Bro da bacteria removal 2012 12 en tcm11 27697

Separators from GEA Westfalia Separator for Milk Clarification and Bacteria Removal

engineering for a better world GEA Mechanical Equipment

2

4 1. Introduction

6 2. MilkClarification

6 2.1 Introduction

6 2.1.1 Clarifyingmilkusingfilters

6 2.1.2 Clarifyingmilkusingtheskimming

separator

6 2.1.3 Clarifyingmilkusingtheclarifier

6 2.1.4 Compositionofsolidsdischarged

byseparators

7 2.1.5 Proportionofnon-milksolidsinmilk

7 2.1.6 Productlosseswhenclarifyingmilk

usingseparators

7 2.1.7 Proteinlosseswhenclarifyingmilk

usingseparators

8 2.1.8 Temperatureswhenclarifyingmilk

9 2.1.9 Reducingtotalbacteriacount

9 2.1.10 Clarificationeffectwhenusing

skimmingseparators

10 2.1.11 Separatingsomaticcells

10 2.1.12 Separatinglisteriafromrawmilk

11 2.1.13 Particularissuesforclarifyingmilk

11 2.1.14 Summary

11 2.2 Clarifyingrawmilkcold–

processtechnology

12 2.3 Clarifyingrawmilkwarm–

processtechnology

13 2.4 Clarifyingmilk–machinery

13 2.4.1 Methodofoperationofclarifiers

14 2.4.2 Processesinthediscinterspace

14 2.4.3 Bowlejections

15 2.5 Machinetypes

15 2.6 Methodsoftestingclarification

efficiency

16 3. BacteriaRemovalfromMilk

16 3.1 General

16 3.1.1 Reasonsforbacteriaremoval

frommilk

16 3.1.2 Technicalprinciples

19 3.1.3 Effectivenessofbacteria-removing

separators

20 3.1.4 Proteinbalanceinbacteria-removing

separators

20 3.1.5 Treatingconcentrate

21 3.2 Bacteriaremovalfromfresh

milk–processtechnology

22 3.2.1 Bacteriaremovalfromfresh

milk–Stage1

23 3.2.2 Bacteriaremovalfromskimmilk

24 3.3 Premiummilkwithalongershelflife

withtheGEAWestfaliaSeparator

prolongprocess

26 3.4 ESLmilkprocesstechnology

27 3.5 Bacteriaremovalfromcheesemilk–

processtechnology

28 3.5.1 Doublebacteriaremoval

28 3.5.2 Variablebacteriaremoval,example:

cheesemilk

30 3.6 Comparisonofmicrofiltration

andseparator

30 3.7 Specialapplications

30 3.7.1 Bacteriaremovalfromwhey

concentrate

32 3.8 Bacteriaremoval–machinery

32 3.8.1 Methodofoperation:

bacteria-removingseparators

33 3.8.2 Methodofoperation:

bacteria-removingseparatorswith

GEAWestfaliaSeparatorproplussystem

34 3.9 Machinetypes

34 4.0 Sampling

34 4.0.1 Prerequisitesinthemilk

processingline

35 4.0.2 Arrangementofsamplingpoints

35 4.0.3 Samplingequipmentrequired

35 4.0.4 Performingsampling

36 4.0.5 Treatingthesamples

36 4.1 Testmethods

36 4.1.1 Overview

36 4.1.2 Testsforanaerobicspores

39 4.1.3 Testsforaerobicspores

39 4.1.4 Testsforlactobacilli

Contents

3

1. Introduction

ClarifiersfromGEAWestfaliaSeparatorGroupand

bacteria-removingseparatorsareused in thedairy

industrytoimprovemilkquality.Centrifugaland/or

membranetechnologyareusedtoseparateimpurities

andbacteriafromthemilk.

Examplesofundesiredconstituentsinrawmilkare

particlesofdirt,bloodresidues,uddercellsandagreat

manydifferentbacteria.

Thistechnicaldocumentationexplainsclarifyingand

bacteriaremovalefficiencyinrelationtotheprocesses

used in the field.Amongother things, this clearly

shows the composition of the phases discharged

in batches when clarifiers and bacteria-removing

separatorsareused,and theextent towhich these

phasescanberecycled.

4

5

2. Milk Clarification

2.1.3Clarifyingmilkusingtheclarifier

Clarifiers are machines specifically designed for

solids/liquid separation. The specific design of

this machine enables it to achieve an optimum

separation rate for impurities.Wewillgo into the

designdifferencesinmoredetailatalaterstage.

2.1.4Compositionofsolidsdischargedbyseparators

Complex studies have been conducted to obtain

preciseinformationaboutthesolidsdischargedby

self-cleaning separators during milk clarification.

Samplesfromdifferentmilkregionsusingseparators

ofdifferentsizeshavebeenanalysed,thusensuring

arepresentativecross-section.

Partial ejectionswereperformedonall separators.

Thetimebetweentwoconsecutivepartialejections

wasselectedsothatthesolidshadadrymassof14to

16percent.Thisensuredthatateachpartialejection,

allthesolidsseparatedweredischarged.Theresults

ofthestudyareshowninFig.1.

2.1Introduction

The most important part of clarifying milk is the

separationofnon-milksolids(NMS).Adistinctionis

generallymadebetweenthedifferentmethodsused

byprocessorstoimprovethequalityofmilk.

2.1.1Clarifyingmilkusingfilters

Thismethodof improving thequalityofmilkhas

beenmoreorlessabandonedthesedaysforavariety

ofreasons.

Oneofitsbiggestdrawbacksisthedropinflowrate

overtimebecauseathickerandthickerfilter layer

buildsup.Runningtimeislimited.Theentiremilk

flow ispassed throughthe filter layer.Thisallows

bacteriologicalproblemstoariseduetoentrainment,

thereisariskofbacterialgrowthinthefilterlayerand

thusreinfectionofthemilk.Whatismore,ifthere

arecracksinthefiltertissue,theclarifyingeffectis

considerablyreduced.Cleaningthefiltersafterpro-

ductionisalsoanextremelylaboriousprocess.

Theuseoffilterstoimprovemilkqualityshouldnot,

however,beconfusedwithinitialstrainingtosepa-

rate“coarse”impuritiessuchasforeignbodies,wood,

cellulose,orpackagingresiduesfromreturnedmilk.It

isessentialthatthemilkisstrainedbeforeprocessing

continuessoastopreventdamagetosensitiveparts

oftheline.Porewidthmaynotexceed0.2mm.

2.1.2Clarifyingmilkusingthe

skimmingseparator

Independentoftheseparationofmilkintoskimmilk

andcream,everyskimmingcentrifugehasasecond-

ary effect, namely separation of solids from the

milk.Theseparatedsolidsaredischargedinbatches

bymeansofpartialejections.Theclarifyingeffect

achievedwithamilk separator isbetterandmore

stablethanwhenfiltersareused.

However,theseparationrateofsolidsisevenhigher

inclarifiersespeciallydesignedforthispurposethan

itisinskimmingseparators.

Fig. 1 Analysis values for an ejection

Composition of a partial ejection

Water approx. 84 % Protein 6 – 8 %

Lactose approx. 4.7 % NMS 1.5 – 3 %

Fat 0.25 – 0.35 %

6

ThevaluesshowninFig.1arebasedonthefollowing

furtherconditions:

• 0.05–0.1percentbyvolumerelatedtothe

quantityofrawmilkfedinwasdischargedby

partialejection

• Separationtemperaturewasbetween45and55°C

Thesignificanceofseparationtemperaturewillbe

explainedinmoredetaillateroninthedocumentation.

2.1.6Productlosseswhen

clarifyingmilkusingseparators

Product is lost as a result of spun-off solidsbeing

discharged from the separator bowl. An example

2.1.7Proteinlosseswhencleaningmilk

usingseparators

Thesolidsdischargedcontainprotein,amongother

things. The absolute loss of protein from partial

ejectioncanbecalculatedasfollows:

2.1.5Proportionofnon-milksolidsinmilk

ThedataavailableallowtheproportionofNMSin

the raw milk to be calculated, with NMS % (DM)

beingassumedtobeequaltoNMS%byvol.asan

initialapproximation.

calculationofproductlosswouldbe:quantityofmilk

fed in25,000kg/h,partialejectionevery30min.,

partialejectionquantity8kg.

