This document discusses principles of fluid milk production including milk reception, storage, and quality tests. Platform tests like sight-and-smell and alcohol tests provide rapid results for quality assessment. Confirmatory tests include resazurine and acidity tests. Factors like microbial load, temperature, and agitation affect milk quality. Pasteurization using batch or HTST methods destroys pathogens and improves shelf life. UHT processing at over 135°C allows milk to be stored for over 6 months without refrigeration.

1. PRINCIPLES OFFLUID MILK
PRODUCTION

2. Milk reception and storage
• Quality assessment
• Characteristic of high quality raw milk
• Free from debris and sediment
• Free from off flavours
• Low in microbial load
• Normal composition and acidity
• Free from antibiotics and chemical residues
• Whitish cream to yellowish in colour

3. PLATFORM TESTS
 Simple milk quality tests that may be carried out
routinely both at the farm and milk collection centre:
Examples of platform tests
 Sight-and-smell (organoleptic)/Sensory evaluationtest
 Clot-on-boiling test
 Alcohol test
 Lactometer test

4. Characteristics of platform tests
 Rapid results
 Simple to carry out
 Suitable for field conditions
 Easy to interpret results
 Provide accurate and reliable results
 Does not involve expensive equipment or
infrastructure
 Provide parameter for payment

5. Confirmatory tests
 Resazurine test
 Peroxide Test
 Titratable acidity test
 Peroxide test
 Compositional tests/ proximate analysis test
 Inhibitor tests
 Antibiotic test

6. ADVICING DAIRY FARMERS ON MILK
QUALITY
Abnormal appearance and smell that may cause
milk to be rejected could be due to:
 Type of feed or atmospheric taint (e.g. feeding silage or
brewer’s waste too close to milking time)
 Cows in late lactation or in some cows when on heat or
soon after conception (due to hormonal changes)
 Bacterial taints (from cows with mastitis)
 Chemical taints or discolouring (may be due to
equipment not rinsed properly)

7. Cont.
 Advanced acidification or souring (milk that is
fermenting)
Marked separation of fat may be caused by:
 Milk previously chilled and subjected to excessive
shaking during transportation
 Adulteration with other solids (may also show as
sediments or particles)
 Boiling, if milk fat is hardened

8. Factors affecting milk quality
 Microbial contamination (load).
 Storage temperatures.
 Time since milking.
 Exposure to light.
 Exposure to air/oxidation.
 Excessive agitation,
 Use of unsterilized equipment
 Prolonged cold storage

9. MILK PRESERVATION AND STORAGE
 Milk preservation is ensuring milk quality does not
deteriorate during storage prior to delivery processing
plant or commencement of processing.
 Done if the milking is not processed immediately
 Milk should be cooled within 2 -4 hours if it is not
collected immediately.
 The common method of preservation is cooling of
milk to below 100 C. Cooling does not destroy (kill) the
microorganisms but makes them dormant (sleep).

10. Remove impurities from milk
 (i) Filtration
 Milk filtration is the trapping and removal of
suspended particles of dirt and debris from milk.
 Raw milk as produced on the farm and transported to
the collection center or a dairy plant generally contains
varying amounts of visible, invisible impurities.
 This foreign matter includes straw and hair pieces,
dust particles, leukocytes (somatic cells or white blood
cells), insects, etc.

11. Factors determining the choice of filter to use
 Resistance to flow
 Clarity of filtrate required
 Resistance to wear (mechanical strength)
 Tendency to blind
 Cost

12. (ii) Clarification
 It involves the use of a centrifugal machine called
‘clarifier’. Thus, clarification is a process of subjecting
milk to a centrifugal force in order to eliminate the
finer but heavier particles from milk, somatic cells,
dust particles, etc
 These steps of aesthetic improvement of product are
particularly useful for overcoming the problem of
sediments in fluid milk and milk products in general,
and homogenized milk in particular

13. Clarification cont.
 Although part of bacteria is also removed along with
the extraneous matter, clarification cannot be
considered an effective means of bacteria removal.
Hence, one should be aware that it cannot be a
substitute for a suitable heat treatment in order to
ensure safety against pathogenic (disease-causing)
microorganisms.

14. (iii) Bactofugation
 This is removal of sediments and bacteria spores using
a centrifugal separator. It operates at about 70°C,
however part of the casein is also separated.
 Typical gram positive bacteria are best known
producers of spores
 This method is applied to milk for some special
applications especially products that are low-
pasteurized eg removal of spores of Bacillus cereus
from beverage milk or of Clostridium tyrobutyricum
and related species from cheese milk.

15. Cont.
 Spores are quite small, but the density difference with
plasma is larger than that of bacteria, and at
separation temperatures of 60 to 70°C, a substantial
proportion can be removed, generally 90 to 95%.
 By using two bactofuges in series, a reduction by over
99% can generally be attained.
 It should be noted that bactofugation is by no means
equivalent to sterilization: the product still contains
heat-resistant bacteria and a small number of spores.

16. Centrifugation
Centrifugal separation is a process used quite often in
the dairy industry. Some uses include:
• clarification (removal of solid impurities from milk
prior to pasteurization)
• skimming (separation of cream from skim milk)
 whey separation (separation of whey cream (fat) from
whey)
 Bactofuge treatment (separation of bacteria from
milk)

17.  Principles of Centrifugation
 Centrifugation is based on Stoke's Law. The particle
sedimentation velocity increases with:
 increasing diameter
 increasing difference in density between the two
phases
 decreasing viscosity of the continuous phase

18.  Separation
 If raw milk were allowed to stand, the fat globules
would begin to rise to the surface in a phenomena
called creaming. Raw milk in a rotating container also
has centrifugal forces acting on it. This allows rapid
separation of milk fat from the skim milk portion and
removal of solid impurities from the milk.

