The phenomena of aggregation and disruption of fat globules in cream subjected to viscous flow were studied, and special care was taken to exclude air bubbles. In classical churning processes the incorporation of air was essential, but it was clearly shown that also in the absence of air rapid and efficient churning was possible. Churning was shown to be satisfactory at a fairly narrow range of shearing rates; higher and lower rates led to excessive churning times, or to abnormal butter formation and high fat content in the buttermilk. The experiments were performed in a cylindrical vessel in which a concentric solid cylinder could be rotated at different speeds. The influence of shear rate (cylinder velocity, annular clearance and cream viscosity), temperature, fat content, acidity and fat globule size were studied in relation to churning time and efficiency. Partly empirical equations were derived, describing the relations. A churning time of a few seconds and a fat content in the buttermilk below 1% could easily be achieved.
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