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Thursday, 15 November 2012

Monday, 5 November 2012

Exercise 2

Answer all the questions.

1.  Diagram below shows a study done on the process of freezing as a method of preserving chicken meat.  Both P and Q were tied in a plastic bag and kept in two different conditions.

(a)  Predict what would happen to the chicken meats P and Q.


(b)  Why do you think that freezing method can be used to preserve chicken meat effectively?


(c)  Suggest one other method that can be used to preserve chicken meat.


(d)  What is the advantage of freezing as a method of preserving food?


(e)  Name two other types of food that can be preserved by freezing.

1.  ___________________________
2.  ___________________________

2.  Diagram below shows the label that contains the information on how the coconut jam is made.

(a)  State three steps involved in the preservation of the coconut jam.

      1. ______________________________
      2. ______________________________
      3. ______________________________

(b)  State two functions of sugar in the jam.

      (i)  _______________________________

      (ii)  _______________________________

(c)  When the cap was left open for three days, it was found that the jam became spoilt.  Give your inference for the above observation.


(d)  Suggest one way to keep the jam in good condition for a longer period of time.


Saturday, 3 November 2012

Exercise 1

Choose the correct answer.

1.  What are the characteristics of spoilt food?

     I    Change of colour
     II   Gives out pleasant smell
     III  Mouldy
     IV  Becomes hard

     A  I and II         C  II and III
     B  I and III        D  III and IV

2.  Which of the following statements is true?

     A  Microorganisms grow well in the surroundings with a temperature above 65° C
     B  Microorganisms does not need water to grow
     C  Microorganisms grow well in warm and damp condition
     D  Microorganisms can live without air

3.  Mrs Chan found out that a piece of meat she bought was spoilt.  How did she know it is spoilt?

    A  It is slimy
    B  It smells nice
    C  It becomes hard
    D  It becomes bloated

4.  Which of the following are true about bacteria?
     X: All bacteria cause diseases
     Y: Bacteria cause food to turn bad
     Z: Bacteria can be destroyed by boiling

     A  X and Y only
     B  X and Z only
     C  Y and Z only
     D  X, Y and Z

5.  Which of the following conditions is not necessary for the growth of bacteria?

     A  Moisture
     B  Temperature at about 20°C
     C  Strong acidic medium
     D  Suitable nutrient

6.  Which of the following food preservation methods will not change the taste of the food?

     A  Pickling
     B  Salting
     C  Canning
     D  Freezing

7.  Diagram below shows two types of food.

     Which of the following methods are suitable to preserve the food shown?

     I    Pickling
     II   Canning
     III  Freezing
     IV  Pasteurising

     A  I and II       C  II and III
     B  I and IV      D  III and IV

8.  Diagram below shows a tin of milk.

     The milk in the tin shown is not safe for consumption because

     A  the tin is dented
     B  the tin is rusty
     C  the tin is broken
     D  the tin is leaking

9.  Diagram below shows a piece of meat.

     Which of the following properties of the meat is not changed by smoking?

     A  Colour
     B  Shape
     C  Taste
     D  Nutritional value

10.  The following are steps involved in the canning process

       W: Air is expelled from the can
       X: The empty can is heated strongly
       Y: Food is filled into the can
       Z: The tin is cooled down

       Which of the following shows the correct sequence of the steps?
       A  W --> X --> Z --> Y
       B  X --> W --> Y --> Z
       C  Y --> Z --> W --> X
       D  Z --> Y --> X --> W

Thursday, 1 November 2012


Waxing of fruit and vegetables is also common.  Apples, oranges, eggplants and tomatoes are dipped into liquid wax to prevent growth of fungi and loss of moisture.

Mighty Microbes

Food undergoes changes that makes it spoilt.  These changes can be detected by their smell, taste, touch or sight.  Spoilt food is unsafe to eat.

Fish is no longer fresh when the flesh has changed texture.  It is no longer firm when pressed with a finger.  It also has an unpleasant smell.  

Stickiness under the chicken wings and darkening of their tips indicate spoilage.

We are blessed with many varieties of food.  However, our food may be infected with microorganisms.  Microorganisms such as fungi and bacteria can cause food to spoil.

The fruit and vegetables in the picture have been affected by moulds.  They become mouldy and change colour.

Food turns sour because the bacteria in it produced acids.  A common example is when milk turns sour, giving it an unpleasant taste.

It is possible for drinks in cartons to spoil.  When it is opened, frothy liquid and an unpleasant smell will indicate spoilage.

There are certain conditions that make this happen.  Microorganisms that cause food to spoil need air, water, nutrient, suitable temperature and suitable acidity to grow and multiply.

Microorganisms need air and nutrient to grow.  They grow on the surface of food when air is present.  The food provide nutrient for them.

Microorganisms also need water to survive.  Water in the food and moisture provide suitable environment for bacteria and fungi to grow.

Microorganisms will grow within a range of suitable temperature, which is between 5°C and 65°C.  They will grow slowly or not at all when the temperature is too high or too low.  Similarly, they also need a range of suitable acidity present on the food in order to grow.

Saturday, 27 October 2012


Pasteurization means heating food to a certain temperature for some time followed by rapid cooling.  Heating at such high enough temperature kills most bacteria.  However, it does not affect the taste and nutritional value of the food.

On-the-Farm Milk Pasteurization


Smoking is the process of drying food with smoke for a long period of time.  This method is mainly used for fish, meat and fruit such as banana.  The drying effects of smoke and the chemicals produced from the smoke help to preserve the food.


As food is heated and cooked, the heat kills the microorganisms.  Boiling kills most bacteria.  However, those not affected by heat will grow when the conditions are suitable.

Monday, 22 October 2012

Cooling and Freezing

Cooling and Freezing are the most common forms of food preservation.  Cooling slows down the action of microorganisms, thus it takes longer to spoil.  It allows fruit from different parts of the world to appear on our supermarket shelves.  At freezing temperature, microorganisms become inactive, thus food cannot spoil when it is frozen.

Vacuum Packing

Vacuum packing keeps food by sucking air out from its packaging.  Food is thus prevented from spoiling because there is no air.

Vacuum packing is commonly used for storing nuts, sliced fish, pickled and dried fruit.


Salting, is a age-old way of preserving food.  The salt draws out moisture and prevents microorganisms from growing.  In this process, food such as fresh fish are gutted, washed and coarse salt is rubbed into it.


A lot of food is preserved by drying under the sun.  Drying removes most water from food.  Most bacteria die or become inactive when the food is dried.

Anchovies and dried chillies are examples of dried food.

A lot of fruit such as raisins, guavas and papayas can be eaten dried.

Saturday, 20 October 2012


Pickling food in vinegar or other acids, makes it difficult for microorganisms to live.  Commonly pickled food include onions, parkias, soya beans and chillies.

Sugar can also be used in pickling fruits such as nutmegs, mangoes and cherries.  The concentrated sugar solution used draws water from the fruit, thus preventing the growth of microorganisms.

Friday, 19 October 2012

Bottling and Canning

Bottling and canning are processes of preserving food by heating and then sealing it in an airtight container.  The food is boiled to kill microorganisms and then sealed to prevent other microorganisms from getting in.

Canned Food

Bottling Food

Let's watch how the canned sardine are made

Bottling process