Cooking of Food

• Cooking of food is an art which requires thought, care, skill and planning.

• Whatever method of cooking is employed the following principles must always be kept in mind:– To keep the flavor in– To draw the flavor out– To preserve the full nutritive value of the food

Cooking

Reasons for Cooking Food• Cooking develops new flavors which render food

palatable and stimulating to the digestive juices.• Cooked food is pleasing to the eye because of the

physiological changes the food undergoes.• Cooking kills bacteria and other microorganisms,

makes it safe for consumption besides assisting in keeping it for a long time.

• Cooking changes the texture of food, promoting mastication and rendering it easy for digestion and assimilation

• It is easy to plan an attractive, palatable and balanced diet when food is cooked.

• Cooking helps to introduce a variety in the daily diet.

Methods of Cooking

• Baking and Roasting• Boiling• Stewing• Steaming• Frying• Cooking in Microwave

Oven

Baking and Roasting• Both these methods are cooking by dry heat.• Roasting is cooking by radiant heat.• The food to be cooked is hung in front of a

glowing fire and turned round and round.• Cooking of Sheek kabab, Tikka, Tandoori

Chicken is done by this method.• The food is smeared with spices and ghee and

cooked directly over bright glowing fire and turned round and round till tender and well-cooked. This method of cooking has given place to oven roasting better known as baking.

Baking and Roasting (contd.)• In baking the food is placed on trays or suspended and

hot air circulation inside the enclosed and well insulated equipment helps to cook the food.

• Both these methods are expensive with regard to fuel consumption.

• Shrinking of food occurs during cooking owing to greater evaporation.

• The food is richer and finer and also more digestible.• Besides meat, potatoes, brinjals and onions can also be

cooked by this method.• The vegetables are usually buried in hot ashes and

cooked till tender.

Boiling

• This is cooking by moist heat.• The food is brought in direct contact with the

boiling water.• Though not a very tasty method, it is a more

digestible method.• Waste of nutrients occurs when the cooking

water is discarded.• There is loss of flavor also. • This requires to use as little water as possible

and the size of the cooking vessel should be suitable to the quantity of food being cooked

Boiling (contd.)• Always add the vegetables to boiling water to save

loss of nutrients and preserve the natural colour of foodstuffs.

• Green vegetables should be boiled rapidly to preserve their colour but carrots, potatoes and turnips should be boiled gently to preserve their shapes

Stewing• This is an economical method of cooking as the

water used for cooking is served along with the cooked food and hence helps to conserve nutrients and flavours.

• Fuel consumption is also low.• It is a slow method because a gentle long cooking

process is necessary to make the food tender• The food to be cooked should be cut in small

equal size pieces to allow exposure to the softening powersof boiling water.

• In case of curries the gravy should not be too thick and fat laden

Steaming• Steaming is cooking by moist heat.• Here the food does not come into direct contact with water.• Food is cooked by steam or water vapour rising from

the water below it. It can be either direct or indirect.• In the direct method food is placed on the steamer

which is then placed over a degchi of boiling water.• The disadvantage being that some of the nutrients fall

through the holes of the steamer into the water below.• Indirect method is more preferred as the food is

placed in a vessel and then introduced into the boiling water.

• This helps to preserve and conserve the natural nutrients and flavours.

Steaming (contd.)• Steamed food is best for invalids because it is light

and easy to digest.• There is also less danger of over cooking and

hardening of proteins or loss of nutrients while cooking.

• The flavor of food is greatly enhanced by this method.

• When food is steamed it is necessary to keep the water boiling throughout except in the case of puddings and custards when it should be just below the boiling point.

• The steamer must fit tightly into the vessel containing the boiling water.

• Care should be taken to prevent food from becoming sodden due to condensation of vapour on lid.

Frying• This is also a method of cooking by moist heat where the food

is cooked in hot oil or ghee.• It is a quick method as the fat can be heated to high

temperature and this rapidly heats the food coming into its contact.

• This results in hardening of the surface of food thereby preventing loss of flavour and juices.

• Frying is suitable only with foods that take a short time to cook• It is not recommended as a method of cooking for invalids

because fried food is fat laden and difficult to digest.• Frying makes food more appetizing , though there is a

considerable loss of nutrients. • The food cooked thus absorbs a lot of fat, hence fried foods

are fattening.

Frying (contd.)• Frying is done by two methods:

– Shallow fat frying

This is done by using a small quantity of fat in a frying pan or 'tawa'. Kababs, cutlets, parathas are cooked by this method.

