Enhancing Food Safety Management by
Understanding the Role of Filtration
by Kathleen S. Berry*, Pall Corporation
Food Safety in a process managed under HACCP1
principles is achieved by applying a proactive
program to analyze, identify, control, monitor,
correct, verify and document critical control points
in the process. If a critical control point in thesystem fails to perform as required, this can resultin adverse effects that can impact food safety.
Even in the absence of formal HACCP procedures,the production of a safe food product is contingent
upon the proper functioning of carefully selected
and maintained equipment to satisfy process
requirements.
Filtration is a process step that can provide criticalprotection of food products during various
manufacturing stages. While some filtration isgeared solely to removing coarse or fine particles
that only impact the sensory attributes of a
product, other filtration steps influence physical,
chemical and microbiological safety.

Physical Contaminant Removal
Physical safety refers to the absence of particles
that could cause injury to the consumer. Examples
are glass shards from damaged UV lights or glass
packaging, or plastic and metal fragments frompumps or equipment with moving parts. These
contaminants can be the cause of costly productrecalls. Although proactive measures can identify
and limit such occurrences, and while detection
equipment can be implemented to find suchcontaminants as part of a quality assurance
program, a final polishing filtration step as a last
barrier can serve as an additional safety measure.
Another area of protection from physicalcontaminants involves culinary steam filtration.
Many food processes utilize direct steam injection
for flash heating and cooking, sanitizing or
sterilizing product contact surfaces on equipment,
steam peeling, hot water creation for CIP systems,
etc. There are requirements for removing particles,
such as rust and debris from steam lines, which
are achieved by filtration2.

Chemical Contaminant Removal
Chemical safety describes a situation whereinfood products are free of unwanted chemical
contaminants, such as cleaning agents, or
uncontrolled amounts of other food plantchemicals inadvertently ending up in the product.

Where such upsets may be caused bymalfunctioning chemical handling devices, which
require instrument quality air or “particle-free”
water for their operation, proper utilities filtration
plays an indirect but important role in safeguarding
against such upsets.
Another very important and growing aspect of
ensuring safety from undesirable chemicalcomponents relates to the verification of foodcontact compliance concerning plant equipment,
which includes filtration devices. Existing andrapidly emerging global regulations ensure thatunwanted extractables from filtration devices
cannot contaminate foods and adversely affectconsumer health. Meeting these regulations anddocumenting compliance on an ongoing basis is a
key aspect of a filtration supplier’s role.

Microbiological Quality
Microbiological quality is by far the most common
food safety aspect safeguarded by filtration. By
applying properly selected filtration devices,
bioburden reduction or commercial sterility of a
product is achieved. Aseptic processes, forexample, rely on sterile air filters on aseptic surge
tanks and fillers to maintain sterility within theprocess and during the packaging step.
Additionally, where ingredients are asepticallydosed into a sterile environment, sterile liquid filters
are selected to provide microbiological removal
where heating would otherwise destroy heatsensitive ingredients. In various types of bottled
water applications, where no heat treatment isinvolved, sterilizing filtration prior to the bottlingstep, used in conjunction with corresponding
well-controlled downstream operations, assuresthe microbiological safety of the bottled beverage.
In certain dry powdered products, proper filtrationof the air that comes into contact with these
powders during manufacturing can reduce or
eliminate unwanted microbes, which could later
thrive in reconstituted form.

Securing Water Quality
Water is often an important source of pathogens
found in food products. With the increasing scarcity
of water supplies and the growing need to reuse
and recycle water, food plants must pay special
attention to their plant water quality, depending on
its source and its previous history of use.

1

Where production plant water comes into directcontact with food materials or could cause
contamination due to equipment malfunctioning,
careful consideration must be given to its
treatment. Process water, depending on its
particular use, should be adequately filtered toremove any microorganisms or parasites that
could contaminate the end product. An example
involving special safety challenges is in the
production of raw or minimally processed fresh
produce, where water used in post-harvest
practices such as washing or cooling must be
carefully monitored for quality and the avoidance ofcross-contamination. Filtration can ensure
microbial levels are controlled.

