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1、TECHNOLOGY,MEASUREMENT AND PROCESSING STRATEGIESOFHOMOGENIZATIONOPTIMIZEDMILK2 CONTENTS Introduction.3 Who is this white paper for?.3 Homogenization is ready for a change.3 Milk composition,quality and behaviour.5 Milk is an emulsion.5 Milk fat is in motion.6 Milk quality.8 Enzymatic effects on long
2、er shelf life.9 Long storage times.10 Homogenizer technology.11 Homogenization mechanics.11 Homogenization with two devices.12 Homogenizer performance.15 Homogenization efficiency.15 United States Public Health(USPH)method.15 Centrifugation method.16 Particle size distribution.16 Factors influencing
3、 homogenization efficiency.19 Homogenization pressure.19 Homogenization device.19 Gap height relationship to pressure,capacity and device diameter.20 Milk composition effects on homogenization efficiency.21 Homogenizer placement in a line.22 Homogenization energy consumption(pressure).23 Planning a
4、homogenization strategy at your dairy.25 How do you know if you are over-homogenizing?.25 Do you need guidance or help with measuring homogenization efficiency?.25 Are consumers complaining about creaming?.26 Tips for pros.27 Remember that we are here for you!.28 Complete dairy support.28 References
5、.29 3 INTRODUCTION Who is this white paper for?This white paper provides a detailed background on homogenization the whys and wherefores,the technologies involved,and in particular how homogenization performance is measured.All of these have a bearing on how you design and operate white milk dairy l
6、ines,as well as how you specify the products you produce and market.As such,it is relevant to technical specialists in dairy processing,such as production managers,quality managers,R&D managers,environmental managers and process engineers.Dairy plant managers and procurement specialists will find in
7、formation relevant to energy consumption and product quality,especially if they are evaluating their current and future needs for homogenization equipment.There is also information relevant to product and marketing managers,who are often involved in shelf life discussions and concerned with customer
8、 feedback.Homogenization is ready for a change Homogenization has been with us for over 100 years,and is an established dairy industrial process.But it is under pressure to change.Dairy producers are seeking ways to extend shelf life through more efficient homogenization.Making milk products includi
9、ng those destined for long transportation more appealing and satisfying to customers,resulting in fewer customer complaints.There is also a need to cut costs,i.e.reduce the energy consumption involved in homogenization.In sum,the goal is to achieve the correct and appropriate level of homogenization
10、 and use an efficient process to do it.As we go deeper into the complexities of homogenization,our research as well as our installed base of more than 7,000 homogenizers worldwide suggests that the dairy industry could benefit from measuring homogenization in a different way.The key is to change the
11、 focus from homogenization pressure a processing parameter to measuring the results of homogenization itself:the resulting size and distribution of fat globules.4 Changing measurement techniques,looking beyond pressure,and fitting processing parameters to varying product objectives can result in:Hig
12、her and more consistent quality,especially as measured in shelf life requirements Cost benefits in production,particularly in energy savings and parts consumption Reduced carbon footprint Since we deliver end-to-end concepts from raw milk reception at the dairy to finished packed products,we have gr
13、eat knowledge on how raw milk quality,processing,packaging,transportation and storage affects the shelf life in terms of creaming.We can therefore make recommendations assuring high product quality.We discuss milk composition and creaming in the first section.If youre already familiar with these bas
14、ics,you might want to skip ahead to the sections on Homogenizer technology or Homogenizer performance.5 MILK COMPOSITION,QUALITY AND BEHAVIOUR Milk is an emulsion Cows milk consists of about 87%water and 13%dry substances,which are suspended or dissolved in the water.Average composition%Water 87.5 F
15、at 3.9 Proteins 3.4 Lactose 4.8 Minerals(Ash)0.8 Milk is an emulsion:a suspension of droplets of one liquid(milk fat)in another(skim milk),where the liquids are not soluble in each other.The milkfat exists as small globules or droplets dispersed in the skim milk(figure 1).Their diameters range from
16、0.1 to 20 m(1 m=0.001 mm).The average size is 3 4 m(figure 2)and there are about 15 x 1010 globules per ml.Figure 1.Milk fat globules in skim milk Figure 2.Particle size distribution of fat globules in raw milk Milk fat globules Skim milk Volume%Fat globule size(m)Raw milk 8%6%4%2%0%0,11101006 The e
17、mulsion is stabilized by a very thin membrane,only 10-20 nm thick(1 nm=109 m),which surrounds the globules and has a complicated composition,consisting of phospholipids,lipoproteins,cerebrosides,proteins,nucleic acids,enzymes,trace elements(metals)and bound water(figure 3).Figure 3.Fat globule compo