– Deep fat frying

In this a large quantity of fat is heated in a pan or karai. Purees, pakoras, chips etc are cooked by this method.

The cooking fat should be sufficient to allow the food to float in it, and it must be very hot.

A few pieces should be introduced in the fat at a time.

Cooking in Microwave Oven

• Food is cooked by electro-magnetic waves.• It can be used for cooking of rice,

vegetables, flesh foods etc.• It can be used effectively for reheating of

foods.• Limitations:

– Cakes, pastry, biscuits do not get browned easily.– They are very expensive

Do's and dont's of Cooking

• Fruits and vegetables should be fresh.• Rotten parts of fruits and vegetables should be discarded• Fruits and vegetables should be washed thoroughly and

then cut.• Washing the fruits and vegetables after being cut could

lead to losing some amount of water soluble vitamins like Vitamin C and Vitamin B complex.

• The vegetable pieces should be cut as big as possible so as to minimise the surface area and to prevent a larger loss of water soluble vitamins.

• Food rich in Vitamin C should be cooked in boiling water

Do's and dont's of Cooking

• Minimum quantity of water should be used• Extra water should not be thrown away rather

food should be simmered in it, so that the nutritional value of food is intact.

• Food should be cooked in shortest duration to minimise the loss of heat sensitive vitamins

• Food should not be over-cooked.• Except for green leafy vegetables all other food-

stuffs should be cooked in a covered vessel so as to minimise the loss of volatile substances.

Do's and dont's of Cooking• In order to retain the colours of fruits and

vegetables the following points should be kept in mind:– Green coloured vegetables should never be cooked

in acidic media, to prevent the changing of natural green to olive green colour.

– Green vegetables should never be over cooked.– The addition of a small amount of soda darkens the

colour of green vegetables.– The carotenoids providing yellow colour to fruits and

vegetables remains unaffected in both acidic and basic media

Do's and dont's of Cooking

– Flavours and flaveuols (onion)providing white colour to vegetables and fruits turn yellow in alkaline media.

– Anthocyanins (water soluble pigment) providing red or purple colour to fruits and vegetables changes to bluish green in alkaline media.

– To prevent it, an acidic fruit should be added to alkali media although there is enough acid in the fruits or vegetables to protect its colour.

Do's and dont's of Cooking• Foods with high protein contents should not be cooked at high

temperature as high temperature denatures the protein and denatured proteins are insoluble in water.

• Dryness of cooked frozen food also denatures the proteins.• In cases of meat in which there is a high protein content high

temperature causes coagulation of protein thereby making meat less palatable and less digestible.

• Vitamin C is easily destroyed by oxidation, so food rich in Vitamin C should not be cut and left for a long time before cooking.

• The fruits and vegetables which turn brown on exposure after cutting due to enzymatic action should be immersed in salt or soda water immediately after cutting.

Do's and dont's of Cooking

• Soda should not be added to food while cooking as it destroys Vitamin B complex.

• A number of spices should not be added to food at a time, as it covers the natural flavour of the food.

• Many flavouring agents should not be added in the same recipe, as it leads to destruction of all flavours . e.g avoid using coriander leaves and curry leaves together.

• Ingredients should be measured in right amounts.• While baking food stuff should be placed in a preheated

oven which should not be opened frequently while cooking.• Fried foods should be taken our and placed on a tissue so

that the extra fat is soaked by the paper.• Fried stuff should be stored in air tight containers to

prevent their contamination

Effect of cooking and heat on food and nutrients

• Boiling– Can result in nutrient loss– Vitamin B & C are water soluble and are

destroyed when submerged in water

• Steaming– Most nutritional way of cooking– Vitamins are kept intact as food is surrounded by

steam and heated through

Effect of cooking and heat on food and nutrients

• Baking– Results in the loss of nutritional value in foods– Higher the temperature and longer the cooking

time, the more likely nutrients will be lost• Slow Cooking

– Cooking foods in a pot for several hours can cause nutrient loss.

– Food should be heated until just cooked through to retain the most nutrients.

• Microwaving– It is a good cooking method to keep the most

nutritional value in foods, as long as no water is added.

Effect of heat on Proteins• Much edible animal material is made of proteins, including

muscle, offal, and egg white. Almost all vegetable matter from vegetable based products, also includes proteins although generally in smaller amounts. They may also be a source of amino acids.

• When proteins are heated to near boiling point they become de-natured and change texture.

• In many cases the structure of the material becomes softer.• In some cases proteins can form more rigid structures such as

the production of stable foams using egg whites. • These are believed to be formed through the partial unraveling of

the albumen protein molecules in response to beating with a whisk.

