The Primary Component Removed: Water
At its core, the main ingredient removed from concentrated milk is water. Regular fluid milk consists of a high percentage of water, typically around 87% to 88%. In order to create a concentrated milk product, a significant amount of this water is eliminated, most commonly through a heating and evaporation process. This reduction in water volume results in a product with a thicker, more viscous consistency and a higher concentration of milk solids, including protein, fat, and lactose. The removal of water is the fundamental step in producing all forms of concentrated milk, from unsweetened evaporated milk to the very sweet and thick sweetened condensed milk.
Advanced Filtration and Selective Component Removal
While simple evaporation is the traditional method, modern dairy processing uses more advanced techniques that can remove or separate other specific milk components during concentration. Membrane filtration processes, such as ultrafiltration (UF) and microfiltration (MF), are designed to remove particular molecules based on their size.
How Filtration Affects Composition
- Ultrafiltration (UF): This technique removes water and smaller water-soluble components, such as lactose and some minerals, while concentrating larger molecules like proteins and fat. The liquid that passes through the membrane is called permeate, while the concentrated milk is known as retentate. This process is useful for creating milk protein concentrates.
- Microfiltration (MF): With a different pore size, microfiltration can be used to separate caseins from whey proteins, or even to remove bacteria from milk without high-temperature pasteurization. The specific components removed depend on the membrane pore size.
This selective removal allows dairy producers to tailor the composition of the final product for different applications, such as cheese making, where a higher protein-to-whey ratio is desired.
The Fate of Volatile Compounds
During thermal evaporation, not only is water removed, but other volatile substances can also escape. This can include dissolved gases and some flavor compounds. The high heat exposure in this process can also cause chemical reactions, such as the Maillard reaction, which gives evaporated milk a slightly caramelized color and flavor.
Comparison of Concentration Methods
| Feature | Evaporation | Ultrafiltration (UF) | Microfiltration (MF) |
|---|---|---|---|
| Primary Removed Component | Water | Water, lactose, soluble minerals | Water, bacteria, whey proteins |
| Effect on Nutrients | Primarily concentrates solids; can affect flavor | Concentrates protein and fat, removes some minerals | Concentrates caseins, separates whey proteins |
| Preservation Method | Pasteurization/Sterilization; High Sugar (Condensed) | High-temperature processing needed afterward | Can reduce bacteria without high heat |
| Energy Consumption | Energy-intensive | Can be less energy-intensive than full evaporation | Can be less energy-intensive |
| Final Product Example | Evaporated Milk, Sweetened Condensed Milk | Milk Protein Concentrates | Cheese ingredients, bacteria-free milk |
The Role of Additives and Fortification
It is also important to note that while water and other potential components are removed, other ingredients may be added during processing.
- For sweetened condensed milk, a large amount of sugar is added after evaporation to act as a preservative.
- Vitamins, such as A and D, are frequently added back into both evaporated and sweetened condensed milk products to fortify them.
- Stabilizing salts may also be added to evaporated milk to prevent the product from separating during storage.
Conclusion
In summary, the most basic answer to what has been removed from concentrated milk is water, often up to 60% or more. However, the specific components removed depend heavily on the processing method used. While heat evaporation simply concentrates the milk solids, advanced filtration techniques like ultrafiltration and microfiltration can selectively remove smaller molecules such as lactose or larger ones like whey proteins. Therefore, what is removed is not just water but can also be specific dairy components, depending on the manufacturer's technology and the desired final product, which in turn influences its nutritional profile, flavor, and texture.
