IIInnntttrrroooddduuuccctttiiiooonnn tttooo cccooooookkkeeerrryyy Cookery is defined as a “chemical process” the mixing of ingredients; the application and withdrawal of heat to raw ingredients to make it more easily digestible, palatable and safe for human consumption. Cookery is considered to be both an art and science. The art of cooking is ancient. The first cook was a primitive man, who had put a chunk of meat close to the fire, which he had lit to warm himself. He discovered that the meat heated in this way was not only tasty but it was also much easier to masticate. From this moment, in unrecorded past, cooking has evolved to reach the present level of sophistication. Humankind in the beginning ate to survive. Now also we still eat to survive, however efforts have been made to make the food more enjoyable like cooking meats and vegetables in different ways to make them more easily eaten, digestible and to make them more attractive, palatable and to have wider choice. This is the art associated with the preparation of food. However it is not solely the artful manipulation and combination of food which results in good tasting products. Nutritional aspects, the effects of combining various foodstuffs and the use of modern technology can be considered the science of cooking. The “how of cooking” can be considered to be the art and the “why of cooking” could be the science. Balancing the art and science must be the goal of every professional chef.
Aims and objectives of cooking food
1. Cooking partly sterilizes food Above 40°C (140°F) the growth of bacteria falls off rapidly and in general it ceases above 45°C (113°F). Non-sporing bacteria are killed at temperatures above 60°C (140°F) for varying periods of time. For example, to make milk safe for consumption, it is pasteurized at 63°C (145°F) for 30 minutes or at 72°C (161°F) for 15 seconds. Boiling kills living cells with the exception of spores, within a few seconds. Spore bearing bacteria take about 4 to 5 hours of boiling to be destroyed (Higher the temperature shorter the time required to destroy them).
2. Cooking helps to make the food more digestible Complex foods are often split into simpler substances during cooking. This helps the body to absorb and utilize the food more readily than in the raw form.
3. Cooking increases the palatability of various dishes.
4. Cooking makes the food more attractive in appearance, and hence more appetizing. 5. Cooking introduces variety Many different types of dishes can be prepared using the same ingredient. 6. Cooking helps to provide a balanced meal Different ingredients of different nutritive values combined together in one dish makes it easier to provide a balanced meal (e.g. a combination of cereals and pulses together gives a complete balanced meal.)
METHODS OF COOKING
In order the food to be cooked, heat must be transferred from the heat source (such as a gas flame or an electric element) to and through the food. Understanding the ways in which heat is transferred and the speed at which it is done helps the cook to control the cooking process. Heat is transferred in three ways- conduction, convection and radiation. Conduction Conduction occurs in two ways –
1. When heat moves (conducts) directly from one item to the other, which is in contact with it. For example from the top of the range to a pot placed on it, from the pot to the milk inside etc.
2. When heat moves from one part to an adjacent part of the same item. For example from the exterior of a roast to the interior, or from a sauté pan to its handle.
Different metals (materials) conduct heat at different rates (speeds) Heat moves rapidly through copper and aluminum, more slowly in stainless steel, slower yet in glass and porcelain. Air is a very poor conductor of heat. Convection Convection occurs when the movements of air, steam, or liquid (including hot fat) spreads heat. There are two kinds of convection
1. Natural Hot liquids and gases rise, while cooler ones sink. Thus in any oven, kettle of liquid, or deep fat fryer there is a constant, natural circulation that distributes heat.
2. Mechanical In convection ovens and convection steamers, fans speed the circulation of heat. Thus, heat is transferred more quickly to the food, and the foods cook faster. Stirring is a form of mechanical convection.
Thick liquids cannot circulate as quickly as thin ones, so the rate of natural convection is slower. This explains in part why it is so easy to scorch thick soups and sauces. Radiation(cooking by radiant heat) Radiation occurs when energy is transferred by waves from the source to the food. The waves themselves are not actually heat energy, but are changed into heat energy when they strike the food being cooked. (Light waves, radio waves, and X – rays are examples of radiation not used for cooking) Two kinds of radiation are used in the kitchen:
1. Infra-red Broiling is the most familiar example of infra -red cooking. In a broiler, an electric element or a ceramic element heated by a gas flame becomes so hot that it gives off infra red radiation, which cooks the food. There is also high-intensity infra red ovens designed to heat food rapidly.
