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S. PATEL, Department of Biosystems and Agricultural Engineering, Oklahoma State University, Stillwater, OK 74078-6016 and S. P. Agrawala, Dairy Engineering Division, National Dairy Research Institute, Head of the Division, Karnal, 132001, India.

The process of coagulum production for manufacture of Paneer, a fresh acid-curd cheese, has always been limited by the problem of localized coagulation. Traditionally, acidulant is gently but quickly mixed with hot milk, with just sufficient stirring to produce coagulum. This aspect makes designing an efficient mechanized system for continuous coagulum production a complex task. In contrast, we hypothesize that by using a transverse jet mixer to vigorously mix acidulant and hot milk, it would be possible to overcome the problem of localized coagulation. Moreover, immediately after mixing, simultaneous reduction in turbulence of the mixture would avoid disruption of the curd structure.

The objective of the study was to determine if a transverse jet mixer could be used for continuous production of milk coagulum suitable for manufacture of Paneer.

A transverse jet mixer was selected based on its capability to achieve the maximum possible degree of mixing. It was then used to standardize operating parameters, viz., flow rates and acidulant concentration, of the coagulation process.

Studies with the transverse jet mixer (jet entry angle with respect to main pipeline=90°; internal diameter of side entry jet d=1 mm; internal diameter of main pipeline D=8 mm; d/D=0.125) and an attached diffuser at a distance of 8D downstream from the point of transverse jet entry revealed that buffalo milk (fat=6.9%; SNF=9.8%; flow rate=250.00 kg/hr), preheated to 90°C/5 min, could be continuously coagulated at 70°C using citric acid solution with concentration (wt/vol)=1.79% and flow rate=28.33 kg/hr) to give coagulum suitable for Paneer manufacture.

A transverse jet mixer makes it possible to employ vigorous mixing for continuous direct acidification of milk without disrupting the coagulum structure. Also, compared to other devices of similar throughput, it is much cheaper, simple to design, and easily adaptable to mechanization. This study can be easily extended for continuous production of similar cheese varieties such as Queso Blanco.