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Dry fractionation, also known as crystallization from the melt, is fractional crystallization in its most simple form, and the economy of the technology allows it to be used for production of commodity fats.
Solvent fractionation, involves the use of hexane or acetone to let the high-melting components crystallize in a very low-viscous organic solvent. This can be helpful with respect to the selectivity of the reaction, but mainly offers advantages in the field of phase separation; much purer solid fractions can be obtained, even with a vacuum filtration. Being a more expensive process, it is less common than dry fractionation and only comes into the picture when a very high added value of (at least one of) the resulting fractions makes up for the high cost (Illingworth D, 2002).
Conducting fractional crystallization
Crystallizer should be able to gently cool down a mass of oil (up to 100 ton/ batch) and keep the resulting crystal suspension as homogeneous as possible. Note that such gentle cooling means in fact imposing very low super cooling conditions, and it will result in a formation of fewer and larger crystals, because the said conditions simply rule out the existence of a mass of tiny crystals. Fat crystallization is a fairly exothermic reaction (up to 180 kJ can be released for every kg of crystals formed), so the efficiency with which this energy can be removed is an important design feature.
The cooling medium eliminating this heat of crystallization from crystallizers is typically clean cooling tower water, sometimes mixed with some propylene glycol to be able to work at sub-zero conditions (as in fish oil fractionation). Cooling by ammonia evaporation can also be considered, but very often turns out to be too expensive for a classic installation. The cooling wall itself can be double-jacket, stainless steel cooling fins (plates) or pipes. Normally, a cooling surface of at least 4m2 per m3 oil is expected to assure proper heat transfer for bulk edible oil fractionation (Timms R.E, 2005).
The Separation Stage
Although the triglyceride separation ideally is already formed during crystallization, it is clear that the separation stage itself effectively determines the product yields as well as the stearin quality. As more residual olein can be expelled from the solids cake, the final stearin will be more concentrated in crystals and will turn out 'purer' and will display higher and steeper melting. The olein quality is determined entirely by the amount and selectivity of crystallization in the preceding stage. In some applications, the formed crystals are often not adequately stress-resistant and get pressed through the filter medium. Obviously, such contamination of crystals in the olein phase affects the efficiency of the fractionation process negatively and results in a liquid phase with inferior cold stable properties. Overall, the 'permitted' degree of olein dilution in the stearin cake determines the choice for the applied separation technology, exemplified in Table 1.
Table 3: Different separation systems for palm oil fractionation
Types of oil
IV Palm Oil
IV Palm Olein
IV Palm Stearin
Solids in cake (%)
Olein Yield (%)
Fig 4: A membrane press filter used in dry fractionation
Membrane press filtration, as also used in for example sludge dewatering systems, is by far the most used separation technology in dry fractionation nowadays. Usually, the filter chambers are first filled with the crystal suspension, and doing so a large portion of the liquid olein is already passing through the filter cloths. Then watertight membranes (one membrane per chamber) attached to the internals of the plates are gradually inflated (with water, liquid oil or air) like internal balloons to the desired pressures, reducing the chamber volume and pushing out residual liquid, which is immediately evacuated via internal channels in the plate towards collecting tanks. The volume reduction of the chamber thus literally compacts and dries the cake. It is also good to note that the mass fraction of solids in the filter cake decays exponentially as a function of the distance to the filter cloth, and consequently thinner filter chambers and longer squeezing times can be helpful (yet costly) means to reduce the entrainment significantly.
The whole filtration plus squeezing operation can vary from 30 to 90 minutes. After this, the filter plate package is opened so the solid cakes can just drop by gravity into a stearin tank underneath the filter to melt (Calliauw G. et al, 2010).
The Fractionation Plant Assembly
The following figure presents a general lay-out of a present-day dry fractionation process. Often multiple crystallizers are used in (overlapping) series. This is not only a matter of capacity, it is also in order to maximize the use of the filter; by a good planning of the crystallization times of filtration, the expensive (batch) filter should be in constant operation.
