Raw milk has not been pasteurized or homogenized, allowing the natural fat globules (cream) to remain intact. Since these fat globules are significantly less dense than the water and protein components, they naturally rise over time, forming a distinct layer at the top. Separating this layer yields two products: high-fat cream and low-fat skim milk. This separation can be achieved through traditional, time-intensive methods or modern, mechanical equipment.
The Simple Gravity Skimming Method
Gravity skimming requires immediate and thorough chilling of the raw milk after milking. The milk must be poured into a wide, shallow container, such as a glass jar or specialized milk pan, to maximize surface area. Keeping the milk undisturbed in a refrigerator near 40°F (4°C) is necessary for effective separation.
The cold temperature causes the fat globules to solidify slightly and cluster, accelerating their upward movement. The cream layer needs time to fully form and solidify at the surface. Complete separation typically takes 12 to 24 hours, depending on the temperature and the milk’s fat content.
Once a clear cream line is visible, the cream can be removed using a shallow ladle or a large, flat spoon. The skimming tool should be gently dipped just below the surface, carefully scooping the thick layer without disturbing the skim milk underneath. This technique works best for smaller batches in wide-mouth containers.
For larger volumes, a cream-setting can equipped with a spigot near the bottom offers an alternative. The skim milk is drained first through the spigot, leaving the cream layer behind. Gravity skimming is less efficient than mechanical methods, often leaving fat suspended in the remaining skim milk.
Using a Centrifugal Cream Separator
A centrifugal cream separator accelerates the natural separation process using mechanical force. The machine uses a rapidly spinning bowl containing conical discs to generate centrifugal force. This force pushes the denser skim milk components outward while concentrating the lighter fat globules toward the center of the bowl.
Before processing, the raw milk must be warmed slightly to optimize efficiency. Heating the milk to 90°F to 105°F (32°C to 40°C) reduces the viscosity of the milk fat. This lower viscosity allows the fat globules to move more freely and separate cleanly under the applied force.
The warmed milk is poured into the machine’s hopper and flows into the spinning bowl assembly. The machine continuously discharges the separated components through two distinct spouts. One spout delivers the high-fat cream, while the other delivers the low-fat skim milk. This method is faster than gravity skimming, completing separation in minutes, and is highly efficient, extracting a greater percentage of milk fat.
Uses for Separated Cream and Skim Milk
The separated cream is a versatile product, with its final use depending on its fat content. High-fat cream is ideal for churning into homemade butter or making cultured sour cream. Cream with a lower fat percentage is suitable for whipping or for enriching coffee and various cooking applications.
The remaining skim milk retains most of the milk’s protein and lactose. It can be consumed as a low-fat beverage or used as the base for making soft cheeses like ricotta or cottage cheese. Skim milk is also used as a liquid component for baking and creating fermented products like yogurt.
Following separation, both the cream and skim milk must be immediately transferred to clean, airtight containers. Proper refrigeration is necessary to maintain freshness and quality. Storing the products at or below 40°F (4°C) ensures they remain safe for several days.