Thismeans that when usingenzyme-containing cleaning solutionsin practice,
theirpreparationdirectlybefore use is required, and also that they can be applied
onlyonce± unless a reneweddosingof the enzymeconcentrate occurs.Through
the addition of freshenzymes, the solutioncan be usedseveral times, thus saving
waterand energy.In this case,pH-regulating substances and surfactants do not
needto be addedagain.
For the ready-maderecipesprovided by theChemischen Fabrik Dr. Weiger,
the influence of extended storageon theirefficiency was investigated.Prepara-
tionsof eachof the enzymesSavinase and Properase1600 L werestoredat 6 ÎC
for 21 months. After this period,freshpreparations of the samerecipewere
produced. Comparisontrialswere performed withthe stored and the fresh
recipes: neither the efficiency of the recipe with Savinase nor that with
Properasehad suffered duringstorageand the removalcurves obtainedfromthe
storedand freshrecipeswere moreor less identical.Additional trialswere
performed withthe aforementionedcool-stored recipesfor a further22 months
storageand again, no significantdecrease in activity wasobserved,i.e. the
stabilized enzyme recipes can accordinglybe heldin stock in practice.A
restriction is, however, thatstoragerefersonlyto the concentrates. Diluted
solutions haveto be usedimmediatelyaftertheirpreparation.
32.4 Fieldtrials
The laboratorytrialshavedisplayedthat it is possible ± afteracid pretreatment±
to obtain optically residue-freesurfacesin the low-alkalinerangepH 9±10by
usingenzymatic preparations on the predominantly proteineousfoulings of
soiledsurfaces of heat exchangers. In conventionalcleaning processes with
highlyalkaline solutions(pH 13 and higher) this is onlypossible afteraddition
of efficientcomplex-formingagents(Grasshoff and Potthoff-Karl,1996),or in
multistagecleaningprocesses (alkaline/acid)witha finaloxidativestep (most
efficient: activechlorine in alkalinesolution)(Grasshoff, 1988).
Therefore it was logicalto undertake a practicalfieldtrial of the cleaningof
milk heat exchangers with enzyme-containing preparations. Two dairies
participated in this trial:dairyA' witha milkheatexchanger(VT60 LOC N, GEAAhlborn), witha performanceof 45 000 L/h, throughwhich459 000 L cheesefactorymilkwas filteredwithina 10-houroperating period, and dairyB'
witha milkheatexchanger(ZE 23 WP1,Alfa-Laval),witha performanceof
25 000 l/h, throughwhich220 000 L consumermilkwas manufacturedwithina
7›-hour operating period.
32.4.1 Dairy`A'
Before the cleaningtrial, the cleaningprogramme, whichusually ran in the
automatic mode,had beenconverted to the manualmode,and the signalsof
malfunctionand automatic emergency shutdownwereturnedoff. After pre-
Enzymatic cleaning in foodprocessing 531