Food preservation using various methods such as salting, drying, fermenting and so on has been used since before recorded history. People have always frequently died or become seriously ill through eating badly preserved food. With modern techniques such as refrigeration, canning and other packaging methods there is less need for using preservatives. There are several methods for preserving foods including, salting, freezing, drying, canning, pickling and jamming.
Type your answer here There are so many different processing methods of foods. Some of the common methods include salting, pickling, using vacuum packs, smoking and so many others. Preserved salmon is exactly that, salmon that has been preserved by various methods. These methods would include smoking, drying, salting, or even placing it in the refrigerator. Log in. Study now. See Answer. Best Answer. Simple air drying works in the same way, but osmosis is not a factor; evaporation is.
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Meat and fruits like apples, apricots and grapes are some examples of drying with this method. Freezing is keeping prepared food stuffs in cold storages. Potatoes can be stored in dark rooms but potato preparations need to be frozen. Smoking is the process that cooks, flavours and preserves food exposing it to the smoke from burning wood. Smoke is antimicrobial and antioxidant and most often meats and fish are smoked. Various methods of smoking are used like Hot smoking, Cold smoking, Smoke roasting and Smoke baking.
Smoking as a preservative enhances the risk of cancer. Vacuum packing creates a vacuum by making bags and bottles airtight. Since there is no oxygen in the created vacuum bacteria die.
Usually used for dry fruit. Salting and Pickling: Salting also known as curing removes moisture from foods like meat. Pickling means preserving food in brine salt solution or marinating in vinegar acetic acid and in Asia, oil is used to preserve foods.
There are various methods of pickling like chemical pickling and fermentation pickling. In commercial pickles sodium benzoate or EDTA is added to increase shelf life. Sugar is used in syrup form to preserve fruits or in crystallized form if the material to be preserved is cooked in the sugar till crystallization takes place like candied peel and ginger.
Another use is for glazed fruit that gets superficial coating of sugar syrup. Sugar is also used with alcohol to preserve luxury foods like fruit in brandy. Lye also known as Sodium hydroxide turns food alkaline and prevents bacterial growth. Canning and bottling means sealing cooked food in sterile bottles and cans. The container is boiled and this kills or weakens bacteria.
Foods are cooked for various lengths or time. Once the can or bottle is opened the food is again at risk of spoilage. Jellying is preserving food by cooking in a material that solidifies to form a gel. Fruits are generally preserved as jelly, marmalade or fruit preserves and the jellying agent is pectin that is naturally found in fruit. Sugar is also added. Potting is a traditional British way of preserving meat by placing it in a pot and sealing it with a layer of fat.
These should be sufficiently high off the floor, at least 50 cm, and be spacious enough to prevent contact spoilage or contamination. This is especially important for storing raw and cooked foods, which must never touch each other, because raw food can contaminate cooked food. Food stored at floor level is more vulnerable to damage and contamination. For example, rats and mice are more likely to find it, and it may be accidentally knocked or kicked if people pass by.
The general rule for food storage is to keep hot foods hot and cold foods cold. Allowing cooked food to cool to room temperature allows microorganisms to start to grow and multiply; therefore, cooked food must be stored very carefully.
If it cannot be eaten straight away, it should be kept as cold as possible, ideally in a refrigerator, to avoid growth of microorganisms. If any food has to be reheated, this must be done thoroughly. If food is only warmed and not reheated properly, microorganisms will multiply in it, so you need to heat it enough to destroy them. Infant foods should not be stored at all, but must be used immediately.
Food is particularly vulnerable to contamination while it is being prepared for eating. Foods intended to be eaten raw, such as fruit and some vegetables, must be washed carefully in clean, safe water Figure Food that is to be cooked must be cooked thoroughly to kill all pathogenic microorganisms.
All parts of the food must reach a temperature of at least 70 o C. You cannot tell how hot the food is just by looking, so it is important to cook the food for long enough to make sure that it is all cooked through.
Cooking, as well as being a very important part of food preparation, is also used for preserving food; this is the subject of the next section. Food preservation includes a variety of techniques that allow food to be kept for extended periods of time without losing nutritional quality and avoiding the growth of unwanted microorganisms.
There are three basic objectives for the preservation of foods:. For storing or preserving food, one or several of the living conditions needed for the growth of microorganisms have to be removed. Like humans, microorganisms need a source of food and water, and they also need a suitable pH and temperature to grow, so food preservation techniques aim to target these requirements.
