(594c) Effect of Cooling-Induced Blooming On Hardness of Milk Chocolate

Milk chocolate is a common household sweet produced on a large production scale.  Precise control of temperature during production can affect material properties tied to product quality.  One such material property is hardness, which is dependent on crystal structure and, therefore, affected by varying cooling rates.

Hershey’s Milk Chocolate bars were melted in a double boiler and allowed to transition back to a solid phase either at room temperature (~20°C) or in a refrigerator at max setting (<5°C).  Both sample sets were then stored at room temperature and tested for hardness over the course of thirty hours.  Results indicated a consistent difference in Brinnell hardness numbers between refrigerated and ambient-cooled samples (p<0.02).  The samples demonstrated a consistent increase in hardness over time that correlated with visual observation of fat bloom.  Hardness of the refrigerated samples also showed a negative correlation with temperature, which is consistent with previous results found in literature.