on the casein micelles.To removethemfromthe solidsublayercomplex, certain
measures are required. Up to now the detectionof the aforementioned measures
occursfundamentallyon an empiricalbasis.Somedetailedissuesin the fieldof
surfacephysicsand chemistryremainunresolved,so it is still not possible to do
without the empiricallevel, experimental studies aimed at developingnew
processes for removingdeposits fromheatexchangerplates.
Mechanismsof the depositremoval
Deposit removalfromthe surfaces in touch withthe product do not happen
spontaneously. Dependingon the persistenceof the soiling,it maytakefroma
few seconds to severalhoursto removethe fouling(Grasshoff, 1983,1988).
Contrary to the general assumption, flow mechanics plays a relatively
subordinaterole in the cleaningof milk heatingplants(Grasshoff,1988,1992).
Its essentialtask is to conveythe cleaningchemicals to the appointedplaceof
theiraction,to ensure that no depletionof the chemicalagentoccursdue to
chemical or metabolic reactions, and,last but not least,to preventsoiling
removedfromone spot of the wall attachingat anotherspot. The requirementfor
a minimumflowvelocity or a minimumwall shearstressof the fluidsduring the
cleaning of plantsis not veryhelpful. The generalrule is that fluidflowsshould
displayat eachspotof the planta clearly turbulent flowpattern(Hoffmann,
1984).The drivingforceis the chemical composition of the cleaning solutions,
wherebya number of essentialfunctions are transferredto water± apartfromits
role as carrierof the thermaland mechanical energy. Initially,the firmness of the
protection matrixis lowered by integratingwatermolecules into it to suchan
extentthat a relativelylow fluid overflow is sufficientto separate individualsoil
particles, or also completelayersfromtheiradhesion bonds withthe solidwalls
(Grasshoffand Potthoff-Karl,1996).As deposits are not water-solublein the heat
exchangerit is the task of chemistry to modify, or destabilizethe structureof the
soilingto suchan extentthat finallywatercan be usedas an actionmediumfor
soil removal.For example,polarly acting chemical substances can wrapsoil
particles in an electrical double layer,so that,contrary to the effectivedirection
of the Van der Waalsforces,they can be spatiallyremovedby some nanometers
fromthe solidwalls(Grasshoff, 1992).Thus,the adhesion bondsof the soilingto
the solidwallcan be weakenedto suchan extent that the kineticenergyof the
aqueous cleaningsolution flowingat a low velocityis sufficient to separate and
take awaythe soilingfromthe baselayer. The proteins of the depositmatrixhave
to be hydrolysed, and dissolvedawayby ingredients fromthe cleaningsolution.
Mineral components of the soil matrix are generally not attacked by the
substances responsible for the degradation of the proteins. The mineral
componentshaveto be disintegratedvia specialingredients(in conventional
cleaning processes, activecomplex-forming agents are addedto the alkaline
cleaning solutions;Grasshoffand Potthoff-Karl, 1996).Synergeticeffectsmay
occuramong the differentingredientsof the cleaningsolutions(Grasshoff, 1988).
The temperatureof the cleaningsolutionsplays an important role in conven-
tionalcleaningprocesses.Whenusing enzyme-containing chemical formulae,
Enzymatic cleaning in foodprocessing 521