When you drive, you take multiple precautions to prevent accidents. You put your cellphone away, use turn signals, observe stop signs, and stay a safe distance from the car ahead of you. No single measure guarantees a safe ride, but each one lowers your risk.
It’s the same with safeguarding your process. Each contamination hazard that you can identify and address reduces your risk. This is why food processors are required to develop a Hazard Analysis and Critical Control Points (HACCP) plan under FDA’s Food Safety and Modernization Act (FSMA).
Why Attention Is Required
A leading contamination risk is the utilities: the compressed air or gases, water, and steam used to perform processing steps. They can introduce dirt and bacteria from the outside world or pick up metal debris and oil from plant equipment. Deposited into food or onto food contact surfaces in a warm, moist environment, minor microbe concentrations can rapidly multiply into harmful colonies downstream.
For this reason, it is essential to address filtering air, gases, water, and steam in an HACCP plan. Generally, there are three areas in every process that require attention to utility filtration.
- Where contaminants could first be generated or introduced. This is usually in utility rooms where water, steam, and compressed air or inert gases are generated or stored. Pre-filtration here with larger micron-size elements that are designed to filter coarser particles can lessen wear and tear on downstream microfilters.
- Where the process or product has direct exposure. These are points of use where utilities come into direct contact with the product or food contact surfaces after traveling through equipment. Filters rated for removing microorganisms at a high capture efficiency should be placed as close as possible to each point of use.
- Where there is a last chance to prevent irreversible damage. This is at the end of a process, before product packaging. In some cases, such as water bottling, final membrane filtration is recommended. Whenever water, steam, or compressed air are used to blow-mold, clean bottles, or open bags, filter those utilities just before the application.
Unique Contamination Hazards of Each Utility
Each utility has unique properties and risks for contamination. Specific filters are designed for each challenge. Effective, cost-efficient filtration is all about placing the right elements and micron sizes in the right locations. The following are examples of applications, their associated risks, and best practices to consider.
Air and Gas
Applications. Gases used in food processing include pure oxygen, carbon dioxide, nitrogen, and most commonly, compressed air. Air moves ingredients, texturizes food, dries sterilized equipment, and forms containers. In storage tanks, compressed air or nitrogen are often injected as protective blankets around product.
Risks. Gas tanks and air compressors can be breeding grounds for microorganisms. As they draw in ambient air, compressors concentrate any bacteria present in that air volume. As compressed air cools, condensation creates the moist environment microbes need to multiply and equipment lubricants provide the food. The end result can be contamination and a permanent biofilm deposited in downstream piping. If you use inert gases such as nitrogen or carbon dioxide—even if supply tanks come from a vendor—changing tanks can expose open lines to airborne contaminants.
Best practices. Keeping air dry and oil-free helps keep it sterile. This can be achieved with a series of filters just after the compressor consisting of a cyclone separator to spin out bulk liquid, one or more 1- to 5-micron coalescing pre-filters to catch oil aerosols, and an adsorption air dryer to remove remaining vapors. At each point of use on air or gas downstream, place an absolute rated 0.2-micron final filter on injection equipment.
Applications. Water is universal throughout food processing, both as an ingredient and as a power source. It is used to wash raw produce, rehydrate concentrations, cook ingredients, heat steam boilers, drive product recovery systems, and sterilize equipment and containers, among other applications.
Risks. Incoming water lines can carry harmful corrosion and debris. Sediment can build up on boiler equipment and interfere with efficient heat exchange or end up in the final product. If water is used as an ingredient, it must be dechlorinated with activated carbon, which can then be a food source for any remaining bacteria. Wash water is a cross-contamination risk that can carry microorganisms onto downstream surfaces.
Best practices. Pre-filter the water line coming into your process using nominal polypropylene depth filters of 10 microns. Higher levels of suspended solids may require a series of 50-, 20-, or 10-micron liquid pre-filters. Analyze water quality and adjust filtration for seasonal changes to help ensure product consistency. A 10-micron element provides an acceptable level of industrial water for non-food contact, steam-in-place (SIP), and clean-in-place (CIP) processes. Downstream in the process, install final filters on water lines dedicated to your washing, cooking, blending, or injection stations. Bacterial-retentive sterile filters of 0.2 microns are recommended. In many cases, microfilters of this grade can be used to produce pasteurized-equivalent water.