2. Microwave In microwave cooking, the radiation generated by the oven penetrates part way into the food, where it agitates the molecules of water. The friction caused by this agitation creates heat, which cooks the food,
a) Because microwave radiation affects only water molecules, a completely waterless material will not heat up in a microwave oven. Plates become hot only when heat is conducted to them by hot foods.
b) Because most microwaves penetrate no more than about 2 inches into foods, heat is transferred to the centre of large pieces of food by conduction, just as in roasting.
It takes time to heat a food to a desired temperature, the temperature at which a food is said to be “done” (meaning that the desired changes have taken place). This time is affected by three factors.
1. Cooking temperature This means the temperature of the air in the oven, the fat in the fryer, the surface of a griddle, or the liquid in which a food is cooking.
2. The speed of heat transfer Different cooking methods transfer heat at different rates, as shown by these examples: Air is a poor conductor of heat, while steam is much more efficient. Jets of steam (212°F/100°C) will easily burn your hand, but you safely reach into an oven at 500°F (260°C). This is why it takes longer to bake potatoes than to steam them. A convection oven cooks faster than a conventional oven, even if both are set at the same temperature. The forced air movement transfers heat more rapidly.
3. Size, temperature, and individual characteristics of the food For example, a small beef roast cooks faster than a large one. A chilled steak takes longer to broil than one at room temperature. Fish items generally cook more quickly than meats. Because there are so many variables, it is difficult or even impossible to determine exact cooking times in most recipes.
Air as medium
Fat as medium
Water/liquid as medium
Roasting (Spit, Pot, and Oven ;)
Frying (Deep fat and shallow fat)
Bar-be-queing (grilling using open fire)
Stir frying ( Shocking) using high temperatures
Grilling ( of fish, steaks etc on a
above and in between) Toasting of bread and making toasted sandwiches etc.
grill using oil )
Cooking methods are broadly classified as “dry heat method” and “moist heat method”. Dry heat methods Dry heat methods are those in which the heat is conducted without moisture, that is, by hot air, hot metal, radiation, or hot fat. We usually divide dry heat methods into two categories: without fat (i.e. using air) and with fat. Moist heat methods are those in which the heat is conducted to the food product by water (including stock, sauces gravies etc.) or by steam. Different cooking methods are suited to different kinds of foods. For example meats high in connective tissue will be tough hence should be broken down slowly by moist heat. Meats, low in connective tissue, are naturally tender and they are at their best and juiciest when cooked with dry heat to rare or medium- done stage. There are many other factors to consider when choosing methods of cooking for meats, fish, and vegetables, such as the flavour and appearance imparted by browning, the flavour imparted by fats, and the firmness or delicacy of the product. Air as medium Baking To “bake” means to cook foods by surrounding them with hot, dry air, usually in an oven. Baking applies to breads, pastries, vegetables and fish. It is more general term than roasting. The degree of dryness of heat may be modified by the amount of steam produced from the items baked. Bread rolls, cakes, pastries, puddings, potatoes, vegetables, farinaceous dishes are baked. During baking the mixture or moisture in the product expands by air, steam or carbon dioxide. Basic rules
1. Items should be placed in the right position in the oven. The cool spots should be avoided.
2. Always pre-heat the oven to the required temperature.
3. The oven should have the correct temperature according to the baked items e.g. rich cakes should have a lower temperature than pastries, which should have a high temperature. Baked yeast goods should have a hot oven 220°C (425°F).
