Which of the following actions primarily helps in the separation of layers when milling?

Grinding is the correct action that helps in the separation of layers when milling. This process involves breaking down food ingredients into finer particles, which results in the separation of the components within those ingredients. Grinding applies mechanical force that fractures the material, allowing for a more pronounced texture and the liberation of layers such as bran, germ, and endosperm in grains.

By grinding, the structure of the food is altered, making it easier to utilize various components, often leading to a uniform texture that is crucial in many food products. This technique is often employed in the milling of grains to produce flour, as it effectively breaks apart the grain kernels and allows different parts to be separated based on their size and density.

The other actions listed do not primarily focus on separation in the same way. Rolling typically compresses or shapes dough and is more about creating a uniform thickness than separating layers. Whipping incorporates air into mixtures to create volume and lightness, while blending combines ingredients thoroughly without emphasizing separation, which is not the primary goal in those methods.