The document summarizes dairy processing technology, focusing on cheese and yogurt production. It discusses the science behind cheese processing including coagulation mechanisms and different types of cheese. It also explains yogurt production, describing the basic science of how milk becomes yogurt through bacterial fermentation. The key steps in cheesemaking are outlined as milk treatment, coagulation, whey removal, shaping, salting, and ripening. The main types of yogurt are described as set, stirred, and drinkable.

1. FOOD PROCESSING
TECHNOLOGY
Lecture Five
By: Shewarega Habtamu (PhD candidate)

2. Chapter 3
Animal products processing
Dairy processing technology
(2/3)
2

3. Learning Objectives
o:-
• At the end of this Lecture, students should be able t
A.Discuss the science behind cheese processing (coagulation
mechanisms),different types of cheese with their respective
processing steps.
B.Explain the science behind production of yogurt and
C.Differentiate between different types of yogurt with respective
properties and processing steps.
3

4. Dairy products

5. 1.Cheese processing
• Cheese is the most complex of the
dairy products, involving chemical,
biochemical and microbiological
processes.
• The steps in all cheese making include
milk acidification, milk coagulation,
whey removal, packaging and storage.

6. 1.1 Classification of cheese
Factors determining cheese types include:
• Source of milk-cow’s, goat’s and buffalo’s milk.
• Moisture content
• Composition of milk (fat and casein)
• Manner of coagulation of milk (pH or chymosin)
• Salt content and manner of salting
• Extent and condition of ripening.
• More than 400 varieties of cheeses are listed by the
International Dairy Federation. (Cheddar,
Mozzarella,..)
▪ Wide flavor profiles

7. 1.2 Cheese Production steps
• Cheese is a concentrated form of 2 major milk
components – milk protein (casein) and
milkfat.
1. Milk treatment- Pasteurization and
standardization
2. Coagulation/curdling
• Milk protein consists of casein (80%) and
whey proteins (20%)

8. 1.2.1 Coagulation methods/mechanisms
• It is the step during which milk undergoes a profound physical
and rheological change that is gelation.
• Coagulation can occur in a few different ways: enzyme action,
acid addition, or acid/heat addition.
• Factors that affect aggregation are casein concentration and
milk pH.

9. Cont’d

10. a) Acidic coagulation
• κ-casein hairs cause casein micelles to bounce off each other in
milk
• Coagulation is getting those casein micelles to stick together
• a “starter culture” of bacteria is added
• to sour it (converts lactose into lactic acid).
• Lactic acid acts as a preservative and gives flavour.
Acid neutralizes casein micelles
and allows them to clot

11. Cont’d
• Different LAB species
results in different
types of products.

12. Cont’d
Curdling time takes 2 – 16 hrs. depending on
• The amount of inoculating agent added (0.1- 5% of the milk used to make
cheese),
• Temperature (20 - 35°C) and
• The starter culture used

13. b) Enzymatic coagulation
• Enzymatic coagulation is accomplished by enzymes from
animal, plant and microorganisms. E.g. rennet.
• Rennet enzymes act live a razor and shave off the κ-casein hairs.
Without the hairs, the micelles can now stick, aggregate, and
form the backbone of cheese structure.

14. The rennet in cheese has two functions
• Rennet causes the milk to coagulate
• Since k-casein stabilizes the other caseins and its hydrolysis leads to the
coagulation of the casein fraction, the primary phase can also be expressed as:
• During ripening, rennet causes milk protein to break down, giving the typical
cheese taste.
Cont’d

15. Cont’d
• Rennet is available in the form of liquid,
powder and tablet
• For soft cheese, No rennet/little

16. c) Acid & Heat Coagulation
• This process permits recovery of caseins and whey proteins in a
single step.
• The basic principle is that whey proteins which are normally acid stable,
become sensitive to acid coagulation after heat treatment.
• Examples of this include ricotta, mascarpone, and paneer.
• Whey proteins are denatured (unraveled) by heat exposing “sticky” portions of
their structure. These sticky ends can bond to each other across whey
proteins or bond to casein proteins.

17. Calcium Chloride
• Cheese makers will dilute CaCl2 in water and add to the vat
before rennet is added.
• CaCl2 helps the coagulation process in two main ways:
• When in solution, it forms calcium ions (Ca2+), calcium is the “glue”
that helps hold together protein structure.
• It can decrease pH slightly, which increases rennet activity and
promotes coagulation.