18、sition Milk fat consists of triglycerides(the dominating components),di-and monoglycerides,fatty acids,sterols,carotenoids(which give the fat its yellow colour)and vitamins A,D,E,and K.Milk fat is in motion As the fat globules are not only the largest particles in the milk but also the lightest,they
19、 rise to the surface when milk is left to stand in a vessel for a while,a process called creaming.The driving force for the creaming process is the density difference,quantified in table 1.How fast the fat globules rise in skim milk(the continuous phase)depends on their size,their density and on the
20、 density and viscosity of the skim milk.Density and viscosity changes with temperature.Thus creaming is more rapid at higher temperatures,due to an increased difference in density and decreased skim milk viscosity.The larger the fat globules are,the faster they rise,which is the main motivation for
21、homogenization:breaking down fat globules into smaller globules to slow down the separation process.The creaming process can be described by Stokes law,as illustrated in figure 4.Table 1.Milk component density at 20C SKIM MILK MILK FAT 1035 kg/m3 915 kg/m3 Membrane Phospholipids Lipoproteins Cerebro
22、sides Proteins Nucleic acids Enzymes Trace elements(metals)Bound water Milk fat Triglycerides Di-and monoglycerides Fatty acids Sterols Carotenoids Vitamins A,D,E,and K 7 g x fat globule size2 x(density milk serum density fat)18 x viscosity milk serum Figure 4.Stokes Law predicts creaming rate from
23、fat globule size,density and viscosity When the fat globules are broken up into smaller ones by homogenization,a new,larger total surface area on these smaller fat globules is created that needs to be covered;otherwise the globules would just move back together again.The new membrane material consis
24、ts of proteins in the milk,mainly casein and whey,which bind to the fat globules,as in figure 5.We will return to this surface area again in the section on Milk composition effects on homogenization efficiency.Figure 5.Confocal microscopy image of homogenized UHT milk.The red dye indicates fat and t
25、he green dye is protein.Raw milk Pasteurized milk UHT milk Weeks Weeks Weeks 4 micron 0.8 micron 0.4 micron Velocity=8 In raw milk,an additional creaming accelerator is in action,called agglutinin.This is an immunoglobulin protein that works as“glue”lumping the fat globules together,making them rise
26、 to the surface faster than smaller individual globules.This protein is,however,inactivated by pasteurization,so it is not relevant to most dairy operations.Milk quality The quality of dairy products is generally measured in four ways:Food safety Microbiological spoilage Taste Visual appearance(colo
27、ur,creaming,sedimentation,viscosity,gelation)In figure 4 above regarding Stokes Law,we showed how reducing the size of fat globules directly relates to shelf life,in that smaller fat globules take longer to rise,and separate.Homogenization makes the milk into a more stable emulsion that will undergo
28、 minimal creaming,thereby positively affecting the milks visual appearance.The effect of homogenization on the physical structure of milk has additional quality advantages:Whiter and more appetizing colour More full-bodied flavour,and better mouthfeel Better stability of cultured milk products In th
29、is white paper we focus on creaming.Note that the creaming does not make the milk bad or unsafe to drink.The risk is that consumers mistake creaming for the milk being bad,because they are unfamiliar with the process.The shelf life of white milk products varies by processing methods and parameters,a
30、s shown in table 2.For pasteurized and Extended Shelf Life(ESL)milk,microbiological properties limit shelf life.Homogenization should be aligned with the bacteriological shelf life.For Ultra High Temperature(UHT)milk it is chemical and physical changes that limit shelf life,since nothing grows in a
31、commercially sterile product.So creaming could be potentially a limiting factor here,and thus the homogenizer could set the limit.Commercial sterility means the absence of microorganisms capable of growing in the food at normal non-refrigerated conditions at which the food is likely to be held durin
32、g manufacture,distribution and storage.Codex Alimentarius Commission(WHO/FAO)CAC/RCP 40-1993)9 Table 2.Common shelf life specifications for milk MILK SHELF LIFE PROCESS Pasteurized milk Up to 10 days Pasteurization alone ESL milk Up to 15 days Bactofugation+pasteurization ESL milk Up to 30 days Micr
33、ofiltration+pasteurization ESL milk More than 30 days High heat(125-127C/2s)ESL milk Up to 90 days(USA)High heat(138C/4s)UHT milk 3 months to 1 year Ultra high temperature Enzymatic effects on longer shelf life Certain microorganisms,e.g.the gram negative psychrotrophic bacteria Pseudomonas fluoresc
34、ens,can produce heat-stable enzymes while they are growing.During the heat treatment the bacteria themselves will die but the enzymes are not destroyed and will remain active during the storage of the milk.The worse the raw milk quality and the longer the raw milk is stored before processing,the lar
