Dairy processing technology

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

2. Chapter 3
Animal products processing
Dairy processing technology
(1/2)
2

3. Learning Objectives
to:-
• At the end of this Lecture, students should be able
A.Understand the nutritional composition of milk and
factors affecting the composition
B.Explain the production of clean milk and spoilage
indicators.
C.Discuss the importance of milk processing.
D.Understand the major unit operations involved for the
production of pasteurized/sterilized milk.
3

4. 1. Introduction
WHAT IS MILK?

5. Cont’d
• Fluid secreted by the female of all mammalian
species for primary function of meeting the complete
nutritional requirements of the neonate of the species.
• Cow, goat, sheep, buffalo and human>>well
characterized milks.

6. Cont’d
• High in protein and essential vitamins
and minerals
• Our most nearly perfect food.
• Per-capita consumption
• FINLAND- 375 L/year
• ETHIOPIA- 16-25 L/year???
• WHO recommend 200 L/year

7. 2. Nutritional content
a) Gross compositions of selected species
Species Total
solids
Fat protein lactose Ash
Human 12.2 3.8 1.0 7.0 0.2
cow 12.7 3.7 3.4 4.8 0.7
goat 12.3 4.5 2.9 4.1 0.8
sheep 19.3 7.4 4.5 4.8 1.0

8. B) Proximate compositions of cow’s milk
Major minerals- Calcium, phosphate, magnesium, sodium, potassium….
Vitamins A, B6, B12, C, D, K, E, thiamine, niacin, biotin, riboflavin, folates

10. Allergy related to milk
• Lactose intolerance
• The inability to digest lactose, a sugar found in milk
and to a lesser extent dairy products, causing side
effects.
• Undigested lactose can be converted by the
microbial flora in the intestine into lactic acid
and gases.
• Consumption of larger quantities of milk thus
causes flatulence, stomach cramps and
diarrhea.

11. 2.1 Factors affecting milk composition
✓ Breed differences
Components Breeds
Ayrshire Brown
Swiss
Guernsey Holstein Jersey Shorthorn
Fat 3.95 3.98 4.72 3.54 5.13 3.5
Lactose 3.48 3.64 3.75 3.29 3.97 3.32
Ash 0.72 0.74 0.76 0.72 0.76 0.75
Total Solids 12.77 13.07 14.04 12.16 14.42 12.27

12. Cont’d
✓ Age of animal
✓ Stage of lactation & pregnancy
✓ Condition of animal-Mastitis
{inflammation of the udder}
✓ Method of milking-
Completeness of milking (Hand
and Machine milking)
✓ Season of the year
✓ Other factors–contamination
and processing

13. 2.2 Production of Clean Milk
• Environmental hygiene – water, insects, rodents
• Hygienic production of milk
• Areas and premises for milk production
• Animal Health
• General hygienic practices including feeding, pest control,
veterinary drugs
• Hygienic milking
• Handling, storage and transport of milk
• Milking equipment
• Storage equipment and premises
• Collection, transport & delivery procedures and equipment
• Documentation and Record Keeping- Weighing

14. Cont’d
➢ Growing of microbes influenced by:
⚫ Initial cell count
⚫ Quality and kind of microbes
⚫ Temperature of milk
➢ Milk from healthy animal: 103-
104 bacteria/ml
➢ Milk must be chilled to 𝟒 𝒐C or below
as soon as it leaves the cow

15. 2.3 Results of Microbial Growth in Milk (Milk
spoilage indicators)
 Souring-Most common, due to transformation of
lactose into lactic acid, other volatile acids &
compounds, principally by lactic acid bacteria.
 Souring & gassiness-Caused by E.coli
group, indicates contamination of milk
and its products.
 Aroma production-Due to production of
flavour compounds such as diacetly.

16. Cont’d
 Proteolysis:- Protein decomposition leading to
unpleasant odor.
Ropiness:- Long threads of milk are formed while
pouring.
 Sweet curdling:- Due to production of a
remain like enzyme curdles milk without
souring

17. 3. Processing of milk
3.1 WHY PROCESSING?
1.Preservation
• Longer shelf life
2.Reduction of health hazard
3.Protection
• safer
4.Added value
• more appealing or
healthier
• Improves nutrition

18. 3.2 Unitoperations for Pasteurization of milk
• Milk receiving
• Pre-heating
• Separation
• Standardization
• Homogenization
• Pasteurization
• Packaging

19. 1. Collection and reception of milk
• The first thing done at
reception is to determine the
quantity of the milk.
• From weighing-in, the raw milk
is pumped to storage tanks to
await processing.
• The empty churns are
conveyed to a cleaning
station.

20. 1.1 Testing milk for quality
i. Taste and smell-deviates in taste
and smell from normal milk
ii. Cleaning checks- The inside surfaces
of farm tanks and churns are carefully
inspected.
iii.Sediment-This applies only to churns. A
sample is taken with a pipette from the
bottom of a churn and is then passed
through a filter. A quality deduction is
made if visible impurities are retained
by the filter.

21. Cont’d
iii.Somatic cell (white blood corpuscles or leucocytes)
count
• A large number (more than 500,000 cells/ml of milk)
of somatic cells in the milk indicates that the cows
are suffering from udder diseases. The cell content
is determined with specially designed particle
counters (Coulter counter, etc.).
Iv. Bacteria count
• A simplified form of bacteria count can also be used to
assess the bacteria content.

