Separators From GEA Westfalia Separator For Milk .

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Separators from GEA Westfalia Separatorfor Milk Clarification and Bacteria Removalengineering for a better worldGEA Mechanical Equipment

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Contents41.Introduction62.Milk Clarification62.1IntroductionClarifying milk using filters62.1.162.1.2 Clarifying milk using the skimming62.1.3 Clarifying milk using the clarifier62.1.4 Composition of solids discharged2.1.5 Proportion of non-milk solids in milk2.1.6 Product losses when clarifying milk72.1.782.1.8 Temperatures when clarifying milk92.1.9 Reducing total bacteria count92.1.10 Clarification effect when using3.2223.2.1 Bacteria removal from fresh233.2.2 Bacteria removal from skim milk243.3Bacteria removal from freshmilk – Stage 1Premium milk with a longer shelf lifewith the GEA Westfalia Separatorprolong processby separators73.1.5 Treating concentrate21milk – process technologyseparator720263.4273.5ESL milk process technologyBacteria removal from cheese milk –process technologyusing separators283.5.1 Double bacteria removalProtein losses when clarifying milk283.5.2 Variable bacteria removal, example:303.6303.7303.7.1using separatorscheese milkComparison of microfiltrationand separatorskimming separatorsSpecial applicationsBacteria removal from whey102.1.11 Separating somatic cellsconcentrate102.1.12 Separating listeria from raw milk323.8112.1.13 Particular issues for clarifying milk323.8.1 Method of operation:112.1.14 Summary112.2333.8.2 Method of operation:122.3132.41314142.4.3 Bowl ejections152.5152.6bacteria-removing separatorsClarifying raw milk cold –process technologybacteria-removing separators withClarifying raw milk warm –GEA Westfalia Separator proplus systemprocess technology343.9Machine types2.4.1 Method of operation of clarifiers344.0Sampling2.4.2 Processes in the disc interspace344.0.1 Prerequisites in the milkMachine types354.0.2 Arrangement of sampling pointsMethods of testing clarification354.0.3 Sampling equipment requiredefficiency354.0.4 Performing samplingClarifying milk – machineryprocessing line364.0.5 Treating the samplesBacteria Removal from Milk364.1Test methods3.1General364.1.1Overview3.1.1Reasons for bacteria removal364.1.2 Tests for anaerobic sporesfrom milk394.1.3 Tests for aerobic spores394.1.4 Tests for lactobacilli163.1616163.1.2 Technical principles193.1.3 Effectiveness of bacteria-removingseparators20Bacteria removal – machinery3.1.4 Protein balance in bacteria-removingseparators3

1. IntroductionClarifiers from GEA Westfalia Separator Group andbacteria-removing separators are used in the dairyindustry to improve milk quality. Centrifugal and / ormembrane technology are used to separate impuritiesand bacteria from the milk.Examples of undesired constituents in raw milk areparticles of dirt, blood residues, udder cells and a greatmany different bacteria.This technical documentation explains clarifying andbacteria removal efficiency in relation to the processesused in the field. Among other things, this clearlyshows the composition of the phases dischargedin batches when clarifiers and bacteria-removingseparators are used, and the extent to which thesephases can be recycled.4