NMSmax=proportionofejectionvolume∙proportionofNMSinejectionvolume

100

Productloss,absolute=ejectionquantitykg/h∙100

feedquantitykg/h

Proteinloss,absolute=ejectionquantity(kg/h)∙proteincontentofejection(%)∙100

feedquantitytoseparator(kg/h)∙proteinfedin(%)

Productloss,absolute=16kg/h∙100=0.064%

25,000kg/h

Proteinloss,absolute=16kg/h∙7%∙100=0.14%

25,000kg/h∙3.2%

NMSmax=0.1∙3=0.003% 100

NMSmin=0.05∙1.5=0.00075% 100

7

• Separationtemperatureshouldbenomore

than55°C;aconsiderableriseinlossofprotein

isfoundabovethis.

A reduction in protein losses to 0.12 percent is

consideredperfectlyfeasible.Theproteinlossesare

illustratedinFig.2.

Therecommendationof these limited temperature

rangesisbasedontwopiecesofinformation:

• Between15°Cand35°C,thereisanincreasedrisk

ofdamagetofat.Thishasbeenfoundasaresult

oftheriseinfreefat(FF)whenthemilkisunder

mechanicalload(e.g.frompumps).Lipasesare

stillactiveuptoapprox.50°C.

• Thetemperaturerangefrom30°Cto45°C

representsanoptimumforthegrowthof

bacteria(evenifthesearepresentonlyintheory).

The following factors are critical for the level of

proteinlosses:

• Thequantityofsolidsdischargedinpartial

ejectionandthetimebetweentwopartial

ejectioncycles(ejectioninterval)

• Theratiobetweenthequantityofsolids

dischargedandrawmilkfedinshouldbe

between0.05and0.1percent.

2.1.8Temperatureswhenclarifyingmilk

A temperature either between 8°C and 15°C

(storagetemperature)orbetween52°Cand58°Cis

recommended.

0.20

0.15

0.10

00

52 °C

61 °C

Proportion of solids quantity discharged to quantity fed in %

Prot

ein

loss

es in

%

0.05 0.1 0.15 0.2

Fig. 2 Protein loss as a function of the quantity of solids discharged and temperature

8

2.1.9Reducingtotalbacteriacount

Morerecentinvestigationsonmodernmilkclarifiers

haveshownthatcomparedtoearlierstatements,a

significantproportionofthetotalgermcount(TGC)

isdischargedwiththesolids.

muchgreaterclarificationeffecttobeachievedwith

theuseofclarifiersthanispossiblewithskimming

separators. Extensive in-house investigations have

shown that only 30 to 50 percent of the NMS are

separatedfromthemilkinaskimmingseparator.

2.1.10Clarificationeffectwhenusing

skimmingseparators

Inmanyareasofthedairyindustry,itiscustomary

formilkclarificationtobecombinedwithskimming.

Thecurrent stateofknowledge,however, allowsa

Fig. 3 Reduction in total bacteria count (TBC) as a function of milk temperature

80

70

60

50

40

30

20

10

00

Temperature in ˚C

Redu

ctio

n in

tot

al b

acte

ria

coun

t (T

BC)

in %

10 20 30 40 50 60

As Fig. 3 demonstrates, however, this can only be

achievedinmilkcleaningatanappropriateproduct

temperature.

Damage to fatGrowth of bacteria

9

The relatively low separation effect in the skim-

mingseparatorcanbeexplainedbythefactthatthe

separationpathforthesolidsinthediskstackofa

skimming separator is much shorter than in the

clarifier. Section2.4.2 goes intomoredetail about

thedesigndifferencesbetweentheseseparators.

• Leukocyteswith“trapped”listeriaare

separatedoff

• Iftherearenoleukocytes,listeriacanfurther-

morenotbetrappedandarethusnotresistantto

heat.Anylisteriawhicharepresentwillbekilled

offduringpasteurization.

This is why clarifying raw milk with clarifiers is

alwaystoberecommended.

2.1.11Separatingsomaticcells

Aclearandeasilyprovenindicatorofthecleaning

efficiencyofaseparatoristheseparationofsomatic

cells.Fig.4compareshowaskimmingseparatorand

aclarifierremovethesecells.

2.1.12Separatinglisteriafromrawmilk

Listeriahaveahighaffinityforleukocytes,inother

wordsforaparticularpartofsomaticcells.Someof

thelisteriatrappedinleukocytesareresistanttoheat,

whereasfreelisteriacanbekilledoffatpasteurization

temperature.

Topreventapotentiallisteriaproblem,ittherefore

makessensetoseparatethesomaticcellsintheraw

milkasfaraspossiblefortworeasons:

Fig. 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)

Num

ber

of s

omat

ic c

ells

[SC

x 1

03 ]

per

ml

Num

ber

of s

omat

ic c

ells

[SC

x 1

03 ]

per

ml)

Effi

cien

cy [

% ]

Effi

cien

cy [

% ]

400

350

300

250

200

150

100

50

0

400

350

300

250

200

150

100

50

0

0

10

20

30

40

50

60

70

80

90

100

0

10

20

30

40

50

60

70

80

90

100

Feed

(0)

Feed

(0)

Dis

char

ge (

1)

Dis

char

ge (

1)

Skimming separator Clarifier

Efficiency=SC0–SC1∙100(SC = somaticcells)

SC0

10

FIC

fact thatasignificantproportionof thetotalgerm

count,butalsoparticlessuchaspulverizedstrawor

hair,areseparatedoff.Separatorshavealsoprovedthe

bestalternativeintheroutinedairytasksofclarifying

fromthepointsofviewofcost, timeandreliability.

Separators are incorporated in the CIP cleaning

circuitof themilkprocessing line, forexample,so

additionalinstallationsordetergentsarenotrequired

specificallyfortheseparators.

2.2Clarifyingrawmilkcold–

processtechnology

Thismethodisfrequentlyusedincountrieswitha

poorinfrastructure,wherethemilkfromsmall-scale

producersiscollectedatcentralpoints.Centrifugal

cleaningtoimprovequalityisthenperformedbefore

themilkistakenonforcentralprocessingatthedairy.

2.1.13Particularissuesforclarifyingmilk

As an example of the many tasks performed by

themilkclarificationstep,wewill lookhereatthe

separationof“pulverized”hairsfrommilk.

In-house studies and studies at the University of

Wisconsinresultedinuptosevendifferenttypesof

hairinapprox.70percentofthecheesesamplesand

about40percentofthefreshmilksamplesexamined.

Itisadvantageousifwarmmilkclarificationisused

inthisinstance,allowingalltheparticlesofhairto

beremoved.

Ifthemilkisclarifiedcold,ontheotherhand,only

approx.50percentoftheseparticlescanberemoved.

2.1.14Summary

Fromthestudies,weareabletodrawtheconclusion

thatwarmclarificationofmilk,e.g.at50to55°C,is

preferabletocoldclarification.Thisresultsfromthe

Fig. 5 Method for clarifying raw milk cold

1 Storage tank

2 Raw milk

3 Pump

4 Flowmeter

5 Constant pressure valve

6 Clarified milk

7 Solids tank

8 Solid

9 Clarifier

1 1

2

3 3

9

8

4

5

6

7

11

FIC

2.3Clarifyingrawmilkwarm–processtechnology

Thismethodachievestheoptimumclarificationeffect

forthemilk.

Fig. 6 Method for clarifying raw milk warm

1 Storage tank

2 Raw milk

3 Pump

4 Feed tank

5 Cleaned pasteurized milk

6 Heat exchanger

7 Flowmeter

8 Constant pressure valve

9 Clarifier

10 Solids tank

11 Solids pump

12 Solids

1

2 3

3

4

5

6

7

8

9

10

12

11

1

12

2.4Clarifyingmilk–machinery

2.4.1Methodofoperationofclarifiers

Thesedays,GEAWestfaliaSeparatorGroupgenerally

suppliesclarifierswithahydrosoftfeedsystem.This

systemcombines thebenefits of softstreamanda

hydrohermeticfeed.

• Adequateflowcross-sectionsmeanlowfeed

pressure

• Optimumdesignmeansgreatflexibilitywith

regardtofeedquantity

• Noribsinthefeedchambermeannoshear

forces–gentleproducttreatment

• Hydraulicsealmeansnoairtrappedinproduct

Figure7:

Themilktobeclarifiedflowsthroughcentralfeed

tube(1) inthefeedchamberwhichrotatesatbowl

speed.Thefeedtodiscstack(5)iseffectedbybores

inthebaseofthedistributor.

