typically requiresonlythreesteps:(rinse, clean, rinse), compared witha mini-
mumof five neededfor two-stagecleaning: (rinse, alkali clean,rinse,acid clean,
rinse) (Timperley and Smeulders,1987).The alkali step generally takesplace
before the acid,althoughthis maybe reversed if the deposit is of highmineral
content. Trialsto comparesingle and two-stage cleaning regimes showed that
Fig. 29.2 (a) Variationin cleaningtimefor dairydepositas a functionof NaOH
concentrationand flowrate,showingminimumcleaningtimesfor 0.5%,and (b) the
effectof changingfromsodiumhydroxide(grey)to water(clear)on cleaningof the three
stagesof a plateheat exchanger;no changein pressuredropoccurswhenwaterreplaces
hydroxide(bothfromChristian,2004).
482 Handbookof hygiene controlin the foodindustry