35、ger is the risk of having high levels of heat-stable enzymes.These enzymes can cut both fat and protein into smaller structures.If the casein micelles are cut into smaller pieces this causes a bitter taste,sedimentation and eventually gelation of the milk.However,the fat globules are also affected.T
36、he enzymes can destroy the protein-rich membrane that covers the fat globules.If the fat globules are in a cream layer,they are surrounded by other fat globules and without their membranes they will coalesce into larger globules.Eventually they can become so large that the visual appearance of the c
37、reaming layer will change:the quantitative amount of creaming remains the same,but it looks unappetizing.This is depicted in figure 6.Figure 6.Normal creaming layer(left)and a creaming layer affected by bacterial enzymes(right).Both layers have the same quantitative amount,but the visual appearance
38、is completely different.The milk in both cases has been stored six months at room temperature.10 Long storage times In these days of expanding geographical markets for milk products,and the uncertainty of chilled distribution in many parts of the world,UHT milk is being transported further and furth
39、er away from its production origins,and may even be at sea for several months.In these cases,predictable shelf life and sustainable quality are paramount to consumer satisfaction.European exports to China,for example,need to have additional shelf life to cover the transport plus the consumer distrib
40、ution chain.For extreme storage conditions like longer shipping voyages,temperature fluctuations can cause both visual and quantitative changes in creaming.Dairies planning for longer transports should take this into account during production.11 HOMOGENIZER TECHNOLOGY Homogenization mechanics Homoge
41、nization is a mechanical process that reduces the fat globule size and thereby diminishes creaming.Milk is forced through a small passage at high velocity,and the fat globules are disintegrated through a combination of turbulence,cavitation and impact.Homogenization reduces fat globule diameters fro
42、m an average of 3.5 m to below 1 m.A homogenizer is essentially a positive displacement pump that pumps liquid from one place to another.It carries this out with a motor on the back end and pistons and valves in the front(figure 7).The most significant part of the homogenizer is,however,the homogeni
43、zing device.The pistons move back and forth and pump the liquid towards this homogenizing device,and it is there that the fat globules are broken down.Figure 7.Homogenizer internal sections Figure 8.Homogenization device construction Seat Forcer Motor Homogenization device Pistons Valves Unhomogeniz
44、ed product Homogenized product Gap height Outlet chamber Forcer Seat 12 The pump builds up a very high pressure(high potential energy)that is then transformed into a high velocity when the milk is forced through a narrow gap created by the seat and the forcer in the homogenization device,as in figur
45、e 8.The magic happens in the outlet chamber just after the gap.In the gap the fluid has a very high velocity.Even though the fat globules are pushed through the gap at these high speeds,they are not yet broken up,but only elongated.This milk coming out of the gap can be compared to a high-velocity j
46、et that enters the large outlet chamber.There the milk comes into an area with almost static liquid,creating a lot of turbulence,creating small eddies or swirls,which are the main forces breaking up the globules.As the velocity increases the pressure decreases,leading to cavitation,which also plays
47、a central role in breaking down fat globules.As vapor bubbles implode they create a jet of the surrounding liquid and cause shock waves,which also breaks up fat globules.Homogenization with two devices For milk it is always recommended to have two homogenization devices connected in series,as in fig
48、ure 9.The two homogenization stages each have a seat and a forcer,so the milk is pushed through two gaps in series.Figure 9.A two-stage homogenizer The actual breakup of the individual fat globules takes part in the first stage,where we have the largest pressure drop,and the effect depends on the de
49、sign of the device.The pressure before the first stage is controlled by the homogenizer piston pump;for example,it can be set to 200 bar.This is often called the total pressure or the homogenization pressure.Measuring pressure Pressure can be measured in three different units,commonly in Bar,or the
50、atmospheric pressure at sea level.One bar=100,000 Pascals(Pa)or 100 kilopascals(kPa).In the US,where psi(pounds per square inch)is still used in some domains,one bar=14.5 psi.13 The second stage has two important roles:To keep a constant,controlled back pressure to the first stage and thereby ensure
51、 that there are good conditions for controlled cavitation.If the machine only has one stage,then the back pressure will change during running time.This is because the back pressure depends on the processing conditions in the piping after the homogenizer,for example on the fouling in a UHT system.To