The reduction of dead time of a filter can also be established by means of a crystallized offer buffer tank; each crystallizer can be quickly drained and made ready to receive the next batch of oil, while the cooled buffer tank will send set volumes of crystal slurry to the filter, whenever it is ready. Continuous filtration systems have been a very elegant strategy in dry fractionation as well, although currently, the demand for purer solid fractions as obtained by filter chamber compaction has pushed continuous belt filters somewhat out of the dry fractionation market.
It should be kept in mind that fractional crystallization of a triglyceride oil is a relatively slow process and is therefore the time determining stage; some simple fractionations can be established in about 5hr crystallizer residence time, whereas more complex oils can require up to 3 days of cooling and crystal maturation before being sent to the filter.
Fig 5: Lay-out of a typical dry fractionation process
Ultra filter in beverage industry
Clarification of beverages
Conventional clarification of beverages uses the techniques of precoat formation and body-aid feeding. Considerable interest has been showing methods for limiting cake growth during the separation of solids from liquids. Cross-flow filtration is process of preventing build-up of cake by shear forces of fluid moving parallel to the membrane. Cross-flow is already employed successfully in ultrafiltration and reverse osmosis systems but is uncommon with micro porous media (0.1 to a few microns pore-size) (M.M Puechot, 1984).
Wine production clarification, or separation of suspended solids from wine, is an extremelyÂ critical step in the processing of wine. Not only is it important to leave the special flavour components untouched but also the disposal of filter aids, such as diatomaceous earth and sheet filters is becoming increasingly problematic in view of growing awareness of ecological and human health issues. Membrane offers an alternative with liqui-flux beverage modules or exchangeable cartridges for cross flow microfiltration with many advantages over conventional methods. Liqui-flux modules utilize micro porous membranes as very efficient and safeÂ separating elements. The advantages of using liqui-flux beverage modules are:
One single step instead of several process steps
Low fouling tendency
No need for additional filter aids
Suitable for completely automated production plants
Easy to change from one to another type of wine
Low losses of wine
Wine filtration costs are reduced
No health hazards such as those associated with diatomaceous earth
To further illustrate how simple and useful cross flow clarification with liqui-flux filtration modules is, the following flow chart provides an overview of the wine making process. Ultra filter offers a broad variety of filters for applications in the food and beverage industry. Individually tailored for different applications and requirements, it is always economic efficiency in combination with security and reliability that is most important (Membrana, 2004).
Fig 6: Process flow diagram for wine production
Beside the optically clarification of the final product the food and beverage industry emphasizes the removal of bacteria and micro-organisms. Consumers do not want fibres, particles of undissolved ingredients in their drinks. Substances that would alter the taste and influence the product's characteristic features are also undesirable. Bacteria and other micro-organisms reduce the self-life and may eventually also lead to a change in taste.
The filtration of wine should neither affect the taste nor the colour of the wine. After the diatomaceous earth filter, depth and membrane filters are used for the filtration before filling and cold stabilization. These remove micro-organisms, bacteria and particles effectively without influencing the 'spirit of the wine'.
Fig 7: Wine application
Apart from the filtration of liquids, large amounts of compressed air, carbon dioxide (CO2) and nitrogen (N2) are also needed in the food and beverage industry. Those have to be filtered too, in order to ensure a consistently high quality within the given products.
A good steam quality is necessary for the sterilization of the filters and the tanks, because it enhances the service life of the filters and more importantly it guarantees a constant product quality.
Water is used for rinsing and cleaning of filling jets, bottles, kegs or other containers. This water should be sterile, so that the rinsing does not result in contamination. Water is also very often part of the final process or even the final product itself. Therefore one must recognize the importance of the fine filtration of table or mineral waters, the sterile filtration or bacteria reduction of water intended for the addition to non-alcoholic drinks, juices, beer or syrup.
Water filtration applications lend a hand in many water filtration specifications, such as pre-treatment of area, surface or well water, boiler water, condensate, process water, clean-up and sterilization, hygiene provisions, and waste water extraction. No matter the exact need, there is an excellent likelihood that some kind of water filtration will be necessary in the food and beverage vertical (Donaldson Co., 2004).
