Novel Online Sensor Technology for Continuous Monitoring of Milk Coagulation and Whey Separation in Cheesemaking COLETTE C. FAGAN,* ,† MANUEL CASTILLO, ‡ FRED A. PAYNE, ‡ COLM P. O’DONNELL, † MEGAN LEEDY, ‡ AND DONAL J. O’CALLAGHAN § Biosystems Engineering, UCD School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Earlsfort Terrace, Dublin 2, Ireland; Department of Biosystems and Agricultural Engineering, 128 C. E. Barnhart Building, University of Kentucky, Lexington, Kentucky 40546-0276; and Moorepark Food Research Centre, Teagasc, Fermoy, Co. Cork, Ireland The cheese industry has continually sought a robust method to monitor milk coagulation. Measurement of whey separation is also critical to control cheese moisture content, which affects quality. The objective of this study was to demonstrate that an online optical sensor detecting light backscatter in a vat could be applied to monitor both coagulation and syneresis during cheesemaking. A prototype sensor having a large field of view (LFV) relative to curd particle size was constructed. Temperature, cutting time, and calcium chloride addition were varied to evaluate the response of the sensor over a wide range of coagulation and syneresis rates. The LFV sensor response was related to casein micelle aggregation and curd firming during coagulation and to changes in curd moisture and whey fat contents during syneresis. The LFV sensor has potential as an online, continuous sensor technology for monitoring both coagulation and syneresis during cheesemaking. KEYWORDS: Optical sensor; light backscatter; coagulation; syneresis; curd moisture; whey fat; calcium chloride; temperature; cutting time INTRODUCTION There is currently a drive toward continuous monitoring and automation in the cheese-processing industry. Control of manufacturing processes through real time analysis of critical quality parameters can improve product quality and consistency. Full automation of the cheese manufacturing process is depend- ent on the development of technologies for monitoring unit operations, which affect final cheese quality. Cheese manufac- ture can be divided into a number of processing steps: milk coagulation in which casein micelles are destabilized and form a gel; syneresis during which whey is expelled from curd particles upon cutting of the gel; followed by drainage, molding, pressing, salting, and ripening of curd. Syneresis is a critical phase in cheese manufacture, with the rate and extent of syneresis playing a fundamental role in determining the moisture, mineral, and lactose content of drained curd and hence that of the final cheese (1, 2). Daviau et al. (3) stated that control of whey expelled during cheesemaking, including the control of syneresis in the vat, was a crucial step in cheese processing as the moisture content of the curd at the drainage step influenced the quality of the final product. Obtaining a measurement of syneresis, which can be used to study and monitor the syneresis process, poses a number of difficulties as highlighted by the numerous and varied techniques that have been employed. A review of these techniques has been provided by Walstra et al. (4). The majority of techniques developed can be classed as either separation or dilution methods. In separation methods, curd and whey are separated and analyzed for curd moisture content or volume of whey, etc., to provide a measure of syneresis (1, 5, 6). However, Lawrence (7) demonstrated a difficulty with separation techniques. He found that the rate of syneresis was affected by the volume of whey which surrounded curd particles and that after the removal of curd from whey, there was a substantial increase in the rate of syneresis. The extent of this rapid expulsion of whey following separation is determined by the strength of curd particles. Therefore, a number of authors have explored the potential of a dilution technique to monitor syneresis. Such techniques aim to monitor syneresis with the curd remaining in the whey by using tracer molecules, which remain in the whey and are therefore diluted during syneresis (8, 9). Zviedrans and Graham (8) followed the progressive dilution of Blue Dextran 2000 in whey and found that it gave a reasonable estimate of the volume of whey expelled. However, it must be ensured that the tracer selected does not interfere with syneresis and/or adsorb to the curd grains. Indeed, the industrial use of markers to trace syneresis is prohibited by food safety regulations. Thus, this * Corresponding author (telephone +353 1 7165541; fax +353 1 4752119; e-mail colette.fagan@ucd.ie). † University College Dublin. ‡ University of Kentucky. § Moorepark Food Research Centre. 8836 J. Agric. Food Chem. 2007, 55, 8836–8844 10.1021/jf070807b CCC: $37.00  2007 American Chemical Society Published on Web 09/14/2007