Broiling To “broil” means to cook with radiant heat from above Broiling is cooking by direct heat and is used synonymously with grilling. It could be done by source of heat above or below. It is dry cooking, and can be done on a grid (iron bars) or pan broiled, where the food is cooked uncovered. Shirred eggs are an example of broiled eggs. The egg is slipped on to an egg dish, cooked on top of the stove, till it white coagulates, and then it is placed in a broiler, heat from above. Most tender and most expensive cuts of beef and fish are most often broiled. Grid markings on steaks add eye appeal. Whole spices broiled on a hot tawa bring out the flavours. In pan broiling the food is cooked uncovered on hot metal such as a grill or a frying pan. The pan or grill is oiled slightly to prevent sticking. The terms broiling, grilling and griddling are sometimes confused. It is better to use the terms that refer to the equipment used. Thus broiling is done in a broiler, grilling on a grill, and griddling on a griddle. Broiling is a rapid, high heat cooking method that is usually used only for tender meats, poultry, and fish and for a few vegetable items. Broiled chicken and meats cooked in “shawarma” machines (Arabic speciality) are examples of broiling. Pan–broiling is like griddling, except that it is done in a sauté pan or skillet instead of on a griddle surface. Grilling is done on an open grid over a heat source, which may be charcoal, an electric element, or a gas heated element. Grilled meats should be turned to achieve desired grill marks. Griddling is done on a solid cooking surface called a griddle, with or without small amounts of fat to prevent sticking. Grooved griddles have a solid top with raised ridges. They are designed to cook like grills, but to create less smoke. Barbecue To “barbecue” means to cook with dry heat created by the burning of hardwood or by the hot coals of this wood. In other words, barbecuing is a “roasting” or “grilling” technique requiring a wood fire.
FAT as a medium Roasting To “roast” or to “bake” means to cook foods by surrounding them with hot, dry air, usually in an oven. Roasting usually applies to meats and poultry. Depending upon the equipment used to roast items, roasting can be classified in three methods, namely:
1. Spit Roasting The food to be cooked is brought in contact with direct flame in front of a clear bright fire. The food is basted with fat and is also turned regularly to ensure even cooking and browning. This method, known now as spit roasting, is very little used, as only good quality meats are suitable for it. Roast meats, however, have a very good flavour, and are still served in large hotels and in specialty restaurants and hotels as barbecued meats.
2. Pot Roasting This method is used to cook small joints and birds if no oven is available. A thick heavy pan is essential for this method of roasting. Enough fat is melted to cover the bottom of the pan. When the fat is hot the joint is browned. It is then lifted out and 2 or 3 skewers or some bones and mirepoix vegetables are put into the pan on which the joint is placed. This is to prevent the joint from sticking to the pan and to facilitate a smooth hot air circulation all around the joint(venting) for even cooking. The joint should just touch the fat. The pan is then covered tightly with a well fitting lid and cooked over a very slow fire. The joint could be basted if lean and turned occasionally to ensure even cooking. Prepared root vegetables and potatoes can be cooked around the meat.
3. Oven Roasting This has now taken the place of spit roasting, because of its convenience, although only first class meat, poultry and vegetables are thus cooked. This is cooking in a closed oven with the aid of fat. The joint is raised out of the fat by means of bones or a trivet to prevent the meat from frying and becoming hard. Frequent basting, however, is essential. The food is put into a fairly hot oven for 5 to 10 minutes and the temperature is lowered to allow the joint to be cooked through. Cooking in a moderate oven for a longer period produces a better-cooked product than cooking at high temperatures for a shorter period. “Tandoor” is an open Indian clay oven, which is used to prepare different rotis, kebabs, chicken and other tandoori items.
Frying This is a method of cooking whereby the food to be cooked is brought into contact with hot fat. Food cooked in this way is said to be indigestible. But if the method is correctly and carefully carried out, the food is quite suitable for normal people. The advantages of frying are: -
1. Fried food is very appetizing.
2. It is a quick method of cooking.
3. The keeping quality of fried food is strengthened. It is however an expensive method of cooking meat as only the best parts are suitable (chops, liver, etc.) For other foods and for re heating of food frying is a good means of providing variety.