52、break up aggregates.When the individual fat globules are split up after the first stage,they are covered by new membrane material(protein from the milk).However,some of the globules will lump together and share the same protein as a membrane;that is,there will be some aggregates.Having a small press
53、ure drop over the second stage assures that these aggregates are in turn broken up into individual fat globules.It requires much less energy to break up fat globule aggregates than to break up individual fat globules.To achieve a large pressure drop over the first stage,good conditions for controlle
54、d cavitation and sufficient breakup of aggregates,we recommend for our devices that the pressure before the second stage is 25-30 bar(see figure 10).An additional benefit of our design with two physically identical stages is that they are interchangeable.So when the first stage gets worn it is easy
55、to swap the seat and the forcer of the first stage with the second stage.It will not matter much for the second stage if the device is worn because there is little actual homogenization taking place there.So the gap height can be larger,making wear less of a problem.Two identical stages in combinati
56、on with a turnable design,i.e.where the devices are symmetrical and can be flipped over,extends the wear time up to four times,reducing spare parts and maintenance costs.14 Figure 10.Definition of pressure in a two-stage homogenizer.In the first stage gap inlet the potential energy from the pressure
57、 is converted into velocity.The velocity is about 200 m/s and the pressure drops to close to zero.The low pressure gives cavitation that,if controlled,aids globule break-up,but if it is not controlled,quickly wears down the device.At the outlet of the gap a high velocity jet is formed and most of th
58、e kinetic energy is transformed into turbulence that further breaks up the globules.A small fraction of the kinetic energy is converted back to pressure,per Bernoullis Principle.This is the second stage pressure.Where the second stage pressure meter is positioned there is about 30 bar pressure and a
59、 few m/s.In the stage 2 gap inlet this 30-bar potential energy is converted into a velocity of less than 100 m/s,generally too low to cause cavitation.With a correct second stage the pressure at the stage 1 gap outlet,and thus the cavitation,can be controlled.P1 200 bar P2 30 bar Piston pump 1st Hom
60、ogenization stage 2nd Homogenization stage Bar Gap one Gap two Pressure recovery at outlet Piston pump Pressure 200 bar 1st Homogenization stage 2nd Homogenization stage Pressure 30 bar 15 HOMOGENIZER PERFORMANCE We measure homogenization in two ways:Homogenization efficiency is the degree to which
61、the milk is effectively homogenized,and is measured as size of the fat globules in the homogenized product,and their distribution.At the end of this section we show how these two measurements can be simply expressed as a single value.Homogenization energy consumption is measured by taking into accou
62、nt the energy or other resources needed to achieve homogenization it depends on the capacity and on the homogenization pressure used in the process.We must emphasize that homogenization efficiency and homogenization pressure are not interchangeable,and that measuring homogenization pressure alone do
63、es not give you a complete picture.Homogenization efficiency Homogenization efficiency is a measurement of how small the fat globules have become.It can be measured either by measuring creaming i.e.how fast the globules rise and form a layer of fat or it can be measured by analysing the fat globule
64、size.The straightforward way of determining the creaming rate is to take a package,store it at the recommended storage temperature until the last day of consumption,open it and check if the cream layer is acceptable or not.This is time-consuming,which creates the need for alternative methods.United
65、States Public Health(USPH)method The USPH method is based on creaming rate,and was developed in 1947 for pasteurized milk.It remains valid only for pasteurized milk.A sample of,say,1,000 ml is stored for 48 hours,after which the fat content of the top 100 ml is determined,as well as the fat content
66、of the rest.Homogenization is reckoned to be sufficient if the ratio of fat in the bottom portion(milk)to the top portion(cream)is greater than 0.9(figure 11).Figure 11.USPH method for measuring homogenization efficiency A=1/10 B=9/10 B/A0.9 16 Centrifugation method The NIZO centrifugation method is
67、 based on the same principle,but is more rapid,because it speeds up the natural creaming process.A sample of 25 ml is centrifuged for 30 minutes at 350 g.The fat content of the 20 ml at the bottom is divided by the fat content of the whole sample,and the ratio is multiplied by 100.The result is call
68、ed the NIZO value,expressed as a percent(figure 12).What is an acceptable percentage depends on the intended storage time and storage conditions.Pasteurized milk is normally 60 70%,while it is not uncommon to see UHT milk with values above 90%.Figure 12.Measuring homogenization efficiency with centr
69、ifugation Particle size distribution We recommend a third,more modern method to measure homogenization efficiency,by measuring particle size distribution(PSD).Milk fat globules are not all of the same size;in raw milk they vary from 0.1-20 micron(see figure 2).After homogenization the globules will
