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ARS Home » Research » Publications at this Location » Publication #122816
Title: RENNET-INDUCED MILK COAGULATION BY CONTINUOUS STEADY SHEAR STRESS

Author
item Konuklar, Gul
item GUNASEKARAN, SUNDARAM - UNIV OF WISCONSIN

Submitted to: Journal of Colloid and Interface Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Cheese is one of the most important commodities of the dairy industry. In 1999 cheese production in the U.S. totaled 7.9 billion lbs with an average bulk commodity price of 1.5 dollars per lb. This number is expected to grow to 10.9 billion lbs by 2009. The process of making cheese consists of four major steps. One of the most important steps in the production of cheese is the time associated with cutting the curd. If the curd is cut either too early or too late, the quality of the cheese suffers and an inferior product is produced. In the cheese making industry the determination of the appropriate time to cut the curd, referred to as the cutting time, is determined through trial and error. In this study we have developed the first objective method to determine the cutting time. The device can be used as an on-line instrument in the cheese making process. This method would allow the cheese producers to make a more consistent product and increase the cost-effectiveness of the process.

Technical Abstract: The effect of continuous steady shear stress (CSSS) on rennet-induced coagulation of milk was examined. The coagulation process was followed by measuring the change in viscosity of the system with time. Our results indicated that applied continuous low shear stresses up to 0.5 Pa do not counteract to deform the strands forming the network during rennet-induced milk coagulation at standard cheese making conditions. Furthermore, it is thought that 0.2 Pa of continuous steady shear stress in fact promotes coagulation by possibly increasing diffusion, collision, and hydrolyzation rates due to near field attractive hydrodynamic reactions. This is evidenced by the high viscosity of the resultant milk coagulum. However, the viscosity profile of the rennet-induced milk coagulum formed in the presence of CSSS followed the same trend as that of the coagulum formed in the absence of CSSS. Viscosity versus time profiles in both cases displayed an initial lag phase followed by steady increase until a plateau value. The viscosity plateau of the rennet-induced milk coagulum formed in the presence of CSSS exhibited several sudden peaks indicating the dynamic structure of the coagulation process. These peaks in viscosity profiles start around 1380 s for standard cheese making conditions. The time at which viscosity first exceeds 40 kPa.s was verified to coincide with manual determination of coagulum cutting time during cheese making.