Dehydration as a method of preservation in food processing. Dehydration means the removal of water or moisture from the food using different mechanisms.

1. DEHYDRATION
GROUP 3

2. Contents
 Dehydration
 Theory of dehydration
 Effects of dehydration
 Factors to consider during dehydration
 Equipment used in dehydration

3. INTRODUCTION
Dehydration in food processing and preservation is a method used to preserve various
foods by the application of heat under controlled conditions(temperature, pessure and
time) to remove moist of the water that is normally present in food by the action of
evaporation. However it does not include removal of moisture from food by mechanical
pressing concentration of liquid foods.
Theory of dehydration
Dehydration involves the simultaneously application of heat and removal of moisture
from foods. The primary principle behind dehydration is that microorganism such as
molds, yeast and bacteria require water to grow.
By reducing the moisture content in food through dehydration the microorganism are
unable to strive. These dehydration methods include air drying, sun drying and air
drying. These methods remove water by evaporation or sublimation that results in
reduction of weight and volume.

4. FACTORS TO CONSIDER DURING DEHYDRATION
 TEMPERATURE: Optimum temperature is critical for efficient moisture without compromising
food quality. The temperature at which dehydration occurs affects the quality of the final product.
Generally, low temperatures are required to preserve nutrients and flavour.
 HUMIDITY:Controlling humidity levels in the drying envitonment is crucial. Low humidity levels
facilitate faster evaporation of moisture from the foood, while high humidity may slow can slow
down the process and increase the risk of microbial growth.
 AIRFLOW: Air flow is necessary to carry moisture away from the foodd surface. Adquate air flow
ensures even drying and prevents the formation of pockets of moisture which can lead to
spoilage proper airflow ensures uniform drying and prevents the formation of moisture pockets.

5. DEHYDRATION
FOOD TYPE
Different foods requires different dydration methods and duration. Fruits, vegaetables and meats and herbs all
dehydrate diffently.
MONITORING AND ADJUSTING
Regulary check the progress of dehydration and adjust the factors such as temperature or air flow if necessary to ensure
optimal results.
FOOD THICKNESS: The thickness of the food slices influences drying time. Thicker slices take longer to dehydrate and
may require adjustments in temperature and air flow to ensure thorough drying without spoilageThinner slices or pieces
dry faster compared to thicker ones.

6. EQUIPMENTS USED IN DEHYDRATION
 Dehydrators: These are electric appliances designed to remove moisture from food products through
controlled heating and equal air circulation
 How it works:
 Heating element: they have heating element to generate heat to raise the tempareature inside the
machine to enable evaporation of moisture from the food.
 Air circulation: dehydraters have a fun inside which circulate air through out the unit which helps to
reduce moiusture frim the food by carrying out the evaporated water.
 Moisture removal: The moist air removed from the food using heat is vented out from the dehydrator
through air vents.

7. AIR DRYER
 Natural air circulation system is used to dry food products.
 Examples of food used under air dryer include Apples, bananas and peaches.
HOW IT WORKS
 Exposure to air : the food is spread out in a well-ventilated space with low humidity such as an attic room whereby the
air circulation helps carry away moisture released from food.
 Evaporation of moisture: As the warm air passes ver the food surface it absorbs the moisture with the help of low
humidity of the surrounding resulting in evaporation.
 Uniform drying: Periodical turning or stirring helps prevent clumping and uneven drying of the food.

8. Air dryer Dehydrator
SOLAR DRYERS
 Makes use of solar enrgy to dehydrate food and it is commonly used in regions with ample sunlight.
HOW IT WORKS
SUNLIGHT ABSORPTION
They are made of silicon cells that absorb sunlight .
ELECTRICITY GENERATION
When the sunlight hits the solar pannels it excites the electrons in the silicon cells creating electric current which is
used to power fans and heaters to facilitate dehaydration.

9. l
Freeze dryer
FREEZE DRYERS
Food is frozen at low temperatures and then subjected to vacuum conditions to remove moisture therough the process
of sublimation.
HOW IT WORKS
FREZING
The food product is frozen under atmospheric pressure to help to solidify water content in the food product.
PRIMARY DRYING
The freeze dryer creates low pressure or vacuum environment causing the frozen water to sublimate.
SECONADRY DRYING
When the free water has been removed the freeze dryer continue to operate at low pessure to eliminate the reamaing
bound water from the food product.

10. Examples of dried fruits

11. POSITIVE EFFECTS OF DEHYDRATION
 Extended shelf life: Dehydrating food significantly extends shelf life compared to fresh produce.
By reducing moisture content, dehydration prevents the growth of bacteria, yeast and molds that
cause food spoilage.
 Retained nutritional: Dehydrated food maintain their original nutritional content including
vitamins, minerals and antioxidants. During dehydration other nutrients become more
concentated leading to high calorie content per weight of dried food.
 Convenience and portability: Dehydrated foods are light weight and compact, making them
convenient for storage, transportation and condumption.
 Intensified flavour and appearance: Dehydated foods have a more intense flavour profile
comapred to resh foods. The remaval of water concentrates the natural sugars and flavours
present in the food resultin in a richer taste. dehydrated foods maintain their oriinal colour and
shape, contributing ro an appealing appearance.

12. NEGATIVE EFFECTS OF DEHYDRATION
Loss of nutritional value: It can lead to the loss of certain nutrients in foods for example
heat sensitive vitamins c and some vitamin B, reducing the overall nutritional quality of the
product.
Changes in taste and texture: dehydration alters the taste and texture of foods, sometimes
resulting in a less appearing final product for example fruits and vegetables may become
overly chewy or tough after dehydration.
Loss of flavour and desired clours. This is due to increased processing time and energy
consumption. It often requires prolonged processing times and intensive methods such as
heating or freeze drying that might end up altering th flavour and desired flavours and
clours.
Limited shelf life :it can lead to reduced stability over time if not properly stored resulting
in spoilage of nutrient concentration.

13. Conclusion
Dehydration is a fundamental technique in food processing, as it offers numerous
benefits including preservation extended shelf life and retention of nutritional
quality.Understanding the theory ,factors to consider during dehydration, equipment
and effects of dehydration is essential for efficient food preservation and maintaining
food quality.

14. THE END