place. Understanding cleaning would require knowledge of the following
aspects:
∑ Deposit removal; understanding of how the depositis removedwill allowthe
process to be improved.
∑ Cleaning process parameters; these include temperature, chemical type,
chemical concentration,flowrate (turbulence,etc. is alsoassociated with
plant design). Determinationand use of optimum conditionswill reduce the
timeto clean.
∑ Process plantdesign; i.e. reducethe `deadlegs' withinthe system and
constitutionof the plant withmaterial that is easilycleanedand maintained
(usingguidelinessuchas thoseof the EuropeanHygienic Engineeringand
Design Group(EHEDG),describedelsewherein this book).
∑ Cleaning regime; suchas the orderand duration of circulation of cleaning
chemicalsand rinsewaters.Knowledgeof a regime to ensure cleaningin the
shortest timeand withthe lowestuse of chemicalsand wateris desirable.
∑ Monitoringthe extentof cleaning; all of the abovefactors could be optimised
if the state of the level of cleaningthroughoutthe plantis sensitively and
accuratelyknown.
Better understandingof the processes involvedwithfouling and cleaningwould
essentiallylead to reduced expenditureand environmentalimpactthrough:
∑ reduced processconditions(i.e. temperature,flowrate, chemicalsand process
water), and
∑ shortercleaningcyclesand hencereduced down-time.
29.2 Processingeffectson foulingand cleaning...
29.2.1 Foulingfrommilk
Foulingand cleaning frommilkand other dairyproducts havebeenextensively
studied and will be usedas an example. Milkis a complexfluidwitha number
of thermallyunstable components.Thecomposition of the depositformed
during thermal treatmentdepends on the processtemperatureand differsgreatly
fromthe compositionof the fluid.Twomajortypes of depositshavebeen
classified(Burton,1968);the compositionand appearance of the two deposit
types (TypeA and TypeB) are given in Table29.3.The proteincontentof Type
A depositis mainly -lactoglobulin( -lg, a wheyprotein);at least50%of the
protein contentof depositformedat 70±80ÎC is -lg (Lalandeet al., 1985;
Tissier and Lalande,1986) althoughit is onlyca.10%of the totalprotein in
milk(Walstraand Jenness, 1984).In the nativestatethis protein is a dimer;
above50 ÎC it dissociatesand between60 and 70 ÎC the monomersunfold(i.e.
denature).Uponunfolding -lg free ±SH groupsare exposed,whichmayreact
withdisulphidebonds on other -lg molecules (or withotherproteins)in a
polymerisationchain reaction(Roefs and de Kruif, 1994). Thisis not reversible;
the aggregatesthat result are waterinsoluble.However, de la Fuenteet al.
472 Handbookof hygiene controlin the foodindustry