The cleaned milk flows inwards and arrives in

centripetalpumpchamber(3).Themilkistakenout

of the rotating separatorbowlunderpressureand

withoutfoambystationarycentripetalpump(2).The

solids slide outwards and accumulate in double

cone-shapedsolidschamber(6).Ahydraulicsystem

discharges the solids from the bowl at intervals

whichcanbeselected.Ejectionisperformedatfull

bowlspeed.

Fig. 7 Bowl cross-section of a clarifier

5 Feed to disc stack

6 Solids chamber

7 Discharge, clarified milk

1 Feed tube

2 Centripetal pump

3 Centripetal pump chamber

4 Disc stack

2

1

3

4

5

6

7

13

With total ejections, the complete bowl contents

aredischarged.Thefeedtotheseparatorhastobe

interruptedbriefly todo this.Totalejectionsclean

allthesurfacesinsidethebowlduetotheveryhigh

flow velocities. This is particularly important for

chemicalCIPofthelineandseparator.Totalejections

ofaseparatorduringCIPguaranteeoptimumresults.

As already mentioned in the section “Separating

somatic cells”, the clarifying action of skimming

separatorsislessthanthatofclarifiers.Thereason

for this isessentially theshorter separationpaths.

Theseparationpath(I–II)oftheskimmingseparator

responsible for the separation of solids (Fig. 8) is

generallyonly¼aslongastheseparationrouteonthe

clarifier(Fig.7).Thecreamwhichflowsoffaccordingly

stillcontainsaproportionofnon-milksolids(NMS).

When the cream is mixed back in with the skim

milk, this proportion of NMS returns to the milk.

2.4.2Processesinthediscinterspace

Thelargenumberofindividualseparationchambers

arranged in parallel between the discs divides the

milkstreamintomanythinlayers.Thisminimizesthe

sedimentationroute.Asolidsparticleisconsidered

separatedonceithasreachedthebottomdiscsurface

ofthetopdisc.Flowspeedislowhere.Theparticleis

nolongerentrainedwiththeflow,butslidesoutwards

undertheinfluenceofcentrifugalforce.Attheendof

thedisc,itleavestheseparationchamber.

The smallest particle which can still be separated

is separated on the separation route (I–II). The

diameterof this typeofparticle is called the limit

particlediameter.Figures7and8showindividual

separationchambers.

2.4.3Bowlejections

Inadditiontoprovidingadjustablepartialejections,

GEAWestfaliaSeparatorGroupejectionsystemalso

allowsthebowltobeemptiedcompletely.Depending

onmilkquality,partialejectionsdischargeacertain

quantity of solids from the solids chamber at

adjustableintervals.Thefeedtotheseparatorremains

open.Partialejectionsdischargetheincomingsolids

loadfromthebowl.

II

Sedi-ment

Clarified milk flowing to the discharge Raw milk

feed

I

Vs

Vr r1

r2

w

a

II

I

Sedi-ment

Skim milk

Cream

Raw milk feed

r1

r2

wa

Fig. 7 Individual separation chamber of a clarifier Fig. 8 Individual separation chamber of a skimming separator

14

2.5Machinetypes

Thefollowingtablelistscurrentmachinetypesand

capacitiesofclarifiersforclarifyingmilk.

Ifproductsotherthanrawmilkareclarified,enquire

aboutthecorrespondingcapacities.

2.6Methodsoftestingclarificationefficiency

Thefollowingmethodissuitablefordeterminingthe

degreeofpurityofthemilk.

Fig. 9 shows the equipment for a method (Funke

Gerber)withthreepuritygradesinaccordancewith

theGermanstandard.

0.5lofmilkarepassedthroughasuitablecottonwool

orfabricfilter.Anyparticlesofdirtareretainedbythe

filter.Thepatternofdirtisassessedandratedafter

thefilterhasdried.

Anothermethodofassessingclarificationefficiency

istomeasurethecontentofsomaticcells(Fig.10).

Fig. 9 Equipment for testing contamination of milk Fig. 10 Automatic machine for determining somatic cells

Separator Nominalcapacity

GEA Westfalia Separator ecoclean 15,000 l / h

MSE 100-06-177 30,000 l / h

MSE 200-06-777 40,000 l / h

MSE 250-06-777 50,000 l / h

MSE 350-06-777 70,000 l / h

GEA Westfalia Separator ecoclean Clarifier type MSI 350

15

3. Bacteria Removal from Milk

In whey processing, removal of bacteria makes

particularsensewhenserumproteinsaretobeobtained

from the clarified skimmed whey in concentrated

form(WPCwheyproteinconcentrate)bymeansof

ultrafiltration.Thelongdwelltimeoftheproductin

thefiltrationunit,someofthattimespentatoptimum

incubationtemperatures,leadstovigorousbacterial

growth.Accordingtotheinformationavailabletous,

thereexistqualitystandardswhichstipulatethat,for

example,thecontentofanaerobicsporesin80percent

WPCmaynotexceedmaximumfivesporespergram

ofpowder.Thissuggeststhatcentrifugalremovalof

bacteriaisthesolutiontoimprovingquality.

Skimmilkcanalsobetreatedbybacteria-removing

separatorsbeforebeingprocessedintohigh-quality

casein/caseinatesothatitisofperfectbacteriological

quality.Lactate-fermentinganaerobicspore-formers

whicharenotkilledoffbynormalmilkheatingcan

leadtobutyricacidfermentationintheproduction

ofcheese.Greaterattentionisthereforepaidtospore-

formers of the genus Clostridium tyrobutyricum

whichcauselateblowingincheese.Lactobacillialso

havetoberemoved in theproductionofrawmilk

cheese.Asthemilkisnotheatedabove50̊ Catany

pointintheentireprocess,thelactobacilliwhichhave

notbeenkilledoffwouldleadtofaultsinthecheese.

3.1.2Technicalprinciples

Fig.11showsbywayofexampletheroutetakenby

Clostridiumtyrobutyricumandthelocationswhereit

proliferatesenroutetotheendproduct.Fig.12shows

anexampleof thedistributionof theClostridia in

rawmilkandthecorrespondingmetabolicproperties.

3.1General

The firstattemptsat removingbacteria frommilk

bycentrifugegobacktothe1950s.However,itwas

notuntil the 1970s thatbacteriawere successfully

removed from cheese milk on an industrial scale.

In the1980s, this technology finallyexperienceda

breakthrough due to the development of bacteria-

removingseparatorswithahighdegreeofseparation

atsimultaneoushourlyoutputsofupto25,000l/h.

Inrecentyears,theuseofbacteria-removingseparators

hasfinallyexpandedsuccessfullyintootherareasof

milkprocessing.Inadditiontocentrifugalremoval

of bacteria, filtration using membrane technology

isalsoperformed.Inbothmethods,impuritiesand

undesiredgermsorbacteriaareseparatedfromthe

milk.Whenmilkistemperature-treatedtoinactivate

bacteriaandspores,undesiredsideeffectssuchas

changes in flavour may occur. However, methods

suchas irradiationwithUV lightorhigh-pressure

technologydonotcurrentlyplayaroleinthedairy

industry.

3.1.1Reasonsforbacteriaremovalfrommilk

A number of objectives are pursued in removing

bacteriafrommilk.Inmilkprocessing,forexample,

spore-formers can cause considerable problems.

Intheproductionoffreshmilk,aerobicspore-formers

(Bacilluscereus)impairshelflifeasaresultofsweet

clotting.

In theproductionofmilkpowder,especially “low-

heat”products,aerobicandanaerobicspore-formers

(Bacilluscereus,Clostridiumperfringens)leadtothe

productspoiling.

Under certain conditions, the removal of bacteria

securesshelflifeinsoftcheeseproducts–forexample,

incaseswheretheso-calledascosporesofthemoulds

Byssochlamys nivea or Byssochlamys fulva have a

negativeimpactonquality.

16

RoutetakenbyClostridiumPreventingthegrowthofbacteria

Areatyrobutyricum

Soil

Silage* Chemically Formic acid, propionic acid etc.