Understanding Filtration Performance
The absence of standards regarding removal
ratings and removal performance in the filtrationworld often causes the improper selection of filters.
Filter retention ratings are often stated to be“nominal”, “absolute”, or microbial (even viral).
Nominal and absolute retention ratings refer to theremoval solely of particles and should not be used
to describe critical microbiological removal
requirements. Particle removal efficiencies statedby filter manufacturers are based on tests, whichdocument the degree of removal of standardized
particles such as fine or coarse test dust or latex
beads, usually hard spherical particles which havelittle to do with the morphology of microorganisms.
Whether nominal or absolute, particle filters state
removal efficiencies as the relationship between an
upstream and a downstream particle count,
expressed as a Beta ratio at a given particle size.
Even the methods used to generate this data,such as the use of single pass or multiple passchallenge tests, type of particles, and the amountof challenge material must be looked at carefully inorder to understand the true performance of aparticle-rated filter.

Food contact compliance of filtration equipment
brings food manufacturers one step closer toconsumer protection.

Nominal filters provide only partial removal ofcontaminants and should never be used whencritically important removal requirements exist.
They can at best, be good prefilters fordownstream final filters. Even within the nominal
filter realm, removal ratings can range anywherefrom 99 % removal efficiency (Beta 100 ratio) on
downwards. Very nominal filters might, forexample, only remove in the 60 % removal
efficiency range, meaning 60 % of all particles at agiven micron size. Additionally, nominally rated
filters sometimes consist of fibrous, non-fixedpore structure media, which tend to unload
contaminants under rising or fluctuating pressures.
Absolute filters are often understood to remove
99.9 % or greater of particles, although the term
“absolute” is often used loosely. It is more precise
to refer to removal efficiencies and specific Beta
removal ratios. A 99.9 % removal efficiency means,that for every 1000 particles which hit the filter,
only 1 particle passes through (Beta 1000 ratio).
High-end absolute filters for critical applications
remove 99.98 % of particles at a given micron
rating, which means that for every 5000 particles
which hit the filter, only 1 particle passes through(Beta 5000 ratio). Table 1 illustrates theseconcepts.

Table 1 - Particle Removal Performance
Beta Ratio1

Influent
Particle Count

Particles Retained

Effluent
Particle Count

Removal Efficiency2

Beta 10

5000

4500

500

90 %

Beta 20

5000

4750

250

95 %

Beta 100

5000

4950

50

99 %

Beta 1000

5000

4995

5

99.9 %

Beta 5000

5000

4999

1

99.98 %

1 Beta Ratio = influent particle count/ effluent particle count
2 Removal Efficiency = (influent particle count – effluent particle count) x 100 / influent particle countPall AriaTM FB Filtration System

Emflon® Filter Cartridges

Membralox® Ceramic
Membranes

Ultipleat® High Flow
Filter Elements2

By contrast, microbiologically validated filters
exhibit much higher removal ratings even thanabsolute rated particle filters. The removal
efficiency of such filters is expressed as a titer
reduction of model microbes, selected by virtue of
their approximate size to express the performanceof the filter. A validated microbial filter should bebacked up by performance data showing thenature of the testing: the amount of microbes
challenged to the filter (challenge level has an
impact on performance!), the type of
microorganisms, their size, the humidity and air
flow rate of the test environment when validatingsterile air filters, and so on. In addition, some filter
manufacturers provide data on specificmicroorganism types and the filters’ removal
performance in specific liquids. It is only whencarefully analyzing the nature of the testing done,that one can evaluate the true performancecapability of the filter. In this respect, requesting avalidation guide from a filter manufacturer will
illuminate much information that would otherwise
not be apparent from a simple data sheet.
Bioburden reduction filters provide a reduction in
microbial levels. For example, a 0.45 micron rated
membrane filter may claim a reduction of 106 whenchallenged with Serratia marcescens (a commonlyused model organism for 0.45 micron rated
membrane filters). It is important to pay special
attention to the stated degree of removal,
the challenge level, and the type of test
microorganisms used. Obviously the resulting
filtrate quality will be highly dependent on theincoming microbial load and on the application.
One example of a situation, in which bioburden
reduction filters contribute indirectly to food safety
is when their effective removal performanceensures that downstream heating equipment
achieves the overall desired microbial kill effect. In
the use of crossflow membrane filters in UHT milk
processing, bacterial spore reduction upstream of
the aseptic processing equipment is achieved.

