make surethereare no traces of the characteristiccomponentsof the previous
solutions.The actualcleaning stepsand timesdependon the production process
to be cleaned.
Fluid mechanics
Fluid mechanics influence the flow of the detergent through the system.
Turbulentflowresultsfromfrictionwherefluid is in contactwithsurfaces, and
is characterizedby the Reynolds number (in practiceReis approximately10 000
for smooth, roundpipes) at the boundary layer withthe surface.
Flowvelocity duringpipecleaning should be around2 m/s (minimum1.5 m/
s). If the flowvelocityis too high,this will causea pressuredropin the pipe
system. Systems should not incorporate pipesof several different diameters,
because the resultingflowvelocitieswill be too low or too high.If differentpipe
diameters cannotbe avoided,theyshould be limited to a maximumof two
differentsizes. It is also important to avoidseparatingthe pipe path into parallel
streams, as this causesundefinedflowand contamination.
Cleaning temperature
Temperature influencesthe effectivenessof the detergent,and the optimum
temperaturefor CIP is determinedby the cleaning task and the detergents used.
Pre-rinsestepsabove40 ÎC are not recommended, sincesoil containingprotein
or starchwill undergochemical changesat thesetemperatures and thus impede
the subsequent washing steps. Typical temperature ranges for different
detergentsare given in Table 27.1.
27.2.2 Disinfectionparameters
Disinfectionmustbe a separate cleaning step, and must onlybe carried out after
cleaning, because soil residues can protect microorganisms against direct
Table27.1 Typicaltemperaturerangesfor detergents
Detergenttype Temperature(ÎC) Cleaningtask
Acid(HNO 3 ) 60±65 Tanks,pipes,milkpasteurizers,etc.
Caustic(NaOH) Coldup to 40 Fermentationtanks,storagetanks,bright
beertanks,fillers.Highertemperaturesare
desirable,but problematicfroma technical
pointof view.
50±80 Milkcollectiontankers,milktanks,cream
tanks,quargand yoghurttanks,filling
machines.
70±90 Brewhouses,lautertubs,mashtuns,wort
coolers,milkpasteurizers,pipes.
90±130 UHT-plants,sterilizersfor puddingsand
desserts,etc.
428 Handbookof hygiene controlin the foodindustry