Factor De Puncuon

Trends in Food Science & Technology 11 (2000) 451–457

Review

Process viscometry for the food industry
P.J. Cullen,* A.P. Duffy,* C.P. O’Donnell*,y and D.J. O’Callaghan{
*Department of Agricultural and Food Engineering, University College Dublin, Earlsfort Terrace, Dublin 2, Ireland (fax: +353-1-475-2119; e-mail: colm.odonnell@ucd.ie) { Food Ingredients Department, Dairy Products ResearchCentre, Teagasc, Moorepark, Fermoy, Co.Cork, Ireland
Real-time monitoring and control of food processing applications have grown significantly over the past decade. Food processors are increasingly demanding automated and realtime techniques, which are capable of withstanding the process environment coupled with meeting sanitary requirements. As a result new process monitoring techniques areemerging and traditional techniques are being modified to meet these demands. Commercial instrument designs are reviewed specifically for the food industry with a focus on their advantages and limitations combined with novel modifications developed to overcome such limitations. Emerging technology, which has potential within the food industry, is also discussed. # 2001 Elsevier Science Ltd. All rightsreserved.

Introduction
Viscosity measurement has emerged as an integral and necessary component of many quality control procedures in food processing. Monitoring viscosity online/in-line provides real-time analysis, enabling the

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Corresponding author.

food technologist to control many unit operations in food processing with greater precision and confidence. Applications include processmonitoring, quality control and process control. A number of reviews are available on process viscometry in general [1–3] and the food industry in particular [4,5]. The food processing environment poses a number of challenges to obtaining rheological measurements. The complex rheological nature of typical fluid foods (including: multiphase, elastic, shear thinning, fibrous, particulate and highlyviscous) calls for robust and innovative sensor design. High temperature and pressure, such as those associated with UHT processing or spray drying, are also problematic demanding specific design. Exposure to hostile process conditions, such as plant vibrations, fouling, cleaning agents, dust, etc., pose additional challenges to instrument manufacturers. The ideal viscometer design should facilitateease of cleaning-in-place with minimal possibility of fouling, a quick response time and good sample renewal to ensure that any measurement obtained is representative. Finally the sensor must meet sanitary requirements. Typical selection criteria are presented in Box 1. To date, no single universal viscometry technique has managed to encompass solutions to all the above problems; selection will,therefore, be specific for each case, requiring some degree of compromise. In a common trend with the general sensor market, food processors are showing a preference for instrumentation that contains few if any moving parts and are easy to use and install. Interest in the potential for nonevasive techniques, such as ultrasonic and optical methods, continues to grow. All instrument designs are takingadvantage of microprocessor developments to overcome limitations, such a noise effects, by incorporating transient filters, and providing options such as temperature compensation allowing comparative measurements in a variable temperature environment. The object of this review is to present a description of the main viscometry instruments and techniques that are currently used or under developmentfor process monitoring in the food industry. This review should be of particular use to those who are concerned with the engineering design of food production plants by discussing the merits and limitations associated with particular process viscometry instruments and techniques, and the benefits of process viscometry to the food

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