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2. Milk Clarification2.1 Introduction2.1.3 Clarifying milk using the clarifierThe most important part of clarifying milk is theClarifiers are machines specifically designed forseparation of non-milk solids (NMS). A distinction issolids / liquid separation. The specific design ofgenerally made between the different methods usedthis machine enables it to achieve an optimumby processors to improve the quality of milk.separation rate for impurities. We will go into thedesign differences in more detail at a later stage.2.1.1 Clarifying milk using filtersThis method of improving the quality of milk has2.1.4 Composition of solids discharged by separatorsbeen more or less abandoned these days for a varietyComplex studies have been conducted to obtainof reasons.precise information about the solids discharged byself-cleaning separators during milk clarification.One of its biggest drawbacks is the drop in flow rateSamples from different milk regions using separatorsover time because a thicker and thicker filter layerof different sizes have been analysed, thus ensuringbuilds up. Running time is limited. The entire milka representative cross-section.flow is passed through the filter layer. This allowsbacteriological problems to arise due to entrainment,Partial ejections were performed on all separators.there is a risk of bacterial growth in the filter layer andThe time between two consecutive partial ejectionsthus reinfection of the milk. What is more, if therewas selected so that the solids had a dry mass of 14 toare cracks in the filter tissue, the clarifying effect is16 percent. This ensured that at each partial ejection,considerably reduced. Cleaning the filters after pro-all the solids separated were discharged. The resultsduction is also an extremely laborious process.of the study are shown in Fig. 1.The use of filters to improve milk quality should not,however, be confused with initial straining to separate “coarse” impurities such as foreign bodies, wood,Fig. 1 Analysis values for an ejectioncellulose, or packaging residues from returned milk. Itis essential that the milk is strained before processingComposition of a partial ejectioncontinues so as to prevent damage to sensitive partsof the line. Pore width may not exceed 0.2 mm.2.1.2 Clarifying milk using theskimming separatorIndependent of the separation of milk into skim milkand cream, every skimming centrifuge has a secondary effect, namely separation of solids from themilk. The separated solids are discharged in batchesby means of partial ejections. The clarifying effectachieved with a milk separator is better and morestable than when filters are used.However, the separation rate of solids is even higherin clarifiers especially designed for this purpose thanit is in skimming separators.Water approx. 84 %Protein 6 – 8 %Lactose approx. 4.7 %NMS 1.5 – 3 %Fat 0.25 – 0.35 %6

The values shown in Fig. 1 are based on the following2.1.5 Proportion of non-milk solids in milkfurther conditions:The data available allow the proportion of NMS in 0.05 – 0.1 percent by volume related to thethe raw milk to be calculated, with NMS % (DM)quantity of raw milk fed in was discharged bybeing assumed to be equal to NMS % by vol. as anpartial ejectioninitial approximation. Separation temperature was between 45 and 55 CThe significance of separation temperature will beexplained in more detail later on in the documentation.proportion of ejection volume proportion of NMS in ejection volumeNMS max 100NMS max 0.1 3 0.003 %100NMS min 0.05 1.5 0.00075 %1002.1.6 Product losses whencalculation of product loss would be: quantity of milkclarifying milk using separatorsfed in 25,000 kg / h, partial ejection every 30 min.,Product is lost as a result of spun-off solids beingpartial ejection quantity 8 kg.discharged from the separator bowl. An exampleProduct loss, absolute Product loss, absolute ejection quantity kg / h 100feed quantity kg / h16 kg / h 100 0.064 %25,000 kg / h2.1.7 Protein losses when cleaning milkusing separatorsThe solids discharged contain protein, among otherthings. The absolute loss of protein from partialejection can be calculated as follows:Protein loss, absolute ejection quantity (kg / h) protein content of ejection (%) 100feed quantity to separator (kg / h) protein fed in (%)16 kg / h 7 % 100 0.14 %25,000kg / h 3.2 %Protein loss, absolute 7

The following factors are critical for the level of Separation temperature should be no moreprotein losses:than 55 C; a considerable rise in loss of protein The quantity of solids discharged in partialis found above this.ejection and the time between two partialejection cycles (ejection interval)A reduction in protein losses to 0.12 percent is The ratio between the quantity of solidsconsidered perfectly feasible. The protein losses aredischarged and raw milk fed in should beillustrated in Fig. 2.between 0.05 and 0.1 percent.61 CProtein losses in %0.2052 C0.150.10000.050.10.150.2Proportion of solids quantity dischargedto quantity fed in %Fig. 2 Protein loss as a function of the quantity of solids discharged and temperature2.1.8 Temperatures when clarifying milkThe recommendation of these limited temperatureA temperature either between 8 C and 15 Cranges is based on two pieces of information:(storage temperature) or between 52 C and 58 C is Between 15 C and 35 C, there is an increased riskrecommended.of damage to fat. This has been found as a resultof the rise in free fat (FF) when the milk is undermechanical load (e. g. from pumps). Lipases arestill active up to approx. 50 C. The temperature range from 30 C to 45 Crepresents an optimum for the growth ofbacteria (even if these are present only in theory).8

