Freezing time formulas for foods with low moisture content, low freezing point and for cryogenic freezing

•Approximate methods for freezing time are compared with results of numerical methods.•The comparison included low moisture content, low freezing point foods and cryogenic temperatures.•Pham’s (1984) method was most accurate, followed by Pham’s (1986) method.•Correction factors are found to allow Pham’s methods to be used in all cases.•Mascheroni and Calvelo’s three-stage approach is vindicated.

Existing food freezing time formulas have not been tested on low moisture, low freezing point foods or cryogenic temperatures. A systematic numerical experiment was therefore performed to generate freezing times over a wide range of parameters, never before covered in the literature, yet still within industrial practice. The results were used to evaluate four well-known freezing time formulas. Pham’s first (three-stage) method has the best theoretical basis and fewest empirical parameters, and agrees best with numerical predictions. By applying simple correction factors, this method agrees with numerical predictions to within ±10% while Pham’s second (two-stage) method is almost as accurate. For the freezing time of fresh foods (Tf ⩾ −1.5 °C), Pham’s first method can be used without modification. The corrected formulas remain accurate under cryogenic freezing conditions.