There are two types of frying: - A. Deep fat frying The food is completely immersed in hot fat(oil) and, therefore, a large quantity of fat is required. The quantity of fat requires some time to heat and special care must be taken to prevent over heating of fat as this spoils both the food as well as the fat. The fat decomposes at high temperatures. If the fat is not hot enough the food breaks up and it absorbs extra fat thus making the product unfit for consumption. Use a frying basket wherever possible to remove fried foods easily. Almost all foods require coatings before frying since not only are the juices and flavour of the food to be kept in but the fat must be kept out. Materials used are egg and breadcrumbs, batter, thinly rolled out pastry, besan batter etc. Quality in a deep fried product is characterized by the following properties: -
1. Minimum fat absorption.
2. Minimum moisture loss (i.e. not over-cooked)
3. Attractive golden colour.
4. Crisp surface or coating.
5. No off flavours imparted by the frying fat.
Guidelines for Deep-frying
1. Fry at proper temperatures. Most foods are fried at 350 to 375 F(175 to 190C) Excessive greasiness in fried foods is usually due to frying at too low a temperature.
2. Don’t overload the baskets. Doing so greatly lowers the fat temperature.
3. Use good quality fat. The best fat for frying has a high smoke point.(the temperature at which the fat begins to smoke and to break down rapidly )
4. Replace about 15-20% of the fat with fresh after each daily use.
5. Discard spoilt/burnt fat. Fat begins to thicken, getting to be what is known as gummy or syrupy, with continuous use. This condition is known as polymerization and such fats are more viscous than fresh fat. Fat that has reached this stage is no longer fit for use.
6. Avoid frying strong and mild flavoured foods in the same fat.
7. Fry as close to service as possible.
8. Protect fat from its enemies like heat, oxygen, water, salt, food particles and detergent.
9. Once fat has been used for frying, strain and store in cans in a refrigerator.
B. Shallow fat frying Only a little fat is used and the food is turned over in order that both sides may be browned or cooked. Generally this method is applied to pre cooked food unless the food takes very little time to cook (omelets, fish, liver etc.) Some foods contain sufficient fat in them (bacon, oily fish, sausages, etc.) and additional fat is not necessary although some cooks prefer to use a little fat. Fat absorption is greater when food is shallow fried than deep fried, (as food is not getting cooked from all the sides at the same time, and the temperature of the fat reduces considerably if not properly controlled etc). Pan–fry To “pan fry” means to cook in a moderate amount of fat in a pan over moderate heat. Pan-frying is similar to sautéing except that more fat is generally used and the cooking time is longer. Pan-frying is often done over lower heat than sautéing. Sauté To “sauté” means to cook food quickly in a small amount of fat. The French word “sauter” means, “to jump” referring to the action of tossing small pieces of food in a sauté pan. Pre heat the pan before adding the food to be sautéed. The food must be seared quickly, or it will begin to simmer in its own juices. Do not over crowd the pan. Meats to be sautéed are often dusted with flour to prevent sticking to the pan and to achieve uniform browning. Pressure frying “Pressure frying” means deep frying in a special covered fryer that traps steam given off by the foods being cooked and increases the pressure inside the kettle. Just like the pressure cooker, the pressure fryer raises the temperature and cooks the food more quickly, without excessive surface browning. Pressure frying requires accurate timing, because the product cannot be seen while it is cooking. Grilling The term “grilling” is used synonymously with “broiling”. This is cooking by dry heat(radiant heat). The food is supported on a grid iron over the fire, or on a grid placed in a tray under a gas or electric grill, or between electrically heated grill bars. Grilling could be done as:
1. Grilling over the heat This is cooking on greased grill bars with the help of fat over direct heat. Only first class cuts of meat, poultry and certain fish can be prepared this way. The grill bars are brushed with oil to prevent the food sticking, and can be heated by charcoal, coke, gas or electricity. The bars should char the food article on both sides to give the distinctive flavour of grilling. The thickness of the food and the heat of the grill determine the cooking time. Grills are typical a-la carte dishes and are ordered by the customer to the degree of doneness (cooking) required, such as au bleu (rare, very under done), saignant (under done), a point (just done, medium) biencuit (well done).