Milk producer

Biologically Wilt, maize, vaccinate

Rumen, faeces, raw milk Milking hygiene

Vat milk Physically Separator

Chemically Peroxide catalase Dairy, cheese-maker

Cheese* Chemically Nitrate, lysozyme, nisin

Technically pH, salt, temperature

Late blowing

Fig. 11 Route and locations for the growth of Clostridium tyrobutyricum* Locations for the growth of Clostridium tyrobutyricum

No. Fraction Clostridiumspecies Metabolicproperties

1 35 % Clostridium sporengens Decomposes protein (proteolytic)

2 12 % Clostridium perfringens Decomposes protein (proteolytic)

3 11 % Clostridium butyricum Decomposes lactose (lactolytic)

4 8 % Clostridium tyrobutyricum Ferments lactate (salt of lactic acid)

5 6 % Clostridium beijerinckii

6 7 % Clostridium tetanomorphum

7 4 % Clostridium pasteurianum

8 4 % Clostridium tertium

9 2 % Clostridium novyi

10 ≈11 % Unclassifiable

Fig. 12 Distribution of Clostridia in raw milk and their metabolic properties

17

Theoccurrenceofindividualstrainsinrelationtothe

criticalmonthsofayearisshowninFig.13.These

valuesare likely toapply tomanymilkcatchment

areasfordairies.

Thereareexceptions,however.Inthesecases,thetotal

numberofanaerobicandaerobicsporescorresponds

approximately to that in Fig. 13, but the ratio of

anaerobictoaerobicsporesismuchmoreunfavourable.

InAustria,forexample,upto50percentofanaerobic

sporesweredetectedinthetotalsporequantity.In

aNorthGermandairy,upto15percentwerefound.

Incontrasttothesesignificantdeviations,aproportion

of2to5percentofanaerobicsporeswasgenerally

foundinotherstudies.

Animportantfactorindeterminingsporesinmilk

for bacteria removal or from which bacteria have

already been removed is the use of suitable test

methods.WhenGEAWestfaliaSeparatorGroupquotes

values,thesearebasedonthetestmethodsdefined

inthisbrochure(seechapter3.9.1).

Alargenumberoftestshasnowbeencarriedout.The

valuesdeterminedresultinastablepictureofspore

contentbeforeandafterremovalofbacteria,allowing

usalsotomakevalidatedstatementsaboutbacterial

clarificationeffect.

650

600

550

500

450

400

350

300

250

200

150

100

50

0

1300

1200

1100

1000

900

800

700

600

500

400

300

200

100

0

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Fig. 13 Number of spores and lactobacilli in raw milk

Ana

erob

ic s

pore

s (p

er m

l)

Aer

obic

spo

res

(per

ml)

Lact

obac

illi (

per

ml)

18

3.1.3Effectivenessofbacteria-removingseparators

Theresultsofmorerecenttests,includingsomeby

independentinstitutesincheese-makingfactories,are

reproducedinFig.14.

Bacteriaremovaltemperature

Thisshouldbebetween55̊ Cand62̊ C.Inthisrange,

milkviscosityisrelativelylow.AccordingtoStokes’

law,thesedimentationvelocityofthebacteriatobe

separatedoffishigherthanatlowertemperatures.

Athighertemperatures,however, there isariskof

damagetoprotein.

Stokes’lawsays:

This equation clearly shows that sedimentation

velocity “v” on the bacteria-removing separator is

proportional to the square of the diameter of the

bacteria, tothedifferenceindensitybetweenmilk

andbacteriaandtotheaccelerationduetogravity.It

isinverselyproportionaltomilkviscosity.

Separatorfeedcapacity

Exceedingnominalcapacityontheonehandresults

in a considerable reduction in bacteria-removing

efficiency. Undershooting nominal capacity, on

theotherhand,onlyachievesa limitedincreasein

efficiency.

v=D2∙Δρ

∙g 18∙η

m2∙kg∙m∙s∙m

m3∙kg∙s2

v =sedimentationvelocity(m/s)

D =diameterofbacteria(m)

Δρ =differenceindensitiesofmilkandbacteria(kg/m3)

η =dynamicviscosityofthemilk(kg/ms)

g =gravitationalacceleration(m/s2)

Fig. 14 Results of double removal of bacteria using CSE 500-01-777 separatorsProcess 1: Bacterially clarified milk after the first machine Process 2: Bacterially clarified milk after the second machine

Sampleno. Sample

Temperature

Output Quantityof Ejection Anaerobicspores

name concentrate time (Clostridia/10ml)

10 ml Effect

Feed Z 1.0 35

Process 1 A 1.0 50 °C 48,000 l / h 1300 l / h 3600 sec. 0.2 99.43 %

Process 2 A 1.1 50 °C 48,000 l / h 1400 l / h 3900 sec. < 0.2 > 99.43 %







Tank sample 4T 12 < 0.2 > 99.43 %





Tank sample 4T 10 0.2 99.43 %

19

3.1.4Proteinbalanceinbacteria-removingseparators

Fig. 15 shows the product flows in the bacteria-

removingseparator.

Theconcentratewhichcontinuouslyforms(entrained

liquid) can be returned to the feed on bacteria-

removingseparatorsfromGEAWestfaliaSeparator

Group,orroutedoffforuseelsewhere.Theeffectof

bacteriaremovalisnotinfluencedbythereturnof

theconcentrate.

Fig.16showsatablewithproductflowsinthebacteria-

removingseparatorandtheirproteincontent.

Theproteincontentmaydeviateaccordingtoregion

and season. The mechanical differences of the

GEA Westfalia Separator proplus design will be

explainedinalatersection.

3.1.5Treatingconcentrate

Inaddition tobacteria, continuousandbatch-wise

concentrate in the bacteria-removing separator

contains protein and other valuable constituents.

Dependingonprocessmanagementandregionally

applicableregulations,theconcentratescanbereturned

completelyorpartlytothemilkfollowingtheappropriate

treatmentorprocessedfurtherelsewhere.Thebatch-

wisephase(ejectionsofthebacteria-removingseparator)

contains practically no non-milk solids if it was

previouslyclarifiedbycentrifugationorfullyorpartly

skimmedby a separator.A temperature treatment

(sterilization)isrequiredtokilloffthebacteria.This

canbeperformedbyUHTequipment,forexample,

whichhasbeenspecificallyadaptedforthetask.Direct

steaminjectionorfineatomizationinasteamchamber

arepossiblemethodsofsterilizingtheconcentrate.

Fig. 16 Product flows in bacteria-removing separator and protein contents

Feed

Dischargeofbacterially Discharge,Discharge,ejections clarifiedmilk concentrate

Measuring I II III IVpoint

With concentrate Without concen- Standard GEA Westfalia Separator recirculation trate recirculation separator proplus separator

Quantity

50,000 l / h 49,960 l / h 48,460 l / h

1500 l / h

40 l / h 10 l / h 49,990 l / h 48,490 l / h

Fraction 100 % 99.92 % 96.92 %

3.00 % 0.08 %

0.02 % 99.98 % 96.98 %

3.40 %

3.396 % 3.387 % 3.70 % 8.00 % 12 %

3.398 % 3.389 %

1700

1696.80 1641.30 55.5 3.2 1.2

1698.80 1643.30

Proteincontent

Protein units / h

Fig. 15 Diagram of a bacteria-removing separator1 Feed of milk

2 Discharge of bacterially clarified milk

3 Ejections

4 Optional: concentrate discharge

1

2

3

4

20

3.2Bacteriaremovalfromfreshmilk–

processtechnology

Inthismethod,theseparationofBacilluscereusis

ofparticularinterest.Thisgermisheat-resistantand

thusstillactiveafterpasteurization,sosweetclotting

ofmilkcanbetheresult.Thespecificweightandsize

ofthisbacillusmakecentrifugalseparationdifficult.

Adapting separator feed capacity to the specific

conditions, however, allows bacterial clarification

efficiencyofover90percenttobeachieved.

Instudiesofpasteurizedmilk,ordersofmagnitudeof

300sporesperlitrewerefoundforB.cereus.

At a storage temperature from 8 to 10̊ C and a

generation time of about 6 hours, the bacillus

multipliesfrom1sporepermltoover107sporesper

mlinaround6days.Thisresultsinsweetclotting.

Thissuggeststhatataleveloflessthan1sporeperml

(e.g.at1sporeperlitre),shelflifecanbeextended

by10generations,correspondingtoaround2.5days.

Lowerstoragetemperaturesofthebacteriallyclarified

andpasteurizedmilk(e.g.4to6°C)canextendthe

shelflifebyupto10days.

Centrifugalremovalofbacteriaenablessporestobe

reducedbyafactorofmorethanten,corresponding

tomorethan3.5generations.

