Analytical methods for dry milk products are an almost forgotten subject in the literature. The only existing publication was issued by GEA in 1978 [31], but updated versions of analytical methods can now be found on GEA's Analytical Methods for Dry Milk Products page.
Since the time of the first publication, many new methods, especially for testing instant properties, have been developed by various milk powder and baby food manufacturers and are considered the intellectual property by these companies. Hence descriptions of these new methods are generally not accessible and are found only sporadically in articles in dairy magazines.
In this chapter, the methods commonly used in practice are described just briefly without unnecessary details of common analytical procedures, anticipating that such are known to the experienced analyst.
Moisture content
Standard oven drying method (IDF Standard No.26-1964 [32])
Free moisture

Total moisture
Water of crystallization
Insolubility index

Bulk density

Particle density
The particle density is the mass in g/ml of the particles. The particle density is always lower than the density of the solids due to the presence of vacuoles (occluded air). The most accurate method for determination of particle density is based on the air pycnometer method, the principle of which is shown on Fig. 11.4. The container with a weighed sample is inserted into the measuring cylinder and the apparatus is hermetically closed. By means of a screw arrangement both pistons are moved simultaneously forward increasing thus the air pressurein both cylinders, but keeping zero differential pressure between the cylinders. When the reference cylinder comes to a stop, the readout on the measuring cylinder indicates the powder volume.





Scorched particles
Wettability

Dispersibility


Other methods for determination of instant properties
Sludge
Property | Powder type | Temperature °C | Standing time min. |
---|---|---|---|
Sludge 25 or cold sludge | Instant powder | 25 | 2 |
Sludge 45 or cold sludge | Agglomerated |
45* |
15 |
Sludge 85 or hot sludge | Both instant and agglomerated |
85* |
15 |
*After standing, remove the skin with a teaspoon. |
Slowly dispersible particles
Hot water sediment
Coffee test
White flecks number


Total fat content
Free fat content


Particle size distribution

Mechanical stability
Hygroscopicity



Degree of caking

Total lactose and α-lactose content






Temperature °C | 0 | 10 | 20 | 25 | 30 | 40 | 50 |
---|---|---|---|---|---|---|---|
x = β : α | 1,65 | 1,62 | 1,59 | 1,58 | 1,57 | 1,54 | 1,51 |
y = (1 + x)/x | 1,61 | 1,62 | 1,63 | 1,63 | 1,64 | 1,65 | 1,66 |
Titratable acidity
% l.a. |
0,01 | 0,10 | 0,11 | 0,12 | 0,13 | 0,14 | 0,15 | 0,16 | 0,17 | 0,18 | 0,19 |
---|---|---|---|---|---|---|---|---|---|---|---|
°Th |
1,11 | 11,11 | 12,22 | 13,33 | 14,44 | 15,55 | 16,67 | 17,78 | 18,89 | 20,00 | 21,11 |
°D |
1,00 | 10,00 | 11,00 | 12,00 | 13,00 | 14,00 | 15,00 | 16,00 | 17,00 | 18,00 | 19,00 |
°SH |
0,44 | 4,44 | 4,89 | 5,33 | 5,78 | 6,22 | 6,67 | 7,11 | 7,55 | 8,00 | 8,44 |
% l.a. |
0,20 | 0,21 | 0,22 | 0,23 | 0,24 | 0,25 | 0,30 | 0,50 | 0,70 | 0,90 | 1,00 |
°Th |
22,22 | 23,33 | 24,44 | 25,55 | 26,66 | 27,78 | 33,33 | 55,55 | 77,77 | 99,99 | 111,10 |
°D |
20,00 | 21,00 | 22,00 | 23,00 | 24,00 | 25,00 | 30,00 | 50,00 | 70,00 | 90,00 | 100,00 |
°SH |
8,89 | 9,33 | 9,78 | 10,22 | 10,67 | 11,11 | 13,33 | 22,22 | 31,11 | 40,00 | 44,44 |
Whey Protein Nitrogen Index (WPNI)


Flowability (GEA Niro [31])

Product | Flowability in s |
---|---|
Rewet aggl. skim milk powder | 5 - 15 |
Agglomerated skim milk powder | 10 - 20 |
Ordinary skim milk powder | 50 |
Agglomerated whole milk powder (MSD) | 20 - 30 |
Agglomerated whole milk powder (SDI) | 50 - 100 |
Instant whole milk powder (MSD) | 40 - 60 |
Instant whole milk powder (SDI) | 100 - 200 |
Ordinary whole milk powder | 200 - 300 |
Fat milk powder (50% fat) | 250 - 500 |
Lecithin content