2. Grilling under the heat (Salamander) Cooking on grill bars or on trays under direct heat. Steaks, chops, etc are cooked on the bars but fish, tomato, bacon and mushroom are usually cooked on trays. This method can also be used in the preparation of foods au gratin and when glazing is required or even for gratinating pizzas.
3. Grilling between heat Food is cooked between electrically heated grill bars etc making toast in a toaster.
4. Infra- red Grilling This is cooking by infrared radiation. This method reduces cooking time considerably e.g. a steak can be grilled in one minute.
Moist methods of cooking Boiling
Boiling is cooking by immersing the food in a pan of liquid (stock or water) which must be kept boiling all the time i.e., quite a number of bubbles should be seen on the surface. Boiling is restricted for meat and poultry for the first few minutes in order to seal the pores, to retain natural juices and then gentle boiling must take place which is known as simmering at 82-99°C (180-210°F) Boiling temperature is 100°C (212°F). Vegetables are boiled at 100°C. Blanching is used when food items need to be precooked or partly cooked. No matter how high the burner is turned, the temperature of the liquid will
go no higher than 100C. The high temperature would toughen the proteins of meats( make it rubbery), and the rapid bubbling breaks up delicate foods, like fish and eggs ( cooked out of shell) Only sufficient liquid should be used to cover the food to be cooked. To retain nourishment and flavour in food, plunge into boiling liquid. Allow to re boil and then to simmer. The liquid thus obtained (after boiling or cooking the products) is known as “Pot Liquor” and contains some nourishment and flavour. This should not be wasted. It could be used as a substitute for stock or can be used to prepare stock. Generally speaking, vegetables grown above the ground are cooked in boiling salted water and vegetables grown below the ground(mainly carbohydrates/ starchy vegetables like potatoes etc) are started in cold salted water with the exception of new potatoes and new carrots. Dry vegetables are started in cold water. Salt is added only after the vegetables are tender. Fish should be put into hot liquid and allowed just to simmer. To “simmer” means to cook in a liquid that is bubbling very gently. Temperature is about 85-96°C (185-205°F). Most foods cooked in a liquid are simmered. The higher temperatures and intense agitation of boiling are detrimental to most foods. Basic rules
1. The food item should be completely immersed throughout the process.
2. The flavour of meat and poultry can be enhanced by the addition of herbs and vegetables to the cooking liquor.
Poaching To “poach” means to cook in a liquid, usually a small amount that is hot but not actually bubbling. Temperature is about 71-82°C (160-180°F). Poaching is used to cook delicate foods such as fish (products having less connective tissues) and eggs out of shell. It is also used to partially cook foods such as variety meats, in order to eliminate undesirable flavours and to firm up the product before final cooking. When poaching eggs, a little vinegar and salt are added to the liquid to help in quicker coagulation and thus prevent disintegration, and allows the water to boil at a lesser temperature than 100C. To “blanch” means to cook an item partially and very briefly, usually in water, but sometimes by other methods (as when French fries are blanched in deep fat) Blanching can be done in three ways, Hot oil blanching as in potatoes, hot water blanching, and cold (ice cold)water blanching as in for green leafy vegetables used for salads to make them remain crisp till service. There are two ways of blanching using hot water:
1. Place the item in cold water, bring to a boil, and simmer briefly. Cool the item by plunging it in cold water to dissolve out blood, salt, or impurities from certain meats and bones etc.
2. Place the item in rapidly boiling water and returns the water to the boil. Remove the item and cool in cold water purpose to set the colour and destroy harmful enzymes in vegetables, or to loosen the skins of tomatoes, peaches, and similar items for easier peeling.