Reductionintotalbacteriacountisoftenconsidered

in assessing the removal of bacteria from fresh

milk.However,itshouldbenotedthatthegenerally

unknown distribution of flora across the various

bacterial strains present can have a considerable

influenceonseparationrate.Onereasonisthefactthat

theoccurrenceofsmall,lightweightbacteriamybe

comparativelylowononeoccasionandcomparatively

highonanother.

Figure17showstheresultsofrecentyearswhichgives

arelativelygoodpictureoftherangeofseparating

efficiency(relatedtototalbacteriacount)whichcan

normallybeachieved.

*Efficiency=TBC0–TBC1∙100

TBC0

Tota

l bac

teri

a co

unt

[ TBC

x 1

03 ]

per

ml

Effi

cien

cy [

% ] *

400

350

300

250

200

150

100

50

0

0

10

20

30

40

50

60

70

80

90

100

Feed

(0)

Dis

char

ge (

1)

Fig. 17 Separation based on total bacterial count in modern bacteria removing centrifuges(Here the efficiency is shown for the specific total bacterial count of 400,000 cells / ml)

21

3.2.1Bacteriaremovalfromfreshmilk–Stage1

In thisprocessvariant, theentiremilk streamhas

bacteriaremovedat55̊ Candisthenfeddirectlyto

theskimmingseparator. In theseparator, themilk

is separated intoskimmilkandcream.Thecream

is then pasteurized and the fraction required to

standardize the milk is diluted to a fat content of

approx.15percentandhomogenized.Thecreamis

thenmixedwiththeskimmilkinthestandardizer.

Thestandardizedfreshmilkthusobtainedisfinally

pasteurizedandcooled.Boththefreshmilkandthe

excesscreamhavehadbacteriaremoved.

Fig. 18 Bacteria removal from fresh milk – Stage 1

1 Bacterially clarified and

standardized fresh milk

2 Excess cream

3 Raw milk

4 Bacteria-removing separator

5 Skimming separator

6 Standardizer

7 Homogenizer

1

2

3

4 5 6 7

22

3.2.2Bacteriaremovalfromskimmilk

Whencreamconcentrationattheskimmingseparator

issetto43percentorhigher,ahighpercentageofthe

sporesremainsintheskimmilk.Thereasonforthisis

thesignificantdifferenceinspecificdensitiesbetween

thesporesandhigh-fatcream.Inthiscase,onlythe

skim milk has the bacteria removed as shown in

Fig.20.

Fig. 20 Bacteria removal from skim milk

1

2

3

4 5 6 7

1 Bacterially clarified and

standardized fresh milk

2 Excess cream

3 Raw milk



6 Standardizer

7 Homogenizer

23

3.3 Premium milk with a longer shelf life with

theGEAWestfaliaSeparatorprolongprocess

Theproductionofpremiummilkwithalongershelflifeis

aquestionoffreshness,naturalness,taste,vitamincontent,

andthenumberofactuallynecessaryshelflifedays.

Freshness and quality indicators are advantages

ofprolong

Thecontentofß-lactoglobulinon theonehandand

lactuloseontheotherarecommonparametersforthe

milk quality and heat indicators. The content of

ß-lactoglobulininrawmilkisapprox.3500mg/l.The

greatertheextenttowhichmilkproteinisdenaturedby

meansofheattreatment,thegreater istheextentto

whichthisvaluedeclines.Inthecaseoffreshmilk,it

amountsto3000mg/linconjunctionwithpasteurization;

in the caseofmicro-filteredmilk, the figure falls to

approx.2500.Inthecaseofmilksubjecttohighheat

treatment,itfallsfurtherto1000to1600mg/l,andmay

even be lower than 1000 mg/l in conjunction with

indirectheating.Bywayofcomparison,theindicatorin

conjunctionwiththeprolongprocessremainsatthe

leveloffreshmilkofapprox.3000mg/l.

Ontheotherhand,lactuloseisnotpresentinrawmilk.

It isaby-productof thechemical reactionofaheat

treatment.Theintensityofheattreatmentisdirectly

relatedtothequantityoflactulosetobefoundinthe

milk.Inthecaseofpasteurizedfreshmilk,lactulose

attainsavalueof10mg/kg;inthecaseoffilteredmilk,

thisfigureis17,andinthecaseofUHTmilk,thefigure

isbetween25and(inconjunctionwithindirectheating)

32mg/kg.Withtheprolongprocess,thisfactorisalso

identical to thefreshmilk factorof10mg/kg.Both

indicators for freshness and quality thus clearly

underlinethebenefitsoftheprolongprocess.

Twobacteriaremovingseparatorsconnectedinseries

For this purpose, two bacteria removing separators

connected in sequence are generally used directly

upstreamoftheskimmingseparatorinordertoachieve

ahighdegreeofreliabilitywithregardtoremovingthe

spores.Thisensuresthatbacteriaaregenuinelyremoved

from theentirequantityof rawmilk, including the

cream.Themilkisthentreatedintheskimmingseparator

withfatcontentadjustmentandshort-timeheating.

Anattractiveeconomicaspectisthattheseparatorscan

beusedforotherdutiesinthedairy,forexamplecheese

production.Anadditionalmajorbenefitfordairiesisalso

thatbacteriaremovingcentrifugescanbeintegratedin

existingpasteurizinglineswithminimaltechnicalinput.

24

Fig. 21 GEA Westfalia Separator prolong process

1 Pasteurized, standardized milk

2 Flow diverting valve

3 Holding tube

4 Heat exchanger

5 Hot water in / out

6 Booster pump

7 Raw milk in

8 Balance tank

9 Ice water

10 GEA Westfalia Separator standomat MC

11 Ice water

12 Cream cooler

13 Bacterial removal separator I

14 Bacterial removal separator II


16 Surplus cream, cooled

17 Product pump

18 Homogenizer

1

23

4

5

67 8

9

10

11 12

1513 1416

17 18

25

3.3ESLmilk–processtechnology

In addition to “pasteurized fresh milk” and “long-

lifemilk”,bothofwhichhavebeenonthefreshmilk

marketforalongtime,anotherkindofmilkhascome

ontothemarketinthepastfewyears,so-called“ESL

freshmilk”.ESLisshortforextendedshelflife.Like

pasteurizedmilk,ESLmilkhastobekeptinacool

chain toprevent it spoiling.Compared to long-life

milk,therearefewerchangesintheflavourofESL

milk,its“freshcharacter”beingretained.Measures

whichleadtoanextendedshelflifeinESLmilkare:

• Greaterreductioningermcountcomparedto

normalpasteurization

• Avoidanceofrecontaminationfollowing

pasteurization.

Oneofthetechnicalsolutionsforadrasticreduction

ingermcountismicrofiltration.

ArrangementofalinetoproduceESLmilkusing

amicrofiltrationunit

Fig.22showsthearrangementofalineofthiskind.

Themilkisheatedupto55̊ C,polishedinthebacteria-

removingseparatorandseparatedintoskimmilkand

creamintheskimmingseparator.Bacteriaarethen

removedfromtheskimmilkduringmicrofiltration

andthecreamissubjectedtoUHT.Astandardizer

dividestheflowofcreamintoexcesscreamandcream

tostandardizethemilk.Moreorlessheatedcreamis

returnedtotheskimmilkdependingonthefatcontent

thestandardizedESLmilkissupposedtohave.Before

remixing,thiscreamisdilutedwithskimmilkand

subjected to partial stream homogenization. After

skimmilkwiththebacteriaremovedhasbeenmixed

togetherwithUHT-treatedhomogenizedcream,the

standardized milk is pasteurized and cooled. The

bacteria-removingseparatorinthefirststagemeans

thatanoptimumproductiontimeisachievedforthe

linedownstream.

Fig. 22 ESL milk line with microfiltration

1

2

3

4 5

6 7 8

1 Standardized ESL milk

2 Excess cream

3 Raw milk



6 Microfiltration

7 Homogenizer

8 Standardizer

26

3.5Bacteriaremovalfrom

cheesemilk–processtechnology

Increasinguseofsilageasfeedinagriculturereduces

milkquality intermsofgermloading,particularly

by spore-formers. These spore-formers cannot be

eliminatedadequatelybyatemperaturetreatment,

which is why removal of bacteria by centrifuge

becamemoreandmoreestablishedinthepast.This

enabledqualityproblems,particularlylateblowing,

tobeavoided.

