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Unit Operations in Food Processing
Dr. Sheweta MuDgil
Assistant Professor
Department of Dairy and Food Technology,
Mansinhbhai Institute of Dairy
and Food Technology,
Mehsana, Gujarat.
Dr. DeePaK MuDgil
Assistant Professor
Department of Dairy and Food Technology,
Mansinhbhai Institute of Dairy
and Food Technology,
Mehsana, Gujarat.
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ISBN: 978-81-962471-4-0 H/B
eISBN: 978-81-962471-6-4 E/B
Printed in India
Preface
Food science is an emerging area having large potential from economic viewpoint and
career perspective. There is an increase in number of universities and colleges which are
oering food science related degrees and diploma programmes in various disciplines
such as Food Science Technology, Food Technology, Food Processing Technology, Food
Engineering and allied courses such as Dairy Technology, Post-Harvest Technology, Foods
and Nutrition, Agricultural and Food Process Engineering etc. The Ministry of Food
Processing Industries of India (MFPI) is putting emphasis on the establishment of academic
programmes in food technology at college and university levels. Unit operation in food
processing is included in fundamental subjects in above mentioned disciplines for M.Sc.,
B.Tech, M.Tech programmes. This book titled “Unit Operations in Food Processing” covers
topics related to unit operations such as material handling, cleaning, sorting, grading, size
reduction, mixing, ltration, membrane separation, pasteurization, canning, evaporation,
dehydration, refrigeration, freezing, freeze drying etc. Recent developments in above
mentioned topics are also covered in this book. This reference book provides the learning
material for under graduate and post graduate students. We wish to acknowledge authors
for their contribution in the preparation of this book. We also appreciate the assistance and
support provided by Scientic Publishers sta members. Last but not least we must thank
our family for their love, support and encouragement.
Deepak Mudgil
Sheweta Mudgil
Chapter 1. Introduction to Unit Operations
Deepak Mudgil*
Department of Dairy Technology, MIDFT, Mehsana-384002, Gujarat, India
Chapter 2. Material Handling
Neha Duhan1*, Deepak Mudgil2, Sheweta Mudgil2
Centre of Rural Development and Technology, Indian Institute of Technology (IIT), Delhi, India
Department of Dairy Technology, MIDFT, Mehsana-384002, Gujarat, India
Chapter 3. Cleaning
Aneeta Khatak*
Department of Food Technology, Guru Jambheshwar University of Science & Technology,
Hisar-125001, India
Chapter 4. Sorting and Grading
Parveen Kumari*, Prerna Sethi and Simran Shali
Department of Food Technology, Guru Jambheshwar University of Science & Technology,
Hisar-125001, India
Chapter 5. Size Reduction
Dhiraj Kumar Yadav1, Shubham Patil2, Manish Tiwari2*, Vipul Mittal3, and Shambhavi
Singh2
1Department of Food Engineering, National Institute of Food Technology, Entrepreneurship and
Management, Kundli, Haryana, India
2Department of Food Science and Technology, National Institute of Food Technology,
Entrepreneurship and Management, Kundli, Haryana, India
3Department of Processing and Food Engineering, Chaudhary Charan Singh Haryana
Agricultural University, Hisar, Haryana, India
Chapter 6. Mixing
Ajay Kumar Swarnakar1* and Chandrakant Genu Dalbhagat2
1Food Science and Technology Department, School of Science, GITAM University Hyderabad,
Hyderabad,Telangana - 502329
2Agricultural and Food Engineering Department, Indian Institute of Technology Kharagpur,
Kharagpur, West Bengal - 721302
List of Contributors
viii List of Contributors
Chapter 7. Filtration
Jhilam Pramanik1*, Sayani Mavai2, Kajol Batta1, Akshay Singh Sengar1
1Department of Food Technology, ITM University, Gwalior, India
2School of Agriculture, Lovely Professional University, Jalandhar, India
Chapter 8. Membrane Separation
Nandani Goyal1, Jhilam Pramanik2, Dimple Chauhan3, Akash Kumar4* and Sarvesh
Rustagi5
1Skill department of agriculture, Shri Vishwakarma Skill University, Transit campus- Gurugram,
India
2Department of Food Technology, ITM University, Madhya Pradesh 474001, India
3Shoolini University of Biotechnology and Management Sciences, Solan, Himachal Pradesh,
India
4*Department of Food Technology, SRM University, Sonepat, Haryana 131029, India
5School of Applied and Life sciences, Uttaranchal University, Dehradun, Uttarakhand India.
Chapter 9. Pasteurization
Divyesh Rameshbhai Vaghela1*, Pankajkumar T. Parmar2, Nirav U. Joshi3, Himanshi R.
Sabhadiya1, Dhruvin Patel4, and Parth Kapupara1
1*Department of Agricultural Engineering, Parul Institute of Technology, Parul University,
Waghodiya – 391760, Vadodara,Gujarat, India
2Department of Dairy Technology, Parul Institute of Technology, Parul University, Waghodiya
– 391760, Vadodara, Gujarat, India
3Department of Processing and Food Engineering, College of Agricultural Engineering and
Technology, Junagadh Agricultural University, Junagadh, Gujarat, India
4Department of Dairy Engineering, Parul Institute of Technology, Parul University, Waghodiya
– 391760, Vadodara, Gujarat, India
Chapter 10. Canning
Sheweta Mudgil*
Department of Dairy Technology, MIDFT, Mehsana-384002, Gujarat, India
Chapter 11. Evaporation
Indu Panchal1*, Sharanagouda B1, Jinu Manoj2, Sumit Mahajan1
1College of Dairy Science and Technology, Lala Lajpat Rai University of Veterinary and Animal
Sciences, Hisar 125001, Haryana, India
2College Central Laboratory, Lala Lajpat Rai University of Veterinary and Animal Sciences,
Hisar 125001, Haryana, India
Chapter 12. Dehydration
Arpit Shrivastava1*, Seerat Kaur2, Dhara Patel2, Deepak Mudgil3
1Amity University Jaipur, Rajasthan, India
2Centre for Health and Applied Sciences Ganpat University Mehsana (Gujarat)
3Department of Dairy Technology, MIDFT, Mehsana-384002, Gujarat, India
List of Contributors ix
Chapter 13. Refrigeration
Dhruvin Patel and Pankajkumar T. Parmar*
Department of Dairy Technology, Parul Institute of Technology, Parul University,
Vadodara-391760, Gujarat, India
Chapter 14. Freezing
Akashkumar K. Solanki*, Ashish D. Patel, Rohit G. Sindhav
Dairy Technology Department, College of Dairy Science, Kamdhenu University, Amreli, India
Chapter 15. Freeze Drying
Gaurav Kumar Gaur1, Rekha Rani2*, Khushal Solanki3 and Bhopal Singh4
1Amity Institute of Food Technology, Amity University, Uttar Pradesh, Noida, India
2Department of Food Technology, Mizoram University, India
3College of Dairy Science and Technology, Sri Karan Narendra Agriculture University, Jobner,
Jaipur, Rajasthan- 303329
4Faculty of Science, Dayalbag Educational Institute, Agra, India
Chapter 16. Frying of Foods
Khushal Solanki1, Rekha Rani2*, Gaurav Kumar Gaur3, Aditya Kumar4
1College of Dairy Science and Technology, Sri Karan Narendra Agriculture University, Jobner,
Jaipur, Rajasthan- 303329
2College of Dairy and Food Technology, Agriculture University Jodhpur-342304, Rajasthan
3Brajratna Group, 3rd Floor, 346A, B Block, Sushant Lok Phase 1, Gurgaon-122002
4SMC College of Dairy Science, Anand, Kamdhenu University, 388110
Chapter 17. Extrusion Technology
Chandrakant Genu Dalbhagat1*, Ajay Kumar Swarnakar2, Rakesh Kumar Raigar3, Hari
Niwas Mishra1
1Indian Institute of Technology Kharagpur, Kharagpur, West Bengal – 721 302, India
2Food Science and Technology Department, School of Science, GITAM University Hyderabad,
Hyderabad Telangana 502329, India
3College of Agricultural Engineering and Post-Harvest Technology, Central Agricultural
University, Ranipool, Sikkim, 737135, India.
