Gravity separation of raw bovine milk: Fat globule size distribution and fat content of milk fractions

This project determined effects of time and temperature on changes of fat g lobule size distribution and fat content in milk fractions during gravity s eparation. Fresh raw bovine milk was gravity separated at 4 or 15 degrees C . After 2, 6, 12, and 48 h, seven fractions, from bottom fraction (F1) to t op fraction (F7), were successively drained from a separation column. Highe r temperature resulted in a faster rate of fat separation. Within 2 h, larg e fat globules had already moved to the top, and the volume mean diameter o f F7 increased from 3.13 mu m (without separation) to 3.48 and 3.64 mu m, r espectively, at 4 and 15 degrees C. In F7, there was little change in gfobu le size distribution after 2 h, but fat content continued to increase with separation time. The fat content of F7 reached 26.6% after 48 h at 4 degree s C, achieving a 58.8% creaming capacity. For F1 to F6, longer separation t ime resulted in smaller fat globule sizes and lower fat contents, especiall y for Fl. After 48 h at 4 degrees C, the volume mean diameter of F1 decreas ed from 3.23 mu m (without separation) to 1.16 mu m, and fat content decrea sed from 3.75% (without separation) to 0.20%. Gravity separation may have u nique applications in the dairy industry today. Its simplicity makes it an effective procedure for small-scale dairy product manufacturers to produce milks with a range of fat contents without using a centrifugal cream separa tor.