Cheese-makers frequently standardize the milk

(proteinandfatcontentareadjusted)intanks.The

adjustedmilkiswarmedupand,dependingonthe

cheeseproductionprocess,pasteurizedorifthishas

alreadyhappened,heat-treated. In these cases, the

bacteria are removed from the milk immediately

beforethecheesevatsarefilled.Figure23showsa

diagramofacheesemilklinewithabacteria-removing

separator.

Fig. 23 Bacteria-removing separator in a cheese milk line1 Standardized cheese milk

2 Cheese maker

3 Bacterially clarified

cheese milk


5 Batch-wise concentrate

(ejections)

1

2

3

4

5

27

3.5.1Doublebacteriaremoval

If a single-stage bacteria removal process is not

adequate to produce cheese without the addition

of nitrate, for example, it is possible to arrange

twobacteria-removing separators in series. In this

arrangement,thesecondseparatoractsasapolisher

andensures lowgermvalues invatmilkunderall

operating conditions in the production line. The

resultsachievedareshowninFig.14.

Fig. 24 shows an example of an installation for

doublebacteriaremoval.Thecontinuousconcentrate

canoptionallybereturnedtothefeedsorroutedaway

forsterilization.Thereisalsotheoptionofmerging

alltheconcentratesproducedbothcontinuouslyand

batch-wise(ejections)andofroutingthemforfurther

processing.

3.5.2Variablebacteriaremoval,example:

cheesemilk

With some types of cheese, the almost complete

separationofall thegermflorahashadanegative

effectandthishadtobecounteractedbyincreased

additionofcultureoradditionofrawmilktothemilk

withbacteriaremoved.

Aconceptforvariablebacteriaremovalwasworked

outtosolvethisproblemincollaborationwiththe

regional dairy teaching and research institute in

Wangen.

Fig. 24 Diagram of 2-stage bacteria removal1 Cheese milk

2 Concentrate

3 Continuous concentrate

4 Bacterially clarified milk

1

2

3

4

28

Theaimofthedevelopmentwastoadapttheeffect

ofbacteria removal to the requirementsof thevat

milkasafunctionofrawmilkquality.Tothisend,

trialcheeseswereproducedintheresearchinstitute’s

technicalcentrebyvaryingthespeedofabacteria-

removingseparator.

In Fig. 25, it can be clearly seen how both the

propionicacidbacteria(Propioni)andthelactobacilli

(atincubationtemperaturesof30̊ Cand45̊ C)drop

dramaticallywhenthespeedofthebacteria-removing

separatorisincreased.

TheseparationofClostridiacontinuedtobeoptimum

evenatreducedspeedsbecauseofitshigherdensity.

Alowernumberofthelactobacillipresentinthevat

milkcausestheformationoflactatefromlactoseto

slowdown.Thismeansthatthepropionicacidand

butyricacidfermentationprocessinthecheeseisalso

sloweddown,whichresultsinfewerholesforming

andtheflavourofthecheesebeingimpaired.

40

35

30

25

20

15

10

5

0 60 70 80 90 100

Resi

dual

ger

m c

onte

nt [

CFU

] pe

r m

l

Speed of bacteria-removing separator [ % ]

Lactobacilli 30 °C

Lactobacilli 45 °C

Propioni

Fig. 25 Dependence of residual germ content on bowl speed

29

Theexcessiveremovalofthepropionicacidbacteria

duetoexcessiveremovalofbacteriafromthevatmilk

likewiseleadstoreducedpropionicacidfermentation.

Inthetrials,bothtypesofbacteriaremovalatmaximum

efficiencyofthebacteria-removingseparatorledto

poorholeformationandtoaslightdeteriorationin

flavour.Reducingthebacteriaremovalefficiencyof

theseparatorbyreducingspeed,ontheotherhand,

considerablyimprovedbothholeformationandthe

flavourandstructureofthecheese.

Conclusion

TrialsconductedbyGEAWestfaliaSeparatorGroup

incollaborationwiththeregionaldairyteachingand

research institute inWangen showed that varying

the speed of a bacteria-removing separator makes

it possible to adapt bacteria removal to guarantee

cheesequalitywhilstsimultaneouslypreventinglate

blowing.

Variable removal of bacteria of this kind leads to

evenholeformationinthecheese.Shelflifecanbe

extendedandmaturingtimestandardizedthroughout

the seasons.Thenewgentleprocess for removing

bacteriameansthatthecheeseretainsthemajority

ofitsnaturalgermfloraandthusitstypicalflavour.

Compensatingmeasures,someofthemveryexpensive,

suchasincreasingtheadditionofculturesorusing

protectivecultures,canbedispensedwith.

3.6Comparisonofmicrofiltrationandseparator

The following table compares the different types

ofbacteriaremovalfrommilkandratesthemfrom

the point of view of quality. This is a qualitative

comparison.

Looking at life cycle benefit (the benefit over the

entirelifetimeofthetechnology),bacteria-removing

separatorsprovetobeparticularlyadvantageous.

3.7Specialapplications

Thenextsectiongoesintomoredetailaboutthemany

applicationsforbacteria-removingseparatorswhich

havebeentestedinthefield–specificallyforwhey.

When selecting bacteria-removing separators,

assessment of the whey type is the priority. The

followingremarkshighlightanumberofoptionsby

wayofexample.

Figure27reflectstheeffectofinitialgermcontenton

bacterialclarificationeffect.Relatedtototalbacteria

count,itcanbeseenthatmuchhigherinitialvalues

resultinalowerbacterialclarificationeffect.Where

species of bacteria were examined individually

(spores, Enterobacteriaceae, heat-resistant strains),

thisisnotfound.Thetestsconductedresultedinthe

followinginitialvalues:

• Spores3to30x103perml

• Enterobacteriaceae0.3to10x106perml

• Heat-resistantstrains10to15x106perml

Significantdeviationsinbacterialclarificationeffect

werenotfoundacrossthefullrange.

3.7.1Bacteriaremovalfromwheyconcentrate

Figure28showsthetestresultsforbacteriaremoval

fromwheyconcentrate.

Itshouldbenotedthattheresultsweremostfavourable

whenoutputwasreducedtoapprox.50percentofthe

nominaloutputofthebacteria-removingseparators.

Therewaslikewiseapositiveeffectwhenthedrymass

ofthewheyconcentratewasnotabove25percentDM.

Another effect can be observed in addition to the

improvementinqualitybroughtaboutbycentrifugal

removal of bacteria from whey concentrate. The

bacteria-removing separators act as high-performance

clarifiers.Inadditiontothebacteria,theyseparate

denaturedwheyproteins,leadingtoaconsiderably

extendedlifeintheconcentrationunitsdownstream.

Fig. 26 Comparison of microfiltration and separator (+ means beneficial)

Microfiltration

Bacteria-removing

Doublebacteria-removing separator withseparators

Efficiency +++ + ++

Investment costs + +++ ++

Process integration costs + +++ ++

Lifetime ++ +++ +++

Operating costs – ++ ++

Service costs +++ ++ +

Total 10points 14points 12points

30

Fig. 27 Bacterial clarification efficiency as a function of the initial bacterial count

0 50 100 150 200 250 300

Bact

eria

l cla

rifi

cati

on e

ffic

ienc

y [ %

]

Total bacterial count · 106 [ pro ml ]

100

98

96

94

92

90

88

86

SampleTem-

Capacity DM

Cont. Discont.TBC Aerobicspores Anaerobicspores

descrip-

perature concen- concen-

tion trate trate

Feed 15 °C 18,000 l / h 27.5 % 80,000 ml 150 ml 0.15 ml

Discharge 500 l / h 50 l / h 30,400 ml 62 % 19.5 ml 87 % * n. m. ≥ 99 % *

Feed 15 °C 18,000 l / h 30 % 400,000 ml 200 ml 0.04 ml

Discharge 500 l / h 50 l / h 16,000 ml 58 % 24 ml 88 % * n. m. ≥ 99 % *

Feed 12 °C 15,000 l / h 22 % 220,000 ml 110 ml 0.1 ml

Discharge 400 l / h 50 l / h 55,000 ml 75 % 9.68 ml 91.2 % * n. m. ≥ 99 % *

Feed 12 °C 15,000 l / h 20.5 % 310,000 ml 190 ml 0.08 ml

Discharge 400 l / h 50 l / h 86,800 ml 72 % 18.43 ml 90.3 % * n. m. ≥ 99 % *

Fig. 28 Bacteria removal from whey concentrate* Efficiency

31

3.8Bacteriaremoval–machinery

Bacteria-removing separators are now exclusively

equipped with self-cleaning bowls. Customer

requirements to reduce the ejection quantities of

separatorshave led to furtheroptimization in this

regardinrecentyears.TheGEAWestfaliaSeparator

proplussystemfeaturesamodifieddisc stackand

solids holding space. By this means, significantly

longerproductionintervalswereabletobeachieved

betweenthepartialejections,resultinginareduction

ofthedischargedvolume.