22. Cont’d
v. Freezing point
• Many dairies check the freezing point of
the milk to determine whether or not it
has been diluted with water. Milk of
normal composition has a freezing point
of -0.54 to -0.59°C.The freezing point will
rise if water is added to the milk.
vi. Protein content
vii.Fat content

23. Cont’d
• Measuring the density of milk is easy
Done with a lactometer
• Lactometer: hydrometer for milk Can
quickly and easily tell if something is
added to milk based on density

24. 2. Balance tank
• After the milk is collected
from the farm or collection
center, it will be stored in
refrigerated storage tank until
it is needed for processing.
• Balance tank is used to weigh
and maintain constant flow of
liquid milk to the next
operation during processing.

25. 3.Milk Separation
• Newer technologies: Both clarification and separation
of milk done together:
• Both activities, clarification and de- creaming are
combined in one operation with a three-phase
separation (Dirt, skim milk and cream)

26. Decreaming Process
• Separation/Centrifugation: the mechanical separation of milk
into cream and skim milk by means of centrifugal force.
• De-creaming process controls the efficiency of the fat
separation due to specific density differences b/n milk fat
(0.93 g/cm3) and skim milk (1.035 g/cm3)
• density differences: Related with Temperature
• Objective of De-creaming:
✓ Obtain a fat-reduced or fat-free milk
✓ Concentrate milk fat for the production of high fat products
✓ Standardize the fat content of milk.
• STOCKS LAW:

27. Centrifugal/Gravitational separation

28. Principles of separation
• The centrifuge bowl has baffle inserts in the form
of conical discs. This increases the area
available for sedimentation.
• The discs rest on each other and form a unit
known as the disc stack. Radial strips called
caulks are welded to the discs and keep them the
correct distance apart.
• This forms the separation channels. The
thickness of the caulks determines the width.

29. Cont’d

30. Cont’d
• The cream, i.e. the fat globules, has a
lower density than the skim milk and
therefore moves inwards in the
channels, towards the axis of rotation.
The cream continues to an axial outlet.
• The skim milk moves outwards to the
space outside the disc stack and from
there through a channel between the top
of the disc stack and the conical hood
of the separator bowl to a concentric
skim milk outlet.

31. Cont’d

32. 4. Standardization
• Standardization of fat content involves adjustment of
the fat content of milk, or a milk product, by addition
of cream or skim milk as appropriate to obtain a given
fat content.
• Various methods exist for calculating the quantities of
products with different fat contents that must be
mixed to obtain a given final fat content.

33. Pearson’s square
• How many kg of cream of 40% fat must be mixed with skim milk
of 0.05% fat to make a mixture containing 3% fat?
• The answer is obtained from a rectangle, where the given figures
for fat contents are placed.
• Subtract the fat content values on the diagonals to give C – B =
2.95 and A – C = 37.
• 2.95 kg of 40% cream 37 kg of 0.05 % skim milk to obtain 39.95
kg of a standardized product containing 3% fat.
• From the equations below it is then possible to calculate the
amounts of A and B needed to obtain the desired quantity (X) of C.

34. Principle of standardization

35. 5.Homogenization
• One of the essential unit operation in dairy Industries
(can reach 65 0C)
• The function of homogenization is to prevent
creaming/the rising of fat to the top of the container
of milk, Disruption of Fat Globules.
• Expected result after homogenization: Milk maintains
a more uniform composition.

36. Cont’d
• At homogenization the milk is forced through a narrow
gap where the fat globules are split.

37. Principles of Homogenizer
• Mechanically increases the number and reduces the size of
the fat globules (from 2-6μm down to < 0.5 μm)
• Milk pumps under high pressure [2000-2500lbs/sq.in(psi)]
through small mesh orifices of a homogenizer .
• There are single and double stage homogenizers
• The homogenization process: Emulsifies the fine fat globules
and as the surfaces of many new fat globules are formed.

38. Cont’d
• Each fat globule becomes coated with a lipoprotein
membrane and additional proteins from casein. These
proteins adsorb to the freshly-created oil surface
preventing globules from reuniting and the fat
remains homogenously distributed throughout milk.
• Homogenization process prior to subsequent
pasteurization

39. Cont’d
• Single-stage and Second-stage Homogenization.

40. Effect of homogenization
• The effect of homogenization on the physical structure of
milk has many advantages:
• Smaller fat globules leading to no cream-line formation,
• Whiter and more appetizing colour,
• Reduced sensitivity to fat oxidation,
• More full-bodied flavour, better mouth feel,
• Better stability of cultured milk products.

41. Cont’d
• However, homogenisation also has certain disadvantages:
• Homogenised milk cannot be efficiently separated.
• Somewhat increased sensitivity to light – sunlight and
fluorescent tubes –can result in “Sunlight flavour”.
Reduced heat stability, especially in case of single-stage
homogenization, high fatcontent and other factors
contributing to fat clumping.
• The milk will not be suitable for production of semi-hard
or hard cheeses because the coagulum will be too soft and
difficult to dewater.

42. 6. Pasteurization
• Pasteurization is a process used to kill harmful microorganisms,
such as certain pathogenic bacteria, yeasts and moulds, which
may be present in the milk after initial collection. This process
extends the shelf life of milk.
• 63 oC- for 30 min
• 72 oC- for 15 sec
• 88 oC- for 1 sec
• Milk’s keeping quality is improved, but nutrient value is not
significantly changed.
• pasteurized milk should have a shelf life of 8 – 10 days at 5 – 7°C
in an unopened package.

43. Pasteurizers: A plate type heat exchangers

44. 7. Sterilization
• 138-150oC for 2 seconds-UHT processing (sterile, aseptic)
• The milk does not require refrigeration until it is
opened.