When making ice cream why do you have to stir or shake it?

Stirring or shaking ice cream while it is freezing helps to prevent the formation of large ice crystals and produces a smoother product.

During the freezing process, water molecules cluster together to form small particles of ice known as nuclei. As ice cream freezes, these nuclei grow by attracting more and more water molecules, leading to the formation of larger and larger ice crystals. The size of these ice crystals directly impacts the texture of the ice cream. Larger ice crystals result in a coarse and icy texture, while smaller ice crystals create a smoother and creamier consistency.

Stirring or shaking the ice cream disrupts the growth of these large ice crystals by physically breaking them apart, resulting in the formation of smaller and more uniform ice crystals. Stirring also ensures even distribution of air throughout the mixture, creating a lighter and fluffier texture. This process is similar to the way whipped cream is made: when cream is beaten, air is incorporated and fat globules are reduced in size, creating a stable foam.

In summary, stirring or shaking ice cream during freezing promotes nucleation, controls the size of the ice crystals, and helps incorporate air. All these factors contribute to achieving a velvety smooth and delectable ice cream.