Filtration in food production: Mesh, microns and millimetres in practice

Coarse mesh protects the equipment. Fine mesh protects the product. The principle is simple enough. But when you’re placing your next order for a filter, the principle only gets you halfway there – what size should you actually go for?

In our ultimate guide to filtration in the process industry, we outlined the big picture of filtration. This time, you’ll get the practical follow-up: a reference guide with specific mesh recommendations for typical food processing applications. We’ll give you an overview of the relationship between the three units, the typical mesh sizes for the most common food processing applications, and finally a handy checklist you can use when ordering your next filter.

Mesh, microns and millimetres. All three units refer to the same mesh size.

Mesh refers to the number of openings per linear inch in the filter mesh. The higher the mesh number, the smaller the opening and the finer the filtration. However, mesh is rarely the only unit of measurement you will encounter. On our data sheets for union gaskets with screens, you will find all three units specified, whilst slotted inserts for, for example, strainers are often specified only in millimetres (mm). A key feature of these filters is that they capture larger particles, such as weld spatter or gasket residue, before they reach sensitive process equipment. 

Microns (μ) are often used as the unit when filtration takes place closer to the end product, for example during bottling or as the final filtration stage in the process line. Here, the tolerances are tighter, and the particles you capture are considerably smaller – often invisible to the naked eye. 

In the table below, we have compiled some of the most common mesh sizes with corresponding μ and mm values for process applications. Please note that the ranges and sizes are indicative. All process lines are unique; the final choice should therefore always be based on your specific process

There is no one-size-fits-all mesh size in food production. Every processing plant is unique, and your specific choice will always depend on your process and the medium involved. Our recommendations are based on what we frequently observe at our customers’ sites.

Breweries: In breweries, it's typically hop residues and yeast residues from the plate heat exchanger that cause problems. If allowed to pass through, they clog the heat exchanger’s channels and reduce heat transfer over time. In many breweries, the mesh size ranges from 40 to 100, depending on the type of hops and the process flow. Before dosing nozzles and bottling, the requirement typically increases to mesh 100–200, as even small particles can affect the clarity and flavour profile of the final product.

Dairy: Milk stones, packaging fragments and proteins are the primary threats in the dairy, and they vary in size depending on where you are in the process. Before the pasteuriser, a mesh size of 60–100 serves to protect the process equipment from coarser impurities. Closer to the bottling stage, we typically see a mesh size of 150–200. This captures the small particles that have passed through the initial filters, ensuring they do not end up in the finished dairy product.

Ingredient and sauce lines: Viscous media such as sauces, syrups and dressings significantly alter the dynamics. The thicker the medium, the faster the pressure difference across the filter increases. This ultimately increases the risk of blockages and production losses. Typically, it makes most sense to start with a coarser mesh (40–60) and only move to a finer one if it turns out that critical particles are getting through. Otherwise, you’ll pay the price in the form of pressure loss and unnecessarily short cleaning intervals.

CIP return: The CIP return flow may carry loose gasket material, rubber particles and limescale deposits. Filtering the return flow – typically using a mesh size of 60–100 – protects spray balls, pumps, nozzles and sensitive gauges from damage. Remember that the choice of filter must be suited to the cleaning temperatures and chemicals, particularly during SIP processes above 121 °C, where the choice of materials is subject to extra strain.

Even with the correct mesh size, implementation errors can prove costly. Here are the three most common ones we see in production:

1. The wrong mesh – too fine or the same size throughout: We see two mistakes recurring. One is choosing the finest mesh just to be on the safe side. It sounds sensible, but the result is the opposite: the filter clogs more quickly, the pumps are put under greater strain, and you end up with more stoppages – not fewer. The other mistake is to use the same mesh size throughout the line. But the filter that protects your pasteuriser from weld spatter is not the same one that ensures the quality of the end product.
2. Failure to monitor pressure differential: If you do not keep an eye on the pressure differential across the filter, you will only notice the blockage when it's too late. And by that point, you are no longer dealing with maintenance but with a production stoppage. A pressure gauge can make the difference between a planned filter change and an unplanned production stoppage.
3. Choice of materials – what is often overlooked after ordering: The filter and gasket must withstand the cleaning temperature and chemicals, not just the product itself. A gasket that remains airtight during production may well fail during a CIP cycle at 85 °C using caustic soda. The result is degraded gasket material ending up in the final product.

Before you decide on a mesh size, you should have answers to three questions:

1. What particle size MUST be captured? Define the critical particle specifically: Is it milk stones, hop residues, welding spatter or rubber fragments? The mesh size is determined by the particle you cannot accept further down the process line – not by a gut feeling that ‘finer is better’.  Don’t know the exact particle size? Analysing the material trapped in your current filters can provide a solid starting point for selecting the correct mesh size.
2. What level of pressure drop can we accept? Know the pump’s capacity and the permissible pressure drop before choosing a finer filter. A mesh that is too fine for the flow rate creates a bottleneck: frequent blockages, increased energy consumption and unnecessary production stoppages.  The correct mesh size is the coarsest that still captures the critical particles. If you do not yet have a figure for your pressure drop, start by measuring the pressure difference across your current filters during normal operation. This will make it easier for you to assess any potential changes.
3. Can the material withstand the entire process? The filter mesh is typically made of AISI 316L grade steel, whilst the gasket may be made of materials such as EPDM, FKM or PTFE. Regardless of the combination, the material must be compatible with the chemistry of the medium, the temperature range and the pressure conditions throughout the entire process. This applies not only to the production process itself, but also to the cleaning phase, which often places the heaviest strain on the system. Every material has its limits, and the wrong choice can result in the filter failing long before it should need replacing.

The correct mesh size is not the finest one. It's the one that matches the critical particle, the pressure drop budget and the process load in your specific production line. With the conversion table, our recommendations and the three check questions, you have a concrete starting point for your next order.

Are you unsure about the right mesh size for your process? Contact us for advice by telephone on +45 7020 0422 or by email at inquiry@alfotech.eu. 

Mesh 100 corresponds to an opening of approx. 140 μ – i.e. 0.14 mm. It's a popular choice for protecting pasteurisation units and for general product filtration in dairies and breweries. This size captures most milk stones and hop residues without creating unnecessary differential pressure in the process line.

Rarely. The product flow requires a mesh that captures particles close to the final product, whilst the CIP return must filter out coarser impurities such as gasket residues. In addition, the CIP mesh must withstand higher temperatures and aggressive chemicals. In practice, you typically end up with a coarser mesh for the CIP return and a finer one for the product side.

Yes, and the relationship is direct. The finer the mesh, the higher the resistance and thus the greater the pressure drop across the filter. For high-viscosity media – such as sauces and thick ingredients – this effect is further amplified. If you choose a finer mesh than the process requires, you place an unnecessary strain on the pumps and shorten the intervals between cleaning or filter changes.

The clearest signs are frequent blockages, rising differential pressure across the filter and a falling flow rate. If you find that the filter needs to be cleaned or replaced significantly more often than expected, it's usually a sign that the mesh is too fine for the particle load and viscosity of the medium. Go one size coarser and monitor the differential pressure to find the right balance.