By delivering lowered microbial loads to the UHT
equipment, not only is quality degradation due toheating minimized but the target overall logarithmic
reduction values are accomplished.
The 2004 FDA Guidance Document for Industry on
Sterile Drug Products produced by Aseptic
Processing3, while referencing drug products andoffering nonbinding recommendations, can beapplied to critical food industry applications. It
describes the use of hydrophobic, integritytestable membrane filters for sterile compressedgas. Further, it describes sterilizing grade filters ingeneral, to have a rated pore size of 0.2 micron
or smaller. They should be validated for
reproducible removal of viable microorganisms
from a process stream, resulting in sterile effluent
under worst-case production conditions whenliquid challenged with 107 specific test organisms
per cm2 of effective filtration area. The common
model microorganism used for this purpose is
Brevundimonas diminuta ATCC 19146, with mean
diameter of 0.3 micron, due to its small size.
Based on the filtration area of a typical 10 inch
filter cartridge, this equates to a titer reduction of>1010 or a logarithmic reduction value (LRV) of>10. Conservative validation methodology provides
a margin of safety beyond this requirement.
To contrast particle removal from microbial removal
performance, while an “absolute-rated” Beta 5000
particle removal filter exhibits a removal efficiencyof 99.98 % of particles challenging a filter, asterilizing grade liquid filter exhibits a removal
efficiency of >99.99999999 % of microorganisms
challenged to the filter! Tables 2 and 3 compare
filter microbial performance and its relation to
downstream contamination.

Table 2 - Microbial Removal Performance
Titer
Reduction1
(Tr)

Log
Reduction
Value (LRV)

Challenge
Level2(cfu/cm2)

Filter Area
(cm2)

Influent
Microbial
Load
(cfu)

Effluent
Microbial
Load
(cfu)

RemovalEfficiency4106

6125/cm2

8000

106

1

99.9999 %106

61.25 x 105/cm2

8000

109

103

99.9999 %106

61.25 x 107/cm2

8000

1011

105

99.9999 %

>1011

>11

1.25 x 107/cm2

8000

1011

0 (sterile) 3>99.999999999 %1 Titer Reduction = influent microbial load / effluent microbial load
2 Colony forming units (cfu) / cm2
3 In cases where the effluent contains 0 microorganisms (sterile effluent), a downstream load of 1 is used to

calculate the titer reduction and resulting removal efficiency, as otherwise no division through 0 is possible
4 Removal Efficiency = (influent microbial load – effluent microbial load) x 100 / influent microbial load

Table 3 - LRV Performance and Rate of Contamination
Log Reduction Value (LRV)

Influent Microbial Load(cfu/Liter)

Effluent Microbial Load(cfu/Liter)

Rate of Contamination

6

1000000.1

1 cfu/10 Liters

11

1000000.000001

1 cfu/ 1000000 Liters

3The 2004 FDA Guidance Document also describes
the use of membrane filters for air filtration on
critical equipment such as tanks containing
sterilized materials, and filters acting as sterileboundaries or supplying sterile gases. HEPA4 filters
are typically referenced mainly for aseptic
processing room filtration, and exhibit at least a
99.97 % removal of particles in gas greater than
0.3 micron in diameter.
Critical applications are described in PDA Technical
Report 40 for Sterilizing Filtration of Gases5 as
those applications in which “process fluids are in
direct contact with sterile final product or criticalsurfaces of the associated equipment”.
For sterilizing gas filters on such criticalapplications, the removal performance should be
exhibited not only in dry, but also in moist gas.
Liquid bacterial challenge testing represents aworst case condition for these filters. Due to theway filtration mechanisms work, Brownian
movement of gas molecules in gas streams (Figure1) causes impingement of entrained particles on
the filter media and their capture (Figures 2, 3),much more easily than when liquid streams passthrough a filter (Figure 4). This is called diffusional
interception. Filtration of gases is always easier toachieve than filtration of liquids, so that a given
filtration removal rating in a gas is always tighter
than the same filter’s performance in a liquid.
As an example, a 0.2 micron microbially validated
sterilizing grade filter removes bacteria in this size
range in liquids but removes much smaller
particles such as viruses (in the nanometer size
range) in gas. In a related example, a 3 micronparticle-rated liquid filter would perform as a muchtighter filter on dry gas, generally removing
particles in the approximate range of 1/5 to 1/10of the particle size.
Sterile air filters that wet out due to moisturecondensation in pipelines, fluctuating pressures, or
malfunctioning of upstream air drying equipment,
revert to their removal rating in liquids (Figure 4).
Unless these filters are validated for sufficient
bacteria removal in liquids, it is questionable
whether sufficient protection is afforded in a critical
air application. Use of hydrophobic filters preventswetting out and the resulting blockage of air flow,
however, as filters vary in their degree ofhydrophobicity, depending on the specific type andtreatment of the filter media, one cannot assume
that all hydrophobic filters are equal, and further,that they will remain constantly hydrophobic evenwith multiple steaming cycles over time.