Analytical methods for milk concentrates
Total solids


Insolubility index
Viscosity
Degree of crystallization


Inhoudsopgave
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1.Introduction
-
2.Evaporation
- 2.1. Basic principles
- 2.2. Main components of the evaporator
- 2.2.1. Heat exchanger for preheating
- 2.2.1.1. Spiral-tube preheaters
- 2.2.1.2. Straight-tube preheaters
- 2.2.1.3. Preheaters to prevent growth of spore forming bacteria
- 2.2.1.3.1. Direct contact regenerative preheaters
- 2.2.1.3.2. Duplex preheating system
- 2.2.1.3.3. Preheating by direct steam injection
- 2.2.1.4. Other means to solve presence of spore forming bacteria
- 2.2.1.4.1. Mid-run cleaning
- 2.2.1.4.2. UHT treatment
- 2.2.2. Pasteurizing system including holding
- 2.2.2.1. Indirect pasteurization
- 2.2.2.2. Direct pasteurization
- 2.2.2.3. Holding tubes
- 2.2.3. Product distribution system
- 2.2.3.1. Dynamic distribution system
- 2.2.3.2. Static distribution system
- 2.2.4. Calandria(s) with boiling tubes
- 2.2.5. Separator
- 2.2.5.1. Separators with tangential vapour inlet
- 2.2.5.2. Wrap-around separator
- 2.2.6. Vapour recompression systems
- 2.2.6.1. Thermal Vapour Recompression – TVR
- 2.2.6.2. Mechanical Vapour Recompression - MVR
- 2.2.7. Condensation equipment
- 2.2.7.1. Mixing condenser
- 2.2.7.2. Surface condenser
- 2.2.8. Vacuum equipment
- 2.2.8.1. Vacuum pump
- 2.2.8.2. Steam jet vacuum unit
- 2.2.9. Flash coolers
- 2.2.10. Sealing water equipment
- 2.2.11. Cooling towers
- 2.3. Evaporator design parameters
- 2.3.1. Determination of heating surface
- 2.3.2. Heat transfer coefficient
- 2.3.3. Coverage coefficient
- 2.3.4. Boiling temperature
- 2.4. Evaporation parameters and its influrence on powder properties
- 2.4.1. Effect of pasteurization
- 2.4.1.1. Bacteriological requirements
- 2.4.1.2. Functional properties of dried products
- 2.4.1.2.1. Heat classified skim milk powders
- 2.4.1.2.2. High-Heat Heat-Stable milk powders
- 2.4.1.2.3. Keeping quality of whole milk powders
- 2.4.1.2.4. Coffee stability of whole milk powders
- 2.4.2. Concentrate properties
-
3.Fundamentals of spray drying
- 3.1. Principle and terms
- 3.1.1. Drying air characteristics
- 3.1.2. Terms and definitions
- 3.1.3. Psychrometric chart
- 3.2. Drying of milk droplets
- 3.2.1. Particle size distribution
- 3.2.2. Mean particle size
- 3.2.3. Droplet temperature and rate of drying
- 3.2.4. Particle volume and incorporation of air
- 3.3. Single-stage drying
- 3.4. Two-stage drying
- 3.5. Expansion of air bubbles during drying
- 3.6. Extended Two-stage drying
- 3.7. Fluid bed drying
-
4.Components of a spray drying installation
- 4.1. Drying chamber
- 4.2. Hot air supply system
- 4.2.1. Air supply fan
- 4.2.2. Air filters
- 4.2.3. Air heater
- 4.2.3.1. Indirect: Gas / Electricity
- 4.2.3.2. Direct heater
- 4.2.4. Air dispersers
- 4.3. Feed supply system
- 4.3.1. Feed tank
- 4.3.2. Feed pump
- 4.4. Concentrate heater
- 4.4.1. Filter
- 4.4.2. Homogenizer/High-pressure pump
- 4.4.3. Feed line
- 4.5. Atomizing device
- 4.5.1. Rotary wheel atomizer
- 4.5.2. Pressure nozzle atomizer
- 4.5.3. Two-fluid nozzle atomizer
- 4.6. Powder recovery system
- 4.6.1. Cyclone separator
- 4.6.2. Bag filter
- 4.6.3. Wet scrubber
- 4.6.4. Combinations
- 4.7. Fines return system
- 4.7.1. For wheel atomizer
- 4.7.2. For pressure nozzles
- 4.8. Powder after-treatment system
- 4.8.1. Pneumatic conveying system
- 4.8.2. Fluid bed system
- 4.8.3. Lecithin treatment system
- 4.8.4. Powder sieve
- 4.9. Final product conveying, storage and bagging-off system
- 4.10. Instrumentation and automation
-
5.Types of spray drying installations
- 5.1. Single stage systems
- 5.1.1. Spray dryers without any after-treatment system
- 5.1.2. Spray dryers with pneumatic conveying system
- 5.1.3. Spray dryers with cooling bed system
- 5.2. Two stage drying systems
- 5.2.1. Spray dryers with fluid bed after-drying systems
- 5.2.2. TALL FORM DRYER™
- 5.2.3. Spray dryers with Integrated Fluid Bed
- 5.3. Three stage drying systems
- 5.3.1. COMPACT DRYER™ type CDI (GEA Niro)
- 5.3.2. Multi Stage Dryer MSD™ type
