± pre-treatment (heatingthe milkto 40 or 50 ÎC prior to pasteurisation)
(Burton,1968;Visser and Jeurnink,1997);
± flowrate (Gordonet al., 1968;Fryer,1985;Belmar-Beinyet al., 1993);
± bulkand wall temperature(Lalandeet al., 1985; Patersonand Fryer,1988;
Belmar-Beinyet al., 1993);
± processingtime(Fryer, 1985;Hege and Kessler,1986a).
Surface treatments have been investigated for a number for years; for
example, Brittenet al. (1988) studied the effectof coatings suchas poly-
methylacrylate, nylon and cellulose acetate and Yoon and Lund (1994)
investigated electropolished stainlesssteel,Teflon- and polysiloxane-coated
plates. Once the initiallayer of deposithas formed, subsequentdeposition is
unaffected, however, the adhesion strengthis altered.Ion implantationmag-
netronsputtering,plasma-enhancedvapourdeposition,dynamic mixing, and
auto-catalyticNi±P±PTFE(poly(tetrafluoroethene))are among the morerecent
surface modifications investigated to reduce fouling (Zhao et al., 2002).
Although littleadvance has beenfoundin reducingfoulingby dairyproducts
usingthesemodificationtechniques, results show(Beufet al., 2003) that
cleaning efficiency of NaOHis considerablyincreasedwith Ni±P±PTFE-treated
surfaces. Rosaninhoet al.(2003)foundthat surface withlow electron donor
values(such as Ni±P±PTFE-treatedsurfaces) are less susceptibleto foulingfrom
calcium phosphate solutions. The effect of modifying surface energy on
cleaning will be discussedlater.
29.2.3 Cleaning of dairydeposits
Thereare a number of issuesto be consideredwhenlookingat cleaning: (1)
processparameters (e.g.cleaningsolution concentration,temperature and flow
rate),(2) the circulationregime (i.e. orderand circulation timeof eachstage),(3)
monitoringof the extent of foulingand hencecleaningand (4) planthygienic
design.Extensive laboratory-scaleresearchhas beencarriedout to determine
whether optimal or minimalcleaning conditionsexist for dairydepositremoval.
Suchinformation could lowerthe cost of the cleaningprocess and reducethe
timethe plantis out of production,whichwouldalso savemoney. Laboratory-
scaleexperimentsallowcontrolled processconditions,includingthe use of
reproducibly fouledsamples,to investigatethe kinetics and mechanismsof
cleaning. However, the complexinter-relationship between temperature, vis-
cosityand flowrate makesit difficultto determine the specificeffect of each
parameter on cleaning, evenundercontrolledconditions.Larger-scaleexperi-
ments(suchas in pilot-scale plateheat exchangers)aid in the overallevaluation
of the cleaningprocess and determinationof the required duration and orderof
cleaning solution circulation.
Industrial CIP involves the circulationof hot cleaningfluidsthroughclosed
systems of pipes,tanksand heatexchangers;this avoids the needto dismantle
equipment. Traditionally dairyCIP involved circulation of alkali and acid
solutions, althoughnowsingle stagecleaners are often used,as theyinvolve
Improvingthe cleaning of heatexchangers 475