70、be smaller,but they will still vary in size(0.1-3 micron).In theory,one way to investigate the entire system the particle size distribution would be to take many microscopic images and count and sort the globules into different size spans.This would,of course,be very time-consuming and impractical.A
71、 much faster way is to use laser diffraction,which is what we do at Tetra Pak.All particles scatter light:larger particles in narrow angles and small particles in wide angles.Together NIZO stands for Nederlands Instituut voor Zuivelonderzoek the Netherlands Institute for Dairy Research which is the
72、creator of this centrifugation method.It is a well-established measurement technique in the dairy industry,and the measurement is often referred to as the NIZO value.Homogenization efficiency=fat content in bottom 20 ml of centrifuged sample fat content in non-centrifuged sample X 100 30 min 350 g 4
73、0C 17 with sensitive detectors and advanced computer models about particle scattering,a particle size distribution can be calculated.The PSD measurement process using laser diffraction is simple.Milk is mixed with a protein dissolving solution,some droplets are added to the dispersion unit,the laser
74、s are turned on and then the software takes care of the measurement.While the USPH method takes 48 hours,and the centrifugation method takes at least an hour,the PSD process only takes 10 minutes.To be able to conveniently compare one particle size distribution with another,single values are needed.
75、Several different statistical average values can be extracted from PSD measurements.There is no established industry standard,but the following values are frequently used:D4;3 volume-based mean value(the diameter of a globule which has the average volume)D3;2 surface-area-based mean value(the diamet
76、er of a globule which has the average surface area)Dv10,Dv50 and Dv90 volume percentiles where 10%,50%and 90%of the volume is smaller than the diameter specified.What we often use in our studies is the D5;3 value.This value has no simple physical explanation,but Walstra and Oortwijn(1975)showed that
77、 for calculations of cream layer formation in milk,the volume proportion of fat that has reached the cream layer after a certain time is proportional to the D5;3 diameter.We have also seen that there is a good correlation between the D5;3 value and the visual creaming.For someone who does not work w
78、ith particle size distributions and average diameters on a daily basis,it can be hard to know if a certain fat globule size is good or bad.Therefore we established a correlation between the D5;3 value and the NIZO centrifugation value,which is a percentage.Figure 13 illustrates this correlation.Figu
79、re 13.Relationship between centrifugation value(%)and homogenization efficiency based on D5;3 derived from PSD 100%90%80%70%60%0,20,40,610,85;3=(51 31)0.5 Ni being the number of globules and Di the diameter Homogenization efficiency=100 x e -ID5;3-0.08019 I 2.06686 1.63085 NIZO centrifugation Fat gl
80、obule D5;3 (m)Measured data Homogenization efficiency calculated 18 Figure 14.Measurement of particle size distribution using laser diffraction at the Tetra Pak lab in Lund,Sweden Laser diffraction settings There are different laser diffraction instruments on the market with many different measureme
81、nt methods.We use the Malvern Mastersizer 3000,with the following settings.Refractive index milk:1.46(red laser)and 1.47(blue laser)Refractive index water 1.33 Absorption index:0.001 Obscuration 1.5-3.5%General purpose as analysis model Analysis with protein dissolving agent solA These setting are b
82、ased on studies presented in the article“Measurement of homogenization efficiency of milk by laser diffraction”by Ransmark et al.(2019)19 FACTORS INFLUENCING HOMOGENIZATION EFFICIENCY Homogenization pressure Increased pressure means improved homogenization efficiency.Ultimately what the additional p
83、ressure does is increase the velocity through the gap,creating a larger and more intense turbulent zone after the gap,resulting in more droplet breakup,and thus smaller fat globules.But contrary to popular belief,homogenization efficiency is determined by many factors other than pressure,as we descr
84、ibe below.These include:Homogenization device Gap height Milk composition Homogenizer line placement Homogenization device Lets take a moment to consider the geometry of homogenization devices,in a historical perspective.The“standard”design for many years was a wide gap design,which was used in the
85、old Tetra Pak HD1,for example(figure 15).It was a long narrow gap,thus leading to much friction loss in the gap and loss of much of the initial high velocity.In other words,much of the energy was lost.Figure 15.Principal drawing of an early wide gap design The knife edge design was developed in the
86、late 1990s,and was used by Tetra Pak in our HD100 device,launched in 1999.It has a very sharp 1 mm edge,so not much energy is lost as friction(figure 16).It represents a good balance of high efficiency and can still handle the wear and allow a long gap lifetime.If the edge is too sharp,it will just