Fig 8: Mixed water filtration
The two largest categories to filter water are granular and membrane.
Granular: Granular is a tried and true pick in the food business, and is a commonplace and renowned filtration selection within. Granular media filtration options include sand filters, carbon elements, fine garnet elements, and anthracite elements. Granular filters remove suspended particles down to 10 microns in width. Some tests have unveiled filtration accomplishment down to the size of 1 micron.
Membrane: water elements use membranes to take out particles. Separate from granular elements, the membrane filters come with pores and can extract small particles. Membrane water filtration is most efficiently detailed by looking at the size range of the filterable particles, described underneath:
Table 4: Different types of filter and their capability to remove different particle based on size
Types of filtration
Particle size that can be removed (Âµm)
Types of Materials Removed
Clay, bacteria, large viruses, suspended solids
Viruses, proteins, starches, colloids, silica, organics, dye, fat
Sugar, pesticides, herbicides, divalent anions
0.0001 - 0.001
Air and gas filtration
Other gases than compressed air are commonly used such as carbon dioxide and nitrogen in the food and beverage industry. These gases must be clean and free of particles and bacteria by hydrophobic membrane filters in order to guarantee the best possible quality of the product.
Aeration and de-aeration
To avoid the contamination of storage tanks or transportation containers for water, wine, juices, liquid sugar or other liquids by bacteria, the use of sterile vent filters are necessary. Aeration and de-aeration filters are designed to work under atmospheric conditions. For this reason a low differential pressure and a reverse flow direction are the most important parameters, apart from a long service life and a high dirt hold capacity.
In the production process of beer normally depth and membrane filters for the removal of particles, bacteria and yeast. Not all breweries have sediment free water sources, it is recommended, for these applications, to filter the water in order to ensure a consistent input quality of the beer.
Fig 9: Production of beer
According to USDA Grading Standards for extracted honey, filtered honey is honey that has been filtered to the extent that all or most of the fine particles, pollen grains, air bubbles, or other materials normally found in suspension, have been removed. Honey that is filtered by packers is filtered for various reasons:
Many consumers prefer honey that is liquid and stays liquid for a long time. All honey crystallizes eventually. Suspended particles and fine air bubbles in honey contribute to faster crystallization. Filtering helps delay crystallization, helping the honey to remain liquid for a much longer period than unfiltered honey.
Many consumers prefer honey to be clear and brilliantly transparent. The presence of fine, suspended material (pollen grains, wax, etc.) and air bubbles results in a cloudy appearance that can detract from the appearance. Filtering is done to give a clear brilliant product desired by consumers. For the filtered style of honey, USDA Grading Standards for Extracted Honey give higher grades for honey that has good clarity. Honey is filtered to remove extraneous solids that remain after the initial raw processing by the beekeeper.
Various filtration methods are used by the food industry throughout the world. Ultra filtration, a specific kind of filtration used in the food industry, should not be confused with other filtration methods generally used in the honey industry.Â When applied to honey, ultra filtration involves adding water to honey and filtering it under high pressure at the molecular level, then removing the water.Â It is a much more involved and expensive process which results in a colourless sweetener product that is derived from honey (Boynton, 2012).
Microfiltration (MF) is a frequently used to clarify wine, but the fouling of the membranes is the main limiting factor for the overall process capacity. In this work, data from MF clarification of a white wine are presented which show that membranes made from polypropylene (PP) yield significantly higher fluxes and through-put than membranes made from polyarylsulfone, both having the same cut-off pore size (0.2 Âµm ).
The following PP membranes from Membrana GmbH, Wuppertal, Germany, have been used:
Capillary membrane AccurelÂ® PP 300/1200
Capillary membrane CelgardÂ® X-30, and flat-sheet membranes
CelgardÂ® 2400 and 2500
The CelgardÂ® membranes have been used only in some of the experiments in order to consider effects of membrane preparation and pore structure. One PES capillary membrane (0.2 Âµm cut-off pore size), used in the field for wine filtration, was used throughout the experiments.