Applications. Large volumes of steam are required in food processing as a heat source for cooking and as a cleaning agent. Steam is either culinary grade—fit for direct injection into food or to sterilize food contact surfaces—or utility steam, suitable for efficient indirect heating.
Risks. Steam temperatures resist microbial growth, but boiler deposits, debris, and rust are a common hazard. Lengthy steam lines are generally made of carbon or galvanized steel, which can corrode quickly under constant condensation and heat. These byproducts threaten both product and equipment. Stainless steel will not rust when exposed to water, but it will when exposed to rust shed by nearby carbon steel. Corrosion can also plug the spray balls on steam injectors and cross-contaminate stainless steel.
Best practices. On each steam line into your process, place an entrainment separator—a pre-filter that coalesces bulk moisture out of the system and drains it away. The relatively dry steam remaining transfers energy more efficiently and reduces the amount of boiler water entering your product. Each pressure reduction valve should also be protected with an entrainment separator. Place a final steam filter at each point of use. For direct steam injection or CIP/SIP use, culinary-grade steam is required by 3-A Sanitary Standards. Culinary grade is defined as steam filtered to remove 95 percent of particles 2 microns and larger.
General Principles for All Utility Filtration
There are general principles that apply to all utility filtration—steam, water, and air or gases—regardless of the process or application. Remember the following tips as you plan your system.
Redundancy. Similar to accident prevention on the road, filtration at multiple points in a process is far more effective than relying on one filter alone. Pre-filtration upstream can help minimize replacement costs and downtime by helping to protect more expensive microfilters on your process line.
Placement. As stated in the outset, place final filters as close as possible to point of use. If there are 1,000 feet of piping between a final filter placed in a utility room and the food contact point, that is 1,000 feet of line that could shed condensation, oil, debris, and microbes into the product.
Filter media. Traditional melt-blown filters are not always less expensive in the long run. Newer pleated cartridge filters have roughly 12 times the surface area and depth-loading capacity of a melt-blown filter. That added surface area supports a long filter life.
Maintenance. Monitor the pressure across each filter element and change it at a pre-determined pressure drop. Watch for sudden reductions in the pressure differential across the filter, which could indicate a filter is damaged. Pressure gauges upstream and downstream from filters are helpful in providing this visibility.
Ratings. Don’t select filters based on micron size alone; double-check the filter’s capture efficiency at the stated particle size and look for verified performance. The standard for filtration in food and beverage processing is a log 5 reduction, meaning the filter must remove 99.9998 percent of contaminants in its listed micron range. For example, Donaldson Co.’s 0.2-micron sterile liquid and air filters are validate to remove 99.999998 percent of particles at 0.2 micron (the higher log 7 reduction observed in the pharmaceutical industry).
Certification. Look for equipment and products with the 3-A symbol. It means an independent third party verified its sanitary design, including 316/316L gauge stainless steel, a fully drainable, easily cleanable design, and a specified surface finish.
After considering these basic principles, there are other factors to weigh with your filtration provider:
- Depth-loading capacity (retention);
- Number of sterilization cycles the element can safely tolerate;
- How often the element will need changing (filter life); and
- Flow rates, which drive energy costs.
All of these performance factors contribute to total cost of ownership.
The design and maintenance of filtration systems is critical. It can be helpful to obtain a comprehensive evaluation of your system by a qualified process filtration consultant. Also, be sure to work with suppliers who are knowledgeable about filter operation and maintenance needs from end to end, and whose equipment is validated to meet objective standards.
Rojina is an application engineer in the Donaldson’s Process Filtration division of Donaldson
Company, a global provider of filtration solutions for sterile air, gas, liquids, and steam used in the food and beverage, and other processing industries. Reach him at Robert.Rojina@Donaldson.com.