This document discusses food processing using hot air. It begins by defining food processing and its history. Foods are heated for reasons like inactivating microorganisms, enzymes, and avoiding browning. Heating induces physical and chemical changes that affect sensory characteristics. Methods of hot air processing include microwave heating, drying, thermal processing, and various cooking techniques. Drying removes moisture using hot air flow. Factors like moisture level, temperature, and air flow impact the drying process. Processing affects properties such as taste, shelf life, texture, flavor, color, and nutrition. Choice of heat treatment depends on contamination level, oxygen presence, organism resistance, and food characteristics. Common drying equipment includes tray, kiln, tunnel, convey

1. HEAT PROCESSING
USING HOT AIR
A R U N G U P T A
1 5 1 5 0 4
UNIT-5

2. Definition
 Food processing is the set of methods and techniques
used to transform raw ingredients into food or to
transform food into other forms for consumption by
humans or animals either in the home or by the food
processing industry.
 Items considered food may be sourced from plants,
animals or other categories such as fungus or
fermented products like alcohol

3. History of Food Processing
 Food processing dates back to the prehistoric ages
when crude processing incorporated slaughtering,
fermenting, sun drying, preserving with salt, and
various types of cooking (such as roasting, smoking,
steaming, and oven baking).
 In 1809 Nicolas Appert invented a vacuum bottling
technique that would supply food for French troops,
and this contributed to the development of tinning
and then canning by Peter Durand in 1810.

4. Reasons for Heating Foods
 Foods are heated for a number of reasons, the main
one being to inactivate pathogenic or spoilage
microorganisms.
 It may also be important to inactivate enzymes, to
avoid the browning of fruit by polyphenol oxidases and
minimize flavor changes resulting from lipase and
proteolytic activity.
 The process of heating a food also induces physical
changes and chemical reactions, such as starch
gelatinisation, protein denaturation or browning,
which in turn affect the sensory characteristics, such as
color, flavor and texture.

5. Food Processing Methods
 Food Processing Using Hot Air:- a) Micro wave heating
b)Drying
c)Thermal Processing
Fermentation e.g. in beer breweries
 Chopping or slicing e.g. diced carrots.
 Fermentation e.g. in beer breweries
 Cooking, such as boiling, broiling, frying, steaming.
 Deep frying
 Baking/ Roasting
 Addition of gas such as air entrainment for bread or
gasification of soft drinks

6. Microwave Heating
Advantages of microwave cooking:
 Food is cooked 2-10 times faster
 Reconstitution of leftovers with their flavour and texture
 Absence of heat in surrounding air and utensils
 Saving electric energy
Disadvantages of microwave cooking:
 Air inside microwave is cool. This produces a surface cooling in
the food-browned
 flavour does not blend well
 Deep-frying eliminated
 Limited to small quantities
 microbial hazard

7. Drying Using Hot Air
There are three inter-related factors that control the
capacity of air to remove moisture from a food:
 1. the amount of water vapor already carried by the
air
 2. the air temperature
 3. the amount of air that passes over the food. The
amount of water vapor in air is expressed as either
absolute humidity or relative humidity.
.

8. Drying Mechanism
When hot air is blown over a wet food, water vapor
diffuses through a boundary film of air surrounding the
food and is carried away by the moving air. A water
vapour pressure gradient is established from the moist
interior of the food to the dry air. This gradient provides
the ‘driving force’ for water removal from the food
*Thermal Processing
Thermal processing or Heat processing is defined as the
combination of temperature and time required to
eliminate a desired number of microorganisms from a
food product

9. Drying Techniques

10. Effects of Hot Air on Food
 Taste:- Taste of processed food enhances , addition of
different kinds of spices and chemicals increases its aroma
 Shelf Life:- Processed food have better shelf life can last
up to 90 days , depending on type of food.
 Texture:- The texture of raw materials is frequently
changed during processing. Textural changes are caused by
a wide variety of effects, including water loss, protein
denaturation which may result in loss of water-holding
capacity or coagulation, hydrolysis and solubilisation of
proteins.

11. Effect of Hot Air on Food
 Flavour:- Flavour is a rather subjective property which is
difficult to quantify. Again, flavours are altered during
processing and, following severe processing, the main
flavours may be derived from additives.
 Colour:- For low temperature processes such as chilling,
freezing or freeze-drying, the colour changes little during
processing, and thus the colour of the raw material is a
good guide to suitability for processing
 Nutritional changes:- especially ascorbic acid
breakdown and vitamin losses.

12. FACTORS INFLUENCING CHOICE OF
HEAT TREATMENTS
1. Level of contamination
2. Presence of oxygen
3. Heat resistance of organisms or enzymes
4. Heat penetration
:-characteristics of the food
5. Packaging material
6. Size of container
7. Sensory qualities desired.
8. Type of food, depending on pH

13. Methods Used in Hot Air Processing
 Tray dryer
 Kiln dryer
 Tunnel dryer
 Conveyor dryer
 Pneumatic dryer
 Rotary dryer
 Spray dryer
 Drying by contact with a heated surface

14. Equipment

15. Bibliography
 http://collections.infocollections.org/ukedu/en/d/Jt
o01ae/3.1.html
 NPTL lecture notes
 https://moisturecontrol.weebly.com/uploads/5/3/5
/3/53532707/book_ch7-_dehydration.pdf