Chapter 18. Baking
Roshanlal Yadav1 and Akanksha Jain*2
1Department of Home Science, Lakshmibai College (University of Delhi), Ashok Vihar, New
Delhi-110052
2*Department of Home Science, Bhagini Nivedita College (University of Delhi), Kair, New
Delhi-110043
Chapter 1. Introduction to Unit Operations 1–6
(Deepak Mudgil*)
Chapter 2. Material Handling 7–24
(Neha Duhan*, Deepak Mudgil and Sheweta Mudgil)
Chapter 3. Cleaning 25–38
(Aneeta Khatak*)
Chapter 4. Sorting and Grading 39–60
(Parveen Kumari*, Prerna Sethi and Simran Shali)
Chapter 5. Size Reduction 61–86
(Dhiraj Kumar Yadav, Shubham Patil, Manish Tiwari*,
Vipul Mittal and Shambhavi Singh)
Chapter 6. Mixing 87–98
(Ajay Kumar Swarnakar* and Chandrakant Genu Dalbhagat)
Chapter 7. Filtration 99–114
(Jhilam Pramanik*, Sayani Mavai, Kajol Batta
and Akshay Singh Sengar)
Chapter 8. Membrane Separation 115–138
(Nandani Goyal, Jhilam Pramanik, Dimple Chauhan, Akash Kumar*
and Sarvesh Rustagi)
Chapter 9. Pasteurization 139–162
(Divyesh Rameshbhai Vaghela*, Pankajkumar T. Parmar,
Nirav U. Joshi, Himanshi R. Sabhadiya, Dhruvin Patel
and Parth Kapupara)
Chapter 10. Canning 163–176
(Sheweta Mudgil)
Contents
Chapter 11. Evaporation 177–190
(Indu Panchal*, Sharanagouda B, Jinu Manoj and Sumit Mahajan)
Chapter 12. Dehydration 191–216
(Arpit Shrivastava*, Seerat Kaur, Dhara Patel and Deepak Mudgil)
Chapter 13. Refrigeration 217–232
(Dhruvin Patel and Pankajkumar T. Parmar*)
Chapter 14. Freezing 233–258
(Akashkumar K. Solanki*, Ashish D. Patel and Rohit G. Sindhav)
Chapter 15. Freeze Drying 259–278
(Gaurav Kumar Gaur, Rekha Rani*, Khushal Solanki and Bhopal Singh)
Chapter 16. Frying of Foods 279–298
(Khushal Solanki, Rekha Rani*, Gaurav Kumar Gaur and Aditya Kumar)
Chapter 17. Extrusion Technology 299–322
(Chandrakant Genu Dalbhagat*, Ajay Kumar Swarnakar,
Rakesh Kumar Raigar and Hari Niwas Mishra)
Chapter 18. Baking 323–348
(Roshanlal Yadav and Akanksha Jain*)
xii Contents
Table of Contents
1. Introduction
2. Market Potential of the Bakery Industry in India
3. Principles and Theories of Baking Process
4. Batch & Continuous Baking Operation
5. Factors Aecting Baking Process
6. Change Occurs During Baking
7. Ovens Used in the Bakery Industry
8. Recent Development in Baking
References
1. INTRODUCTION
During baking, heat gets transferred through radiation and convection modes. Baking
is a method of cooking using dry heat in which the dough is changed into nutritionally
improved food (nutritional improvements). At the same time, microbes resulting in
spoilage are destroyed, extending the shelf life of the food product (food preservation).
Baking does not signicantly aect the nutritive value. In baking, heating is carried out by
infra-red energy, which is radiated from the walls of the oven, by hot air circulation and
by the process of conduction through the baking pan/tray. The eectiveness of the baking
method depends on the appropriate usage of the walls, tray and ventilation system. Dry
heat involved in baking alters the starch structure of the food item. It imparts the outer
layer brown colour (owing to sugar caramelization and Maillard reaction), thus, making it
more appealing in appearance and taste while locking the free water of the food product to
some extent. Although free water does not get locked entirely in, during the baking time,
the product becomes dry. Bakery comprises conventional products and is signicant in
the food processing segment. Consumption of bakery food items has become familiar to
all sections of society. In India, the bakery category used to be divided into three major
classes, including bread, biscuits and cakes but currently, Indian bakery is not limited to
only these. It is now categorized in terms of state and art technology. Bakery precognition
items include pastries, danish pastries, croissants, rusk, pizzas, pancakes, crisp bread, bread
sticks, kulchas, crackers, garlic bread, fruit bread, focaccia, buns and pav, ciabatta, French
baguette, rye Bread etc.
Roshanlal Yadav and Akanksha Jain*
18 Baking
Chapter
324 Unit Operations in Food Processing
In the 14th AD, the rst premier baker’s guild was recognized in Rome under the
sovereignty of Emperor Augustine, and bread was crucial for military personnel. Initially, the
government gave cereal grains to the masses for free, resulting in the launch of professional
bakeries for making bread instead of a meager amount of cash. Most households did not have
ovens to make bread, so they generally purchased it from commercial bakers. Traditionally,
the ovens were massive and red using wood; hence the huge-sized ovens were limited to
commercial bakeries. In the 14th century, there were more than 2000 bakeries for fullling
the requirements of individuals needing bread. Modern bakery establishments create many
products, including bread, cakes, pastries, cookies etc., while earlier, bakeries were limited
to preparing bread and biscuits (Bali, 2018).
2. MARKET POTENTIAL OF THE BAKERY INDUSTRY IN INDIA
Owing to urbanization, bakery food products have become essential food items for the
great majority of the population in India, leading to elevated demand for convenient foods
at aordable prices. Consumers now have greater health awareness, so the demand for
nutritious and good-quality bakery items is also rising. It is becoming famous across all
segments of the population and people of all age and income groups.
According to the International Market Analysis Research and Consulting Group
(IMARC) bakery market analysis report:
· In 2022, the market size of Indian bakeries reached US$ 11.3 billion. As per the
IMARC Group forecasts, by 2028, the market is expected to reach US$ 21.2
billion, demonstrating a compound annual growth rate (CAGR) of 10.8 percent
between 2023-2028.
· Burgeoning junk-food chains accelerate bread demand since they are utilized in
preparing sandwiches, burgers and other snack items, thus, becoming one of the
major driving factors leading the market of Indian bakeries.
3. PRINCIPLES AND THEORIES OF BAKERY
The baking process started a chain of biochemical, chemical, and physical reactions in the
product, including air cell formation, volume expansion, hydration, protein denaturation,
gelatinization of starch, crust and porous structure formation, and browning reaction
(Sablani et al., 2002). The basic principles involved in baking are explained here:
3.1 Air Cell Formation
Air cells are visible in bread, cakes and other bakery products. These air cells create
porosity in texture from inside the baked item, also known as the crumb. The formation of
air cells is an essential component of the leavening process. The air cells comprise open
spaces enclosed by elastic cell walls generally made of proteins like gluten/egg albumin.
Gases formed by leavening agents are trapped in the interior of the air cells. In baking, the
gases expand, the cell walls become elastic, and the size increases. Gradually, the heat in
baking results in solid cell walls, which structure the bakery product. While no new air
cells are formed during the baking process, all the air cells that are part of the leavening
process are formed as soon as the mixing process begins and the mixing duration is the
governing factor for the texture of the bakery item. An ample air exists between the our
Baking 325
particles and other dry ingredients. In some instances, extra air cells are formed when some
liquids are incorporated like when folding in egg foams.
Formation and expansion of gases: The primary gas responsible for leavening the bakery
product is carbon dioxide, which is released by the following modes:
· Action of yeast, baking powder and baking soda
· Air incorporation in the dough and mixing of the batters
· Steam generated during baking
Carbon dioxide also exists in the dough in the case of proofed bread dough and air in
sponge cake batters – as it is heated, the gases tend to expand and result in the leavening of
the bakery product. Certain gases do not come into action without the application of heat.
When the gases expand, the bakery product rises, resulting in the thinning of cell walls as
they are stretched because of the expansion of gases. Which in turn forms a tender product.
At the start of baking itself, gases start producing and expanding. At 140°F (60°C), yeast
no longer produces carbon dioxide, while steam production continues throughout baking.
Release of water vapour and other gases: During baking, some of the water is converted
into steam and released in the air, resulting in leavening if done before protein coagulation.
