1995).Thereis still the challenge of designing and optimisingthe cleaning
systems in termsof efficiencyand economy.This implieschoosing the right
sprayball for a giventankin sucha waythat the hygienicstaterequired is
obtained all overthe tank. In designingthe cleaning procedure, attention should
also be paidto the qualityof the processwater,steamand other additivesused.
Aspects suchas surfacetopographyand material properties, the fluiddynamics
as wellas the specificmicrobial floraand other soil componentsaffectthe
cleaning efficiency (Wirtanen, 1995;Storga rds, 2000).Several studieshave,
however, shown that thereare onlyweakrelationshipsbetweenthe surface
roughness and the cleaningefficiency (Verranet al., 2001). To be ableto
minimise costs,the consumptionof waterand cleaningchemicals and also the
lengthof the cleaning timemust be minimised.
The initialhygienicdesign of the process equipmenthas a big impacton
reducingthe risksof foodbecoming contaminatedduring production,whichalso
meansthat the shelf-lifeof productsis improved. Hygienic requirements should
be adoptedat the initialstagein developing processequipmentand components.
On the basisof EU MachineryDirective98/37/EECequipment is granted a CE
mark,whichin theory should ensure safe food,but unfortunatelythis directive
clearlyfalls shortof hygienerequirements. The EuropeanHygienicEngineering
& Design Group (EHEDG) has developed an evaluation and certification
programme whichensuresthat thereis hygienicallydesignedprocessequipment
available on the market(Kastelein and Wirtanen,2003).The guidelines, which
are importantin evaluatingthe hygienic designof process equipment and
components in closed systems, are Hygienic equipment design criteria', Document No. 8 (1993a),Hygienic design of closed equipment for the
processing of liquidfood',DocumentNo. 10 (1993b) and `A methodfor the
assessment of in-placecleanability of foodprocessingequipment',Document
No. 2 (Timperleyet al., 2000).
In closedcleaningsystemspre-rinsingwithcoldwater is carried out to
removeloose soil,and the CIP treatmentis normallyperformedusing a hot
cleaning solution,but a coldsolution can alsobe used in handlingfat-free
products (Wirtanen, 1995). The chlorine-basedagents loosen the biofilmfrom
the surface, break it and finallyeliminate the microbes. Chelatingagentsin the
cleaning solutionenhancethe breakageand removalof biofilms.The cleaning
agentmanufacturerscan delivereffectivecleaningprogrammesapplicablefor
mostpractical situations. Mechanical grinding, chemical bathing or passivation
is usedas post-treatmentof the surfaceto obtainstainlessproperties on the tank
surfaces. The passivationcan be performedusingan oxidisingacid,e.g. < 20%
nitricacidat 0±60 ÎC for 3±5 min (Taulavuoriet al., 2004).
TheCIP treatment in dairies is normallyperformedusing hot cleaning
solutions, but coldsolutionscan be usedin the processing of fat-freeproducts,
e.g. in breweries (Chistiand Moo-Young,1994;Wirtanen,1995;Storga^ rds,
2000).In dairyCIP cleaning the warmalkalinecleaning solution,normally of
1±1.5%sodiumhydroxide (NaOH),is heatedto 75±80ÎC and the cleaningtime
is 15±20min. The equipment is rinsedfor 3 min withcold waterbeforethe acid
Improvingthe cleaningof tanks 499