EHEDG documents (EHEDG2001,2003, 2004).If only dry cleaningpro-
cedures are applied,lessstringent requirementscan be allowed as willbe
describedin the following sections.However,it is importantto establishthat it
is possible to suffice with dry procedures only. Sometimes factories do
infrequentwet cleaningand it is known fromtrendanalysesthat microbiological
contamination occurs afterthese periods.
If wet cleaning proceduresare appliedit is extremely important that the
equipmentis dried immediately,because:
∑ remainingwet spotscan be the causeof lump formation in the subsequent
batch;
∑ the proliferationof microorganismsin the wet spotscan contaminatethe
powders.
Moreover,the combinationof powdersand waterprovides an idealsource for
microbiological growth! It is particularly important that critical areassuchas
deadlegs, sharpcornersare behindsealsand gaskets are locationsthat can be
dried withina reasonabletimein orderto avoidthe favourableconditionsfor
microbiological contamination. In this senseit shouldbe emphasisedthat the
needof wet cleaning should be takeninto seriousconsideration.Wet cleaningis
a critical hazardin the dry material handling areaand dry cleaningprocedures
are preferredin all respects.
Dry cleaning is applicablefor dry foodmaterial contactsurfaces where:
∑ dry material remainingin the equipmentas loose layers or dust covering does
not present any risk of degrading the quality of the dry materialsubsequently
produced;
∑ possible cross-contamination of dry material duringa production changeto
another material presentsno problem to the quality or safetyof the dry
material subsequentlyproduced;
∑ dry material remaining in the equipment does not present any risk of
microbial growth occurringdue to the prevailingmoisturecontent,tempera-
ture and humidity conditions;
∑ dry materialis non-hygroscopicand non-sticky.
Dry cleaning procedures includethe use of vacuumcleaners, brushes and
scrapers.However,procedures can alsobe applied in which the equipment is
rinsed with`neutral' agentssuchas salt and starch.
13.4 Design principles
Compared withliquids, dry materials handlingmust takeintoaccountthe
possibilityof material lumpformation, creationof dustexplosionconditions,
high moisturedepositformation in the presenceof hot air, and material remaining
in the equipmentafterplantshutdown (evenif a degreeof self-emptyingis
achieved).Powders tendto stickin the process equipmentmore thanliquids.
222 Handbookof hygiene controlin the foodindustry