Transcript Cooking of Food

Cooking of Food
Cooking
• 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
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
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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 wellcooked. 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 foodstuffs 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 denatured 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/ Washing
Use 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.
• Peeling
All 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
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 opentopped 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, wellknown, 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
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.