A great number of operational parameters and conditions influence the performance of a spray drying plant. One essential factor is the quality of the processed milk, evaluated not only according to general quality standards, but also composition and physical-chemical properties as influenced by the composition itself.
Raw milk quality
Milk composition
Component | % in liquid milk | % in total solids | ||
---|---|---|---|---|
range | average | range | average | |
Water | 88.5-85.3 | 87.1 | - | - |
Fat | 3.4-5.0 | 3.9 | 27.4-34.7 | 29.8 |
Protein | 3.3-3.9 | 3.5 | 26.0-27.0 | 26.7 |
Lactose | 4.8-5.0 | 4.9 | 33.9-39.7 | 38.0 |
Ash | 0.68-0.74 | 0.7 | 5.0-5.8 | 5.5 |
Non-Fat-Solids | 8.8-9.6 | 9.1 | 65.2-72.2 | 70.2 |
- fat/NFS ratio
- content of total protein in NFS
- content of lactose in NFS
- total protein/lactose ratio
- casein/albumin ratio
- mineral salts/protein ratio.
Total protein in non-fat-solids | 36.2-48.0 1) |
Lactose in non-fat-solids | 51.7-54.9 |
Protein/lactose ratio | 0.63-1.06 1) |
Casein/non-fat-solids-ratio | 27.6-34.0 1) |
Whey protein/non-fat solids ratio | 7.4-8.3 1) |
Whey protein/casein ratio | 0.19-0.22 1) |
1) The high range limit applies for Channel Islands breeds and end of season. |

Components of milk solids
Milk proteins
Milk fat
Milk sugar

Milk sugar or lactose is a carbohydrate, existing only in milk, in true water solution.
It is a disaccharide C12H22O11 consisting of glucose and galactose and occurs in two isomeric forms α- and β-lactose (see Fig. 9.2). They have different physical properties, especially solubility in water and polarized light rotation. Both forms can crystallize, but for the production of milk and whey powders the most important is α-lactose, which crystallizes as α-lactose-monohydrate from the supersaturated solution of lactose below the temperature of 93.5°C. During the production of normal milk powders, the water evaporation during spray drying is so fast that despite supersaturation, the lactose cannot crystallize but remains in the powder as amorphous lactose, also called lactose glass. Amorphous lactose is very hygroscopic. This can cause caking problems with powders having high content of lactose, as for instance whey powders. To avoid caking the lactose has to be crystallized as α-lactosemonohydrate, which is non-hygroscopic. This is done by pre-crystallization of the concentrates. The rate of crystallization in solutions of lactose is controlled by the rate of mutarotation, i.e. transformation of β-lactose into α-lactose. The rate of mutarotation decreases with falling temperature, being fairly high in the range of 40-20°C, but practically zero at temperatures below 10°C. The solubility of lactose is shown on Fig.9.3.

The specific optical rotation of α-lactose in water is [α]D/20°C = +89.4° and melting point 201.6°C under disintegration. The corresponding values for α-lactose are [α] D/20°C = +33.5° and 252.2°C. The equilibrium specific rotation is [α] D/20°C = +55.3°.
α-lactose-monohydrate crystallizes in prism shapes often called tomahawk. These crystals in milk products are detectable on one’s teeth. With crystals larger than 10 μm there is a “flourish” and over 15 μm a “sandy” feel on the teeth.
The density of pure α-lactose-monohydrate is 1.54 g/ml. The sweetness of lactose is only 30% of that of sucrose. For whey powder manufacturing technology a most important physical property is the heat of crystallization, which is 10.63 kcal/kg. This must be taken into consideration when calculating the consumption of cooling water for the crystallization tanks. The relationships between various forms of lactose acc. to. King [3] are shown in Fig. 9.4.

Minerals of milk
Physical properties of milk
Viscosity

















Density

where: %F = percent of fat
%NFS = percent of non-fat-solids
%W = percent water
ρfat = specific gravity of fat (acc. Hunziker 0.93)
ρNFS = specific gravity of non-fat-solids (acc. Hunziker 1.608)
ρwater = specific gravity of water (Hunziker used 1 for t=15°C)
Concentrate density at a temperature, t, can be calculated with a reasonable degree of approximation by:









Boiling point

Acidity
A | B | |||
---|---|---|---|---|
°Th | °SH | °D | % 1.a. | |
°Th | - | 0.4 | 0.9 | 0.0009 |
°SH | 2.5 | - | 2.25 | 0.0225 |
°D | 1.11 | |||
% lactic acid | 111.1 | 44.44 | 100 | - |
Strenght NaOH | 0.1 N | 0.25 N | 0.11 N | 0.1 N |
°Th=Thörner, °SH=Soxhlet-Henkel, °D=Dornick, %1.a.=% as lactic acid |
Redox potential
Crystallization of lactose



Water activity


GAB model:







- ease of which water is evaporated from a liquid droplet,
- particle temperature history during the whole water removal process (see also section 3.2.3. Droplet temperature and rate of drying),
- the equilibrium moisture content which can be achieved under given conditions atinfinite residence time,
- the stickiness of the product (sticking temperature) and the outlet conditions (air temperature and moisture content) that can be used to dry without sticking problems occurring.
Stickiness and glass transition



Component | Tg(oC) |
---|---|
Fructose | 5 |
Glucose | 31 |
Galactose | 32 |
Sucrose | 62 |
Maltose | 87 |
Lactose | 101 |
Maltodextrin DE 36 (MW ~ 550) | 100 |
Maltodextrin DE 25 (MW ~ 720) | 121 |
Maltodextrin DE 20 (MW ~ 900) | 141 |
Maltodextrin DE 10 (MW ~ 1800) | 160 |
Maltodextrin DE 5 (MW ~ 3600) | 188 |
Starch | 243 |
Lactic acid | -60 |
Water (amorphous) | -135 |

İçindekiler tablosu
-
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
-
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
-
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
-
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
-
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
-
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
-
References