Stewing This is a very gentle method of cooking in a closed pan using only a small quantity of liquid (just enough to cover the products) The food should never be more than half covered with the liquid and the food above this level is thus really cooked by steam, if stewing is done in a casserole or other suitable containers/ vessels. As the liquid is not allowed to boil during cooking the process is a slow one. It is a time consuming method of cooking, but the advantage is that the coarser, older and cheaper types of poultry and meats are used, as they are unsuitable for grilling and roasting. Cheaper cuts of meat and certain fish dishes (bouillabaisse, matelotte) are prepared by this method, as it renders it tender and palatable. “Stewing” is gentle simmering in a small quantity of water or stock just enough to cover completely the cut food items, and simmering until they become very tender, and both liquid and food are served together. Stewing is done in covered saucepans or casseroles on top of the cooker, or in the oven-but always at a low temperature. Advantages of stewing Cheap cuts of meat, old fowls and tough or under ripe fruits may be prepared by this method, as the slow, moist method of cooking softens fibers, rendering the food tender. Meat and vegetables may be cooked and served together making an appetizing dish, while saving fuel and labour. Stewed food may be cooked in the oven after other food is cooked or it may be cooked on the side of the fire or on a very small gas or oil flame thus again saving fuel. All nourishment and flavour are retained hence the food is very appetizing. General rules
Have a pan ready with a well–fitting lid. Prepare the food and cut into pieces convenient for serving. Use tepid liquid and only sufficient to half cover the food. Bring just to boiling point and then simmer very gently until the food is perfectly tender. The liquid should not reach too high a temperature, as the slow process of cooking by gentle heat, converts the connective tissues into gelatin so that the
meat fibers fall apart easily and become more digestible. The proteins are coagulated without being over hardened and the soluble nutrients and flavour pass into the liquid, which is served. Never boil a stew for a stew boiled is a stew spoilt. Braising To “braise” means to cook covered in a small amount of liquid, usually after preliminary browning. In almost all cases, the liquid is served with the product as a sauce. This is a combination of “roasting” and “stewing” in a pan with a tight fitting lid. For correct use this method requires a special pan but a casserole dish or a stew pan makes a good substitute. The meat should be sealed by browning on all sides and then placed on a lightly fried bed of vegetables (mirepoix). Ideally a sauce may be added even though a stock or gravy is usually used which should come to two-third of the meat. The flavouring and seasoning are then added. The lid is put and it is allowed to cook gently on the stove or preferably in the oven. When nearly done the lid is removed and the joint is basted frequently to glaze it. This latter process is always done in the oven. Oven braising has three major advantages- uniform cooking, less attention required, and range space is free for other purposes. Braising also refers to cooking some vegetables, such as lettuce or cabbage, at low temperature in a small amount of liquid, without first browning in fat, or with only a light preliminary sautéing. Items of meat, poultry and game suitable for braising are those of a tough nature, rather than those of a tender nature. Braised vegetables are better if served with a good sauce made separately. The braising liquor is strong and similar in taste to the vegetables. Steaming To steam means to cook foods by exposing them directly to steam. Steaming is cooking by moist heat, i.e. steam-direct or indirect. Indirect steaming is done when the food is placed in a closed pan, which is surrounded by plenty of steam from fast boiling water or in a steamer. The food item could be protected with grease–proof (GP) paper, or cloth or aluminium foil to prevent water getting into the product. Direct steaming is by placing the article in a perforated container or on a covered plate over a sauce pan of water. Steaming also refers to cooking an item tightly wrapped or in a covered pan, so that it cooks in the steam formed by its own moisture. This method is used in cooking items en papillote, wrapped in parchment paper (or foil). Jacket potatoes baked wrapped in a foil are actually steamed. Steam at normal pressure is 100°C (212°F), the same as boiling water. However, it carries much more heat than boiling water and cooks very rapidly. A pressure steamer is a steam cooker that holds in steam under pressure. The temperature of steam then goes higher than 212F as the following charts shows:-
N.B.: “psi” stands for pounds per square inch. Because of these temperatures, pressure steaming is an extremely rapid method of cooking and must be very carefully controlled and timed. Advantages of steaming
1. Food cooked by this method is easily digested.(good method of cooking for invalids)
2. All nourishment and flavour are kept in the food.
3. Food cannot be easily overcooked.
4. Pudding basins and other containers need not be filled to the top, thus allowing room for food to raise making food light.
