microbes can initiate fatalcontaminationof the fermentation. In severecases,
poorcleaning can causea biofilmformation on equipmentsurfaces, whichcan
bothcontaminatethe processand also causecorrosionand evenhealthproblems
(Wirtanen,1995;Geesey and Bryers, 2000).
The hygienicstate of tanks is importantin orderto avoidcontamination of the
end productand,therefore, tankcleaningis receivingincreasing attention. The
specific casesstudiedcomprisedairy-and brewery-processtanks.These tanks
are madeof high-grade stainlesssteel but for financialreasonsthe outer shell
can be madeof a lower-quality steel coatedwithanti-corrosionpaint.The
bottom of a tankslopesdownwardswithan inclineof about6% towardsan
outletin order to makecomplete drainageeasy(Bylund, 1995).Improper
cleaningof tank surfacesin dairies leads to re-contaminationof pasteurised milk
witheitherpsychrotrophicor thermotolerant bacteria(Geesey and Bryers, 2000;
Wirtanenet al., 2002).It has alsobeenreportedthat thermotolerantcontami-
nants extendthe productiontimeof fermentation milkproducts and cause
undesired growthin closedprocesses (Austinand Bergeron, 1995;Wirtanenet
al., 2002).
The hygiene of processsurfaces is also crucialin beer production because the
fermentation of nutritious wortinto beerincluding maturationin the fermenting
tankmaytakeseveralweeks.Thislongproductiontimeleadto changes in
restrictingfactors for growthof contaminants.The commonsizesof tanksin
breweries vary from 10 000 L to 900 000 L. For instance the size of main
fermentation tanksin threebiggest breweries in Finlandvariesfrom250 000 L to
510 000 L. Minibreweriescan havebatch sizes as smallas 60 L. The con-
sequencesof contamination in the fermentationcan, therefore, be disastrousto
the quality of the beer. Hence it is veryimportantto design the production lines
so that theyare compatiblewiththe cleaningprocedureused(Storga rds, 2000).
The fermentationtanks in breweries mostly haveconical bottomswithan inner
angle of 70±80Î.They are advantageousbecausetheyallowsimpleemptyingof
the yeastaseptically, effectivetemperature control,easycleaningwithcleaning-
in-place(CIP)systems, easycollectionof carbondioxideand small losses of
beercomparedwithtankswithflat and inclined bottoms. The tanksusedfor
storageand stabilisationare normally tanks withflat and inclined bottoms(Enari
and Ma»kinen,1993).The wholefermenting process can take placein the same
tank, whichis calleda combitank.These combitanks have alsoconical
bottoms.
30.2 Factors affecting cleaningefficacy
It is generally understood that the most successfulway of preventingmicrobial
contamination is to ensure that the cleaning is properly performed.In the food
industry thereis a trendtowardslonger production runswithshortintervals for
sanitation(Lelieveld,1985).Factorsaffecting the cleaning processare basedon
mechanicaland chemicalimpact, holding timeand temperature (Wirtanen,
498 Handbookof hygiene controlin the foodindustry