19.  Centrifuges can be used to separate the cream from the
skim milk. The centrifuge consists of up to 120 discs
stacked together at a 45 to 60 degree angle and
separated by a 0.4 to 2.0 mm gap or separation
channel.

20.  Milk is introduced at the outer edge of the disc stack.
The stack of discs has vertically aligned distribution
holes into which the milk is introduced.

21.  Under the influence of centrifugal force the fat
globules (cream), which are less dense than the skim
milk, move inwards through the separation channels
toward the axis of rotation. The skim milk will move
outwards and leaves through a separate outlet.

22.  Standardization
 The streams of skim and cream after separation must
be recombined to a specified fat content. This can be
done by adjusting the throttling valve of the cream
outlet; if the valve is completely closed, all milk will be
discharged through the skim milk outlet.

23. • Homogenization
• Milk is an oil-in-water emulsion, with the fat globules
dispersed in a continuous skimmilk phase. If raw milk
were left to stand, however, the fat would rise and form
a cream layer. Homogenization is a mechanical
treatment of the fat globules in milk brought about by
passing milk under high pressure through a tiny
orifice, which results in a decrease in the average
diameter and an increase in number and surface area,
of the fat globules.

25.  Pasteurized milk does not necessarily need to be
homogenized. However, homogenized milk should be
pasteurized to inactivate native enzymes that
deteriorate fat (lipases) and cause rancidity, which
results in off-flavors and reduced shelf life in milk.

26.  The purpose of homogenization is to reduce the milk
fat globules size to less than 1.0 µm which allows them
to stay evenly distributed in milk.
 Homogenization is a high pressure process that forces
milk at a high velocity through a small orifice to break
up the globules.

27. Pasteurization Process
 There are basically two methods of pasteurization in
use today – batch and continuous flow
 In the batch process a quantity of milk is held in a
heated vat at 65oc for 30 minutes followed by quick
cooling to 4oc.

28. Pasteurization Process CONT,D
 In the continuous flow process also known as High
Temperature Short Time (HTST) method. The milk is
forced between metal plates in a plate heat exchanger
or through pipes in tubular heat exchangers.
 While flowing under pressure the milk is held at 72oC
for at least 15 seconds and the quickly cooled to 4oc. It
flows through a heat exchanger to pre-warm cold milk
entering the system.

29. Pasteurization Process CONT,D
 The ultimate goal in heat treatment of milk is the
destruction of all pathogenic (disease causing
microbes) and to improve the keeping quality by
reducing the number of spoilage microbes as much as
possible.

30. UHT Milk Processing
 Introduction
 While pasteurization conditions effectively eliminate
potential pathogenic microorganisms, it is not
sufficient to inactivate the thermoresistant spores in
milk.

31.  The term sterilization refers to the complete
elimination of all microorganisms. The food industry
uses the more realistic term "commercial
sterilization"; a product is not necessarily free of all
microorganisms, but those that survive the
sterilization process are unlikely to grow during
storage and cause product spoilage.

32.  Milk can be made commercially sterile by subjecting it
to temperatures in excess of 100° C, and packaging it in
air-tight containers. The milk may be packaged either
before or after sterilization.

33.  The basis of UHT, or ultra-high temperature, is the
sterilization of food before packaging, then filling
into pre-sterilized containers in a sterile atmosphere.

34.  Milk that is processed in this way using temperatures
exceeding 135° C, permits a decrease in the necessary
holding time (to 2-5 s) enabling a continuous flow
operation.

35. • Long shelf life:
• Greater than 6 months, without refrigeration, can be
expected.

36.  Difficulties with UHT
 Sterility:
 Complexity of equipment and plant are needed to
maintain sterile atmosphere between processing and
packaging (packaging materials, pipework, tanks,
pumps); higher skilled operators; sterility must be
maintained through aseptic packaging

37.  Particle Size:
 With larger particulates there is a danger of
overcooking of surfaces and need to transport material
- both limits particle size
 Equipment:
 There is a lack of equipment for particulate
sterilization, due especially to settling of solids and
thus overprocessing

38.  Keeping Quality:
 Heat stable lipases or proteases can lead to flavour
deterioration, age gelation of the milk over time -
nothing lasts forever! There is also a more pronounced
cooked flavour to UHT milk.

39.  Packaging for Aseptic Processing
 The most important point to remember is that it must
be sterile! All handling of product post-process must
be within the sterile environment.

40. • There are 5 basic types of aseptic packaging lines:
• Fill and seal: preformed containers made of
thermoformed plastic, glass or metal are sterilized,
filled in aseptic environment, and sealed
• Form, fill and seal: roll of material is sterilized,
formed in sterile environment, filled, sealed e.g.
tetrapak
• Erect, fill and seal: using knocked-down blanks,
erected, sterilized, filled, sealed. e.g. gable-top cartons,
cambri-bloc

41. • Thermoform, fill, sealed roll stock sterilized,
thermoformed, filled, sealed aseptically. e.g. creamers,
plastic soup cans
• Blow mold, fill, seal:
• There are several different package forms that are
used in aseptic UHT processing:
• cans
• paperboard/plastic/foil/plastic laminates
• flexible pouches

42.  Thermoformed plastic containers
 Flow molded containers
 Bag-in-box
 Bulk totes
 It is also worth mentioning that many products that
are UHT heat treated are not aseptically packaged.

43.  This gives them the advantage of a longer shelf life at
refrigeration temperatures compared to
pasteurization, but it does not produce a shelf-stable
product at ambient temperatures, due to the
possibility of recontamination post-processing.