General rules for steaming
1. Prepare the vessel and have the water boiling fast.
2. If a basin is to be used as a container inside the steamer, see that it is greased and that it is covered with a well –fitting lid or with greaseproof paper. This is to prevent condensed moisture from falling on the food.
3. Keep a kettle of boiling water handy so that the water in the steamer can be replaced as it boils away.
4. Never allow the water in the steamer to go off the boil, except when preparing dishes with eggs, such as custard, for this water must be kept at simmering point, or else the custard will curdle.
5. Dish food quickly and serve hot. An appropriate sauce must be served with steamed foods, as they are generally bland.
Pressure Cooking As the pressure increases, the boiling point of water increases. This is the theory used in pressure- cooking. In a pressure cooker the water is allowed to boil only at 127°C instead of the normal 100°C. Hence the cooking time for the food items are considerably reduced by pressure cooking. Microwave Although a form of energy, it is not heat. The principle of microwave involves a type of electronic heating and is concerned with the production of high frequency waves from an oscillator tube called a “magnetron”. The electromagnetic waves have energy and this energy is transported to the desired load for heating. The energy created penetrates articles of food to a depth of 3 inches and causes the molecules of water to agitate and create friction, supplying the heat which cooks or re heats the food. Microwaves do not heat the oven cavity. Microwaves are reflected by metal items and therefore are unsuitable for use with this equipment. The advantage lies in the speed of operation. It is excellent as a re-heater. Electricity can be converted into microwaves using a special valve/device called a magnetron. The microwaves pass through air or glass, china, plastics and paper without heating them, but when they strike solid and liquid foods, they are absorbed. Their energy is transferred to the food molecules that vibrate rapidly. The resultant heat cooks the food. Microwaves are absorbed by most types of food in varying degrees depending on the cellular structure of the food. Factors affecting Microwave cooking.
1. Density: The denser the food, the more difficult it is to cook.
2. Quantity: The heating is proportional to the quantity of food placed in the oven. For instance if one portion takes 30 seconds to heat, two portions will take 45 seconds, whereas three portions will take 60 seconds. For each additional portion, half the time taken by the first portion is added.
3. Shape. The thicker the product, the longer it will take to cook. Shape as far as possible should have uniform thickness e.g. truss chicken
4. Containers. They should be of glass, china, plastic or paper to allow transmission of microwaves.
Solar Cooking It is similar to what we use in the kitchen to cook food. Solar cooker works only on solar energy. It emits no smoke; no soot spoils the cooking utensils. It keeps the surroundings clean. Above all, it conserves the precious energy resources of the country and saves us the money. Principles of solar cooker Solar cookers can be broadly divided into two categories:
1. Cookers utilizing solar heat with little or no concentration of rays It may be termed as a “hot box”. This consists of a well- insulated box the inside of which is painted dull black and is covered by one or more transparent covers. The purpose of the transparent covers is to trap the heat inside the solar cooker. These cookers allow the radiation from the sun to come inside but do not allow the heat from the black absorbing plate to go out of the box. It is because of this that the temperatures of the blackened plate inside the box increases and can heat up the space inside to temperature up to 140C which is adequate for cooking.
2. Cookers which deflect solar energy from a large surface to a smaller area to produce high temperatures This type of solar cooker uses a lens or a reflector suitably designed to concentrate the solar radiation over a small area. This cooker is able to provide high temperature on its absorbing surface when suitably designed.
The cooking time is about 2 to two and a half hours for cooking depending upon the kind of food and the season. Advantages of solar cooker
1. It cooks up to four items at a time.
2. It preserves the nutrition of the food because the cooking is done at low temperature.
3. It does not require constant attention.
4. It is safe and does not burn.
5. Saves fuel.
6. Keeps food hot for a long time.
1. It needs the sun and will not give results on a cloudy day.
2. Only simmering method is adopted.
Usually hotels normally use solar energy for heating water for supplying hot water in the kitchens for
cooking purposes and in toilets, bathrooms and public areas etc, and not for actual cooking of dishes.