Also, carbon dioxide and other gases are released too along with the steam. In yeast-based
food products, alcohol produced during fermentation also acts as one of the gases. The
outer surface of the bakery product becomes challenging as the surface moisture is lost, and
the crust starts forming much before the product browning. When the bread is baked in the
steam-injected oven, it results in the slow formation of the crust by delaying the supercial
drying, which in turn helps in the continuous rising of the bakery product. During baking, a
sizeable amount of moisture is lost. At the same time, the proportion of weight loss diers
signicantly, depending on factors like the proportion of surface area to volume, baking
duration, and the baking vessel (pan or oven hearth).
3.2 Hydration
Hydration refers to the absorption of water. Dierent bakery ingredients absorb water
in several ways. Starch forms the most signicant component of dough and batters by
weight and volume. While insoluble in water, it is hydrophilic and tends to bind with water
molecules and alter its form. Water molecules attach to the surface of starch granules,
creating a shell around them. With the heat involved in the baking process, starch tends to
absorb water and gelatinize and the gelatinization process helps impart structure to bakery
products. Hydration is essential in the mixing process, with which gelatinization can occur.
Although proteins are usually water-insoluble but are hydrophilic and tend to attract and
bind with water molecules. In dry our, gluten proteins create tight coils, and after contact
with water, they start uncoiling. Mixing process results in straightened proteins attaching
to form long strands of gluten bres. Hence, water is essential for gluten formation. For
leavening, the yeast becomes active in water, ferment sugars, and escape the carbon dioxide
gas. Similarly, salt, sugar, and chemical leaveners like baking powder do not aect bakery
foods in a dry state. Therefore, they must be solubilized in water to perform their various
functions. Water also confers several other functions. For instance, by regulating water
temperature, one can adjust the temperature of the dough/batter too. By adjustments in the
amount of water/any other liquid, the baker can correct the consistency of the dough/batter.
326 Unit Operations in Food Processing
3.3 Oxidation
It is the process that takes place when atmospheric oxygen reacts with proteins and other
our components during mixing. The oxidation process is directly proportional to the
mixing time and hence is a critical factor during the mixing of the yeast-based dough.
When the duration of mixing time is less, like in the case of cakes, cookies and pastry
dough, the oxidation process is not that important and needs to be given more consideration.
Oxidation eects are important when gluten proteins and pigments are present in the our.
During the mixing process, oxygen tends to get mixed with the gluten proteins, making
them rm and strong, giving a better structure to the bread dough. With continued mixing,
oxygen combines with our pigments conferring a bleaching eect and making the bread
appear white; however, this process somewhat deteriorates the bread›s avour and aroma.
The addition of salt slows down the process of oxidation. It may be noted that the addition
of salt during the early stages of the mixing process delays the bleaching eect of pigments
resulting in a lesser white bread but with improved and better avour; and if the baker wants
to have a whiter bread, then probably salt can be included at a later stage of mixing process
when the majority of the pigments are already oxidized. A certain amount of oxidation
is required to give a better gluten structure to the bakery product, but over-oxidation is
avoided to retain avours.
3.4 Gelatinization of Starch
Starch imparts structure and bulk to most bakery products. On baking, starches give a
softer structure as compared to proteins. In the case of baked bread, the crumb softness is
mainly due to the starch. The protein-based structure provides chewiness to bread. Starch
molecules are arranged as tiny and hard granules. During the mixing process, these granules
are hydrophilic. Although the water is not absorbed by the granules when cold, it attaches
itself to the outer surface of the granules. When heat is applied during baking, the granules
absorb the water, which tends to swell and increase in size (Fig.1). While some starch
granules burst, some are released with any available water. This makes the baked dough dry,
while unbaked doughs possess moisture. Majority of the water exists but is bonded with the
starch. The gelatinization process starts when the interior temperature reaches about 105°F
(40°C) and continues throughout the baking process or till the temperature reaches about
200°F (95°C). Depending on the amount of water in the dough/batter, not all the starch gets
gelatinized, as insucient water might be available. While in the case of dry bakery items
like cookies and pie dough, majority of the starch does not get gelatinized; in bakery foods
prepared from the batter with high water content, like cakes, a more signicant proportion
of the starch gets gelatinized.
Fig. 1. Starch gelatinization
Baking 327
3.5 Regulating the Development of Gluten
Although our comprises mainly starch, the amount of gluten-forming proteins signicantly
aects the bakery product. As gluten proteins are required to impart structure to bakery
products, it is essential to control the gluten content. When the our is mixed with water,
the glutenin and gliadin proteins combine to form gluten. As the dough is kneaded, the
gluten proteins form a strong, elastic network, which gives the dough its structure and
texture. The gluten network traps carbon dioxide produced by yeast or other leavening
agents, allowing the dough to rise and giving baked goods their airy texture. The amount of
gluten development is critical in determining the nal texture of the baked goods. Longer
mixing times and higher speeds can lead to more gluten development, resulting in a denser
and chewier texture, while shorter mixing times and slower speeds can result in a more
tender crumb. For instance, French bread must be rm and chewy, requiring a high amount
of gluten. On the other hand, cakes are desirably tender, requiring less gluten. Glutenin and
gliadin are proteins in wheat our and lesser proportions in other grains like rye and barley.
3.6 Coagulation of Proteins
Coagulation refers to the hardening of gluten proteins due to heat application. During
baking, when gluten proteins are coagulated, they get rm and form a solid structure.
Soft and pliable bread dough transforms into a rm bread crumb that holds its shape.
To understand the coagulation process, an example of eggs can be taken that are liquid
when cold but become rm when heated till they are solid. During this ongoing process,
gases are continuously expanding and at the same time, the protein strands continue to
stretch. At last, when the coagulation process is over, the air cells stop expanding and the
bakery product no more rise. Most of the water bonded with the protein during the mixing
process is released and either evaporated or absorbed by the starch. The bakery product
can hold its shape and structure as soon as the protein structure gets entirely coagulated.
The exact temperatures at which coagulation begins and is completed depend on numerous
factors, including presence of other ingredients too – specically sugars and fats aect the
temperature of protein coagulation. Majority of the proteins get completely coagulated at
185°F (85°C). Therefore, appropriate baking temperature is crucial while making bakery
products. The coagulation process is faster in case of higher baking temperatures and occurs
even before the gases expand and reach their peak. The resultant bakery item is thus poor in
volume and has a split crust. On the other hand, if the temperature is shallow, there is a delay
in the process of protein coagulation and the bakery product might collapse. A signicant
drawback of the coagulation process is that the proteins release ample water, which is
absorbed during the mixing process. While a certain amount of water is evaporated, some
get absorbed by the starch. The proportion of bakery ingredients and the mixing method
also aect gluten development.
4. BATCH & CONTINUOUS BAKING OPERATION
The industrial baking process uses two types of ovens: (i) continuous ovens, where the
baking strategy is rst-in-rst-out; and (ii) batch ovens, where production is discontinuous
and can be tailored to requirements (Pinelli& Suman, 2017). Continuous ovens use forced
convection and radiation, while batch ovens use natural convection and conduction.
328 Unit Operations in Food Processing
Food manufacturers can choose the proper baking operation for their specic needs by
understanding the dierences between these two methods. Each method has advantages
and disadvantages, and the choice of which one to use will depend on various factors,
including the type of product being baked, the production volume, and the desired quality.
4.1 Batch Baking
Batch baking is a method where a xed amount of ingredients is mixed and baked in a
single batch. This process is typically used for products requiring longer baking, such as
bread and cakes (Fast, 1990). The oven is loaded with a xed amount of product in batch
baking, and the baking process begins. Once the batch is nished baking, the product is
removed from the oven, and the oven is reloaded for the next batch.
Batch baking requires specic instruments to ensure the consistency and quality of
the products. Appropriate instruments for batch baking are essential to ensure that the nal
product is consistent in texture, taste, and appearance. Here are some standard instruments
generally used in batch baking (Fig. 2):
1. Mixing Bowls and Paddles: Mixing bowls come in various sizes and are used
for mixing ingredients. Paddles are attached to mixers and are used to combine
ingredients thoroughly.
2. Measuring Cups and Spoons: Measuring cups and spoons are used to measure
the correct ingredients for the recipe.
3. Digital Scale: A digital scale is used to weigh ingredients precisely, which is
essential in baking.
4. Rolling Pins: Rolling pins are used to roll dough to the desired thickness for
various baked goods.
Fig 2. Instruments used in batch process (A) Mixing bowl (B) Measuring spoons/cups (C)
Digital scale (D) Rolling pin (E) Cookie Cutter (F) Pastry bags & tips (G) Baking pans
(H) Cooling rack (I) Thermometer (J) Oven mitts
Baking 329
5. Cookie Cutters: Cookie cutters are used to cut dough into specic shapes for
cookies or other baked goods.
