br /> Cooking e meat, vegetables,<br /> eggs, etc.<br /> Domestic refrigeration<br /> Freezing<br /> Canning/ bottling<br /> Dehydration<br /> Curing<br /> Pickling<br /> Jam making<br /> Gas or vacuumpacking<br /> Chemicalpreservatives<br /> Irradiation<br /> Match these statements against food preservation methods.<br /> a. slows down reactions considerably; ‘removes’ water by turning it into a solid so thatit<br /> cannot be used<br /> b.salt is added which makes the liquid environment very concentrated; inhibits the<br /> action of enzymes and the processes of microorganisms<br /> c. substances such as sulphur dioxide and sodium benzoate interfere with microbial<br /> growth<br /> d.high temperatures destroy enzymes and microorganisms; removes and excludes<br /> oxygen<br /> e. destroys enzymes and most microorganisms<br /> f.adds sugar which makes the liquid environment very concentrated; inhibits the<br /> action of enzymes; inhibits the processes of microorganisms<br /> g.removes water completely; makes the food a solid<br /> h.adds (usually) vinegar; makes the environment too acidic for enzymes and<br /> bacteria to function normally<br /> i.rays from a radioactive source are passed through food; microorganisms are<br /> destroyed<br /> j.slows down reactions<br /> k removes and excludes oxygen to inhibit the growth of organisms which require it