87、wear down directly and quickly lose efficiency.The Tetra Pak homogenization seat and forcer are turnable,so when it gets worn on one side it can be flipped over.Furthermore it is offered in different materials with different hardness,to match the requirements of different products.Figure 16.Modern k
88、nife edge gap 20 In 2012 we launched the next device generation,called HDEnergy IQ(figure 17).It splits up the flow over many gaps,creating narrow gap heights,making it even more efficient.(See discussion below in Gap height relationship to pressure,capacity and device diameter.)Figure 17.Multiple h
89、omogenization devices in the HD Energy IQ As figure 18 shows,homogenizing with the three different devices at the same pressures yields very different homogenization efficiencies.Figure 18.Milk Homogenization efficiency vs Homogenizing pressure from three different homogenization devices Gap height
90、relationship to pressure,capacity and device diameter The gap height depends on the capacity,the pressure and the device diameter,according to the following formula.Gap height Flow ratePressure x Device diameter 80000060Tetra Pak Homogenizers 350,33 000 l/h,3.5%fat Homogenizing pressure(bar)HHD Ener
91、gy IQ HHD 100 HHD1 Homogenizing efficiency(%)21 The smaller the gap height,the greater the shear and the denser the energy is in the turbulent area in the outlet chamber but if the gap height is too small,there are friction losses and loss of velocity during the passage(see figure 19 and figure 20).
92、Figure 19.Effects of large gap heights on energy density Figure 20.The relationship of gap height and product flow It is important that the homogenization device diameter has a gap height optimized for the intended operating capacities and pressures.This also means that the same machine will result
93、in different homogenization efficiency values at different capacities.Milk composition effects on homogenization efficiency When fat globules are broken up into smaller ones by homogenization,new surface areas are created.This is visualized in figure 21.As a single large globule breaks up and become
94、s many small ones,its surface area is drastically increased.Comparing raw milk and pasteurized milk,the surface area increases up to 10 times,and for UHT milk(which requires a higher degree of homogenization)the surface area can increase as much as 20 times.This new area needs to be covered;otherwis
95、e the globules would just move back together again.The new membrane material consists of proteins in the milk,mainly casein and whey,which position themselves in the interface between the skim milk and the fat globules.Outlet chamber Optimal gap height(high energy density)Too low/too high gap height
96、(low energy density)Too low/too high gap height Optimal gap height Gap height(m)Homogenization efficiency 22 This means that the amount of available membrane material(milk protein)can actually limit how small the fat globules can become after homogenization of milk.Milk contains excess protein to be
97、 used as membrane material,but if the fat content is increased,which means more fat globules that are closer together,and more surface area to be covered,there will be shortage of proteins to use as membrane material.It also requires more energy for breakup.In summary,given a constant pressure,incre
98、ased fat content leads to decreased homogenization efficiency.This higher fat content needs to be taken into account when running partial homogenization,in which the milk passing through the homogenizer has a fat content between 12-18%,and some of the skim milk bypasses the homogenizer.The milk is s
99、tandardized after the homogenizer.This reduces energy consumption,since the flow rate through the homogenizer is much smaller.But you have to remember that the pressure needs to be slightly higher than with full stream homogenization.Partial homogenization,however,is a great way to save energy;takin
100、g both the reduced capacity and the increased pressure into account,more than 65%of the energy can be saved,depending on fat content.Figure 21.Relative surface areas of treated fat globules Homogenizer placement in a line To ensure that the fat is in a liquid state the homogenizer should be placed a
101、t a temperature 55C.A higher temperature will yield higher efficiency,but factors such as fouling and cleaning frequency also have to be considered.Upstream vs.downstream of final heat treatment For a normal pasteurizer and for indirect UHT heat treatment,the recommendation for normal milk is to hav
102、e the homogenizer upstream,because it is cheaper both in capital and running costs.For direct heat treatment systems the recommendation is to place it downstream,because when milk meets steam,protein aggregates form;in order to avoid sediment in the milk package,these aggregates need to be broken up
103、.So in direct systems the homogenizer has two roles:both to break up fat globules and to break up protein aggregates.Likewise,for products with high fat or protein content,for best results the homogenizer should be placed downstream to break up aggregates formed during the heat treatment.Raw milk Pa