Food preservation depends on procedures which effectively manage the microbial content of foods and on processes that alter or delay the activities of enzymes in the food.
The techniques may be applied separately or in combination. Their aims are to prevent contamination in the first place, to remove or reduce the numbers of contaminants, and to prevent microbial growth. We describe them below. This technique simply means to prevent contamination of the food by spoilage agents or by contact with them.
The technique requires either using an artificial covering for the food, or keeping its natural protective covering if there is one.
Leaving the natural covering of the food intact, or applying a clean artificial cover, can prevent microorganisms from entering or dropping on to the food. Microorganisms can be physically removed from food, or their numbers reduced, by techniques like washing, trimming, sieving and filtration. For example, vegetables and fruit should be washed in clean water; any damaged or dirty parts of vegetables should be trimmed off with a clean knife; flour can be sieved to remove any unwanted contaminants.
Heat is one of the oldest methods of destroying microorganisms in food processing and preservation. The greatest advance in food hygiene was inadvertently made when humans discovered the advantage of boiling, roasting, baking and other heat treatments of food, hence preserving the food for longer periods. Food is also rendered safe by the application of heat because most pathogenic microorganisms are comparatively heat-sensitive.
Some of the methods of heat treatment used for food preservation are discussed below. Spores of some bacteria are extremely resistant to heat and are not killed at this temperature, although their growth is prevented. For this reason, boiling food can rarely be relied upon to ensure complete destruction of all organisms. However, most pathogens are killed, provided that sufficient exposure time is maintained.
Although the spores of Clostridium botulinum , which causes botulism, are extremely heat-resistant, the toxin produced by this organism is readily destroyed by boiling. However, some toxins produced by other bacteria such as staphylococci are not easily inactivated. Thermophilic heat-loving organisms may survive the effects of boiling and can cause food spoilage if environmental conditions are favourable for them.
Bacterial destruction by heat is affected by time and temperature variation. The higher the temperature, the more rapid is the destruction. On the other hand, as the temperature is lowered, the time of exposure holding time needs to be longer. Cooking can have some disadvantages. Nevertheless, the advantages of cooking outweigh the disadvantages because it inhibits spoilage and possible disease transmission.
Pasteurisation is a process of heat treatment of milk, beer and some other beverages. It requires sufficient holding time to assure the thermal destruction of pathogens and organisms responsible for spoilage, without altering the nutritional value.
It involves heating the food to a specific temperature for a specific time and then cooling rapidly. Pasteurisation kills most but not all of the microorganisms present. It is a very useful method when more rigorous heat treatment could harm the quality of the product, as in the case of milk, and when the aim is to kill only the pathogens that are not very heat-resistant.
The temperature applied and the holding time of pasteurisation vary with the equipment available and the type of food product. In milk pasteurisation, the time-temperature combination is selected on the basis of the thermal death time of the most resistant pathogens TB bacilli that may be present in raw milk, and the maximum temperature and time at which the taste, palatability and nutritive value of milk are maintained.
Normally milk is pasteurised at UHT milk is sterilised, meaning all forms of life are destroyed. This extends its storage time but does affect the taste. It means the application of boiling water or steam for a short time. It wilts some bulky vegetables and prevents discolouring of others. It cleans peas of the moist and sticky material around them.
Blanching vegetables prior to canning, freezing or drying helps to remove soil, insects and microorganisms, and destroys or slows the action of enzymes. It sets the green colour and generally facilitates dicing, peeling and packing. Canning is one of the most widely used modern methods of processing and preserving food.
The canning method involves the following steps: sterilising the food to be canned, packing it in sterile, air-tight stainless metal, glass or plastic containers, and then hermetically sealing i.
In the heat process, all vegetative bacteria are destroyed and spores cannot grow. Any can that is damaged or swollen should not be used. A swollen, bulging can indicates that gas is being produced on the inside and demonstrates there is microbial activity in the food, so it would not be safe to eat.
Unlike high temperature, cold is not an effective means of destroying pathogenic bacteria, viruses and toxins in foods, but it can retard their multiplication and metabolic activities. No food or food product is rendered free from microorganisms by low temperature by freezing or refrigeration. This explains the generally accepted danger of refreezing any kind of thawed foods.
The most important prerequisite for successful preservation by cold is that the food must be clean to start with. Freezing of food, when carried out properly, is one of the best methods of preserving foodstuffs in as nearly natural a state as possible.
Freezing preserves the storage life of foods by slowing down enzyme reactions and the growth of microorganisms.
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