2.1.9 Reducing total bacteria countAs Fig. 3 demonstrates, however, this can only beMore recent investigations on modern milk clarifiersachieved in milk cleaning at an appropriate producthave shown that compared to earlier statements, atemperature.significant proportion of the total germ count (TGC)Reduction in total bacteria count (TBC) in %is discharged with the solids.80706050403020Damage to fatGrowth of bacteria1000102030405060Temperature in CFig. 3 Reduction in total bacteria count (TBC) as a function of milk temperature2.1.10 Clarification effect when usingmuch greater clarification effect to be achieved withskimming separatorsthe use of clarifiers than is possible with skimmingIn many areas of the dairy industry, it is customaryseparators. Extensive in-house investigations havefor milk clarification to be combined with skimming.shown that only 30 to 50 percent of the NMS areThe current state of knowledge, however, allows aseparated from the milk in a skimming separator.9

2.1.11 Separating somatic cellsThe relatively low separation effect in the skim-A clear and easily proven indicator of the cleaningming separator can be explained by the fact that theefficiency of a separator is the separation of somaticseparation path for the solids in the disk stack of acells. Fig. 4 compares how a skimming separator andskimming separator is much shorter than in thea clarifier remove these cells.clarifier. Section 2.4.2 goes into more detail 0Fig. 4 Separation of somatic cells in the milk separator(Here the efficiency is shown for the specific somatic cell number of 430,000 cells / ml)Efficiency SC0 – SC1 100 (SC somatic cells)SC0 Leukocytes with “trapped” listeria areListeria have a high affinity for leukocytes, in otherwords for a particular part of somatic cells. Some ofseparated off If there are no leukocytes, listeria can further-the listeria trapped in leukocytes are resistant to heat,more not be trapped and are thus not resistant towhereas free listeria can be killed off at pasteurizationheat. Any listeria which are present will be killedtemperature.off during pasteurization.To prevent a potential listeria problem, it thereforemakes sense to separate the somatic cells in the rawThis is why clarifying raw milk with clarifiers ismilk as far as possible for two reasons:always to be recommended.1080100Clarifier2.1.12 Separating listeria from raw milk70900100Skimming separator60Efficiency [ % ]40350Discharge (1)20030Efficiency [ % ]25020Discharge (1)3000400Feed (0)10350Number of somatic cells [SC x 103 ] per ml)0400Feed (0)Number of somatic cells [SC x 103 ] per mlthe design differences between these separators.

2.1.13 Particular issues for clarifying milkfact that a significant proportion of the total germAs an example of the many tasks performed bycount, but also particles such as pulverized straw orthe milk clarification step, we will look here at thehair, are separated off. Separators have also proved theseparation of “pulverized” hairs from milk.best alternative in the routine dairy tasks of clarifyingIn-house studies and studies at the University offrom the points of view of cost, time and reliability.Wisconsin resulted in up to seven different types ofSeparators are incorporated in the CIP cleaninghair in approx. 70 percent of the cheese samples andcircuit of the milk processing line, for example, soabout 40 percent of the fresh milk samples examined.additional installations or detergents are not requiredIt is advantageous if warm milk clarification is usedspecifically for the separators.in this instance, allowing all the particles of hair tobe removed.2.2 Clarifying raw milk cold –If the milk is clarified cold, on the other hand, onlyprocess technologyapprox. 50 percent of these particles can be removed.This method is frequently used in countries with apoor infrastructure, where the milk from small-scale2.1.14 Summaryproducers is collected at central points. CentrifugalFrom the studies, we are able to draw the conclusioncleaning to improve quality is then performed beforethat warm clarification of milk, e. g. at 50 to 55 C, isthe milk is taken on for central processing at the dairy.preferable to cold clarification. This results from the1FIC1456789332Fig. 5 Method for clarifying raw milk cold1Storage tank6Clarified milk2Raw milk7Solids tank3Pump8Solid4Flowmeter9Clarifier5Constant pressure valve11

