Rheological properties of milkfat and butter

Butter and milkfat are examples of plastic materials for which texture is a critical factor in determining functionality and consumer acceptance. The methods by which butter rheology is characterized are discussed, including large deformation techniques such as cone penetrometry, compression, sectil ity and extrusion, and methods which involve testing at low levels of strai n. Correlations between instrumental tests and sensory- evaluated propertie s of the fats are explored. Rheological properties, including hardness, spr eadability, setting, work softening, and thixotropy are described, and the models which have been proposed to characterize these behaviors are reviewe d. Techniques which have been devised recently to quantitatively relate str uctural measurements to rheology are also examined. Modification of butter' s rheological properties can be accomplished through alterations in composi tion or in the manufacturing process. These approaches are discussed and ev aluated.