6. Pastry Bags and Tips: Pastry bags and tips are used for frosting or llings onto
baked goods.
7. Baking Pans: Baking pans come in various sizes and shapes and are used for
baking dierent baked goods, such as cakes, bread, and pastries.
8. Cooling Racks: Cooling racks are used to cool baked goods after they are
removed from the oven. They allow air to circulate the baked goods, preventing
them from becoming soggy.
9. Thermometer: A thermometer checks the internal temperature of baked goods to
ensure they are fully cooked.
10. Oven Mitts: Oven mitts protect the hands and arms from the oven’s heat when
removing hot baking pans.
Several factors should be considered when designing a batch-baking process, such as
the type of product being baked, the quantity needed, and the equipment available. Here
are the steps involved in a typical batch-baking operation:
Ingredient Preparation: The rst step in batch baking is to gather all the necessary
ingredients and prepare them for mixing. Ingredients should be measured accurately to
ensure consistent results.
Mixing: The ingredients are mixed in a mixer until a consistent dough or batter is formed.
The mixing time and speed depend on the recipe and the type of mixer used.
Shaping: The dough or batter is then shaped into the desired form. This could include
rolling out dough, using cookie cutters, or lling moulds.
Baking: The shaped dough or batter is then baked in an oven at the appropriate temperature
and time for the recipe. The baking time and temperature depend on the baked goods being
made.
Cooling: After baking, the baked goods are removed from the oven and cooled on a rack.
Cooling allows the baked goods to be set and prevents them from becoming soggy.
Packaging: Once the baked goods are cooled, they are typically packaged in containers,
bags, or boxes. The packaging should be appropriate for the type of baked goods and
protect them during transport and storage.
Quality Control: The baked goods are checked for quality to meet the desired standards.
Quality control can include checking the product’s appearance, texture, and taste.
Advantages of Batch Baking
· Flexibility: Batch baking allows for more exibility in terms of product
customization and recipe adjustments. Each batch can be adjusted to meet specic
requirements, such as changing the baking time or temperature.
· Quality: Batch baking is known for producing high-quality products because
each batch is closely monitored for consistency and quality.
· Equipment Cost: Batch baking equipment is typically less expensive than
continuous baking equipment, making it a more cost-eective option for smaller
production runs.
330 Unit Operations in Food Processing
Disadvantages of Batch Baking
· Time: Batch baking is slower than continuous baking because each batch must
be loaded and unloaded from the oven. This can result in longer production times
and lower production volumes.
· Labour: Batch baking requires more labour because each batch must be loaded
and unloaded from the oven, and the oven must be cleaned between batches.
4.2 Continuous Baking
Continuous baking is a process where the product is baked continuously as it moves
through the oven on a conveyor belt. This process is typically used for products that
require a shorter baking time, such as cookies and crackers. In continuous baking, the
dough or batter is fed into the oven at one end, and the nished product is removed at the
other (Cappelli et al., 2021). This process is highly automated and designed to optimize
eciency and productivity while maintaining consistent quality.
Continuous baking requires specialized instruments and equipment to ensure
the process runs smoothly and eciently. Here are some standard instruments used in
continuous baking:
1. Dough Feeders: Dough feeders (Fig. 3) automatically feed the dough into the
continuous process. They can be customized to handle dierent dough types and
quantities.
Fig. 3. Dough Feeder
2. Continuous Mixers: Continuous mixers (Fig. 4) are used to mix ingredients and
maintain a consistent product. They can be customized to handle dierent mixing
speeds and times.
Fig. 4. Continuous Mixture
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3. Extruders: Extruders (Fig. 5) are used to shape dough into dierent forms such
as bread, rolls, or pastries. They can be customized to produce dierent shapes
and sizes.
Fig. 5. Dierent Types of Extruder
4. Proofer: A proofer is a temperature and humidity-controlled chamber that allows
the dough to rise and develop avor. They can be customized to handle dierent
types of dough and proong times.
5. Continuous Ovens: Continuous ovens are used to bake the products at high
speed with consistent temperature and humidity control. They can be customized
to handle dierent baking times and product types.
6. Cooling Conveyors: Cooling conveyors (Fig. 6) are used to cool the baked
products before packaging. They can be customized to handle dierent product
shapes and sizes.
Fig. 6. Cooling Conveyor
7. Packaging Equipment: Packaging equipment is used to automatically package
the baked goods into various types of packaging. They can be customized to
handle dierent types of packaging and product shapes and sizes.
8. Quality Control Instruments: Quality control instruments such as temperature
probes and moisture meters are used to monitor the quality of the baked goods
during the continuous process.
A continuous baking process optimizes eciency and productivity while maintaining
consistent quality. It requires signicant capital investment in equipment and infrastructure
but can lead to signicant cost savings over time. When designing and selecting a continuous
baking process, the following steps should be considered:
332 Unit Operations in Food Processing
Ingredient Handling: Raw ingredients are stored in silos or other containers and
automatically transferred to the mixing area.
Mixing: In a continuous baking process, mixing is typically done using large, high-capacity
mixers equipped with automated feeding systems. This ensures that the dough or batter is
consistent in texture and quality.
Forming: Once the dough or batter is mixed, it is transferred to automated forming
machines that shape it into the desired product. This can be done using extrusion or other
forming methods.
Proong: After forming, the product is typically transferred to a proong area where it
can rise and develop avour. The proong time is closely monitored to ensure that it is
consistent and optimized for the specic product being made.
Baking: The products are then baked using continuous ovens designed to optimize
eciency and productivity. These ovens can be congured to bake products in various
shapes and sizes and are designed to ensure that products are baked evenly and thoroughly.
Cooling and Packaging: Once baked, the products are typically cooled using automated
cooling racks before being packaged using high-speed packaging equipment. Packaging is
designed to protect the product during transport and to maintain freshness.
Quality Control: The baked goods are checked for quality to meet the desired standards.
Quality control can include checking the product’s appearance, texture, and taste.
Advantages of Continuous Baking
· Production Volume: Continuous baking increases production volumes more
than batch baking because the product is baked continuously.
· Time: Continuous baking is faster than batch baking because loading and
unloading the oven between batches is unnecessary.
· Labour: Continuous baking requires less labour than batch baking because
loading and unloading the oven between batches is unnecessary.
Disadvantages of Continuous Baking
· Equipment Cost: Continuous baking equipment is typically more expensive
than batch baking equipment, making it a less cost-eective option for smaller
production runs.
· Quality: Continuous baking can result in lower product quality because there is
less control over each product as it moves through the oven.
5. FACTORS AFFECTING BAKING PROCESS
The quality of the bakery product is signicantly governed by the rate and amount of heat
applied, the humidity level in the baking chamber and baking time (Sablani et al., 1998;
Pyler, 1988), while the rate of heat transfer is aected by the temperature and atmospheric
humidity in the baking chamber (Mondal & Datta, 2008). It has been documented that
it is not always desirable to have a maximum heat transfer rate; however, it is rather
benecial to control the heat transfer rate as it implies that the process is reliable, can be
regulated/controlled and is reproducible. Changes in the heating rate during the baking
process can alter the kinetics, level of disarrangement of the amylopectin crystals, swelling
Baking 333
of starch granules, syneresis and hence, the eective crumb structure formed within the
bakery product. These alterations would then aect the texture of the bakery product on
storage (Patel &Waniska, 2005). Baking temperature is the most critical factor inuencing
the three modes of heat transfer – convection, conduction and radiation. Temperature is
also a prominent factor resulting in various physical, chemical and biochemical changes
during baking, including expanding the bakery product volume, crust formation, yeast
inactivation, enzyme-related reactions, coagulation of proteins and starch gelatinization
(Pyler, 1988). Humidity signicantly impacts the heat transfer rate by letting the water
vapour condense on an object. So during condensation of water, heat gets transferred
to the object, referred to as latent heat of condensation and this energy is equivalent to
the heat required for conversion of water to steam. Direct heat in a dry environment will
require higher temperatures to attain the same heat transfer since latent heat aects the
humid environment. Atmospheric humidity also inuences the rate of heat transfer – the
greater the humidity level, the greater the specic heat capacity to retain more energy.
