Post on 22-Jul-2016
description
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 %
Process 1 A 2.0 50 °C 48,000 l / h 1300 l / h 3600 sec. < 0.2 > 99.43 %
Process 2 A 2.1 50 °C 48,000 l / h 1400 l / h 3900 sec. < 0.2 > 99.43 %
Process 1 A 3.0 50 °C 48,000 l / h 1300 l / h 3600 sec. 0.2 99.43 %
Process 2 A 3.1 50 °C 48,000 l / h 1400 l / h 3900 sec. < 0.2 > 99.43 %
Process 1 A 4.0 50 °C 48,000 l / h 1300 l / h 3600 sec. 0.2 99.43 %
Process 2 A 4.1 50 °C 48,000 l / h 1400 l / h 3900 sec. < 0.2 > 99.43 %
Tank sample 4T 12 < 0.2 > 99.43 %
Process 1 A 5.0 50 °C 48,000 l / h 1300 l / h 3600 sec. < 0.2 > 99.43 %
Process 2 A 5.1 50 °C 48,000 l / h 1400 l / h 3900 sec. < 0.2 > 99.43 %
Process 1 A 6.0 50 °C 48,000 l / h 1300 l / h 3600 sec. < 0.2 > 99.43 %
Process 2 A 6.1 50 °C 48,000 l / h 1400 l / h 3900 sec. < 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
4 Bacteria-removing separator
5 Skimming separator
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
15 Skimming separator
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
4 Bacteria-removing separator
5 Skimming separator
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
4 Bacteria-removing separator
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
5 times 1.00 ml 5 positive
5 times 0.10 ml 1 positive
5 times 0.01 ml 0 positive
Dilutionseries Evaluation
5 times 10.00 ml 1 positive
5 times 1.00 ml 0 positive
5 times 0.10 ml 0 positive
5 times 0.01 ml 0 positive
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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EN
GEA Group is a global engineering company with multi-billion euro sales and operations in more than
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process technology. GEA Group is listed in the STOXX® Europe 600 Index.
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