104、steurized milk UHT milk Diameter Same volume,smaller globules,different surface area Number of globules 1 220 1900 4 m 0.8 m 0.4 m Surface area 50 m2 440 m2 950 m2 23 Downstream homogenization requires an aseptic machine,requiring different gaskets that can handle pre-sterilization temperatures,as w
105、ell as a steam barrier on the pistons,making sure they are always sterile when in contact with the milk.In addition the utility cost for steam also has to be considered,which is why it is more expensive.Homogenization in pre-treatment In UHT processing the milk is sometimes homogenized twice,both in
106、 the pre-pasteurization and in the UHT treatment.This normally results in smaller fat globules compared with using only one homogenizer.A single homogenizer can compensate,however,by increasing the pressure.Homogenization energy consumption(pressure)The easiest setting to vary on a homogenizer is th
107、e pressure,and pressure relates directly to the energy consumption of the process.It is important to emphasize that the same pressure on different machines will not result in the same homogenization efficiency.As we showed earlier in figure 18,homogenization efficiency is dependent on both the press
108、ure used as well as the device type and size.The performance of each machine can vary,depending on the homogenization device.So saying“you need to homogenize at 300 bar”is not specific enough.Saying that“you need to achieve a homogenization efficiency of 90%”is specific enough,because it specifies a
109、 final result,and the pressure that can be used by different machines to reach that result will vary.Energy consumption=Pressure x Capacity 24 Figure 22 illustrates this by comparing the indexed energy consumption per litre milk to reach the same homogenization efficiency for some different scenario
110、s.The first bar represent a standard design to compare with the other set-ups.Thus the standard has an indexed energy consumption of 1.When the capacity is decreased to half,the gap height will be smaller and the pressure needed to achieve the same efficiency can be lowered thus the energy consumpti
111、on is lower.When fat content is doubled the pressure needs to be elevated to ensure breakup of all the globules,which results in increased energy consumption.If the device is changed to one with just half the diameter,then the gap height will be larger,lowering the energy density in the outlet chamb
112、er,and in order to achieve the same homogenization efficiency,the gap height needs to be compensated with increased pressure,resulting in increased energy consumption.The last bar shows the HDEnergy IQ device,which has multiple gaps resulting in smaller gap heights,which enables lower pressure and l
113、ess energy consumption.Figure 22.Energy consumption under different operating conditions Using the homogenization efficiency as a reference target allows dairy operators to configure their homogenization processes and adjust parameters to achieve a given product specification.This also provides the
114、procurement process with more detailed specifications.Energy index Standard Half capacity Double fat content Half device diameter Energy IQ device 25 PLANNING A HOMOGENIZATION STRATEGY AT YOUR DAIRY Given the complexity of the homogenization process,here are some questions you can examine regarding
115、your own dairy operations as well as some ways to answer them,based on our descriptions above.How do you know if you are over-homogenizing?If you homogenize at a higher pressure than needed,you are wasting both energy and money.But how to determine the correct settings?First and foremost,dont trust
116、homogenization pressure as the ultimate parameter the pressure is not telling you everything.Based on your machine design,200 bar can give very different homogenization efficiency values.An easy first approach for pasteurized and ESL milk is to open a package at the end of its shelf life and check t
117、he creaming status.If you are satisfied,try lowering the pressure 5-10 bar at a time and check again.These may seem like small changes,but for equipment that operates 24/7 year-round,small changes may also yield large economic and environmental benefits.For UHT milk,where shelf life can be up to a y
118、ear,this approach is very time-consuming and impractical.Check the homogenization efficiency instead.It should correlate with your required shelf life and your markets sensitivity towards creaming.If you need help with measurement or guidance around homogenization efficiency values,we are here to su
119、pport you.Do you need guidance or help with measuring homogenization efficiency?We can calculate the homogenization efficiency of our homogenizers based on your input parameters.This to be sure that every machine is delivered equipped for the varying needs of our customers.We can give you confident
120、recommendations about which pressure to use for the shelf life you require for your individual products.We also offer experimental measurement of the particle size distribution and homogenization efficiency,and based on this we can predict the creaming rate,as in figure 23.26 Figure 23.Sample foreca