• The formation of a relatively rigid but flexible matrix from egg white provides an important component of much cake cookery and also many desserts based on meringue.

Effect of heat on Fat• Fats and oils come from both animal and plant sources.• In cooking, fats provide tastes and textures.• The most significant attribute is the wide range of cooking

temperatures that can be provided by using a fat as the principal cooking medium, rather than water.

• Commonly used fats and oils include butter, olive oil, sunflower oil, lard, rapeseed oil or Canola, and peanut oil.

• The inclusion of fats tend to add flavor to cooked food even though the taste of the oil on its own is often unpleasant.

• This fact has encouraged the popularity of high fat foods.• Oils are commonly emulsified with water-based fluids such

as vinegar or lemon juice to make mayonnaises. In this the fatty content of egg yolk is used as the emulsification agent

Effect of heat on Carbohydrates

• Carbohydrates used in cooking include a variety of sugars and starches including cereal flour, rice, arrowroot, and potato.

• Long chain sugars such as starch tend to break down into more simple sugars when cooked or made more acidic, such as with lemon juice or vinegar.

• Simple sugars can form syrups. If sugars are heated so that all water of crystallization is driven off then caramelization starts with the sugar undergoing thermal decomposition with the formation of carbon and other breakdown products producing caramel.

• Cooking is a process that is adopted to make food easily digestible, destroy the disease causing germs and to enhance its taste and flavour

Effect of cooking on key nutrients• Carbohydrates: The starch swells during cooking and gets

gelatinized . Thus cooking helps in proper digestion.

• Proteins: Moderate heat splits proteins and shrinks it in size. As a result it becomes easily digestible. However, severe heat such as during roasting, baking and frying reduces the nutritive value of proteins.

• Fats: Deep little adverse effect on the cooking oil

• Vitamins A & D: Frying and roasting can result in loss of the vitamins due to oxidation by air.

• Thiamine: About 20%-50% thiamine is lost. Riboflavin: This vitamin is lost while cooking due to exposure to strong heat, light and discarding water after cooking. It is also lost if you add soda for cooking dals and vegetables.

Effect of cooking on key nutrients• Folic Acid & Vitamin B12: Both these vitamins

are lost during cooking methods such as pressure cooking, roasting or by frying. In addition to the loss of heat, folic acid and vitmain B12 are also lost when excess water is discarded after cooking.

• Vitamin C: This vitamin is lost by oxidation due to exposure to air and by discarding excess water after cooking. After 10%-60% vitamin C is lost during cooking depending upon its method and the vegetable cooked.

• Calcium and Phosphorus: These minerals are lost when excess cooking water is discarded.

Effect of cooking on key nutrients

• Iron: It is lost when excess water is discarded after cooking. Iron percentage of food increases if vegetables are cut with iron knife or are cooked in cast iron pans.

• Sodium, Potassium & Magnesium: These minerals are lost when excess water is discarded after cooking . Addition of common salt increases the sodium content of food. Increased sodium decreases potassium levels.

Preparation before Cooking

Pre-cooking Procedure Commonly needed for

Cleaning/washing Cereals, pulses, fruits and vegetables

Peeling Vegetables, fruits

Cutting Vegetables, fruit, cheese

Pounding Rice, spices, masalas, meat

Grinding Batters, chutneys, masalas, cereals, dals

Beating/ Whipping Eggs, cake, mixtures, ice-creams

Soaking Cereals, dals, legumes

Sprouting Cereals, dals, legumes

Mixing Batters, masalas

Kneading Dough for puri, parantha, chapathi, mathi

Fermenting Dosa, Idli, Dhokla, Bread, Bhaturas

Grating Cheese, vegetables, fruits, coconut

Common pre-cooking procedures

• Cleaning/ WashingUse of clean raw materials for cooking is very important to ensure microbiological safety of foods. The dry ingredients like cereals, and pulses are cleaned to remove stones, dirt and other foreign matter before they are used for cooking.

• PeelingAll fruits and vegetables have a firm outer covering which protects the inner portion. This is called peel. If the peel is too tough to be cooked or digested it should be removed before the fruit or vegetable is cooked

Common pre-cooking procedures

• Cutting– Most of the vegetables and fruits are cut before use.

Cutting vegetable in uniform pieces helps them to cook faster as more surface areas are exposed to heat.

– It mixes well with other ingredients in a dish and is easier to eat.