Regulation of the rate of heat transfer and level of humidity level of the baking chamber
can be benecial in the following ways:
· Products can be heated with greater ecacy
· Reduction in the production cost
· Greater yield of bakery products
· Reduction of baking time since the required temperature is attained quicker
· Improved consistency and increased rate reproducibility of products
· Humidity inuences the product performance during baking and the quality of the
nal product, including crust thickness, colour and formation of crumb
During baking, there are many changes in the dough’s physical and chemical attributes.
The atmospheric humidity in the oven during the process of baking is known to have a
more signicant impact on the oven rise, i.e. expanding the fermented dough in the initial
stages of baking; however, few researchers have reported the impact of the amount of
injected steam on bread and the structure of the crust (Scanlon &Zghal, 2001; Le-bail et
al., 2011a). Sommier et al. (2005) have reported the eect of baking conditions, including
vault and hearth temperatures, water vapour injection on dough expansion, scar opening,
and crust formation in French bread baking. The investigators have documented that water
vapour has a role in the expansion of volume, while vault and hearth temperatures mainly
inuence crust. The eect of baking time and temperature was assessed on the quality
attributes, including volume, weight, crust colour, crumb rmness and moisture content of
par-baked French bread. It was documented that low temperature and long baking duration
decrease the ultimate bread’s crumb rmness (Chul-Soo-Park & Byung-Kee-Baik, 2007;
Dessev et al., 2020).
In reference to the above fact the responsible factors are explained below:
5.1 Selection of Flour
The proteins in severe wheat our form good-quality gluten, imparting strength and
elasticity. Wheat ours are divided broadly as strong or weak, depending on the content
of protein. Strong ours are derived from hard wheat and possess higher protein content,
while weak ours are sourced from soft wheat with lower protein content. Hence, strong
334 Unit Operations in Food Processing
our is used for baking bread, while weak our is used for making cakes. Gluten from
rye our is of poor quality gluten and is usually insucient for preparing bread; however,
specic specialty bread is prepared using rye our with a heavy texture. Spelt also has
less amount of poor-quality gluten. Most other grains like corn, buckwheat and soy do not
contain any amount of gluten protein. For making rye bread, high gluten content our must
be used with a balanced formula, or it will result in a heavy loaf of bread.
5.2 Fat and Sugar as Tenderizers
Fat in baking is usually referred to as shortening as it shortens the strands of gluten protein.
Fat surrounds the starch particles and forms a coating around them, so they do not stick
along; hence, fats are referred to as tenderizers. For example, a cookie or pastry with a
crumbly texture owing to fat present in it and lesser development of gluten is therefore
known to be short in the case of French bread, which has signicantly less or no fat at all,
while cakes comprise an enormous amount of fat. The two-stage cake mixing procedure
involves thorough mixing of our and the shortening, resulting in minimal gluten
development despite the sucient duration of mixing. Another example of a tenderizer is
sugar is another tenderizer which interferes with the process of gluten formation. It may
be noted that sugar has a hygroscopic tendency, i.e. it attracts and binds with water and the
amount of water attracted to sugar is unavailable to hydrate gluten strands. Therefore, a
dierent mixing technique is employed for making certain sweet doughs in which gluten
development occurs before adding sugar.
5.3 Water
Before gluten development, gluten proteins need to absorb sucient water. The quantity of
water in the formula greatly inuences the toughness or tenderness of the bakery product.
Generally, gluten proteins absorb nearly two times their weight in water. Most of the
water added to our is absorbed by the starch granules and is made unavailable to the
proteins. Making the proteins decient in water tend to make the bakery products tender
by preventing the development of. For example, piecrusts and crisp cookies are prepared
with less liquid to make them tender. Adding even extra water to these formulas may result
in greater gluten activation and toughening bakery products. When all the gluten proteins
absorb water, additional water does not impact gluten development. The gluten strands
become weak and diluted if a large amount of water is added. Various conditions related
to water added to bread dough, like pH, hardness, etc., also inuence gluten development.
Water hardness refers to the number of minerals in water, particularly calcium. Water
with more signicant amounts of minerals is termed hard water. Minerals in hard water
impart strength to the gluten strands, thus, making the dough too elastic and dicult
to work with. Too soft water makes the dough very loose and sticky. Therefore, water
treatment or dough conditioners can manage such eects.
Water pH helps assess the acidity and alkalinity of water on a pH scale of 0 to 14. A
strong acid has a pH of 0, while a strong alkali has a pH of 14. Pure water is considered
neutral with a pH of 7. The mineral content of water results in increasing the pH of water.
Slightly acidic pH of 5 to 6 results in strong gluten development. Therefore, tenderness of a
bakery product can be regulated by addition of either an acid like fruit juice or by reducing
Baking 335
the pH content beyond the range of 5-6 by addition of an alkali-like baking soda. Acidic
sourdough makes softer and sticky dough as compared to ordinary yeast dough.
5.4 Method and Duration of Mixing:
During the mixing of the dough ingredients, three crucial processes take place:
1. The mixing action tends to blend the water with the our, so the our proteins
absorb water and hydrate. This is the primary step in developing gluten.
2. Air incorporation in the dough – atmospheric oxygen reacts with the gluten
protein, imparting greater strength and elasticity.
3. The act of mixing helps in gluten development by way of providing stretchability
and elasticity to the gluten strands.
Initially, the bread dough is soft and sticky, then as the gluten develops, the bread
dough becomes smoother in texture, losing stickiness and is referred to as mature. With
prolonged mixing, gluten strands tend to break and the resultant dough gets sticky and
tricky. Overmixing results in poor loaf as gluten strands tend to break and cannot support
the structure. In bakery products which require tenderness like cookies, cakes, and short
dough, the duration of mixing is reduced. To a lesser extent, gluten development is required
for these bakery items, or they will become too crumbly in texture. Pie dough will not be
able to hold together; biscuits will collapse instead of rising and cookies might crumble
while overmixing leads to toughness.
Dough relaxation is an eective method for producing a majority of dough. After
mixing/kneading, gluten strands possess stretchability and become rigid, making it
somewhat problematic to manage and mould the dough. A certain amount of relaxation to
the dough permits gluten strands to adjust to their new length/shape and become less rigid;
the dough can then be handled more eciently and has a lesser tendency to shrink.
5.5 Leavening
Fermentation of yeast helps develop gluten because yeast’s expansion of air cells imparts
stretchability to the gluten strands, similar to mixing. Also, acids produced in fermentation
process help in giving structure to gluten. After fermentation, the gluten in yeast dough is
stronger with more excellent elasticity. At the same time, it strengthens gluten, leavening
results in tenderization of bakery products. This is because the cell walls become thinner
as they are stretched, making the nished product easier to chew. Too much fermentation,
on the other hand, can hurt the gluten structure because the gluten becomes overstretched,
causing its strands to tear and lose their elasticity. Over-fermented doughs have poor
texture, similar to overmixed dough. Adding more baking powder to a cake batter is like
over-fermenting a yeast dough. The protein structure of the batter is stretched too far and
cannot hold, leading to its collapse or a dense cake with poorer volume.
5.6 Temperature
Greater gluten development occurs at a warmer room temperature compared to colder
temperatures. Hence, the optimum temperature for mixing bread dough is 70° to 80°F
(21° to 27°C). On the other hand, tender products like pie dough are most suited to using
336 Unit Operations in Food Processing
ice-cold water and mixed at a cold temperature to restrict gluten development. Moreover,
baking temperature also play an important role in the quality of baked products In general
180 to 220°C temperature is required in the oven which also vary and depends on the
product type.
5.7 Other Ingredients and Additives
Salt is an essential additive in yeast dough-making. It helps regulate yeast fermentation,
strengthens gluten, and makes it more elastic. Yeast doughs without salt are dicult to
handle and the gluten is more likely to tear. As salt helps strengthen the bonds of gluten, a
more signicant duration of mixing is required for developing the structure. This is because
only some bakers add salt at the end of the mixing process; however, this method has
a signicant limitation. Salt also slows oxidation of the our, so delaying the addition
of salt implies that the dough gets more signicant time to oxidize before adding salt
– resulting in avour loss. Therefore, to impart the best avours, salt is added to start
mixing. Bran interferes in gluten development by preventing some gluten strands from
sticking together, and the sharp edges cut through the formed gluten strands.
