Methods of food processing


Food has been processed since communities first come together thousands of years ago. Most need some form of processing and preparation to make them more attractive to eat. Grains, vegetable, meat and fish are each un-palatable in their raw state and some food, such as cassava are dangerous if eaten, with processing are edible. Even nuts, milk and fruits that are eaten raw can also be processed late a wide range of other products.

Processing does more than change the eating quality of raw food, all foods are biological material that begins to decay as soon as they are harvested the deterioration and thus allow food to be preserved for extended periods.

Processing offer opportunities for village to diversity their source of income. When farmer in an area grow similar crops, processing help to avoid the effect of lowered prices and income when seasonal glut occurs at harvest time. Processing also enable farmer who grow low-value staple crops to add value and increase house-hold income, for example, in many African countries processing cassava into garri or snack food can form very successful small scale business in many Asian countries, values is similarly added to fruits and vegetables by processing them into a wide range of pitches, chutney and other relishes.

The small scale operation is major source of employment in rural villages estimated at up to 60% of employment in some countries. Many government and international development agency promote food processing as a means of alleviating poverty in rural area. These are many advantages in choosing food processing over other income generating activities.

Definition of food processing

Food processing is the set of method and techniques used to transform raw ingredient into food or to transform food into other forms for consumption by human or animal either the home or by the food in or industry. Food processing typically takes. Clean, harvested crop or slaughtered and butcher animal product and use these to produce attractive, marketable and often long-life food. (Noble Science Publishers)

Food processing method

Food can be processed inexpensively by using canning, freezing or drying techniques.

But firstly the method of processing food is as follows;

  • Drying
  • Refrigeration
  • Fermentation
  • Processing by use of heat
  • Canning and boiling
  • Picking
  • Frying
  • Roasting
  • Hanging Basket
  • Potting
  • Jugging
  • Jelly


Drying is the oldest method known for preserving and processing food. When you dry food, you expose the food to a temperature that’s high enough to remove the moisture or water out, low enough that it doesn’t cook. Good air circulation assists in evenly drying the food, also drying lower the moisture content of foods to create an unfavourable environmental condition for the action of food enzymes and micro-organisms hence preventing spoilage.

Types of drying

  1. Sun (solar) drying: It is the oldest method of food processing, practiced by most communities in the tropics food product mostly raw foods are dried through the exposure to direct energy from sun rays. Foods such as maize, millet, yam, cassava, pepper, okra, vegetable, pawpaw e.t.c are usually dried in the sun.
  2. Dehydration: in this drying technique, moisture is removed from foodstuff while heat energy is supplied to the foods. Mechanical devices called dehydrates are used in transferring heat energy to foods in the process of dehydration. These include radiant microwave drier, hot air driers, infrared drier and vacuum drier. Foods such as eggs, meat, fish, cereals, vegetable and milk are often dehydrated.
  3. Freeze drying: It is a method used in freezing food materials and lowering moisture using a low vacuum in a process called sublimation. Foods such as vegetables, fish and meat are dried by freezing.

We also have roller drying, oven drying and spring drying.

Importance of drying

  • Dried foods have shelf or storage life.
  • Sun drying is less costly than most method of processing.
  • Drying eliminates wastes.
  • Dried foods contain less weight and not bulky therefore they require less storage space, less transportation and less handling cost.
  • Dehydrated foods contain higher total solids than other foods.

2)    Refrigeration

The activities of micro-organism (e.g. Bacterial, yeasts, and moulds) are adversely affected by low temperature hence refrigeration has become one of the most widely used means of food preservation on. Refrigeration is a general purpose devices or cabinet in which foods are kept cold, and also refrigeration is the act of preparing, packing, and can freeze most fresh fruit and vegetables, meat and fish, bread and cake, and soup.

Refrigeration is of two types

  • freezing
  • chilling


  • Freezing: Freezing describes a state in which food is held at temperature for below freezing point. In freezing a relatively low temperature of about -180C (00F), which is for below chilling is required. Freezing is commonly called freezer storage or deep-freezer storage and article kept in the freezing compartment are said to be deep frozen. Food poisoning organism e.g. salmonellae are destroyed in deep freezing processing. Food usually preserved in deep-freezer storage includes meat, fish and poultry. Frozen food that has thawed should not be refrozen.
  • Chilling: Chilling is also called cold storage. It is a units operation in which the temperature o f food is reduce to temperature between -3 and 4cC (26.6 and 450F) which retard micro- organism activities. Chilling prevent growth of pathogens. Several fresh foods are refrigerated in chilling storages e.g. fruits, milk, eggs, vegetable, poultry and meat.


  1. Fermentation      

This involves the decomposition of some of the food component to produce and that makes the food unfavourable to micro-organism e.g. locust bean seeds (iru), melon seeds (ogiri),cassava (Akpu), maize, ugba, alcoholic beverages such as kaikai and palm wine.

Fermentation improves the flavour and texture raw agricultural produce imparting a desirable sour taste to many foods such as garri and pap and leading to the production of distinct flavour component characteristics of many fermented foods. Fermentation may lead to significant improvement in the nutrition quality of food by increasing the digestibility of proteins.

4. Processing by the use of heat


This is a broad term which include baking, boiling, roasting, frying and stewing. The former three methods is that baking, boiling and roasting required dry heat (temperature greater than 2120F) while boiling and stewing required moist heat. Frying involves cooking in oil at a temperature such as higher than 2120F – foods such as yam, potato, plantain, chicken, fish, meat, e.t.c. can be processed by cooking.

