Membrane Filtration of Milk: An Essential Step in Dairy Processing

Filtering raw milk is necessary to ensure consumers receive a high-quality product free of harmful pathogens. In addition, filtering protects the milking equipment. Because particles of differing sizes must be removed from the milk, there are four different types of membrane filters.

The four processes are reverse osmosis, nanofiltration, ultrafiltration, and microfiltration. This post discusses these dairy product filtration processes, why filtration is important, and how to maintain a healthy filtering system.

The Filtration Process

In the milk filtration process, a pump forces raw milk into contact with a filter. From there, a pressure difference from one side of the filter to the other drives particles through the filter. Thereby particles that are small enough to fit through the filter are allowed through, while bigger ones are held back.

The most common type of filter used are in-line filters, which can be made of different kinds of paper, cloth, or fiber. The filter is fit over a metal support within a metal tube. The metal support is also perforated. Using this process, it is best to filter the milk before it is cooled, so more particles can be removed. Filtering before cooling also prevents later damage to the cooling plates.

Specifically, there are four different milk filtration processes. Each is slightly different.

Reverse Osmosis

Reverse osmosis utilizes the narrowest membrane possible, allowing only water to pass through. Every other particle—either dissolved or suspended material—is held back. For this technique to be most effective, pressure, temperature, flow rate, concentration, and pH levels must be optimized. Reverse osmosis increases milk’s concentration by increasing the total solids, which is common in skim and whole milk production.

Nanofiltration

This filter is similar to reverse osmosis, but a little less strict. Nanofiltration removes minerals from the milk by only letting liquid and specific monovalent ions pass through. Most of the divalent ions are held back. A nanofiltration membrane often performs special tasks, like partially removing minerals from whey, lactose-free milk, or lowering the volume of whey. Removing the minerals helps create a purer lactose end product.

Ultrafiltration

Ultrafiltration accepts larger particles such as lactose, salts, acids, and some other undissolved elements. This method allows fat and protein to be present in the milk, which is often desired by consumers. Ultrafiltration rejects larger substances, while keeping whey and milk proteins in the milk. Keeping these proteins in the milk adds health benefits and enhances taste.

Microfiltration

Microfiltration uses the most open filter membrane. It lets dissolved substances through but holds back most non-dissolved material. Microfiltration plays a key role in milk safety;  it removes fat, pathogens, and spores from the milk. As milk is an ideal place for bacteria to populate, removing microorganisms during filtration minimizes health hazards to consumers. In addition to health hazards, too much bacteria can alter the milk’s chemical composition and cause problems with preservation. This is another reason why microfiltration is essential for milk quality.

Types of Milk Filters

There are a few different types of milk filters, and they each provide reliable filtration of milk. There are disposable filters such as sock and sleeve filters and filter disks, and reusable filters with mesh or stainless screens.

For those milking with a pipeline, sock and sleeve filters are used. Both of these filter types use a piece of folded milk filter fabric, but sleeve filters are open at both ends whereas sock filters are closed at one end.

Permanent filters are also used in a pipeline system. They are made of stainless steel, plastic screens, or mesh, and can be used repeatedly—thus, they must be cleaned often to remove debris and maintain cleanliness.

Those who filter by hand or use buckets utilize filter disks. Filter disks can be round or rectangular shaped, and don’t offer a high filtration capacity. This is why they are less commonly used.

Fabric Filter Maintenance

Disposable milk filters are single-use only, so it is essential to change them consistently. If they are not regularly changed, milk quality and the equipment’s lifespan can suffer.

For plate coolers, it is recommended to change the filters after milking and before the pipeline wash, which ensures the equipment is not washed with dirty filters. Installing a fresh filter before the next milking protects the process from prior debris. 

Just like with plate coolers, systems without plate coolers should not be washed with an in-line filter. Beginning the wash with the filter present—especially when it is dirty—will make the wash less thorough.

In general, to keep the filter clean, it is important to wear gloves or sanitize the hands prior to contact. Dipping a fresh filter in the sanitizing solution can help with easy, smooth installation.

Conclusion

From consumer safety to taste, milk filtration is key to creating a consistent, high-quality product. Ready to optimize your milk filtration process with innovative membrane filters? Contact Filter Holdings today to learn more about our high-quality filtration solutions and expert support.