The texture and aroma of bakery products are changed due to altered structure and a
loss of moisture by the starch granules. As a result, stale bakery items have a diminished
fresh-baked aroma and a rmer, drier, and crumblier texture than their fresh counterparts. It
is crucial for bakers to prevent staling as most bakery products rapidly lose quality. Starch
retrogradation, which begins shortly after baking items cool, causes starch molecules to
bond, forcing out moisture, resulting in increased complexity and dryness. Despite other
ingredients, such as sugar, absorbing the moisture, the item›s texture feels drier due to this
chemical reaction of starch. Even tightly wrapped, bread can become drier in texture. Starch
retrogradation is quicker at refrigerator temperatures than at room temperature, but it nearly
stops at freezer temperatures. Therefore, it is best to store bread at room temperature for
short-term storage or freeze it for long-term storage. Heating bakery products can partially
reverse chemical staling, but only to a certain extent. For example, bread, muns, and
coee cakes can be refreshed by putting them in the oven briey. However, this results in
signicant moisture loss to the air, so the items should only be reheated just before serving.
Loss of crispness is the opposite of staling and is caused by moisture absorption, especially
in low-moisture products such as cookies and piecrusts. Proper storage in airtight wraps or
containers is usually the solution to this problem to protect the products from moisture in
the air. Prebaked pie shells should be lled as close to service time as possible to prevent
loss of crispness.
In addition to refreshing baked goods in the oven, three main techniques are used to
slow staling:
1. Protecting the product from air: Two examples of protecting baked goods are
wrapping bread in plastic and covering cakes with icing, which is incredibly thick
and rich in fat. Hard-crusted bread, which stales rapidly, should not be wrapped,
or the crusts will quickly become soft and leathery. These bread products should
always be served very fresh.
2. Adding moisture retainers to the formula: Fats and sugars are good moisture
retainers, so products high in these ingredients keep best. Some of the best French
bread has no fat, so it must be served within hours of baking, or it will begin to
Baking 337
stale. For longer keeping, bakers often add minimal fat and sugar to the formula.
3. Freezing: Baked goods are frozen before they become stale and maintain quality
for extended periods. For best results, freeze soon after baking in a blast freezer
at –40°F (–40°C) and maintain at or below 0°F (–18°C) until ready to thaw.
Bread should be served quickly after thawing. Frozen bread may be reheated with
excellent results if they are to be served immediately. Refrigeration, on the other
hand, speeds staling. Only baked goods that could become health hazards, such as
those with cream llings, are refrigerated (Gisslen& Wayne, 2013).
6. CHANGE IN BAKERY PRODUCT DURING BAKING
Baking is a complex process that involves a variety of chemical and physical changes in
food. Understanding these changes is crucial to producing the desired texture, avor, and
appearance in baked goods.Here are some of the key changes that take place during baking:
6.1 Maillard Reaction
This is a chemical reaction that occurs between amino acids and reducing sugars in food
(Balts, 1982). During baking, the heat causes the amino acids and reducing sugars in
the dough to react with each other, forming new compounds that contribute to the avor
and aroma of the nal product. These compounds include a range of volatile and non-
volatile substances, such as aldehydes, ketones, and pyrazines. The Maillard reaction
also contributes to the browning of the crust on bread and other baked goods. This occurs
because the compounds formed during the reaction are brown in color, giving the crust
its characteristic golden-brown hue. It can be inuenced by a range of factors, including
temperature, pH, and the presence of certain enzymes or catalysts. For example, adding
an alkaline substance like baking soda to a recipe can increase the rate of the Maillard
reaction, resulting in a more pronounced browning eect (Mazumder et al., 2019).
6.2 Caramelization
This is a process where sugar is heated to high temperatures, and it starts to break down,
forming a brown, caramelized color and avor. During baking, the heat causes the sugars
in the bakery products to break down and form new compounds, which gives rise to a wide
range of avors and aromas (Purlis, 2010). The process of caramelization is accelerated by
the presence of moisture and alkaline substances, such as baking soda or baking powder.
The extent of caramelization depends on several factors, such as the type of sugar used,
the temperature of baking, and the baking time. For example, high-temperature baking
for a short duration can lead to surface browning, while lower temperatures for a longer
duration can result in more uniform caramelization throughout the product. Caramelization
is an important aspect of the avor and appearance of many baked goods, including bread,
cakes, and pastries. It gives these products their distinctive taste and visual appeal, making
them more desirable to consumers.
6.3 Denaturation of Proteins
During baking, the heat causes the protein molecules in bakery products to vibrate, and this
movement disrupts the bonds that maintain the protein’s three-dimensional structure (Liu
338 Unit Operations in Food Processing
et al., 2018). As a result, the protein molecules unfold and lose their shape, which can aect
the texture, avor, and appearance of the product. The extent of denaturation depends on
several factors, such as the type of protein, the baking temperature, and the baking time. For
example, egg proteins are particularly sensitive to heat and can denature rapidly, leading
to the solidication of baked goods such as cakes and pastries. Denaturation of proteins
can also result in the formation of new compounds, such as Maillard reaction products,
which contribute to the avor and aroma of baked goods. While denaturation can alter the
functional properties of proteins, it is an important aspect of baking, as it contributes to the
overall structure and texture of many bakery products.
6.4 Evaporation
As baked goods are heated, the moisture content within the dough or batter begins to
evaporate, creating steam (Xue & Walker, 2003). This steam creates a leavening eect,
causing the dough or batter to rise and expand. As the steam continues to evaporate, the
surface of the baked good dries out, creating a crispy crust. However, too much evaporation
during baking can result in baked goods that are dry, tough, and unappetizing. To prevent
excessive evaporation during baking, it is important to keep the oven temperature within
the recommended range for the recipe, cover the baking dish with foil or a lid if necessary,
and ensure that the dough or batter has a sucient amount of moisture.
6.5 Leavening
Leavening during baking is the process by which baked goods rise and become light and
uy. Leavening agents, such as yeast, baking powder, and baking soda, produce carbon
dioxide gas when they react with moisture, heat, or acidic ingredients in the dough or batter
(Neeharika et al., 2020).Yeast is a leavening agent that is activated by warm water and sugar.
The yeast feeds on the sugar and releases carbon dioxide gas, causing the dough to rise.
Yeast is commonly used in bread and pizza dough recipes.Baking powder is a leavening
agent that is a mixture of baking soda, cream of tartar, and cornstarch. When mixed with
moisture and heat, baking powder releases carbon dioxide gas, causing the batter to rise.
Baking powder is commonly used in recipes for cakes, muns, and quick breads.Baking
soda is a leavening agent that reacts with acidic ingredients such as buttermilk, yogurt,
or vinegar to release carbon dioxide gas. Baking soda is commonly used in recipes for
pancakes, waes, and biscuits.
6.6 Gelatinization
During baking, the gelatinization of starches takes place that helps to give baked goods their
structure and texture. As the batter or dough heats up in the oven, the water in the recipe
is absorbed by the starch molecules, causing them to swell and thicken (Awuchi et al.,
2019). This thickening helps to provide the structure of the baked good, preventing it from
collapsing or becoming too dense.The degree of gelatinization can also aect the texture
of the nal product. For example, if the starch granules are only partially gelatinized, the
baked good may have a more dense or doughy texture. If the starch is fully gelatinized,
the baked good may have a lighter, more tender texture. The gelatinization of starches is
responsible for the texture of baked goods, such as the crumb of bread and the tenderness
of cakes.
Baking 339
7. OVENS USED IN THE BAKERY INDUSTRY
Ovens are one of the most signicant machineries of any bakery unit. It is a thermally
insulated cabinet designed for baking, heating, cooking and drying dierent food items.
Decent ovens have many xtures and mounting to control and monitor the operation.
There are smart ovens, which are programmed per the recipe and control the operation
in sequence. They can be thermally charged using dierent sources, including gas,
electricity, wood, and coal. They may have various features such as temperature controls,
timers, and fans to control the cooking process. The selection of any oven will be decided
after such considerations as required bakery production-throughput capacity, product
diversity, available oor space, energy source, an economy in operation, construction and
maintenance. Dierent types of ovens (Fig. 7) are described in this chapter.
7.1 Rack Oven
A rack oven is a large oven designed for commercial baking operations that can
accommodate entire racks lled with sheet pans. While standard baker’s racks typically
hold between 8 to 24 full-size sheet pans, racks specically made for rack ovens usually
hold about 15 to 20 pans. Rack ovens can hold one to four racks at a time and often come
equipped with steam injectors. In bakeries that produce high volumes of bread and bagels,
rack ovens, also known as revolving ovens, are often used. In this type of oven, the racks
revolve around a central shaft above a heating element typically located at the bottom of
the baking chamber. A typical rack oven has several metal or stone shelves connected to
a central horizontal shaft. An external motor spins the shaft, which moves the shelves in a
revolving motion that creates even baking.