2.3 Clarifying raw milk warm – process technologyThis method achieves the optimum clarification effectfor the milk.Fig. 6 Method for clarifying raw milk warm5161FIC73842103129111Storage tank5Cleaned pasteurized milk92Raw milk6Heat exchanger10 Solids tank3Pump7Flowmeter11 Solids pump4Feed tank8Constant pressure valve12 Solids12Clarifier

2.4 Clarifying milk – machineryFigure 7:The milk to be clarified flows through central feed2.4.1 Method of operation of clarifierstube (1) in the feed chamber which rotates at bowlThese days, GEA Westfalia Separator Group generallyspeed. The feed to disc stack (5) is effected by boressupplies clarifiers with a hydrosoft feed system. Thisin the base of the distributor.system combines the benefits of softstream and ahydrohermetic feed.The cleaned milk flows inwards and arrives in Adequate flow cross-sections mean low feedcentripetal pump chamber (3). The milk is taken outpressureof the rotating separator bowl under pressure and Optimum design means great flexibility withwithout foam by stationary centripetal pump (2). Theregard to feed quantitysolids slide outwards and accumulate in double No ribs in the feed chamber mean no shearcone-shaped solids chamber (6). A hydraulic systemforces – gentle product treatmentdischarges the solids from the bowl at intervals Hydraulic seal means no air trapped in productwhich can be selected. Ejection is performed at fullbowl speed.Fig. 7 Bowl cross-section of a clarifier17234561 Feed tube5 Feed to disc stack2 Centripetal pump6 Solids chamber3 Centripetal pump chamber7 Discharge, clarified milk4 Disc stack13

2.4.2 Processes in the disc interspaceWith total ejections, the complete bowl contentsThe large number of individual separation chambersare discharged. The feed to the separator has to bearranged in parallel between the discs divides theinterrupted briefly to do this. Total ejections cleanmilk stream into many thin layers. This minimizes theall the surfaces inside the bowl due to the very highsedimentation route. A solids particle is consideredflow velocities. This is particularly important forseparated once it has reached the bottom disc surfacechemical CIP of the line and separator. Total ejectionsof the top disc. Flow speed is low here. The particle isof a separator during CIP guarantee optimum results.no longer entrained with the flow, but slides outwardsunder the influence of centrifugal force. At the end ofAs already mentioned in the section “Separatingthe disc, it leaves the separation chamber.somatic cells”, the clarifying action of skimmingThe smallest particle which can still be separatedseparators is less than that of clarifiers. The reasonis separated on the separation route (I – II). Thefor this is essentially the shorter separation paths.diameter of this type of particle is called the limitThe separation path (I – II) of the skimming separatorparticle diameter. Figures 7 and 8 show individualresponsible for the separation of solids (Fig. 8) isseparation chambers.generally only ¼ as long as the separation route on theclarifier (Fig. 7). The cream which flows off accordingly2.4.3 Bowl ejectionsstill contains a proportion of non-milk solids (NMS).In addition to providing adjustable partial ejections,When the cream is mixed back in with the skimGEA Westfalia Separator Group ejection system alsomilk, this proportion of NMS returns to the milk.allows the bowl to be emptied completely. Dependingon milk quality, partial ejections discharge a certainquantity of solids from the solids chamber atadjustable intervals. The feed to the separator remainsopen. Partial ejections discharge the incoming solidsload from the bowl.IIClarified milkflowing to thedischargeVsVrIIRaw milkfeedCreamr1ISedimentRaw milkfeedr1aISedimentSkimmilkwr2Fig. 7 Individual separation chamber of a clarifierwar2Fig. 8 Individual separation chamber of a skimming separator14