• Pounding– When a pestle and mortar are used to crush foods to

make them smaller in size or flat, it is called pounding. – It leaves food in a desirable form to be used.– Meat, rice, spices etc. are at times pounded to make

cooking faster

Common pre-cooking procedures

• Grinding– Grinding of food can be done using a

traditional stone or in electrically operated mixers or grinders

– It reduces food to a very fine form.– Food can either be ground in a dry or a wet

form.

• Soaking– It implies immersing food in water to make

them soft so that cooking or grinding is faster.

Common pre-cooking procedures

• Sprouting– It is used for whole grains or legumes.– Grains are soaked in water, tied in a wet

cloth and allowed to germinate for 2-5 days.– Longer the period, lengthier the sprout will

be.– These are used for making salads or curries– Sprouting increases certain nutrients and

digestibility of food.• Mixing

– Mixing is one of the frequently used methods of preparing foods while and after cooking. e.g mixing batter for pakoda

Some pre-cooking procedures• Kneading

– For some preparations like chapati, after mixing, the dough needs to be very well blended by applying pressure using hands.

– This is called kneading which helps to make chapatis softer.

• Fermenting– This helps to improve texture, taste and

digestion of food.– It increases the shelf life.– It is used for preparation of bread, dosa, idli

etc. – The dough is allowed to become sour after

mixing or grinding.– Fermentation is natural but its speed can be

accelerated by using yeast– Fermentation increases B complex vitamins

in foods.

Some pre-cooking procedures

• Beating/whipping– It allows to incorporate air in a

product so that it will have a soft, spongy texture

• Grating – Some foods are grated or

shredded to small pieces to make cooking easier or to just ad variety to cooking

The Shortening Power of Fats

• The shortening power of certain fats make them essential in the preparation if pastries, pie crusts, biscuits and cakes.

• The more highly saturated fats tend to have greater shortening power.

• Incorporated into a flour mixture, fat separates the flour's starch and protein and when heated melts into the dough, leavening the air spaces that give the finished product its characteristic delicate texture.

• A fine grain from certain cake and cookie batters with the use of shortenings that gently encase the numerous air bubbles, serving as a starting point for the air to expand and increase overall volume.

• Baked goods also become more tender, up to a point, as fat concentration increases.

The Shortening Power of Fats

• The surface area covered determines the shortening power of a fat or oil in baked products.

• The degree of shortening produced by a fat or oil in a given product depends primarily upon the surface area of the flour particles covered by the fat or oil

Manipulation• The manipulative factors include creaming, the

thoroughness with which the fat is mixed with flour, and the manner or rolling, kneading etc.

• In products containing sugar, if the fat and sugar are creamed so that air is incorporated, the product may be shorter or more tender.

• This will depend on the proportion of fat and sugar and whether the maximum amount of air is incorporated .

• The increased shortness of the product may be attributed to the increased porosity.

• Creamed fat is also more plastic and thus more easily blended with flour.

• In addition the sugar crystals absorb fat which may aid in distributing fat in a batter but will probably reduce the area of the flour covered by the fat and thus tend to reduce the shortening power of the fat

Temperature

• Temperature affects the plasticity of a fat and mobility of a melted fat or of an oil.

• At lower temperature the plasticity of fats such as butter is not great.

• At higher temperatures the surface area covered by a melted fat may decrease because of the increased tendency to form an oil-in-water emulsion.

• In addition, in temperatures at which the fat is melted or very soft the gluten absorbs water rapidly and becomes developed rapidly

Technologies –Do Not Harm Environment

Solar Cooker A Parabolic Cooker

Solar cookers use a couple of different methods to harness this heat.The box cooker is a simple type of solar cooker. At maybe 3 to 5 feet (1 to 1.5 meters) across, it's essentially a sun-powered oven -- an enclosed box that heats up and seals in that heat. At its most basic, the box cooker consists of an open-topped box that's black on the inside, and a piece of glass or transparent plastic that sits on top. It often also has several reflectors (flat, metallic or mirrored surfaces) positioned outside the box to collect and direct additional sunlight onto the glass.

To cook, you leave this box in the sun with a pot of food inside, the pot sitting on top of the black bottom of the box. When sunlight enters the box through the glass top, the light waves strike the bottom, making it scorching hot. Dark colors are better at absorbing heat, that's why the inside is black. The molecules that make up the box get excited and generate more heat. The box traps the heat, and the oven gets hotter and hotter. The effect is the same as what goes on in a standard oven: The food cooks.Box cookers can reach up to 300 degrees F (150 degrees C). That's hot enough to safely cook meat.

A Parabolic Cooker• A parabolic cooker can get even hotter, up to 400

degrees F (204 degrees C), which is hot enough to fry food or bake bread. This slightly more complicated design uses curved, reflective surfaces to focus lots of sunlight into a small area. It works a lot like a stove, and it's big, sometimes up to several feet across.