6.2 Filtration unit
One cross-flow unit with 19 m2 membrane area (2 devices of 9.5 m2; LiquiFluxÂ® B22, AccurelÂ® PP 300/ 1200, 2400 capillaries, module length 1092 mm, module diameter 125 mm, housing material polysulfone).
One cross-flow unit with 42 m2 membrane area (6 devices of 7 m2; polyarylsulfone capillary membranes, cut-off pore diameter 0.2 Âµm, inner diameter 1.1 mm, 2000 capillaries, module length 1092 mm, module diameter 125 mm, housing material polysulfone).
The following substances have been used for adsorption experiments or as reference material.
Commercial red grape marc extract (from grapes after fermentation)
"Synthetic wine" was composed of 12.7% ethanol, 6 g/l citric acid, 3g/l maleic acid, 100 mL/L acetic acid, 367 mg/L calcium chloride, 100 mg/L potassium sulphate, 42 mg/L magnesium chloride, all adjusted to pH 3.5 with 5N potassium hydroxide solution.
The following solutions were used for the adsorption experiments:
Tannic acid in "synthetic wine" as a model for polyphenols
Arabinogalactan in "synthetic wine" as a model for wine polysaccharides
Dextran in "synthetic wine" as model for an "bio inert" polysaccharide
"synthetic red wine" consisting of red grape marc extract in "synthetic wine" (2.5g in 250 mL for several hours on a shaker, then filtered with a Sartorius 0.45 Âµm cellulose acetate membrane, revealing an insoluble fraction of about 1wt%; and then diluted to 4 g/L)
A white wine was used for the filtration experiments
Measurement of membrane specific surface area and pore size distribution: Membranes were analysed using the Surface Area Analyser according to the method of nitrogen adsorption and desorption. First, membrane samples (about 100 mg) were extracted with ethanol (p.a.) overnight and then dried at 40Â°C to constant weight. By means of the data of the adsorption isotherm, the specific surface area of the membranes was determined using the method of Brunauer, Emmet and Teller (BET). Additionally, the pore size distributions (up to a maximum pore size of 80 nm) were quantified via the BJH method and the Kelvin equation.
For all adsorption experiments, the adsorbed amounts on the membrane were quantified measuring the reduction of the concentration in the solution used as the contact medium (difference between start concentration and the concentration at equilibrium). For proper quantification of the substances, a complete wetting of the membrane samples and an exact knowledge of all volumes (adsorption solution and wetting solution in the membrane, i.e. in the lumen and in the membrane pores) are mandatory. The sum of specific lumen and pore volume (normalized to membrane mass) of the capillary membranes was determined gravimetrically from the difference between dry and wet membrane. The treatment of the membrane samples in order to ensure complete wetting of all pores was always performed as follows.
Weighing of a defined piece of membrane (between 120 and 150 mg), wetting with ethanol, solution exchange facilitated by rinsing the capillary lumen with help of a syringe and then wetting with "synthetic wine" to equilibrium (4 hours), weighing of the filled membrane, transfer of the membranes to the a desorption solution (15 mL), facilitation of liquid exchange by rinsing the capillary lumen with help of a syringe and 5 days of adsorption in a closed vessel (20 mL polyethylene beaker), and thereafter analysis of the concentrations of the supernatant.
The Liqui-FluxÂ® B22 modules with PP membranes had been assembled in a RS2 CS unit (ROMFIL GmbH , Wolfsheim, Germany) for two modules; backwashing was performed after every 7 min. for 8 sec into a separate tank; the accumulated backwash volume was concentrated at the end of the filtration. The elements with the polyarylsulfone membranes had been accumulated in a ROMFIL RS6 CS unit including a 400 L feed recycling tank; backwashing was done after every 6 min for 20 sec into the recycling tank.