2.5 Machine types2.6 Methods of testing clarification efficiencyThe following table lists current machine types andThe following method is suitable for determining thecapacities of clarifiers for clarifying milk.degree of purity of the milk.Fig. 9 shows the equipment for a method (FunkeGerber) with three purity grades in accordance withSeparatorNominal capacitythe German standard.GEA Westfalia Separator ecoclean15,000 l / h0.5 l of milk are passed through a suitable cotton woolMSE 100-06-17730,000 l / hor fabric filter. Any particles of dirt are retained by theMSE 200-06-77740,000 l / hfilter. The pattern of dirt is assessed and rated afterMSE 250-06-77750,000 l / hthe filter has dried.MSE 350-06-77770,000 l / hAnother method of assessing clarification efficiencyis to measure the content of somatic cells (Fig. 10).If products other than raw milk are clarified, enquireabout the corresponding capacities.Fig. 9 Equipment for testing contamination of milkFig. 10 Automatic machine for determining somatic cellsGEA Westfalia Separator ecocleanClarifier type MSI 35015

3. Bacteria Removal from Milk3.1 GeneralIn whey processing, removal of bacteria makesThe first attempts at removing bacteria from milkparticular sense when serum proteins are to be obtainedby centrifuge go back to the 1950s. However, it wasfrom the clarified skimmed whey in concentratednot until the 1970s that bacteria were successfullyform (WPC whey protein concentrate) by means ofremoved from cheese milk on an industrial scale.ultrafiltration. The long dwell time of the product inIn the 1980s, this technology finally experienced athe filtration unit, some of that time spent at optimumbreakthrough due to the development of bacteria-incubation temperatures, leads to vigorous bacterialremoving separators with a high degree of separationgrowth. According to the information available to us,at simultaneous hourly outputs of up to 25,000 l / h.there exist quality standards which stipulate that, forIn recent years, the use of bacteria-removing separatorsexample, the content of anaerobic spores in 80 percenthas finally expanded successfully into other areas ofWPC may not exceed maximum five spores per grammilk processing. In addition to centrifugal removalof powder. This suggests that centrifugal removal ofof bacteria, filtration using membrane technologybacteria is the solution to improving quality.is also performed. In both methods, impurities andSkim milk can also be treated by bacteria-removingundesired germs or bacteria are separated from theseparators before being processed into high-qualitymilk. When milk is temperature-treated to inactivatecasein / caseinate so that it is of perfect bacteriologicalbacteria and spores, undesired side effects such asquality. Lactate-fermenting anaerobic spore-formerschanges in flavour may occur. However, methodswhich are not killed off by normal milk heating cansuch as irradiation with UV light or high-pressurelead to butyric acid fermentation in the productiontechnology do not currently play a role in the dairyof cheese. Greater attention is therefore paid to spore-industry.formers of the genus Clostridium tyrobutyricumwhich cause late blowing in cheese. Lactobacilli also3.1.1 Reasons for bacteria removal from milkhave to be removed in the production of raw milkA number of objectives are pursued in removingcheese. As the milk is not heated above 50 C at anybacteria from milk. In milk processing, for example,point in the entire process, the lactobacilli which havespore-formers can cause considerable problems.not been killed off would lead to faults in the cheese.In the production of fresh milk, aerobic spore-formers(Bacillus cereus) impair shelf life as a result of sweet3.1.2 Technical principlesclotting.Fig. 11 shows by way of example the route taken byIn the production of milk powder, especially “low-Clostridium tyrobutyricum and the locations where itheat” products, aerobic and anaerobic spore-formersproliferates en route to the end product. Fig. 12 shows(Bacillus cereus, Clostridium perfringens) lead to thean example of the distribution of the Clostridia inproduct spoiling.raw milk and the corresponding metabolic properties.Under certain conditions, the removal of bacteriasecures shelf life in soft cheese products – for example,in cases where the so-called ascospores of the mouldsByssochlamys nivea or Byssochlamys fulva have anegative impact on quality.16

