Soft Curd Character Induced in Milk by Intense Sonic Vibration

Abstract

Summary Reduction in the curd tension of milk was accomplished by flowing the fluid in a thin layer over electromagnetically driven diaphragm sources of intense sonic vibration. A study was made of the curd reducing effectiveness of oscillators operating at 1100, 1200, 2160, 3000, 610, and 360 cycles as related to original curd tension of the milk, temperature, time of exposure (velocity of flow), acoustic energy output, and variations in the mechanical features of the apparatus. The percentage reduction in curd tension was greatest in hard curd (60 grams and more) milks. Final curd values approached a constant level in the soft curd range no matter what the original curd texture. No reduction in curd tension was obtained in milk treated below 18° C. and very little at temperatures below the melting point of butter fat. It was found that one of the oscillators (360 cycle) was most efficient when the milk flow was maintained at 250 gallons per hour. With a sound output of about 900 watts more than 50 per cent reduction was attained. With the 360 cycle oscillator the degree of reduction in curd tension was found to bear a direct linear relationship to the power input up to 2000 watts when the velocity was 250 gallons per hour. This represents an output of about 18 watts per one per cent decrease in tension. Other oscillators at different frequencies showed much the same effectiveness with equivalent outputs per unit volume of milk. Hence differences in frequency were found to be negligible within the range explored. A direct relationship was found to exist between degree of fat dispersion and degree of curd tension reduction. The increased number of fat particles was shown to influence curd texture by weakening the curd matrix and by providing increased adsorptive area on which protein was fixed. Since but a small proportion of the total fat in milk need be finely subdivided to reduce the curd tension, a method was devised for producing soft curd milk by vibration without impairing the final cream volume.