6.6 Results and Discussion
a. Wine microfiltration with two different membranes
In field filtration employment with a typical white wine we surprisingly measured a much higher initial flux and also a higher filtrate volume flow over time with a 19 mÂ² filtration unit containing PP membranes compared to a 42 mÂ² unit containing polyarylsulfone membranes. Details are presented in Figure 10. Taking into account that the membrane area of the PP modules was about half of the area of the polyarylsulfone modules and that the filtrate volume flow was about two fold after 4 hours of filtration, the superiority of the PP membranes is obvious. The mean trans-membrane pressures were about 1.3bar for the PP modules and about 2 bar for the polyarylsulfone modules.
Fig 10: Filtration of white wine (graphical representation of filtrate volume vs. filtration time) 
Although the quality of the filtered wine is only slightly different (see Table 5), there are hints that the adsorptive behaviour of the two types of membranes might be different with respect to some ingredients. From this result it could be argued that the polyarylsulfone membranes show higher adsorptive capacity for the sum of the non-sugar components. However, it also has to be taken into account that the area of the polyarylsulfone membranes was much higher. To be able to differentiate among these two possible effects or even to find a different explanation it is necessary to perform experiments under more controlled conditions in the lab. Therefore, the study performed as described in this paper.
Table 5: Typical data obtained for the White Wine, before and after MF with the two different membranes
Total alcohol (%)
Sugar free extract (g/L)
pH value (-)
Total acid, pH = 7 (g/L)
Carbon dioxide (g/L)
b. Pore structure of the membranes used for adsorption studies
The main aim of this work was to elucidate the influence of the membrane polymer and adsorptive fouling. This has been done with two groups of materials:
Two capillary membranes, from PP and PES, already used for wine filtration and focus of the adsorption tests
Three other capillary or flat-sheet membranes from PP (in order to elucidate the effect of the membrane material).
In order to take into account the different porosity, the adsorbed amount had to be related to the specific surface area of the membranes. In addition, the fraction of smaller pores may also have influence onto the adsorbed amounts, especially for high-molar mass solutes. Both kinds of information can be retrieved from gas adsorption measurements, and an overview on pore structure data for the membranes is given in Table 6.
Table 6: Specific surface area (BET model) and pore volume
Specific surface area
Pore volume (dp< 80 nm)
AccurelÂ® PP 300/1200; type a
AccurelÂ® PP 300/1200; type b
CelgardÂ® 24( flat-sheet)
Both capillary membranes, from PES (#1) and PP (#2) have markedly different pore structure. The specific surface area of the PP membrane, as of all other PP membranes investigated in this study, was significantly larger than for the PES membrane. This is mainly due to the larger fraction of pores with diameters in the range of 20 to about 180 nm for the PP membranes (as seen from pore size distribution obtained via the BJH model; data not shown in detail). The three membranes (#4 to # 6) made by a stretching process and having completely different pore morphology, had consistently larger specific surface area and pore volume in the diameter range, d< 80 nm.
c. Adsorption Studies
All adsorption experiments were performed in a 12% ethanol/water buffer (pH 3.4) to ensure "wine -like" conditions. Flavane -3-ols, from monomers to oligomers with a molar mass of about 3.8 kg/mol, had been used also in other studies as relatively well-defined model substances for polyphenols (Cartalade.D et al, 2006). Arabinogalactan is an important polysaccharide occurring in wine (Vernhet A et al, 2002), while dextran has a completely different structure but had already been used in other studies of adsorptive fouling (Susanto.H et al, 2005) & (Susanto.H et al, 2007).
Figure 11 shows the adsorption of tannic acid on the two capillary membranes normalized to the specific surface areas. The adsorbed amounts are in the range of what had been interpreted as monolayer coverage of PES with flavan-3-ols (0.6 to 2.0 mg/m2, depending on the orientation of the molecules). This is also in agreement with previous results, indicating that almost complete surface coverage has been achieved at a solute concentration of 100 mg/L (Cartalade.D et al, 2006). All these arguments point to a relatively high affinity due to the attractive polar interactions. Consequently, the affinity of PP for this polyphenol under the adsorption conditions was much lower; this can well be explained by the matrix, especially ethanol, which will not favour attractive interactions between the polar solute and the non-polar surface. In addition, hydrogen bonding between polyphenol and PES likely also contributes to the driving force for adsorption; PP does not support the formation of hydrogen bonds to the surface. From Figure 11, it can also be seen that the amounts of adsorbed tannic acid did not change much in mixture with a ten-fold excess of polysaccharide; for PES a reduction of about 10% was observed while the data for PP were very low anyway.
