Download Preparing Food VT

Preparing Food
© ORCA Education Limited 2005
New
Words
Why Cook Food?
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Cooking destroys harmful bacteria:
it is more appetizing
improves appearance, flavour, texture
and smell
aids digestion
makes food easier to eat
preserves food to stop it decaying
improves and enhances flavour
gives variety in the diet
reduces bulk so more can be eaten.
What different ways are there
to cook potato? *
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The Transfer of Heat
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Heat energy is used for cooking.
It can be transferred in three ways:
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Conduction; heat is conducted
from one molecule to another.
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Convection; liquids and gases
create convection currents
transferring heat to the food.
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Radiation; heat travels from one
object to another in waves or rays
e.g. barbeque, grill or microwave.
Most food is cooked using more
than one method of heat transfer.
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How is heat transferred
for baking bread? *
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Conduction from the hot
grill
bars cook food
stripes
Conduction
on
the fish
surface
against
the
hot
casserole pan
Convection
of stock
The frying pan conducts
heat directly to the fish
Convection
Heat
from
Heatof
from
thecoals
fire
hotthe
air
radiates
the food
heats thetofrying
pan
Moist Methods of Cooking
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Food can be cooked in four ways
according to how heat is applied.
Moist methods involve heat being
applied through liquid such as
water, milk, steam, stock, wine, etc.
This method uses relatively low
temperatures over a long period.
Prolonged moist cooking causes
water soluble vitamins C and B to
be leached into the cooking liquid.
Some moist cooking examples are:
What type of foods would be
suitable for this method? *
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pressure
cooking
stewing &
braising.
poachin
g
simmerin
g
steaming
boilin
g
Dry Methods of
Cooking
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In dry cooking, as with these
sausages in a commercial oven,
heat is applied directly onto food.
Other examples are roasting,
grilling and barbecuing.
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During dry methods of cooking
e.g. grilling (toasting) or baking,
heat turns starch a light golden
colour known as dexrinisation.
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When sugar is heated under the
grill, it turns brown called
caramelisation.
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How does dry cooking change
the nutrients in food? *
Frying
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Heat is applied through fats or oils.
Some fat is absorbed increasing the
the fat content of the food cooked.
In frying high temperatures destroy
heat sensitive nutrients.
In deep frying the food is immersed
in fat or oil at up to 200ºc.
Butter or margarine can be used for
shallow frying as temperatures are
not as high.
Foods high in fat can be dry fried
using non-stick pans.
What other method of frying
is more healthy? *
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Microwave Cookery
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Microwaves generate heat by
electro-magnetic rays from a
magnetron valve.
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Microwaves are reflected off
the metal walls of the cooker
and are absorbed by the food.
They vibrate millions of times
a second causing friction and
heat in the food molecules
Paper china and some plastics
allow microwaves to pass
through them.
This method of cooking is
very quick, therefore there is
less destruction of nutrients.
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Which foods are not suitable
for microwave cooking? *
Preserving Nutrients
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Vegetables and fruit contain the
water soluble vitamins B and C
which dissolve into cooking water.
This loss can be minimised by
careful preparation and cooking.
Cook with a lid on and cook for
the minimum amount of time.
Vegetable water can be
used for gravy.
Eat cooked vegetables
immediately.
Steaming vegetables reduces
loss of nutrients from leaching.
Oxygen in air and water encourages
the destruction of vitamin C.
Avoid peeling as vitamins and
minerals are under the skin.
Vegetables should be chopped
quickly and leaf vegetables torn not
cut to avoid tissue damage.
What is the best way to
cook cabbage? *
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Which Method of Cooking?
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You have a chicken and some
vegetables to cook.
Your choice of cooking method will
depend on:
time for cooking and preparation
facilities available
nutrient loss and healthy eating need
the needs of the individual
e.g. small child or adult
individual preference on
taste, texture, smell and
flavour.
From the points above decide
on a set of circumstances..
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..how would you then cook the
chicken and vegetables? *
Macro-Nutrients & Heat
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How has an increase in temperature caused
these foods to change?
Protein foods like the meat are permanently
changed called denaturation.
Meat like this chicken hardens and darkens.
Other proteins like eggs coagulate and set.
The starch grains in the stew break open
and form a gel with the liquid called
gelatinisation which thickens the liquid.
When toasting or baking as with the roll the
dry heat turns starch to dextrin.
The fats in the meat melt to a liquid when
heated.
Fats can decompose at a high temperature,
give off a bluish haze and burst into flames
called the flash point. *
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and suppliers, all rights reserved
Acids in Cooking
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Acids effect flavour, appearance, texture and
nutritional value of food.
There are several kinds of acid used in these foods.
Citric acid (lemon juice) helps pectin make a gel
for the jam. It also prevents enzymatic browning
of cut fresh fruit and coagulates protein in cold
desserts using cream.
Acetic acid (vinegar) is used in preserves like
chutney, it marinates meat to tenderise it and
gives a sharp flavour to salad dressing.
Ascorbic acid (Vitamin C) is used as flour
treatment for yeast fermentation.
Tartaric acid(cream of tartar) is used with
bicarbonate of soda in baking.
Lactic acid starter is used to coagulate milk in
cheese making. *
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and suppliers, all rights reserved
Alkalis
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These scones rely on alkalis for their light
open texture.
Alkalis are used in cooking as raising agents.
When these are mixed with
other ingredients and heated, a
chemical reaction takes place
and carbon dioxide is produced.
There are 3 types of chemical
raising agents:
bicarbonate of soda
bicarbonate of soda and acid
(sour milk or cream of tartar)
baking powder.
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and suppliers, all rights reserved
How are these 3
types different? *
Vocabulary
Some words or terms to learn
bacteria
 pressure cooking
 poaching
 leached
 water soluble
 tissue damage
 coagulate
 tenderise
 raising agents
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© ORCA Education Limited (2005)
and suppliers, all rights reserved
conduction
 convection
 radiation
 braising
 microwaves
 gelatinisation
 marinate*
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The Task
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You can enter here a task for your students.
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and suppliers, all rights reserved
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