Milk Filtration - What is the Filtration Process?

cows with yellow tags on ears on a dairy farm

Milk is one of the most nutrient-rich consumables. It’s an essential source of proteins and calcium, which is why it’s so important that it goes through the proper filtration process. Filtering milk correctly ensures that it’s of the highest quality and helps dairy farmers detect health problems like mastitis in their cattle. The filtration process for milk is made up of four filter membranes to remove various particle sizes. These membranes include reverse osmosis, nanofiltration, ultrafiltration, and microfiltration.

How to Process Milk

Raw milk is filtered using a pump that forces it across the porous surface of a filter. The pressure on either side of the filter is different, which forces any particles that are smaller than the pore size of the filter to pass through. These particles might include water, fat, protein, minerals, bacteria, somatic cells, and other tiny elements. Larger particles, like flakes, straw, hair, insects, or clots, are not able to pass through, so they are prevented from passing into the bulk tank.

The filters that are used in milk filtration are most commonly in-line filters that may be made of different types of fiber, paper, or cloth that are fitted over a perforated metal support inside a cylindrical tube. When in-line filters are used, the milk should be filtered before it’s cooled. This allows more sediment to be removed and protects the cooling plates from becoming damaged later.

 

Filtration Processes

White Eaton Membrane Filters with red ends

There are a variety of methods that are used for milk filtration. The common goal of all methods is to separate various substances from one another. In the dairy industry, that means separating unwanted particulates from the milk. There are four different membrane filtration processes that are typically used to filter milk. The processes are:

     • Reverse Osmosis – This process provides the tightest membrane possible in liquid separation. That means that only water can pass through the membrane while all other material (dissolved and suspended) is removed.

     • Nanofiltration – This process removes a range of different minerals from liquid, letting only the liquid and specific monovalent ions to pass through the membrane.

     • Ultrafiltration – This process separates skim milk (also called the feed) into two different streams, which allows water, salts, lactose, and acids to pass through the membrane in either direction while keeping (and concentrating) proteins and fat.

     • Microfiltration – This process uses the most open kind of membrane. It’s used to remove spores, bacteria, and fat globules from the liquid and also for fractionation of skim milk.

Milk filtration that is done on-farm may also use a mechanical filter to remove any solid particles from the raw milk. These solid particles may include manure, dirt, straw, hair, insect, and clots, and they are filtered out before the milk reaches the bulk milk tank.

Filter Types Needed for Dairy Filtration

There are various types of milk filters available that are made with food-grade materials with a strong seam, evenly sized pores, and high wet strength. These provide reliable, consistent milk filtration. Common disposable milk filters include sock and sleeve filters and filter disks. Permanent filters with stainless screens or mesh can also be used.

Sock and Sleeve FiltersThese types of filters are used by producers milking with a pipeline. Both sock and sleeve filters are made with a folded sheet of milk filter fabric. The sock filter is closed at one end, while the sleeve type of filter is open at both ends.

Filter Disks – This type of filter is used by producers who milk by hand or with buckets. They may be round or rectangular and don’t provide a high filtration capacity. As a result, filter disks are not used as often as the other types.

Permanent Filters with Stainless Steel Screens or Mesh – This type of filter is designed to be used in the pipeline system. They are similar to disposable milk filters, but instead of being made of nonwoven fabric like disposable filters, permanent filters are made of stainless steel or plastic screens or mesh. Permanent milk filters are able to run continuously. Because of that, it’s important that they are cleaned thoroughly and regularly to remove any trapped debris and maintain sanitary filtering conditions.

 

How to Change Milk Filters

cow on farm with big nose

Changing milk filters regularly is imperative in the dairy industry. Not doing so can greatly impact milk quality and the lifespan of the equipment that’s used. When plate coolers are used, it’s recommended that milk filters be changed after milking is completed and before the pipeline wash. This prevents washing equipment with a dirty filter in place. Installing a clean filter before another milking prevents any debris that was caught in the wash cycle from impacting the quality of future milkings.

For producers without a plate cooler, it’s recommended that the in-line filter be removed prior to starting the wash. The filter holder or spring can be washed in-line or while still left in the wash sink, depending on what type of gasket is used in the pipeline for wash. However, the wash shouldn’t be done with the filter in place – especially a used filter. Doing so with a filter in place will reduce the flow during the wash and therefore, reduce the effectiveness of the cleaning.

Here are a few key points to remember:

     • Avoid filter contamination. Wash hands before or wear clean gloves when changing filters.

     • Filters can be dipped in a wash/sink sanitizing solution before installation. This helps slide the filter into place easily.

     • Milk filters are single use only. Don't re-use a disposable milk filter.

Benefits of Filtration in the Dairy Industry

Proper filtration is essential in the dairy industry to ensure the highest quality milk makes it to milk-drinkers all over the country. It not only ensures a superior product, but milk filtration can also help identify health concerns in cattle, which can greatly help dairy farms act promptly for the benefit of their animals and their bottom line. Effective filtration is also beneficial because it will help save money on milking equipment by protecting it from harmful particulates. 

Though we're familiar with the process of dairy and milk filtration we are currently unable to adequately supply the dairy industry with the filters required for this process.