Route taken by ClostridiumtyrobutyricumPreventing the growth of bacteriaAreaSoilSilage *Chemically Formic acid, propionic acid etc.Rumen, faeces, raw milkMilking hygieneVat milkCheese*Biologically Wilt, maize, vaccinateMilk producerPhysically SeparatorChemically Peroxide catalaseDairy, cheese-makerChemically Nitrate, lysozyme, nisinTechnically pH, salt, temperatureLate blowingFig. 11 Route and locations for the growth of Clostridium tyrobutyricum* Locations for the growth of Clostridium tyrobutyricumNo.Clostridium speciesMetabolic properties1 35 %Clostridium sporengensDecomposes protein (proteolytic)2 12 %Clostridium perfringensDecomposes protein (proteolytic)3 11 %Clostridium butyricumDecomposes lactose (lactolytic)4 8 %Clostridium tyrobutyricumFerments lactate (salt of lactic acid)5 6 %Clostridium beijerinckii6 7 %Clostridium tetanomorphum7 4 %Clostridium pasteurianum8 4 %Clostridium tertium9 2 %Clostridium novyi10Fraction 11 %UnclassifiableFig. 12 Distribution of Clostridia in raw milk and their metabolic properties17

The occurrence of individual strains in relation to theAn important factor in determining spores in milkcritical months of a year is shown in Fig. 13. Thesefor bacteria removal or from which bacteria havevalues are likely to apply to many milk catchmentalready been removed is the use of suitable testareas for dairies.methods. When GEA Westfalia Separator Group quotesThere are exceptions, however. In these cases, the totalvalues, these are based on the test methods definednumber of anaerobic and aerobic spores correspondsin this brochure (see chapter 3.9.1).approximately to that in Fig. 13, but the ratio ofA large number of tests has now been carried out. Theanaerobic to aerobic spores is much more unfavourable.values determined result in a stable picture of sporeIn Austria, for example, up to 50 percent of anaerobiccontent before and after removal of bacteria, allowingspores were detected in the total spore quantity. Inus also to make validated statements about bacteriala North German dairy, up to 15 percent were found.clarification effect.In contrast to these significant deviations, a proportionof 2 to 5 percent of anaerobic spores was 88003507300250200Aerobic spores (per ml)13Anaerobic spores (per ml)65065700600500440033001002200501100000150Fig. 13 Number of spores and lactobacilli in raw milk18Lactobacilli (per ml)found in other studies.

3.1.3 Effectiveness of bacteria-removing separatorsThis equation clearly shows that sedimentationThe results of more recent tests, including some byvelocity “v” on the bacteria-removing separator isindependent institutes in cheese-making factories, areproportional to the square of the diameter of thereproduced in Fig. 14.bacteria, to the difference in density between milkand bacteria and to the acceleration due to gravity. ItBacteria removal temperatureis inversely proportional to milk viscosity.This should be between 55 C and 62 C. In this range,milk viscosity is relatively low. According to Stokes’Separator feed capacitylaw, the sedimentation velocity of the bacteria to beExceeding nominal capacity on the one hand resultsseparated off is higher than at lower temperatures.in a considerable reduction in bacteria-removingAt higher temperatures, however, there is a risk ofefficiency. Undershooting nominal capacity, ondamage to protein.the other hand, only achieves a limited increase inefficiency.Stokes’ law says:v D2 Δρ18 η m2 kg m s m gm3 kg s2 v sedimentation velocity (m / s)D diameter of bacteria (m)Δρ difference in densities of milk and bacteria (kg / m3)η dynamic viscosity of the milk (kg / ms)g gravitational acceleration (m / s2)Sample no.SamplenameTemperatureOutputQuantity ofconcentrateEjectiontimeAnaerobic spores(Clostridia / 10 ml)10 mlEffectFeed Z 1.0 35Process 1A 1.050 C48,000 l / h1300 l / h3600 sec. 0.2 99.43 %Process 2A 1.150 C48,000 l / h1400 l / h3900 sec. 0.2 99.43 %Process 1A 2.050 C48,000 l / h1300 l / h3600 sec. 0.2 99.43 %Process 2A 2.150 C48,000 l / h1400 l / h3900 sec. 0.2Process 1A 3.050 C48,000 l / h1300 l / h3600 sec. 0.2 99.43 %Process 2A 3.150 C48,000 l / h1400 l / h3900 sec.Process 1A 4.050 C48,000 l / h1300 l / h3600 sec. 0.2 99.43 %Process 2A 4.150 C48,000 l / h1400 l / h3900 sec.Tank sample4T 12 0.2 99.43 %Process 1A 5.050 C48,000 l / h1300 l / h3600 sec. 0.2 99.43 %Process 2A 5.150 C48,000 l / h1400 l / h3900 sec. 0.2 99.43 %Process 1A 6.050 C48,000 l / h1300 l / h3600 sec. 0.2 99.43 %Process 2A 6.150 C48,000 l / h1400 l / h3900 sec. 0.2 99.43 %Tank sample4T 10 0.2 99.43 % 0.2 99.43 %0.2 99.43 %Fig. 14 Results of double removal of bacteria using CSE 500-01-777 separatorsProcess 1: Bacterially clarified milk after the first machineProcess 2: Bacterially clarified milk after the second machine19 99.43 %