Rack ovens can produce large quantities of uniformly cooked products, with 20 to 40
standard sheet pans capacity. Pans are loaded onto metal racks, then rolled into the oven.
Inside the oven, a motorized lift revolves around the rack for even cooking. Rack ovens
use forced convection to distribute heat evenly and many models can inject steam into the
cavity to enhance shine and crust of baked goods. It is worth noting that the term “rack
oven” is sometimes used to refer to conventional ovens found in restaurant ranges, where
pans are placed on racks rather than directly on the bottom, as in deck ovens. However, this
usage is not strictly correct.
7.2 Deck Oven
Deck ovens are named after the fact that items are baked directly on the bottom, or deck,
of the oven, either on sheet pans or freestanding for some bread. Hearth bread, also known
as artisan bread, is often baked directly on the oor of these ovens, sometimes referred to
as hearth ovens. Multiple decks, typically made of ceramic or stone, are present in deck
ovens for placing food items to be baked. There are two heating methods in the deck
oven, i.e. conductive heat and radiant heat. Conductive heat transferred directly from the
deck to the dough and radiant heat from the hot air in the baking chamber are the two
heating methods used in deck ovens. Steam injection systems are occasionally found in
deck ovens, releasing water vapour into the cooking chamber for perfect, crisp, brown
bread crusts covering a soft and uy interior. Baguettes, ciabatta, and sourdough bread
are ideal for deck ovens. Multi-deck ovens with gas circulation heating can save an average
340 Unit Operations in Food Processing
of 35% energy compared to steam-tube ovens. The electric multi-deck oven is still popular
among craft bakers, in-store bakeries, and hot-bread shops due to its exibility and ease
of use. They are appropriate for all products, with high output relative to oor area, and
are cost-eective when managed correctly. However, the height or thickness of the food
product can be a limiting factor.
7.3 Conveyor Oven
A conveyor oven is a type of oven that uses a conveyor belt to move food products through
a heated chamber. The oven is designed to cook food products consistently and quickly,
making it famous for commercial kitchens, restaurants, and food production facilities. The
oven consists of a belt conveyor that moves through a baking chamber. Food items are
placed on the conveyor belt and the oven blows hot air onto the food to cook it. This hot air
quickly penetrates the cold air barrier around the uncooked food, leading to faster cooking.
Since the belt speed is constant, all items come out of the chamber evenly cooked. These
ovens have programmable controls for time and speed settings, making them simple and
easy to use. However, conveyor ovens have limitations as they are unsuitable for all baked
goods. The narrow openings typically measuring 3» to 5» in height, limits the items you
can bake to those not taller than the opening. Also, cakes, bread, pu pastries, and other
baked goods that need to rise or retain their moisture may break down or dry out under the
strong blasts of hot air.
7.4 Reel Oven
Reel-oven carriers are designed to hold baking trays of various sizes and shapes, including
pan straps. These versatile ovens can be used to bake hearth bread directly on the carriers or
bread rolls, which are rst proofed on dusted boards and then transferred onto the carriers.
Reel ovens are popular for baking various fermented products and confectionery items
because they oer even temperature distribution due to the paddle eect of the carriers and
are easy to load and unload. However, rack ovens have become a more convenient option
for smaller and in-store bakeries of grocery chain stores as they oer a quicker solution for
batch production of various products. The reel oven has some limitations, including a large
oor area compared to its baking capacity, many moving parts involved in its construction,
and diculty controlling steam distribution for specic products.
7.5 Wire Band Tunnel Oven
A wire band tunnel oven is an industrial oven that uses a continuous conveyor belt,
usually made of stainless steel wire mesh, to transport products through a heated tunnel.
The conveyor belt passes through multiple heating zones, each with its heating element,
allowing for precise temperature control throughout the baking process. The wire-band
tunnel oven is the most technologically and economically advanced bread-baking oven,
boasting excellent thermal eciency. It stands out from other types of ovens due to its
fully continuous operation, with dough pieces being fed at one end of the chamber and
discharged at the other. These ovens are designed for use in line-production systems, where
the baking stage needs to be synchronized with all previous and subsequent production
stages. To prevent signicant loss of production capacity and bread quality, the technologist
Baking 341
should be familiar with all potential corrective control measures for breakdowns and ow
disturbances.
7.6 Convection Ovens
Conveyor ovens are rectangular housing containing a baking cavity or chamber open on
two opposite sides. These ovens use a motorized fan or blower to force hot air throughout
the oven’s cavity, aecting cooking time and uniformity based on the speed and pattern
of airow. Conveyor ovens are rectangular housing with a baking chamber or cavity, with
openings on two opposite sides. A conveyor system carries the product on a wire rack
through the baking chamber, and some ovens have multiple conveyors for varying speeds.
Oven controls adjust heat input and conveyor speed, and newer conveyor ovens often
have multiple cooking zones within the chamber. Some also have a hinged glass door
beside the chamber for easy loading and unloading of food. Conveyor ovens are available
using four dierent heating processes: infrared, natural convection with a ceramic baking
hearth, forced convection, or a combination of infrared and forced convection. These ovens
come in various sizes and congurations and can be stacked up to three units high without
taking up additional oor space. Gas is the most popular fuel source for these ovens. They
can have single or multiple burners at the bottom of the cavity or between the cavity and
the insulated oven wall. Recently, many gas convection ovens have begun using infrared
burners instead of atmospheric ones, and they may employ dierent methods of directing
ue gases and mixing them with cavity air. Full-size (18 x 26 x 1”) and half-size (18 x 13
x 1”) forced convection ovens are also available and can accommodate standard full-size
or half-size sheet pans. Countertop, range-type convection, and high-capacity roll-in or
rack ovens are also oered. Convection ovens provide better cooking control than standard
ovens, thanks to accurate electronic sensors and thermostats. Gas models may feature
electronic ignition and controls, while newer gas and electric models have programmable
cooking computers. Some ovens allow users to regulate fan speed, temperature, humidity,
and cooking time to manage cooking.
7.7 Combination Oven
Ovens are convection-type ovens with a steam generator. This allows them to function as
both a traditional oven and a steamer, providing more versatility in cooking. They can be
used as a convection oven, a pressure-less steamer, or in combination mode. Combination
ovens come in dierent sizes, from smaller countertops or half-size models to larger full-
size units with up to 20 standard full-size sheet pans. They can hold traditional-sized
half- and full-sized sheet or steam pans, and large-capacity roll-in rack models are also
available. Although electric combination ovens are more common, some manufacturers
have recently introduced gas alternatives.
7.8 Rotisserie Oven
Rotisserie ovens are designed for batch cooking, with individual spits arranged on a rotating
wheel or drum within an enclosed cooking cavity. These ovens typically use gas burners or
electric elements as a heat source, and some models also incorporate high-wattage quartz
lamps for display and browning. Gas rotisserie ovens may use various burner systems,
including atmospheric ame type, radiant, and infrared, as well as dual burner systems
342 Unit Operations in Food Processing
that combine infrared with an open ame and radiant heat. Most gas models also feature
electronic ignition systems. Rotisserie ovens come in dierent sizes, from high-volume
oor models suitable for commercial kitchens to space-saving countertop models suitable
for home use. Most models come equipped with essential time and temperature controls,
but more sophisticated control packages with programmable channels and cook-and-hold
controls are also available.
7.9 Dutch Oven
A Dutch oven is a heavy, deep pot typically made of cast iron with a tight-tting lid. The
name ‹Dutch oven› comes from the fact that it resembles a pot used by early Dutch settlers
in America. Dutch ovens are known for their versatility and durability. They can be used
on the stovetop or in the oven, and they are great for cooking a wide range of dishes,
including soups, stews, casseroles, roasts, and bread. The cast iron construction of Dutch
ovens allows them to distribute heat evenly and retain heat well, making them ideal for
slow cooking and braising. One of the main advantages of using a Dutch oven is that it
allows for various cooking methods in one pot. Moreover, a tight-tting lid helps to trap
moisture and avour, resulting in tender and juicy meats and vegetables.