Figure 1 - Gas molecules are in a state of random
motion, or Brownian movement.

Figure 2 - Small particles or aerosol droplets in thegas are struck by the moving gas molecules anddisplaced.

Filter Pore

Figure 3 - Due to Brownian motion, diffusional
interception is the key filtration mechanism occurringin dry gas. Particles many times smaller than the filter
pore size are intercepted.

Hydrophobicity is expressed in terms of CWST
(critical wetting surface tension), which isdetermined by a drop test and the measurementof the contact angle of a liquid with known surface
tension on a solid surface. Measured in dynes/cm,
with lower values indicating increasedhydrophobicity, CWST of filter media is dependent
on materials of construction and surface
roughness of the media.

Figure 4 - Diffusional interception does not work
under moist conditions.

4Filter Integrity Monitoring
Finally, the proper monitoring of filter integrity is an
important assurance that a filter is continuing to dowhat it is expected to do. Filter integrity test
devices measure and document whether an
integrity breach to the filter has occurred. Suchintegrity tests only make sense in sub-micron
microbial filters.
Particle filter performance is monitored by virtueof differential pressure devices. Differential
pressure should constantly and predictably rise
across a particle removal filter, as it loads withcontaminants. A sudden drop, or no pressure riseat all, would either indicate the filter is unloading
contaminants or has actually been damaged.
In the pharmaceutical industry, microbial filters areoften monitored for integrity both pre- and postuse. Food manufacturing plants often do not
routinely integrity test before and after filtration but
should consider the value of doing so. Pre-use
monitoring documents any damage that may haveoccurred during shipment or installation. In situ
monitoring can also document any potential
bypass situations or system leaks once the filter
is installed in its housing. Post-use monitoring
provides a record of batch integrity. A special caseis to monitor filter integrity after steaming a filter
but before production. As steaming is the single
most potentially damaging stress situation that afilter can undergo, a post-steaming integrity test
makes good sense.

Figure 5 - Pall Flowstar: Sophisticated integrity test
devices allow integrity testing of both liquid and gas filters.

Integrity test devices (Figure 5) are designed foruse either on liquid or gas membrane filters. Depth
filters cannot be integrity tested. There are many
types of integrity tests, with those used on liquid
membrane filters requiring the simplest handling,
and those used on gas filters requiring more
specialized procedures. Integrity test values arelinked to microbial removal performance.

Conclusion
In summary, filtration is a key step in the
manufacturing process, which impacts food safety.
Users should be aware of the intricacies of filtration
mechanisms and filtration terminology, criticallyevaluate the various filtration products they use
and rely on the proven expertise of filtration
manufacturers to assist with their proper selection.
* K.S. Berry, Global Marketing Manager,
Pall Food and Beverage
E-mail: kathleen_berry@pall.com

References and Footnotes
1 Hazard Analysis Critical Control Points
2 3-A Accepted Practices for a Method of

Producing Culinary Steam, Number 609-03
3 Guidance for Industry: Sterile Drug Products

Produced by Aseptic Processing—Current Good
Manufacturing Practice, Sept. 2004
4 High Efficiency Particulate Air
5 PDA Technical Report 40 (TR 40), Sterilizing
Filtration of Gases

About Pall Corporation
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and cost-effectiveness. Easy to install and simple
to use, our systems satisfy a wide
range of filtration requirements. Our
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Please contact Pall Corporation to verify that the product conforms to your national
legislation and/or regional regulatory requirements for water and food contact use.
Because of technological developments related to the products, systems, and/or
services described herein, the data and procedures are subject to change without notice.
Please consult your Pall representative or visit www.pall.com to verify that thisinformation remains valid. Products in this document may be covered by one
or more of the following patent numbers: EP 0422 410; EP 0667 800; EP 0982 061;
EP 1380 331; US 5,543,047; US 5,690,765; US 5,725,784; US 6,113,784; US 7,318,800;
US 7,083,564; US 7,318,800.
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April 2010