During the freezing process, water turns into ice crystals through a process called crystallization. This process has two main stages called nucleation and crystal growth, which determine the ice’s content, size, shape, and distribution. The main factor that drives nucleation is supercooling, and it usually requires a large force to create nuclei. Once nuclei form, the next stage is crystal growth, where the initial few crystals act as a template for the rest of the ice to form. The crystal size distribution is determined by the interaction between growth and nucleation steps, and these two stages can occur simultaneously.
The process of how crystals form and grow is complicated and involves different scientific principles. Large ice crystals can damage frozen food, while smaller and evenly distributed crystals can preserve it better. Scientists are researching how to control the formation of ice crystals to enhance the quality of frozen food. Faster freezing rates can lead to smaller and more numerous crystals. To improve product quality, industries try to maximize freezing rates by using low temperatures, exposing more surface area of food, and using high air velocity to increase convective heat transfer coefficients.