Influence of temperature treatment and season on the dilatometric behaviour of butterfat

Abstract

The ratio of solid to liquid butterfat is a major factor influencing the hardness of butter. Two main variables determining this ratio are variations in temperature treatment during the buttermaking process and seasonal variations in the chemical composition of the butterfat.Results have been reported from this laboratory on studies of the chemical composition of Alberta butterfat (i), and hardness of butter as affected by season and manufacturing method (2). Important hardness differences were observed, and the purpose of this report is to correlate these hardness differences with the proportion of solid fat found by a dilatometric technique.Conventional buttermaking involves comparatively slow cooling of the fat in the cream, whereas rapid cooling takes place in the chilling units of continuous buttermaking machines. Differences in the rate of cooling of the fat may cause large variations in the hardness of the resulting butter. Two phenomena have been investigated as possible causes. The first is polymorphism, which is the occurrence of unstable crystal modifications. It is the general opinion, however, that polymorphism is of minor importance in fats with a complicated glyceride composition (3), and a recent study (4) revealed no important effects of polymorphism in butterfat. Moreover, polymorphism, if it occurs in butterfat, will be a short-term effect, while the effect of cooling-rate variations is a permanent one. Mixed crystal formation offers a more satisfactory explanation of the differences in crystallization behaviour of slowly and rapidly cooled butterfat (5). Mixed crystal formation involves the inclusion of dissimilar molecules in the crystal lattice and, therefore, results in an increase in the ratio of solid to liquid butterfat. EXPERIMENTAL PROCEDUREThe dilatometers were of the volumetric type with a capacity of approximately 10 ml. and a stem calibrated in mm. 3 . The confining fluid was water coloured with a dye, and it was always boiled and cooled before use. Butterfat was prepared from butters of minimum, intermediate, and maximum hardness, obtained in June, September and December respectively (2). The pure fat was prepared from butter by melting, centrifuging and filtering. Before transfer to the dilatometers the filtered fat was dried and de-aerated in round-bottom flasks under reduced pressure (5-10 mm. Hg) for at least 30 min. at 90° C.