Estimating and understanding the freezing time of food product is important as it affects the quality of the foods. The freezing time is generally influenced by the temperature difference between food material and freezing medium.  Characteristics such as thermal conductivity, density, thermal resistance, types of food packaging material, surface heat transfer coefficient and total dimensions of food could influence the freezing time as well. These varying factors could render the calculations of freezing times difficult. 

 

There have been many models developed to predict the freezing time of food. In this page, we will discuss the two commonly used ones - Planck's equation and Nagoaka's equation. Equations 1 and 2 represent the respective equations. The main difference between the two equations is that in Planck's equation, it ignores the pre-freezing step whereas in Nagoaka's equation the pre-freezing step is considered. Particularly, the freezing time can be experimentally determined by measuring the product temperature at its slowest cooling point - Planck's equation. Alternatively, freezing time can also be defined differently in terms of “Total freezing time” where it refers to the time required to lower the temperature of a food from its initial value to a pre-determined final temperature at the thermal center - Nagoaka's equation.