7.10 Rotary/Revolving/Mechanical Oven
Mechanical ovens, such as revolving ovens, are designed to rotate the food during the
baking process, which helps to ensure even cooking and eliminates the problem of hot
spots. This is particularly useful in high-volume operations where large quantities of food
must be cooked quickly and eciently. Revolving ovens can also be equipped with steam
injectors, which can help to keep the food moist and prevent it from drying out during the
baking process.
Fig. 7. Dierent Types of Oven
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8. RECENT DEVELOPMENT IN BAKING
Recent developments in baking include an increase in plant-based and healthier options, the
use of technology to improve the baking process and the quality of bakery products. These
developments make baking more diverse, healthier, and accessible to people with dierent
dietary preferences and lifestyles. Nowadays, a new development in bakery industries has
been observed in two directions, i.e. baking process and baking product.
8.1 Recent Development in Baking Process
Several recent developments in the baking process aim to address consumer demands for
healthier, more sustainable, and more convenient baked goods. Here are some of the recent
developments in the baking process:
8.1.1 Microwaves with IR Heating
Combining microwaves with IR heating has been found to have several benets in the
context of baking. Combining these two heating methods can result in reduced baking time,
improved browning and crisping, and better texture than microwaves alone. In microwave
baking, the heating mechanism is primarily through the excitation of water molecules,
which can result in uneven heating and poor crust formation. However, the addition of IR
radiation can help to compensate for these shortcomings by providing direct heating to the
surface of the food, resulting in better browning and texture. Furthermore, the combination
of these two heating methods can result in a reduction in overall baking time. This is
because microwaves can penetrate deep into the food, while IR radiation provides surface
heating, resulting in faster and more uniform food heating (Yolacaner et al., 2017).
8.1.2 Heating with Steam
Steam-assisted baking is a hybrid method that combines the advantages of steam baking
with natural and forced convection baking. This method has several benets, including
shorter baking times, lower formation of harmful compounds, and nutrient preservation.
Research has shown that steam-assisted baking can produce baked goods of similar quality
to those produced using other methods but with a lower level of acrylamide and larger
pore structure. Isleroglu et al. (2012) compared a steam-assisted oven with a domestic
convection oven at dierent baking temperatures with cookies. The cookies produced with
steam-assisted baking had the same quality in terms of spread ratio, bulk density, and
textural properties but with a considerably lower level of acrylamide. Similarly, Bredariol
et al. (2020) found that steam baking of bread resulted in larger pores than bread baked at
160 and 220 oC without steam. They also found that the crumb structure of bread baked
without steam appeared more fragile, which could be attributed to higher expansion. These
results suggest that steam-assisted baking can improve the texture and structure of baked
goods, resulting in higher-quality products.
8.1.3 Vacuum Baking
Vacuum baking is a technique that involves baking food products in a low-pressure
environment to reduce the boiling point of water and speed up the baking process. This
method has been shown to improve bread characteristics and reduce the baking time. In
one study, vacuum baking in combination with conventional baking produced bread with
344 Unit Operations in Food Processing
similar characteristics to commercially-produced bread in a signicantly shorter time
(Ruttarattanamongkol et al., 2011). The combination generated a slightly drier product
but a signicantly softened crumb texture. Another study found that baking dough rolls
at low temperatures in a partial vacuum resulted in more extraordinary oven rise than that
reached atmospheric pressure and demonstrated the eectiveness of the partial vacuum
in modifying the gas fraction of dough before the crust set (Grenier et al., 2019). Overall,
vacuum baking is a promising technique for improving the eciency and quality of baked
goods.
8.1.4 Infrared Burners
Infrared burners are becoming increasingly popular in gas ovens because they are more
ecient than traditional atmospheric burners. An infrared burner uses a ceramic plate to
produce infrared radiation, which heats the food directly rather than heating the air inside
the oven. This results in faster cooking times and more even heating. Infrared burners are
also more ecient because they consume less gas than atmospheric burners. An infrared/
forced convection oven combines the penetrating heat of infrared radiation with convection
to sharply reduce baking time compared to natural convection ovens. In this type of oven,
the infrared radiation heats the food directly, while the forced convection helps to circulate
the hot air around the food, resulting in faster and more even cooking.
8.1.5 Air Impingement
Air impingement is a newer technology used in conveyors and some rotisserie ovens that
use a ported manifold to direct jets of air or «ngers» onto the surface of the food being
cooked. This high-velocity airow helps to remove the insulating layer of air and moisture
around the food, resulting in faster cooking times and more even cooking. Conveyor ovens
using air impingement technology can quickly cook large volumes of food, making them
ideal for fast food restaurants and other high-volume operations. Additionally, the precise
control of the airow and temperature in air-impingement ovens allows for consistent
results and high-quality food production.
8.1.6 Quartz Halogen Lamps
Quartz halogen lamp ovens use infrared energy and visible light to cook food. The lamps
emit a high-intensity light that produces radiant heat, cooking food quickly and evenly.
This type of oven is benecial for browning and crisping the exterior of food and cooking
foods that require a high degree of precision, such as baking pastries and delicate desserts.
One of the benets of quartz halogen lamp ovens is that they start heating instantly, which
means they have no preheating time. This makes them ideal for busy commercial kitchens
where time is of the essence. Additionally, the lamps can be turned o when the oven is in
idle mode, which saves energy and reduces operating costs.
8.1.7 Optimization of Energy Demand
Optimizing energy demand using the modelling and computational uid dynamics is a
promising approach for improving production eciency and reducing carbon footprint
in the food industry. By quantifying the energy required to bake the dough and analyzing
oven losses, this approach can identify areas for improvement in oven design, operating
conditions, energy eciency, and baking. The approach proposed by Paton et al. (2013) is
Baking 345
an innovative method that models heat ow in a continuous industrial oven, including losses
to the ambient environment. It could reduce per-loaf energy consumption by approximately
2% and baking time by up to 10%. This could result in signicant cost savings for the food
industry and a more than 5000 tons of CO2 reduction in annual carbon footprint. Moreover,
this approach could identify additional areas for energy savings, such as heat recovery from
ue gases, improved heat transfer, and oven wall insulation. Optimizing energy demand
using modelling and computational uid dynamics can revolutionize the baking industry
by improving eciency, reducing costs, and minimizing environmental impact.
8.2 Recent Development in Bakery Products
Baking products have developed signicantly in recent years, driven by consumer demand
for healthier, more convenient, and more diverse options. Some signicant development
is as follows:
8.2.1 Gluten-Free Products
With the rise in celiac disease and gluten sensitivity, the demand for gluten-free bakery
products has increased. Bakers use alternative ours like almond, coconut, and rice our
to make delicious gluten-free bread, cakes, and pastries. In addition to this, some natural
binding agents can also be added such as gums and stabilizers to bind the dough and
provide structure the bakery items.
8.2.2 Functional Bakery Products
Functional bakery products are baked goods that have added ingredients or components
that oer additional health benets beyond their basic nutritional value. These added
components can be vitamins, minerals, ber, or other functional ingredients that have been
shown to promote health. Bakers now incorporate functional ingredients like probiotics,
bre, and protein into their baked goods to create healthier options that promote digestive
health and overall well-being.
8.2.3 Keto-Friendly Bakery Products
The popularity of the keto diet has led to the creation of bakery products that are low
in carbohydrates and high in healthy fats. Bakers use almond our, coconut our, and
erythritol to make delicious keto-friendly bread, muns, and cakes. These products are
suitable for those following a ketogenic diet, which involves consuming a high-fat, low-
carbohydrate diet that forces the body to burn fat for energy instead of glucose.
8.2.4 Vegan Bakery Products
Vegan bakery products are baked goods that are free from animal products such as eggs,
dairy, and honey. These products are suitable for those following a vegan diet, which
involves avoiding all animal-derived products for ethical, environmental, or health reasons.
Veganism has become more mainstream, and bakers are now creating vegan versions of
traditional bakery products like cupcakes, brownies, and cakes. They use plant-based
ingredients like almond milk, coconut oil, and vegan butter to make delicious and healthy
vegan bakery products.
346 Unit Operations in Food Processing
8.2.5 Artisanal Baking
Artisanal baking has become increasingly popular in recent years, with many bakers
focusing on creating unique and handcrafted baked goods. This trend focuses on traditional
techniques, natural ingredients, and creative avour combinations.
8.2.6 Sustainable Baking
With growing environmental concerns, bakers seek ways to reduce waste and operate
sustainably. This includes using locally-sourced ingredients, composting and recycling,
and reducing energy consumption in baking.
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