Fig 11: Adsorption of tannic acid (0.1 g/L) from single solute solution and mixtures with arabinogalactan or dextran (1 g/L; in "synthetic wine") to PES and PP membranes (#1 and #2), relative to the membrane specific surface area
From the above experimental study it can be concluded that, individual polyphenols and polysaccharides in "wine-like" ethanol-containing buffer are only marginally adsorbed by PP but strongly adsorbed by PES MF membranes. Adsorption of polysaccharides from the model "synthetic red wine" prepared from red grape marc extract is greater than from the buffer "synthetic wine" with model substances, and there is a correlation between the adsorbed amounts of polysaccharide and polyphenol from "synthetic red wine"; both findings back the hypothesis that aggregates of polyphenols and polysaccharides present in red wine have a major contribution to adsorptive fouling. This fouling is strong for PES, but very weak for PP membranes. The low adsorption tendency of wine ingredients to PP membranes results in higher fluxes and longer service life of the respective filtration modules in wine clarification.
ENHANCING FOOD SAFETY MANAGEMENT BY UNDERSTANDING THE ROLE OF FILTRATION
Food Safety in a process managed under HACCP principles is achieved by applying a proactive program to analyse, identify, control, monitor, correct, verify and document critical control points in the process. If a critical control point in the system fails to perform as required, this can result in 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.Â Food safety management is related to the following points.
Physical contaminant removal
Chemical contaminant removal
Securing water quality
Understanding filtration performance
Filter integrity monitoring
Filtration is a process step that can provide critical protection of food products during various manufacturing stages. While some filtration is geared 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 (K.S. Berry, 2010).
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 from pumps or equipment with moving parts. Although proactive measures can identify and limit such occurrences, and while detection equipment can be implemented to find such contaminants as part of a quality assurance program, a final polishing filtration step as a last barrier can serve as an additional safety measure. 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 filtration (K.S Berry, 2010).
Chemical Contaminant Removal
Chemical safety describes a situation where in food products are free of unwanted chemical contaminants, such as cleaning agents, or uncontrolled amounts of other food plant chemicals inadvertently ending up in the product. Where such upsets may be initiated by faulty chemical handling devices, which need 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 chemical components relates to the verification of food contact compliance concerning plant equipment, which includes filtration devices. Existing and rapidly emerging global regulations ensure that unwanted extractable from filtration devices cannot contaminate foods and adversely affect consumer health. (K.S Berry, 2010).
Microbiological quality is by far the most common food safety aspect safeguarded by filtration. By applying appropriately filtration devices, bioburden decline or commercial sterility of a product is attained. Aseptic processes, for example, rely on sterile air filters on aseptic surge tanks and fillers to maintain sterility within the process and during the packaging step. Additionally, where ingredients are aseptically dosed into a sterile environment, sterile liquid filters are selected to provide microbiological removal where heating would otherwise destroy heat sensitive ingredients. In various types of bottled water applications, where no heat treatment is involved, sterilizing filtration prior to the bottling step, used in conjunction with corresponding well-controlled downstream operations, assures the microbiological safety of the bottled beverage. In certain dry powdered products, proper filtration of the air that comes into contact with these powders during manufacturing can reduce or eliminate unwanted microbes, which could later thrive in reconstituted form (K.S Berry, 2010).
Securing Water Quality
Water is often a vital cause 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. Where production plant water comes into direct contact 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 to remove 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 of cross-contamination. Filtration can ensure that microbial levels are controlled (K.S Berry, 2010).