3.8.1Methodofoperation:

bacteria-removingseparators

Bacteria-removing separators now also have a

GEAWestfaliaSeparatorhydrosoftfeedsystem.

Themilkforbacteriaremovalflowsthroughcentral

feed tube (1) into feed chamber (2) which rotates

atbowlspeed.Thefeedtodiscstack(4)iseffected

byboresinbaseofthedistributor(3).Thebacteria

areseparatedoffbycentrifugalforce.Theirhigher

specificweightcauses themtoslideoutwards into

concentratechamber(5).Bacteriaareseparatedeither

directlyoutintotheconcentratechamberoronthe

liquidrouteinwardsassoonasthebacteriareachthe

undersidediscsurfaceofthediscabove.

Atthispoint,thespeedoftheliquidflowinthedisc

interspaceisvirtuallyzero,sothatthebacteriaareno

longerentrainedbytheproductflow.Theseparated

bacteriaslideoutwardsalongthebottomsurfaceof

thediscundercentrifugalforcetowardstheendof

thediscandleavetheseparationchamber.Themilk

withbacteriaremovedflowstowardsthecentreofthe

bowlandispumpedtothedischargepointbycentri-

petalpump(6).Thebacteriaconcentratecontinuously

drawnoffflowsoverseparatingdisc(7)intothetop

centripetalpumpchamber.Concentratecentripetal

pump(8)pumpstheentrainedliquidtothedischarge

pointunderpressureandwithoutfoam.

Inadditiontocontinuousdischargeoftheconcentrate

bythecentripetalpump,partialejectionsalsotake

place.At set intervals, sliding piston (9) is moved

hydraulicallyandpartofthecontentsofthesolids

chamberareejectedthroughthedischargeports(10)

inthebowlbottom.

Milk

Bacterially clarified milk

Concentrate

Solids

1 Feed tube

2 Feed chamber

3 Base of distributor

4 Disc stack

5 Concentrate chamber

6 Centripetal pump for milk

7 Separating disc

8 Concentrate centripetal pump

9 Sliding piston

10 Discharge ports

Fig. 29 Bowl cross-section of a bacteria-removing separator

8

76

123

4

5

9

10

32

Fig. 30 Bowl of a bacteria-removing separator with the GEA Westfalia Separator proplus system

1 Separation disc inlet

2 Disc stack

3 Solids chamber

4 Supplementary separation zone

1

2

3

4

Milk

Bacterially clarified milk

Concentrate

Solids

3.8.2Methodofoperation:bacteria-removing

separatorswithGEAWestfaliaSeparatorproplus

system

Fig.30showsadiagramof thebowlofabacteria-

removingseparatorwiththeproplussystem.

Preciselymatcheddesignmodificationsofthedisc

stack and separating disc create a supplementary

separation zone (4) in this model between solids

chamber(3)–thisisthespaceoutsideseparationdisc

inlet(1)–anddiscstack(2).Inthisarea,thebacteria

are separated fromproteinbya specific flow.The

proteinarrivesinthediscstackfromoutsidewiththe

milkwhichhasalreadyhadsomebacteriaremoved.

Thegermsremaininginthemilkarethenseparated

off in the disc interspace in analogy to bacteria-

removingseparatorswithouttheproplussystem.

33

Examplecalculationforthecommercialbenefitofthe

GEAWestfaliaSeparatorproplussystem.

• Annualoperatingtime:4000hours

• Proteincontentofskimmilk:3.36percent

• Priceperlitreofskimmilk:0.30EUR

Thefollowingtableshowsthepotentialsavingsfrom

theproplussystemwithregardtoreducingprotein

lossesandtheprofitwhichcanbeachievedasaresult.

3.9Machinetypes

Thetableshownbelowliststhecurrentmachinetypes

andoutputsofbacteria-removingseparatorsformilk.

If bacteria are removed from products other than

milk,enquireaboutthecorrespondingoutput.

4.0Sampling

Microbiological tests in milk processing lines can

haveavarietyofobjectives:qualitycontrols,seeking

possibleproductcontaminationorprovidingevidence

oftheefficiencyofbacteria-removingseparatorsarea

fewexamples.Therefollowsomehintswhichmaybe

helpfulingeneratingmeaningfulresults.

Deviationsmayariseasaresultofdifferentoperational

situations,rawmaterialscostsorquantitiesofmilk

processed.Thecostsofprocesswaterandwastewater

arealsoconsiderablyreduced.

4.0.1Prerequisitesinthemilkprocessingline

Instrumentsandcontroldevicesinthemilkprocessing

linemustalwaysworkperfectly.Chemicalcleaningof

thecompletelinemustbeguaranteedandvalidated

byvisualinspection.Allscrewedconnectionsmust

betight,andnoairmaybetrappedintheproduct.

Flow quantities, pressures and temperatures

must be maintained at a constant level during

production/testing.Thebacteria-removingseparator

mustbeadjustedperfectlytosuitproductqualityand

feedquantity.Thisincludesthedischargepressure

of themilkwithbacteriaremoved, thequantityof

concentratereturnedandthesizeandfrequencyof

partialejections.

Machinetype CSE230-01-777 CSE230-01-777

GEAWestfaliaSeparatorproplus

Partial ejection interval 20 min. 60 min.

Ejection quantity 8 kg 8 kg

Protein in solids 9 % 12 %

Number of annual ejections 12,000 off 4000 off

Annual protein loss 8640 kg 3840 kg

Additional annual profit 4800 kg

Corresponds to a skim milk quantity of 142,857 kg

Corresponds to an annual profit of 42,857 EUR(just as a result of reducing protein losses)

Machinetype Nominalcapacity GEAWestfaliaSeparator

proplussystem

GEA Westfalia Separator ecoclear 7500 l / h Available

CSE 140-01-177 15,000 l / h Available

CSE 230-01-777 30,000 l / h Available

CSE 400-01-777 / CSI 400 40,000 l / h Available

CSE 500-01-777 / CSI 500 50,000 l / h Available

34

4.0.2Arrangementofsamplingpoints

Thearrangementofthesamplingpointsdependson

thedesiredtest,thearrangementofthelineandthuson

processmanagement.Inprinciple,thesamplersneed

tobeeasilyaccessible.Furthermore,thearrangement

needstobeselectedsothatarepresentativesample

canbetaken.Iftheassessmentisonlyofthebacteria-

removingseparator, thesamplersneedtobefitted

directly in the feedanddischargeof themachine.

Samplersmaynotbefittedindeadspacesorinlines

withinadequateflowspeeds(<1m/s).

4.0.3Samplingequipmentrequired

Only sterile systems may be used for sampling.

Goodexperiencehasbeenacquiredusingproducts

fromJANZ-LABORTECHNIK(Fig.31),forexample.

Samplersneedtobeabletobesterilizedwithablow-

torch,forexample.Sterilecontainersarerequiredto

store the product sample. Sterile instruments – a

lanceorasyringeandcannula–arerequiredtotake

thesample.

4.0.4Performingsampling

Arecordmustbekeptinparallelwithsampling.This

recordsdate,timeandnameofsampletogetherwith

alltheprocessparametersandsettings.

Thequantityofproducttobetakenisbasedonthe

desiredtestmethodsandshouldbeadequateforthis

purpose.Theinstrumentsrequiredforsamplingmust

remainsterileuntilimmediatelybeforeuse.

Thesameappliestothesamplecontainers,whichneed

tobelabelledclearlywithapenorpreparedlabels

inamannerwhichcanwithstandwaterandwiping.

Thesamplershouldbesterilizedimmediatelybefore

thesampleistaken.Samplingshouldbeperformed

rapidlytoavoidcontaminationoftheproductsample

withambientairasfaraspossible.Theinstruments

usedmaynotbeusedagainwithoutbeingcleaned

andsterilizedagain.Fig.32showsexamplesofsterile

sampling.

