Explain why the cream in raw milk separates out but the cream in homogenised milk doesn't.

Sure, here's a step-by-step explanation:

1. Raw milk is milk in its natural, unprocessed state. It contains fat particles, or globules, that are of different sizes. These fat globules are less dense than the water content of the milk, which causes them to rise to the top over time. This process is known as creaming or separation, and it results in a layer of cream forming at the top of the milk.

2. Homogenised milk, on the other hand, has been processed to break down the fat globules into smaller, more uniform sizes. This is done by forcing the milk through small holes under high pressure in a process known as homogenisation.

3. The smaller fat globules in homogenised milk are dispersed evenly throughout the milk and are less likely to separate and rise to the top. This is because the smaller globules have a higher surface area to volume ratio, which increases their interaction with the proteins in the milk. This interaction helps to stabilise the fat globules and prevent them from clumping together and separating from the rest of the milk.

4. Additionally, the process of homogenisation also results in a change in the milk's viscosity or thickness, which further helps to prevent the fat globules from separating.

5. Therefore, while the cream in raw milk separates out due to the larger, less dense fat globules rising to the top, the cream in homogenised milk doesn't separate because the smaller, more uniformly sized fat globules are dispersed evenly throughout the milk and are stabilised by their interaction with the milk proteins.