4123Fig. 15 Diagram of abacteria-removing separator1Feed of milk3Ejections2Discharge of bacterially clarified milk4Optional: concentrate discharge3.1.4 Protein balance in bacteria-removing separators3.1.5 Treating concentrateFig. 15 shows the product flows in the bacteria-In addition to bacteria, continuous and batch-wiseremoving separator.concentrate in the bacteria-removing separatorThe concentrate which continuously forms (entrainedcontains protein and other valuable constituents.liquid) can be returned to the feed on bacteria-Depending on process management and regionallyremoving separators from GEA Westfalia Separatorapplicable regulations, the concentrates can be returnedGroup, or routed off for use elsewhere. The effect ofcompletely or partly to the milk following the appropriatebacteria removal is not influenced by the return oftreatment or processed further elsewhere. The batch-the concentrate.wise phase (ejections of the bacteria-removing separator)Fig. 16 shows a table with product flows in the bacteria-contains practically no non-milk solids if it wasremoving separator and their protein content.previously clarified by centrifugation or fully or partlyThe protein content may deviate according to regionskimmed by a separator. A temperature treatmentand season. The mechanical differences of the(sterilization) is required to kill off the bacteria. ThisGEA Westfalia Separator proplus design will becan be performed by UHT equipment, for example,explained in a later section.which has been specifically adapted for the task. Directsteam injection or fine atomization in a steam chamberare possible methods of sterilizing the concentrate.MeasuringpointFeedDischarge of bacteriallyclarified milkDischarge,concentrateDischarge, ejectionsIIIIIIIVWith concentraterecirculationWithout concen-trate recirculation49,960 l / h48,460 l / h49,990 l / h48,490 l / h99.92 %96.92 %99.98 %96.98 %Protein3.40 %content3.396 %3.387 %3.398 %3.389 %Protein1700units / h1696.801641.30Quantity50,000 l / hFraction100 %1698.80StandardseparatorGEA Westfalia Separator1500 l / h40 l / h10 l / h3.00 %0.08 %0.02 %3.70 %8.00 %12 %3.21.255.51643.30Fig. 16 Product flows in bacteria-removing separator and protein contents20proplus separator

3.2 Bacteria removal from fresh milk –Centrifugal removal of bacteria enables spores to beprocess technologyreduced by a factor of more than ten, correspondingIn this method, the separation of Bacillus cereus isto more than 3.5 generations.of particular interest. This germ is heat-resistant andReduction in total bacteria count is often consideredthus still active after pasteurization, so sweet clottingin assessing the removal of bacteria from freshof milk can be the result. The specific weight and sizemilk. However, it should be noted that the generallyof this bacillus make centrifugal separation difficult.unknown distribution of flora across the variousAdapting separator feed capacity to the specificbacterial strains present can have a considerableconditions, however, allows bacterial clarificationinfluence on separation rate. One reason is the fact thatefficiency of over 90 percent to be achieved.the occurrence of small, lightweight bacteria my beIn studies of pasteurized milk, orders of magnitude ofcomparatively low on one occasion and comparatively300 spores per litre were

efficiency of a separator is the separation of somatic cells. Fig. 4 compares how a skimming separator and a clarifier remove these cells. 2.1.12 Separating listeria from raw milk Listeria have a high affinity for leukocytes, in other words for a particular part of somatic cells. Some of

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