Understanding Filtration Performance
The absence of standards regarding removal ratings and removal performance in the filtration world 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 the removal solely of particles and should not be used to describe critical microbiological removal requirements. Particle removal efficiencies specified by filter producers are based on tests, which state the degree of removal of standardized particles such as fine or coarse test dust or latex beads, usually hard spherical particles which have little to do with the structure of microorganisms. Even the methods used to generate this data, such as the use of single pass or multiple pass challenge tests, type of particles, and the amount of challenge material must be looked at carefully in order to understand the true performance of a particle-rated filter (K.S Berry, 2010).
Nominal filters provide only partial removal of contaminants and should never be used when critically important removal requirements exist. They can at best, be good pre-filters for downstream final filters. Even within the nominal filter realm, removal ratings can range anywhere from 99 % removal efficiency (Beta 100 ratio) on downwards. Very nominal filters might, for example, only remove in the 60 % removal efficiency range, meaning 60 % of all particles at a given micron size. Additionally, nominally rated filters sometimes consist of fibrous, non-fixed pore 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. 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 purpose eliminate 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).
[Beta Ratio = influent particle count/ effluent particle count
Removal Efficiency = (influent particle count - effluent particle count) x 100 / influent particle count]
By contrast, microbiologically confirmed filters display far higher removal ratings even than absolute rated particle filters. A validated microbial filter should be backed up by performance data showing the nature 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 validating sterile air filters, and so on. It is only when carefully analysing the nature of the testing done, that one can evaluate the true performance capability of the filter. In this respect, requesting a validation guide from a filter manufacturer will illuminate much information that would otherwise not be apparent from a simple data sheet (K.S Berry, 2010).
Filter Integrity Monitoring
Finally, the proper monitoring of filter integrity is an important assurance that a filter is continuing to do what it is expected to do. Filter integrity test devices measure and document whether an integrity breach to the filter has occurred. Such integrity tests only make sense in sub-micron microbial filters. Particle filter performance is controlled by the use of differential pressure devices. Differential pressure should continually and probably rise across a particle removal filter, as it piles with contaminants. A sudden drop or no pressure rise at all, would either indicate the filter is unloading contaminants or has actually been damaged. Food manufacturing plants often do not regularly take integrity test before and after filtration but should consider the value of doing so which is very vital.
Integrity test devices are designed for use 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 are linked to microbial removal performance. (K.S Berry, 2010)
There are few areas in our lives that are not touched by filtration. We are surrounded by filters in the home, from tea bags and coffee makers to dish washers, food products in our cupboards from mustard and flour to sugar and cereal, all of which involve some form of filtration. Chemical engineering knowledge can be accredited with improving the conversion of raw foodstuffs into safe consumer products of the highest possible quality. Chemical engineers routinely develop advanced materials and techniques used for, among other things, chemical and heat sterilization, advanced packaging, and monitoring and control, which are essential to the highly automated facilities for the high-throughput production of safe food products.
Definition of filtration and related theory are included in the dissertation to have a simple clear concept about it. Various types of food industry more or less use filtration technique for different purposes. Among them the clarification of beverages, wine and beer production, honey, cheese, milk, water, fruit puree etc. are important which are also explained here.
An experimental example has been presented where comparison among various membrane filters has been shown. At a glance it can be said from the experimental result that PP is best for wine production. But polyacrylsulfone also has some exclusive characteristics such as turbidity removal efficiency is more of this type of membrane than PP. A self-cleaning filter reduces product waste and minimizes time. Different types of filters which are discussed here are now continuous type of process which replaces old batch process. By using innovative filter equipment we can reduce labour cost and can get better quality products, maximize the yield in lesser time. Monitoring system of filtration is also a very important factor for food processing industries.
On the basis of the dissertation it can be said that filtration is a key step in the food manufacturing process, which impacts food safety. Individual should be conscious of the details of filtration mechanisms and filtration terminology, critically assess the various filtration products they use and rely on the proven expertise of filtration manufacturers to assist with their proper selection.