Some changes that take place due to cooking are;

  1. Destruction or reduction of micro organism and inactivation of undesirable enzymes take place due cooking of food.
  2. Changes in colour, flavour and texture take place due to cooking of food.
  3. Improved of digestibility of food components of those produce by micro-organism.


It is the heat treatment of food prior to freezing, drying or canning. Blanching inactivate enzyme and remove tissue gases. It also increases the temperature of the tissue and wilting of the tissue facilitates packing. e.g. slices of Yam for Elubo production are heated in hot in a pot for some time.


It is the heat treatment that kills partly but not all pathogenic organisms, it issued for foods which are to be further handled and stored to minimized microbial growth. Example of food processed by pasteurization is milk.

The two process of pasteurization are;

  1. HTST or high temperature short time method in which food is held at 1010F for 15 second and cooled rapidly.
  2. LTLT or low temperature long time method in which food is held at 1450F for 30 minutes and cooled rapidly.


This is another way of preserving and processing farm produce like chicken, meat, fish, sweet potato and plantain. Vegetable oil or palm oil could be used for the frying. Frying remove water from the farm produce and the fried foods can be kept for a long time without spoiling. Fat oil is gotten from different product, for oil, oil is gotten from palm tree or extracted from palm fruit while groundnut oil is extracted from groundnut.


Canning is a method of food preservation in which ca-fully selected and prepared food stuffs are filled” into cans and air is expelled from the cans. The can sealed and heated to a specific temperature of about 1200C for a period of time according to the size of the cans and nature of food being canned.

Canning is a dependable source of food processing which record only minimal incident of food poisoning certain food product (e.g. meat) are partially cooked before being packed into cans, other are only sterilized after cans or bottles are sealed.


Below is the principal units operation of caning;

  1. Cleaning and preparation of food: Extraneous matter, contaminants, inedible parts and all unwanted particle are removed from raw food, and the food is washed afterwards. Washing reduces contaminant and micro organism population in the food to a minimum. Food preparation process involve activities such as peeling, slicing, trimming, slaughtering and cutting depending on the product size and market or consumer demand.
  2. Blanching: food product such as vegetable and fruits are usually blanched for some few minutes. They are immersed or exposed to live steam which drives out air bubbles in the food thereby causing food shrinkage. Blanching also destroy autolysis enzymes. That cause colour changes in food.
  3. Filling; in most countries, automated filling machines are used to fill food material such as meat, fish, vegetable, fruit juice, milk, bear and beverage into already washed or cleaned cans or bottles.
  4. Vacuuming and sealing; cans are subjected to an exhaust box or vacuum machine which create air free vacuum on top of cans. In exhausting operation cans are heated with steam to expel residual air.
  5. Sterilization; High temperature between 1040C and 1200C are used in heating or cooking the sealed container for sufficient time in order to destroy pathogenic food spoilage micro organism and their spores.
  6. Cooking after sterilization procedure: The cans, bottles or glass containers are immediately cooled at temperature of about 380C (1000F). This is necessary to prevent product from over-heating or over cooking which could destroy some food nutrient.
  7. Labelling and packing; label is the printed matter found on the body of canned or bottled product.


Roasting is another method of processing food. This impact desirable sensory qualities, enhances palatability, reduce anti-nutritional factors. Peanut and are roasted by stirring in hot sand in a flat bottom frying pot over hot flame.

Hanging basket

Hanging basket over the cooking area for preserving and drying food    e.g. fish.


This method relies on the use of clay pot that are lined with sand and kept cool through the addition of water. This method relies on evaporation and therefore only work when the weather is dry. The use of pot-in-pot fridge helps to ensure that the farms produce remain in good fresh condition during the time they stored and prevent decomposition e.g. vegetable.

Benefits of processing food

  1. Increasing the variety of food in the diet.
  2. Food processing creates special foods for cultural or religious occasions, thus re-inferring cultural identities.
  3. Creating opportunities for sales and income generation.
  4. It enables crops to be sold out of seasons when prices are higher.
  5. It enables food to be stored as a reserve against time of shortage increasing food security. (ensure that sufficient food is available and that essential nutrient are eaten throughout the year)
  6. If chosen correctly, processed food can have a good demand and offer the opportunity to generate good profit by adding value to raw material.
  7. Crops or animal that are the raw material for processing are usually readily available.
  8. Often the most different types of processing technologies most are suitable for small. Scale operation with an affordable level of investment by rural people.
  9. Domestic utensils can be used in processing when starting up; when production expands, many types of processing equipment can be manufactured locally by metal workshop or carpenters, therefore, which create further employment.
  10. Most type of processing has few positive environment effects.
  11. Processing help to prolong the shelf life of the food or product.
  12. Processing of food help to easy transportation of food to distant places.
  13. Processing of food to prevent wastage and save surplus for future
  14. Processing of food enable some one to take of emergency situation.
  15. Processing also enable farmer who grow low value stable crops to add value and increase household income.


Food processing and preparation are important to humans, to ensure their food security, it increase variety in people diet and it a means of generating diversified income and employment. Food processing is important to improve the health and nutrition of humans.


Agidi, E.K. (2013) Lecture on Food production for Students of Nutrition and Dietetics. Delta State, College of Health Technology, Ofuoma – Ughelli (Unpublished).

Food and Agricultural Organisation of the United Nation, (2001) Benefit of food preparation and processing for creating healthy families and sustainable livelihoods Michigan department of Agricultural and rural development.

Hull, Janet, M.D, (2006) Bleaching agent in four linked to diabetes from the Idaho Observer cited on .

Noble Science Publisher .

Public Library of Science (1992). “Benefit of processing food”. .

Wilson, Lawrence, M.D, F.I.C.B, (2001) why take nutritional supplement.

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