Fig. 31 Samplers and equipment for sterile sampling

Fig. 32 Example of sterile sampling

35

4.0.5Treatingthesamples

Immediatelyafterthesamplecontainershavebeen

sealedtoexcludeair,thesamplemustbecooledtoa

temperature<3̊ Cusingicedwaterordryice.This

temperaturemaynotbeexceededuntilthesamples

areexaminedafternomorethan24hours.

4.1Testmethods

4.1.1Overview

Fig.33showsvariousmicroorganismswithpossible

damagecausedandtestmethodstypicallyused.

The standards and regulations quoted in the

correspondingtestmethodsmustalsobefollowed.

4.1.2Testsforanaerobicspores

Themethodofdetermininganaerobicsporesinmilk

isexplainedinmoredetailinFig.34(Page38)byway

ofanexample.

• Preparingthenutrientmedium

Thenutrientmediumiscomposedof1000ml

sterilemilkand100mlglucose/lacticacid

mixture.Themilkispreparedfromskimmilk

powder(100gpowderto900mlH₂O)and

sterilizedat115̊ Cfor15minutes.The

glucose/lacticacidmixtureconsistsof5g

glucoseand20mllacticacidtoppedupto

100mlwithdistilledwater.Thenutrient

mediumshouldhaveapHof5.4to5.5.

AlowpHvaluefavoursvigorousgrowthof

theanaerobicsporesononehandandonthe

other,itinhibitstheproliferationofother

microorganisms.

Evidenceof Usedin Damage Nameof Reference

(product) caused method method

Total bacteria count

Fresh milk, factory General quality Koch’s plate

IDF standard

milk, whey defects method 100B: 1991,

colony count MB* Vol. VI, 6.3.1

Aerobic spores of the Fresh milk, UHT milk

Sweet clotting, Plate method using

MB Vol. VI, 7.17.2Bacillus genus, slime formation,

GCA agar

e. g. Bacillus cereus gas formation, swelling

Fig. 33 Typical test methods* Handbuch der landwirtschaftlichen Versuchs- und Untersuchungsmethodik, Methodenbuch Band VI [Manual of agricultural experimental and test methods, method book volume VI] published by the VDLUFA [Verband Deutscher Landwirtschaftlicher Untersuchungs- und Forschungsanstalten – Association of German Agricultural Test and Research Institutes]

Anaerobic spores e. g. Clostridium tyrobutyricum,C. butyricum

Cheese milkLate blowing in cheese, butyric acid formation

Nizo method, setting up dilution series, evaluation as per MPN method, Weinzirl sample

MB Vol. VI7.18.27.18.37.18.4

36

• Preparingthetesttubes

Thetesttubesareprovidedwithparaffinrods

andsealedwithacottonwoolplugoraluminium

foil.Theyaresterilizedatatemperatureof121̊ C

for15minutes.

• Selectingthedilutionseries

Thedilutionseriesisbasedineachcaseonthe

numberofsporesexpected.Inotherwords,itis

determinedbythesamplingpoint(rawmilk,

milkwithbacteriaremoved).

5testtubesperdilutionseriesareprepared,

e.g.5times10ml,5times1ml,5times0.1ml

and5times0.01ml.Itisimportantthatthefinal

sampleisnegative.

• Preparingthesample

10mlofnutrientmediumareputinthesterile

testtubeswiththeirparaffinrods.Dependingon

dilution,1ml,0.1mlor0.01mlofthesampleto

betestedareadded.Oncethetesttubeshave

beenfilled,theyareshakeninadefinedmanner

onamachine.ThepHshouldbecheckedfrom

timetotime.Thismethodalsoallows10mlof

sampletobetested.Inthiscase,10mlofsample

milkand1mlofglucose/lacticacidmixtureare

addedto5testtubesasnutrientmedium.

• Heatingthesamples(I)

Thesamplesarethenheatedat80̊ Cfora

maximumof5minutes.Thesamplemust

becoveredbyatleast1.5cmofwaterinthis

process.Undesiredgermsarekilled.The

paraffinbecomesliquidandsealsthetesttubes

tomakethemairtight.Coolingtakesplacein

awaterbathat45̊ C(II).

• Incubation(III)

Incubationisfor4daysat37̊ Cinan

incubationcabinet.

• Evaluation(IV)

Asampleisconsideredpositiveifthe

paraffinplughasclearlycomeawayfromthe

sampleliquid.Aftercountingout,evaluationis

performedinaccordancewiththeMPNtable.

Complete milk pasteurization plant

37

Total bacterial count Anaerobic spores

Glucose-lactic acid5 g glucose20 mllactic acid 1 nabout 75 ml dist. H2O(nutrient medium)

Sterile milk lactic acid mixturepH = 5.5 – 5.4

(nutrientmedium)

Sterile milkGlucoselactic acid5 g glucose20 ml lactic acid 1 n,about 75 mldist. H2O

5.7 g plate countagar with dist. H2Ofill to 244 ml (nutrient medium)

½ Ringer tabletto 500 ml dist.H2O, 9 mlRinger solution(diluting agent)

9 mlRingersolution

9 mlRingersolution

Kill bacteria anddissolve paraffinwax plug

Turn petri dishesCondensation water can run off

Count of feed and discharge

1 Sterile Petri dishes (qty. 3)2 Flask with plate count agar sterilized 121 °C 25 – 30 minutes3 Test tubes (qty. 3) sterilized 121 °C 20 minutes4 Specimen bottle > 100 ml sterilized 121 °C 20 minutes5 Test tubes (qty. 20) sterilized 121 °C 25 minutes filled with paraffin wax plugs6 Flask sterilized 121 °C 20 minutes7 Flask sterilized 180 °C 120 minutes8 Flask sterilized 121 °C 20 minutes

Count of feed and dischargeIV

I

II

III

V

VI

Take values from MPN table

Calculation of bacterial clarification efficiency

Calculation of bacterial clarification efficiency

Water bath80 °C, 10 ml

Water bath45 °C, 10 ml

Incubator37 °C, 4 days

Incubator30 °C, 3 days

0.001 ml

0.01 ml

1 x 1 ml

1 x

1 m

l

5 x

1 m

l

5 x 1 ml1 x 1 ml

1 x 1 ml

5 x 1 ml

5 x 10 mlapprox. 20 ml

approx. 20 ml

approx. 20 ml

1 x

1 m

l

1 x

1 m

l

1

0.01 ml

1

0.1 ml

1

3 5 5555

10 ml

5

2 4Sam ple

5

7 8 9

5 x 1 ml

6555

1 ml

5 5

5 x 10 ml approx. 1000 ml

approx. 100 ml5 x 10 ml

5 x

10 m

l555

0.1 ml

53

3

5555

feed – discharge x 100

% feed

[] feed – discharge

x 100

% feed

[]Fig. 34 Method for testing milk for anaerobic spore-formers

Calculationexample

Calculationofbacterialclarificationeffect

MPNZ=MPNvalueatseparatorfeed

MPNA=MPNvalueatseparatordischarge

• AccordingtotheMPNtable,thismeansthatthe

resultis34.8/10ml

• AccordingtotheMPNtable,thismeansthatthe

resultis0.199/10ml

Dilutionseries Evaluation

5 times 10.00 ml 5 positive




Dilutionseries Evaluation





Sample upstream of bacteria-removing separator Sample downstream of bacteria-removing separator

Effect=MPNZ–MPNA·100 MPNZ

Effect=34.8–0.199·100 34.8

Effect=99.4%

4.1.3Testsforaerobicspores

Themilksamplesarepasteurizedinaspinglassat

over80̊ Cforatleast10minutes.Thesampleisthen

centrifugedinatesttubecentrifuge(15minutesat

1000g).Oncethesedimenthasbeenredilutedto1:10

of itsoriginalvolume,thebacterialcontentcanbe

determinedusingDIFCONUTRIENTAGAR.

It is extremely important to reach the incubation

temperatureof37̊ Casquicklyaspossibletofacilitate

apreciseevaluation.

4.1.4Testsforlactobacilli

ThenumberoflactobacilliisdeterminedusingTGV

5.4AGAR.Incubationtimeis5to7daysat30̊ C.

39

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GEA Group is a global engineering company with multi-billion euro sales and operations in more than

50 countries. Founded in 1881, the company is one of the largest providers of innovative equipment and

process technology. GEA Group is listed in the STOXX® Europe 600 Index.

We live our values.Excellence • Passion • Integrity • Responsibility • GEA-versity

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