• A pot of food sits on an arm that holds it in the center of the curved reflectors, suspended slightly above the bottom point of the oven, where all the light is concentrated. This small point gets so hot -- and the molecules vibrate so much -- that the heat waves move upward in a steady stream to strike the bottom of the pot.

Biogas• Biogas systems make use of a relatively simple, well-known,

and mature technology. • A biogas system comprises a large tank, or digester. Inside

this tank, bacteria work symbiotically to convert organic waste into methane gas through the process of anaerobic digestion.

• Each day, the operator of a biogas system nourishes the bacteria inside the digester with household by-products such as market waste, kitchen waste, and manure from livestock.

• The methane gas produced by the bacteria inside biogas system may be used for cooking, lighting, and other energy needs. Waste that has been fully digested exits the biogas system in the form of organic fertiliser.

Benefits of Biogas• Biogas has several external benefits: • biogas replaces the unsustainable use of

biomass, • slows deforestation and • reduces greenhouse gas emissions; emissions

of methane (a strong greenhouse gas) associated with the decomposition of livestock manure are mitigated;

• the import of both kerosene and foodstuffs are reduced, thereby improving the trade balance; and healthcare costs are decreased through improved indoor air conditions and better environmental sanitation.

Biogas Cooking• Cooking on biogas is easy and efficient. A biogas stove

is analogous to the gas stoves found in many western homes.

• Biogas stoves are safe for indoor use and a switch to biogas will eliminate the dangers of indoor air pollution – a threat to the lives and livelihoods of women and children in many (sub)tropical regions.

• The alleviation of health risks associated with indoor air pollution may directly result in a reduction in healthcare costs and as well as an increase in productive days.

• Moreover, cooking on biogas is fast. Biogas eliminates the process of preheating, which is a necessary step when cooking on biomass

Nutrients lost during cooking

• Vit A is found in methi,spinach,carrot . When we cook veg not much of Vit A is lost ,but when we fry Vit A gets destroyed as it dissolves easily in fats and oils.

• Vit B: When we wash rice it washes away Vit B as it is water soluble. The more you wash more Vit B is washed away .We add cooking soda to rajma,channas which destroys Vit B

Nutrients lost during Cooking• Vit C : When we cut vegetables nutrients are easily destroyed by

cooking.Vit C is lost when we wash veg and fruits after cutting and exposing the cut vegs to air for longer period of time.

• Cooking soda also washes Vit C when added to food.• Proteins: All proteins present in food gets coagulated by heat.

Cooking results in softening of proteins in food such as egg, fish and meat . If the coagulated protein is heated , it looses moisture and becomes dry and rubbery and becomes difficult to digest.

• Oils and Fats: When fat is heated it has the tendency to separate from food. Eg heating milk results in the fat layer on top. If fat is heated over and over again ,to fry pakoras and bhajias its quality becomes poor.

• Minerals: Sodium ,potassium dissolve in water . Minerals get lost when food is first cut ,then washed and extra water in which they are boiled ,is thrown away.

Enhancing Nutrients Content of Food

• To meet the nutritional requirements of the body.• To make proper selection and preparation of

foods.• To consume food in a balanced manner.• To improve the flavour and texture of the food.• To get variety in food.• To assist in planning the daily menu, keeping in

view the nutrient content of the food.• To prevent deficiency diseases in the body.• To develop good food habits.

Methods of Enrichment of Nutrients.

• Combination: Combining of foods from different food groups is the easiest way of eating all nutrients.

• i) Eat a diet that has good quality nutrients.

• ii) Use cheaper and easily available foods that enhance the nutrient content of food considerably.

• iii) Provide balanced diet to your family.

• Fermentation: It is a process in which some micro-organisms are added to the food. They change nutrients already present in the foods into simpler and better forms and also make other new nutrients.

• Fermentation improves the digestibility of foods

• Foods become spongy and soft and are liked by children and adults.

Germination: It is a process in which small shoots come out of the dal or cereal when these are kept with small amount of water. The grains and pulses to be sprouted need to be soaked in just enough water so that all of it is absorbed. If the extra water in which they are soaked is thrown away, you will be loosing a lot of nutrients i)Increase the digestibility of foods. Do you know why?a) Some carbohydrates and proteins are broken down into smaller and easily digestible forms.b) Grains and pulses become soft after sprouting, so they take less time for cooking and are easy for you to digest.ii) Increase the nutritive value of food with no additional cost.