Saturday, June 5, 2010

Food Preservation

Subject: Food Preparation & Service

Lesson 8

Grade : 9

Unit Entrepreneurship

Topic: Food Preservation

Time: Two 90 minutes sessions


At the end of lesson students should be able to:

1. Explain what is meant by the term Food Preservation

2. List the method of preservation

3. Sterilize a bottle using heat

4. Use two method of preparation to preserve a food item.

Instructional Aid:

Text, bottle, salt bleach, hot water, vinegar, vegetables

Reference: Text book: Food and Nutrition –By Anita Tull page 140-145


Food can be preserved in order to have them when they are out of season.

- Reason for preservation
- Preservation is the act of preventing natural and microbial decay in food, by modifying the conditions which favors enzyme activity and micro- organism growth.
- Preservation helps to add variety to the diet by providing food out of season, providing cheaper foods and to prevent spoilage of some products.
Aim of preservation should be to: retain color, flavor, texture, appearance and nutritional value.

Method of Preservation
- Heating – to destroy micro-organisms & stop enzyme activity
- Removal of Moisture- drying
- Removal of air- to prevent further entry of micro-organism- sealing & canning
- Reductive of temperature to inhibit microbial growth & enzyme activity (freezing)
- Addition of Chemical preservatives- to destroy or inhibit microbial and enzyme activity

Preservation- Using Heat

Heat will destroy most yeast, bacteria, mould and enzyme at 100 C ( 212 F). However some bacteria and bacterial spores are resistant to such temperature and require higher temperature to destroy them.

The main method of heat treatment are:
a. sterilization- as in milk and canned or bottled food this may however destroy heat sensitive, vitamins thiamine and vitamin C. Color and flavor of mild maybe changed.
b. Pasteurization- is a less severe heating & rapid cooling. This only destroys the harmful microbes, the food will not keep for very long as other naturally occurring microbes in the food will begin to cause decay. Some products using this method – are- milk and milk products. Fruit juices, liquid eggs, vegetable juices, beer , vinegar and wine
c. Canning  and bottling: both of these methods rely on heat sterilization to destroy microbes and enzymes and sealing to prevent contamination.

Removal of Moisture

Dehydration is a very old method of food preservation where moisture is removed from food by leaving to dry in hear such as the sun, or spray through rotating tray with dry heat. Method of moisture removal are:

1. Roller drying – not used much

2. Spray drying – use on products like egg, milk

3. Accelerated freeze drying

Food preserved by dehydration are milk, coffee, tea, fish , meat, vegetable, pulses, egg, soup, instant snack. Many of these can be reconstituted by adding water.

- Students and teacher will discuss reasons for preserving food

- Types of preserved food. Class discussion on important points above.

- Sterilizing a jar using boiling or bleaching.

- Preparing- pickled vegetable, cucumbers , chocho ,carrot, pepper,  etc.
Example fresh firm vegetables.Carrot and chocho.
2.wash peel and cut using different types of decorative cuts.
3. Sprinkle with salt and leave in salt water for 2-3 hours in the refrigerator
drain off water and .
4. Blanch in hot boiling water for 2 minutes.
5. strain and pack into jars. cover.
boil 1 pint vinegar with 2tbsp sugar and 1tsp salt.pour over vegetables and cover hot


Students answer a short quiz on the process they went through to preserve the vegetable and the ingredients used.

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