soil residueon the surfaces tested. The last step is the detectionof the residual
soil in the equipment.To give a statement on the cleanability of the equipmentit
is important to havea reference for whichthe cleanability levelis known.
Subsequentlythe assessment of the cleanability of the test equipment couldbe
comparedwiththe reference.Mostof the published test methodsuse microbes
as tracersin the soil. To be ableto assess the cleanability of large-scale
equipmentor wholeprocesslinesin the industry an organic or inorganic non-
toxictracershouldbe used.
At BioCentrum-DTUa 80 L pilotscalestainlesssteeltankwithan inner
diameter of 400 mm and height of 800 mm and a conical bottomwas testedwith
a spray ball mounted in the tank lid. The lengthof the shaftof the sprayball was
145 mm and the rotatingtip measured50 mm.The positionof the sprayball was
60 mm fromthe centreof the tank.In the first situation the tankwas soiledwith
beer containingyeastcells. In the second case the tank was soiledwithsour milk
containingBacillus stearothermophilusvar.calidolactis(NIZOC953) spores
and subsequentlydriedat roomtemperature for 3 hours. The cleaning was
performedusinga pilot plant CIP cleaningsystem consisting of pre-rinsingwith
coldwater for 1 min,cleaning with 60 ÎC detergentsolution (1%EHEDG
Testcleaner) for 10 min and a finalrinsingwithcoldwaterfor 1 min.The mean
flow velocityin the pipebefore the sprayball in the tanklid was adjusted to
1.5 m/s.The hygienicstate of the tankwas studiedusingcontactagarmethods
(HygicultTPC’and PetrifilmAC’) and ATP-assay. Samples weretakenfrom
the tanklid, the spray ball and selectedpositions on the tankwalls (upper,
middle and lowerparts). On the basisof the detectionmethods used,the smooth
partsof the tankdid not contain any microbial contaminantsafterthe cleaning
procedure.The tests showed,however, that some residual microbes werepresent
on the rougher partsof the tank. Theseplaceswerethe screwsin the lid, the
gasket betweenthe tankand the lid and some unhygienic scratches on the tank
wall.
30.4 Detecting the cleanliness of tanks
In dealingwithclosedprocesses, one problemis alwaysthe validation of the
cleaningprocedure. In some casesvisualinspectioncan be utilised, whichis the
casefor largetanks.Differenttestsfor evaluatingcleaningefficiencyby means
of fluorescent substances are commercially available (Wirtanen, 1995;
Storga^ rds, 2000). By usingUV light,fouling not visible with normal lamp
lightor daylightbecomesvisible(Koldand SkrÒ, 2004 ). Despite this,it was
occasionallydifficult to determineif shining was due to the surface finish,the
type of steelor actually because of fouling. The fouling appearedas a dim white
and occasionally pinkcoating. A thicklayerof foulingwas on some occasions
foundin pipes connected to cleaningnozzles, on areasaround lids and on
gaskets. Jacoband Brandl(2002)also noticedlimitationsin the visual inspection
when theymonitoredthe efficiencyof the cleaningand disinfectionprocedures
502 Handbookof hygiene controlin the foodindustry