- 5.3.3. Spray drying plant with Integrated Filters and Fluid Beds - IFD™
- 5.3.4. Multi Stage Dryer MSD™-PF
- 5.3.5. FILTERMAT™ (FMD) integrated belt dryer
- 5.4. Spray dryer with after-crystallization belt
- 5.5. TIXOTHERM™
- 5.6. Choosing a spray drying installation
- 6.Technical calculations
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7.Principles of industrial production
- 7.1. Commissioning of a new plant
- 7.2. Causes for trouble-shooting
- 7.3. Production documentation
- 7.3.1. Production log sheets
- 7.3.2. General maintenance log book
- 7.3.3. Product quality specification
- 7.3.4. Operational parameter specification
- 7.4. Product quality control
- 7.4.1. Process quality control
- 7.4.2. Final quality control
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8.Dried milk products
- 8.1. Regular milk powders
- 8.1.1. Regular skim milk powder
- 8.1.2. Regular whole milk powder
- 8.1.3. Whole milk powder with high free fat content
- 8.1.4. Butter milk powder
- 8.1.4.1. Sweet butter milk powder
- 8.1.4.2. Acid butter milk powder
- 8.1.5. Fat filled milk powder
- 8.2. Agglomerated milk powders
- 8.2.1. Agglomerated skim milk powder
- 8.2.2. Agglomerated whole milk powder
- 8.2.3. Instant whole milk powder
- 8.2.4. Agglomerated fat filled milk powder
- 8.2.5. Instant fat filled milk powder
- 8.3. Whey and whey related products
- 8.3.1. Ordinary sweet whey powder
- 8.3.2. Ordinary acid whey powder
- 8.3.3. Non-caking sweet whey powder
- 8.3.4. Non-caking acid whey powder
- 8.3.5. Fat filled whey powder
- 8.3.6. Hydrolysed whey powder
- 8.3.7. Whey protein powder
- 8.3.8. Permeate powders
- 8.3.9. Mother liquor
- 8.4. Other Dried Milk Products
- 8.5. Baby food
- 8.6. Caseinate powder
- 8.6.1. Coffee whitener
- 8.6.2. Cocoa-milk-sugar powder
- 8.6.3. Cheese powder
- 8.6.4. Butter powder
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9.The composition and properties of milk
- 9.1. Raw milk quality
- 9.2. Milk composition
- 9.3. Components of milk solids
- 9.3.1. Milk proteins
- 9.3.2. Milk fat
- 9.3.3. Milk sugar
- 9.3.4. Minerals of milk
- 9.4. Physical properties of milk
- 9.4.1. Viscosity
- 9.4.2. Density
- 9.4.3. Boiling point
- 9.4.4. Acidity
- 9.4.5. Redox potential
- 9.4.6. Crystallization of lactose
- 9.4.7. Water activity
- 9.4.8. Stickiness and glass transition
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10.Achieving product properties
- 10.1. Moisture content
- 10.2. Insolubility index
- 10.3. Bulk density, particle density, occluded air
- 10.4. Agglomeration
- 10.5. Flowability
- 10.6. Free fat content
- 10.7. Instant properties
- 10.7.1. Wettability
- 10.7.2. Dispersibility
- 10.7.3. Sludge
- 10.7.4. Heat stability
- 10.7.5. Slowly dispersible particles
- 10.7.6. Hot water test and coffee test
- 10.7.7. White Flecks Number (WFN)
- 10.8. Hygroscopicity, sticking and caking properties
- 10.9. Whey Protein Nitrogen Index (WPNI)
- 10.10. Shelf life
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11.Analytical methods
- 11.1. Moisture content
- 11.1.1. Standard oven drying method (IDF Standard No.26-1964 [32])
- 11.1.2. Free moisture
- 11.1.3. Total moisture
- 11.1.4. Water of crystallization
- 11.2. Insolubility index
- 11.3. Bulk density
- 11.4. Particle density
- 11.5. Scorched particles
- 11.6. Wettability
- 11.7. Dispersibility
- 11.8. Other methods for determination of instant properties
- 11.8.1. Sludge
- 11.8.2. Slowly dispersible particles
- 11.8.3. Hot water sediment
- 11.8.4. Coffee test
- 11.8.5. White flecks number
- 11.9. Total fat content
- 11.10. Free fat content
- 11.11. Particle size distribution
- 11.12. Mechanical stability
- 11.13. Hygroscopicity
- 11.14. Degree of caking
- 11.15. Total lactose and α-lactose content
- 11.16. Titratable acidity
- 11.17. Whey Protein Nitrogen Index (WPNI)
- 11.18. Flowability (GEA Niro [31])
- 11.19. Lecithin content
- 11.20. Analytical methods for milk concentrates
- 11.20.1. Total solids
- 11.20.2. Insolubility index
- 11.20.3. Viscosity
- 11.20.4. Degree of crystallization
- 12.Troubleshooting operations
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References