18. 3. SYNERESIS
• Expelling entrapped liquid (Whey).
• accelerated by cutting the coagulum into small cubes.
• The amount and extent of syneresis has an effect on the final
moisture content (obviously), and by extension the texture and
flavor

19. Cont’d
• There are a few ways syneresis can be accelerated:
• Cutting curd into smaller pieces (like with Grana-style cheeses) – more
surface area allows for more whey to leak out
• Cooking the curd – heating the curd can contract the protein structure
squeezing out whey
• Stirring the curds/whey – the motion and agitation can encourage whey
expulsion
• Pressing the curds – literally squeezing the sponge
• Salting the curds – salt draws out moisture
• Acidification – starter is producing acid which can encourage syneresis

21. 4. SHAPING AND SALTING
• The curd-shaped into some form
and salted.
• Salt expels additional whey.
The salted curd is then hooped
in molds and pressed overnight.

22. 5. RIPENING
• Natural process of microbial, chemical and biochemical
reactions that occurs in a cheese after its manufacture and
during storage.
• Gives different cheeses their unique flavors, textures, and
appearances.
• Temperature and humidity are factors that cheese makers can
control during ripening.
• The ripening of cheese involves 3 primary biochemical
processes— glycolysis, lipolysis, and proteolysis.

23. To summarize …

24. 1.3 Types of cheese
Depending on ripening characteristics
1. Fresh Cheeses: are easy to identify
because they are white, shiny & have no
rind.
o lowest Fat content of all the cheese
categories 19–21 percent.
o Highest moisture content of all the
cheese categories.
Halloumi, Ricotta, Feta,
o Examples:
Mozzarella.

25. Cont’d
2. Ripened Cheeses: allowed to age and dry
out in special temperature- and humidity.
o They lose moisture and shrink as they age.
o As the cheeses age, the texture inside
gradually changes from moist, and slightly
crumbly to dense, compact, flaky and
brittle.
o They have a fat content of 22–23 percent.
o Examples: Valencay, Clochette,

26. Cont’d
• Depending on moisture content:
1. Soft White Cheeses:
o Has white crust that can be stained with reddish pigments
or yellow-gray blotches of mold.
o They have a high moisture (>67%) content, which keeps fat
content of 24–26 percent.
o <30 days of aging
o Examples: Brie de Melun, Capricorn Goat, Sharpham

27. Cont’d
2. Semi-Soft Cheeses: All semi-soft cheeses are washed in brine
to discourage unwanted molds.
o They have a fat content of 22–30 percent.
o They retain a lot of moisture (61-69%) as they are only
lightly pressed.
o It is considered ripe from three weeks to three months.
o Examples: Taleggio, Langres, Stinking Bishop

28. Cont’d
3. Hard Cheeses: The amount of whey expelled determines the
texture. The more moisture removed, the longer the
maturation, and more complex the final flavors.
o considered ripe from a few weeks old to three years.
o They have a fat content of 28–34 percent and moisture
content of (49-56%).
o Example: Manchego, Emmentaler, cheddar cheese.

29. Cont’d
Flavor-added Cheeses:
o Hard or semi-soft cheeses combined with fruit, spices, Garlic,
Nuts and herbs.
o Examples: Nagelkaas, Idiazabal.

30. To summarize
Production of cheese

31. 2. Yoghurt production
• Yoghurt is produced by the controlled fermentation of milk by
two species of bacteria Lactobacillus sp. and Streptococcus sp.
• For a satisfactory flavor to develop, approximately equal numbers of
both species should be present.
• They have a stimulating effect on each other’s growth.
• Volatile compounds produced by the yogurt bacteria include
small amounts of acetic acid, diacetyl, and most importantly,
acetaldehyde.

32. Cont’d
• Streptococcus thermophilus brings the pH of the milk down to 5.5
• Lactobacillus bulgaricus converts lactose to lactic acid
• Proteolytic enzymes from L. bulgaricus break down milk proteins into
peptides.
• The lactic acid coagulates the remaining milk proteins, causing the
yoghurt to thicken.

33. 2.1 Basic Science of Yogurt
• Chemically, when milk becomes yogurt it is changing from
an emulsion to a colloid.
• Emulsion: mixture of two liquids,like oil and water. Milk is
an emulsion of water and oil (milk fat)
• Colloid: a dispersion of solid particles in a liquid

34. Cont’d
• The predominant protein
in milk is casein
• In raw milk casein forms
micelles
• Bacterial growth results
In acid production
• Acid (low pH) breaks up
micelles
• Casein then forms a net
that traps water

35. 2.2 Types of yogurt
1. set yogurt
• Incubated and cooled in the final package
• A solid set(curd) where the yogurt firms in a container and nor disturbed
2. Stirred yogurt
• Incubated in a tank
• Coagulum broken by stirring prior to cooling and packing
• Less firm texture…like a thick cream
3. Drinkable yogurt
• Similar to stirred yogurt
• Additional milk and flavors are mixed in.

36. 2.3 Production steps