121、sts of particle size distribution and creaming rates at different homogenization efficiencies Are consumers complaining about creaming?Since we deliver end-to-end dairy processing concepts from raw milk reception at the dairy to finished products,we have developed a great deal of expertise regarding
122、 how raw milk quality,processing,packaging,transportation and storage affect shelf life in terms of creaming.We can help you analyse your situation and recommend remedies,such as those suggested in figure 24.Figure 24.Troubleshooting guide for creaming issues 10,10,01100%2%4%6%8%10%Particle size dis
123、tribution Volume Fat globule size(m)Creaming,1L package,25C storage temperature Fat present as cream layer Storage time(weeks)Consumer complaints about creaming Raw milk quality Extreme storage conditions Homogenization efficiency not in correlation with shelf life expectation Homogenizer device wor
124、n Measure psychrotrophic count Check storage times before processing Are the visual and quantitative creaming not aligned?Can to some extent be taken into account during processing choices Measure homogenization efficiency Adjust pressure or upgrade machine with new device design Increase service in
125、tervals Change to a more durable device design Homogenization efficiency 95%90%80%27 Tips for pros Dont be afraid to experiment just start with small changes.Keep these tips in mind:Running the same pressure for all applications is a waste of energy and money.If you are running different fat content
126、s,you can lower pressure if you run 0.5%compared with 3.5%If you are running different capacities,change the pressure as well to make up for the change in gap height.When you are running products with different shelf lives,youll need to change the pressure if,for example,youre changing from normal p
127、asteurized milk to extended shelf life,or moving from locally consumed UHT milk to export milk,where the additional transport time“eats”some of the shelf life.Very often the second-stage pressure is set too high,with the optimum setting being 25-30 bar.Too much pressure here steals energy from the f
128、irst stage and lowers your homogenization efficiency.If you are investing in a new machine and want the same milk homogenization efficiency value as your old machine,measure the homogenization efficiency of the milk produced on your current machine and then order your machine based on this not based
129、 on pressure.If you are expanding your product lines to achieve longer shelf life,or planning for export transportation,take into account that storage and transportation can have a big impact on creaming.28 REMEMBER THAT WE ARE HERE FOR YOU!Our specialists are ready to assist you if you are adjustin
130、g your processing lines,and need specific help with:Measuring particle size distribution and the milk homogenization efficiency.Calculating correct milk homogenization efficiency values and other parameters for required shelf life for your products.Help at solving your homogenization and shelf-life
131、issues.Our research programme will continue to produce processing models and practical tools that can be used to improve dairy processing performance.Complete dairy support Complete dairy line concepts and technology support for dairy producers include:Extensive knowledge of processing technology an
132、d ability to support its implementation Processing modules(homogenizers,pasteurizers,and more)and line concepts based on proven technologies End-to-end offering from raw materials through processing,and all the way to palletized products.As an innovator,we remain dedicated to further exploring and d
133、eveloping the dairy industry.We collaborate with customers,universities,and other business partners to develop new applications and find the best solutions for producing new products with flexibility.We develop customized solutions for your needs and have taken a leading position in the development
134、of new processing line concepts.At our Product Development Centres,customers can carry out product trials together with our specialists with unique comprehensive expertise in food processing and packaging.The PDCs provide highly flexible industrial pilot plant facilities for processing and packaging
135、 trials,which ensures fast and reliable scale-up.Customers are given the opportunity to experiment with recipes and use the latest processing equipment.We also have pilot plants for rental where trials are conducted for customers on-site with the support of our expertise.For further information,plea
136、se contact your Tetra Pak representative or contact us through References Ransmark,E.,Svensson,B.,Svedberg,I.,Gransson,A.,&Skoglund,T.(2019).Measurement of homogenisation efficiency of milk by laser diffraction and centrifugation.International Dairy Journal,96,93-97.Walstra,P.,&Oortwijn,H.(1975).Eff
137、ect of fat globule size and concentration on creaming in pasteurized milk.Netherlands Milk and Dairy Journal,29,263-278.30 We reserve the rights to introduce design modifications without prior notice.Tetra Pak,and PROTECTS WHATS GOOD are trademarks belonging to the Tetra Pak G Tetra Pak International S.A.,Tetra Pak Processing Equipment AB 2019,GB