Proper Milk Filtration

The importance of milk filters on any dairy farm can easily be overlooked, yet they provide some significant benefits by helping to:

  • provide high quality milk to dairy processors;
  • identify mastitis and other udder health problems;
  • identify insufficient bedding or an unclean environment;
  • and ensure plate coolers remain clean, free of debris and functional

Filtering milk is also a requirement under the regulations. Section 5.(2) of Regulation 761 under the Milk Act (Ontario) states that no producer shall sell or offer for sale milk that has not been filtered by means of a single-service filter or a stainless steel mesh-type filter approved by the Director. The purpose of filtration is to separate any solid particles suspended in the milk before it reaches the bulk tank.

How it Works

When raw milk is pumped across the porous surface of the milk filter, a pressure difference on both sides of the filter is created forcing particles that are smaller than the pore size of the milk filter (such as bacteria, somatic cells, water, fat, protein, minerals, etc.) to pass through. Milk filter pore size ranges from 100 to 250 micrometres while bacteria are much smaller - typically 1 to 10 micrometers. Particles that are larger than the pore size (such as straw, hair, flakes, clots or insects) are caught on the filter preventing them from entering the bulk tank.

Milk Filter Location

Milk filters should be installed only on the discharge side of the milk pump; usually in the pipeline between the milk pump and the bulk tank. In systems with plate coolers, the milk filter is always located before the plate cooler to ensure the milk is warm when filtering. Warm milk (36° to 38°C range) can be filtered easily whereas cold milk will block disposable filters.

Modern disposable milk filters are made of food grade materials with 'high wet strength', a sturdy seam, and evenly sized and distributed pores for consistent, reliable filtration of milk.

Milk Filter Types

Modern disposable milk filters are made of food grade materials with 'high wet strength', a sturdy seam, and evenly sized and distributed pores for consistent, reliable filtration of milk. Producers milking with a pipeline typically use a sock and sleeves type filter. Producers milking by hand or with buckets will use a filter disk (Figure 1). Permanent filters constructed with fine stainless screens or mesh are also available but are not widely used on dairy goat farms and must be approved prior to use. There may be a slight advantage in using a blue coloured filter. Clots or flakes indicating mastitis may be more visible on a blue filter. That said, a close examination of a white filter will also reveal problems.

A milk strainer with a properly secured filter disc

Figure 1. A milk strainer with a properly secured filter disc.

Sizing the Milk Filters

Filters come in a variety of sizes and fabric weights to meet dairy goat producer's needs. A filter that is oversized for the milking system is not cost effective, whereas a milk filter that is too small has insufficient surface area for effective filtering.

In situations where milk filters are too small, the flow rate during the milking session gradually decreases as debris builds up on the filter. This could lead to milk by-passing the filter or, in some cases, the filter could burst. The milking system could also 'trap out' - meaning milk in the receiver jar flows over to the sanitary trap where the ball or float rises, shutting down the milking system. If this happens, additional manual cleaning of the trap and piping to the trap is often required.

Producers expanding their milking parlour need to work closely with their equipment dealer, including selecting the proper size of milk filter. If a producer experiences frequent milk filter issues they should work with their equipment dealer and OMAFRA inspectors to determine the root cause.

Plate Cooler Considerations

Poor milk filtration allows debris to pass through the system resulting in a buildup of debris in the cooling plates. The impact is a reduction in heat exchange efficiency as well as a dirty plate cooler which will eventually lead to elevated Bactoscan (bacteria) results. Using a new filter before and after each pipeline wash helps to ensure debris and sediment do not pass through to the cooling plates.

Steps To Take if Abnormalities Observed on the Filter

If you see clots or abnormalities on the milk filter, you should consider using a strip cup and/ or the California Mastitis Tester (CMT) during the next milking to try to identify the problem goat(s). If you have individual goat milk meters you can check for a drop in milk production or a change in milk conductivity.

If you use a disk filter and observe slow milk filtering through the strainer, it may be an indication of high somatic cell count milk. Again, the CMT will often help identify problem goat(s).

If the milk filter appears to have more residue than normal, re-evaluate cleanliness of the environment including pens and holding areas. Udder preparation procedures should also be reviewed. Milk filters often indicate that fly control measures need improvement.

