0960–3085/02/$23.50+0.00# Institution of Chemical Engineers

www.ingentaselect.com=titles=09603085.htm Trans IChemE, Vol 80, Part C, December 2002

EDITORIALManaging Interfaces

Putting heat transfer theory into practice in the processing offoods and bioproducts is still problematical. Application ofresults from analyses of conduction, convection, etc. iscomplicated not only by the nature of the � uids (or suspen-sions) involved, but the behaviour of those � uids as a resultof heat transfer. Unlike the liquids and gases used infundamental studies, many food and bioproduct streamsview the heat transfer surface as a dynamic interface andproceed to interact, attach, corrode or colonize it. Fouling,and the associated topics of cleaning – removal of unwantedsurface layers – and disinfection – reducing microbialactivity on these interfaces – dominates many heat transferapplications in these sectors, and large amounts of capitaland operating resources are dedicated to this ‘major unre-solved problem in heat transfer’. The consumable productssector imposes particular challenges, as technologies avail-able to other sectors, such as chemical additives or particularexchanger designs, are precluded by concerns over contam-ination or other losses of product quality.

There is clearly a need to understand what is going on atheat transfer surfaces in order to manage them mosteffectively. It is not straightforward, as one must considerwhether a system designed to minimize the onset or growthof surface layers is also optimized for their removal. Inpractice, the material to be cleaned is a descendant of theoriginal attaching species, following ageing, cookingand/or colonization by microbiological species whichwould not normally attach to the engineer’s polished stain-less steel. The subject is therefore truly interdisciplinary,requiring communication and collaboration between engi-neers, surface scientists and microbiologists, across thelength scales from process units to surface crevices. It isalso sustainable, in that the process streams are oftenchanged or feature new formulations, requiring the devel-opment of new operating and cleaning protocols as well asavoiding cross-contamination.

The majority of papers in this special issue were presentedin short form at a conference entitled ‘Fouling, Cleaning andDisinfection in Food Processing’ at Cambridge in April2002. The meeting continues a series of regular eventsentitled ‘Fouling and Cleaning in Food Processing’ whichstarted in Lund in Sweden in 1981. In organizing the 2002meeting, the technical committee considered it appropriateto include disinfection in order to emphasize the critical linkto microbiology made possible by the explosion in measure-ment techniques since the Lund event. This was re� ected bya third of the submitted papers dealing with microorganismattachment at surfaces. One of the strong features of theconference was the presence of engineers and microbiolo-gists, both academic and industrial, actively engaging indiscussion across the length scales over some very nicelyprocessed food and drink. Further details of the conference,and availability of the conference proceedings, are availableat www.cheng.cam.ac.uk=conferences=FCD2002.html. ThisSpecial Topic issue of Food and Bioproducts Processing

also includes a number of other papers submitted to thejournal in this area in 2002.

There is a strong dairy � avour to the papers, drivenprincipally by the importance of fouling and cleaning inthis sector where ultra-high-temperature (UHT) and high-temperature-short-time (HTST) processing inherentlypromote fouling. The techniques which have been devel-oped under dairy sponsorship are likely to be applicable toother applications, particularly regarding issues in monitor-

ing, sensors and microbial contamination.Figure 1 indicates that papers at these conferences have

changed their focus from understanding the mechanisms bywhich gross soils (foulants) are deposited, to the sequentialproblem of how to remove such soils, or the smallermicrobial species which can attach to surfaces as a resultof foulants conditioning the surface. Understanding attach-ment is still a key factor, however: mitigating or reducingfouling by design of the surface material has been suggestedon several occasions but it is now much more feasible totailor surfaces to particular installations. The paper onSMUF fouling by Andritsos and co-workers describes aninvestigation of modi� cation of 316L stainless steels – thedairy industry standard – undertaken under the EuropeanMODSTEEL programme. Academic studies of dairy foul-ing tend to feature model solutions, hence the papers byChristian et al. and Morrison and Tie on fouling andcleaning using whey protein solutions with calcium contentssimilar to those of milk, and the effect of other species, willhelp to link laboratory studies to industrial practice. Knowl-

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Figure 1 Topic areas of papers presented at fouling, cleaning and disinfec-tion meetings 1994–2002

edge of a fouling layer’s properties is always useful, either indetermining its source or for optimizing its removal.Advances in technology now mean that AFM measurementsappear with the regularity of SEM images in 1981, but studyof the macro-layers found in severe fouling cases hasprompted the development of useful engineering micro-tools. The work by Liu et al. on micro-mechanical manip-ulation of food soils represents an advance towards the goalof being able to specify the mechanical (i.e. � uid) conditionsrequired in CIP systems, while the micro-gauging work byTuladhar et al., illustrates how the properties of evenswelling � lms can be monitored quantitatively in real time.

The papers on cleaning mark how the understanding ofthis key process step has advanced. The two papers on wheyprotein concentrate cleaning from New Zealand, from Xin etal. at Auckland and Morison and Thorpe at Canterbury,demonstrate somewhat reassuringly that models derivedindependently from synthetic polymer dissolution conceptsdescribe the rate-determining step of these thermally agedbiopolymers very effectively. The CFD studies by Jensenand Friis illustrate how such simulation tools can now becombined with knowledge of deposition and cleaningmechanisms to help assess the likely cleaning performanceof individual items of process plant. The paper on spray-ballcleaning from Canterbury considers the fundamentals ofoperation of such units, and presents in a short fundamentalstudy some very practical guidelines for their use andinsights into their performance. The account of enzymaticcleaning of dairy equipment by Graßhoff arises fromconcerns about environmental impact of cleaning chemicals,and the need to reduce the overall impact of fouling on plantoperations.

Cleaning operations must include strategies for monitor-ing and assurance. Truong and co-workers describe howheat � ux sensors can now be installed at the process plant

scale to give reliable indicators of fouling and cleaningperformance, generating more information to assist processoptimization. Interpretation of some of the different types ofprocess data available, particularly from chemical analysis,is discussed in a commercial setting by van Asselt et al. Theuse of Weibull statistics by Durr to interpret and classifycleaning steps in milk pasteuriser cleaning represents thesuccessful application of an old concept to a differentproblem. As with polymer dissolution theory, it is likelythat answers to fouling and cleaning problems already exist– somewhere.

The � nal group of papers bears a distinctly microbial� avour, and that by Verran bears a strongly tutorial � avouras it seeks to educate by illustration some of the issues inlanguage and classi� cation concerning one important typeof microbial fouling, namely bio� lms. The pitfalls whichcan result from the engineer’s desire to describe bio� lms bya single uni� ed model are spelled out, as are the connectionswhere discussions with microbiologists can usefully start.Lelievre and co-workers describe the fate of microbacteriaattached to bare surfaces undergoing cleaning, while Hintonet al. present a simulation of another industrial problem,where the bacteria are present within a heavy fouling layer.The paper from Klavenes et al. considers modifying theattaching organism rather than the surface. This paperemphasizes the sustainability of the fouling and cleaningtopic – as nature will no doubt adjust to counter any well-managed interfaces.

Production of this special issue has been sponsored by theIChemE Food and Drink Subject Group, and their assistanceis gratefully acknowledged.

Ian WilsonSubject Editor – Food Fouling

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