In some cases producers with a large group of goats in heat have noticed slight compositional changes in the milk which can lead to clogged milk filters. Producers in this situation should consider switching to a different type of filter during this time. Check with your supplier for milk filters that are less prone to clogging.

Milk Filter Storage

Store milk filters in a clean area protected from moisture and dust. The heavy cardboard box that filters come in may be good enough, however disk type filters often come in a light duty cardboard box and should be transferred to a sturdy dust-proof and moisture-proof container for storage (Figures 2 and 3).

An example of a dust-proof, water-proof filter storage container.

Figure 2. An example of a dust-proof, water-proof filter storage container.

Another example of a dust-proof, water-proof filter storage container.

Figure 3. Another example of a dust-proof, water-proof filter storage container.

Inspectors have seen milk filters stored in close proximity to open containers of livestock medicines, which could lead to contamination of milk. In fact, one case of a positive inhibitor detection was probably caused by contamination of milk filters that were improperly stored. Filters should never be stored in a cabinet or fridge containing drugs or medicines.

Changing Milk Filters

Producers with plate coolers are advised to change their milk filters after milking is completed and before the pipeline wash to avoid washing equipment with a dirty filter. Installing another clean filter prior to the next milking ensures any debris caught in the wash cycle will not impact the quality of subsequent milkings.

Producers that do not have a plate cooler should remove the in-line filter before starting the wash. The filter holder / spring can be washed in-line or left in the wash sink depending on the type of gasket used to connect the pipeline for wash. Do not wash with a filter in place, particularly a used filter. Filters can reduce the flow in the discharge line during the wash cycle and reduce cleaning effectiveness.

Although installation is second nature for experienced producers, there are a few points to keep in mind:

  • Care should be taken to avoid filter contamination. Make sure hands are clean or clean gloves are worn when changing filters (Figure 6).
  • Some producers choose to wet the filter (i.e., dip in wash sink sanitize solution) prior to installation to help the filter slide into the pipeline easily.
  • Milk filters are intended for single use. Attempting to re-use a disposable milk filter will reduce milk quality.

Care should be taken to avoid contamination when installing a new filter

Figure 4. Care should be taken to avoid contamination when installing a new filter.

Milk Filter Disposal

After each milking, filters should be closely examined for abnormalities. A good practice is to thoroughly rinse the milk filter to remove any residues prior to disposing the filter in a garbage can. Even a rinsed milk filter can attract flies and become a fly breeding area so used milk filters should be removed from the milk house regularly.

Interesting Irish Study

A 2013 study conducted by the Food Safety Authority of Ireland (Raw Milk and Raw Milk Filter Microbiological Surveillance Programme (12NS2), 2015) looked at isolation rates of pathogens (micro-organisms that cause illness) on in-line raw milk filters and the corresponding bulk tank of raw milk. The results (Table 1) indicated a significantly higher detection of pathogens on raw milk filters than bulk tanks thus demonstrating the importance of not re-using milk filters. These findings are consistent with other similar international studies and support the on-going need to pasteurize raw milk to eliminate pathogens and ensure that the milk is safe for consumers.

Table 1: Overview of pathogen detection rates across samples tested.

Percentage Detction Rate a

Raw Milk Filters

Raw Milk
L. monocytogenes (detection only) 20% (38/190) 7% (15/208)
Campylobacter spp. 22% (42/190) 3% (6/200)
Verotoxigenic E.coli (O157 and O26)b 6% (12/190) Not Tested
Salmonella spp. 1% (2/185) 0.5% (1/206)
More than one pathogen detected in same sample 8% (15/190) 0 %

a Percentage value based on numbers of samples tested for each pathogen
b Isolates of E.coli O157:H7 and E. coli O26 which had at least one verocytotoxin gene, VT1 or VT2 detected


Raw Milk and Raw Milk Filter Microbiological Surveillance Programme (12NS2)(2015). Food Safety Authority of Ireland.

For more information:
Toll Free: 1-877-424-1300
Author: Mike Foran, Dairy Food Safety Program, OMAFRA
Creation Date: 09 August 2017
Last Reviewed: 28 August 2017