To achieve a consistently acceptable cleaning operation in food operations, it is necessary to give consideration to the following: 
 

• Selection of cleaning compound for the job. 
• Determination of concentration needed to most economically accomplish the desired cleaning. 
• Selection of external energy factors to facilitate cleaning. 
• Method of application of the cleaning compound. 

• Cleaning compound selection depends upon a number of interrelated factors, which include: 
• The type and amount of soil on the surface. 
• The nature of surface to be cleaned. 
• The physical nature of the cleaning compound. 
• Method of cleaning available. 
• Quality of water available. 
• Cost. 
• Service. 

Under normal dairy and food plant operations the variations in the surface finish of stainless steel has little influence on cleaning efficiency under practical conditions. The surface finish of the material must be considered in cleaning compound selection for materials such as aluminum, rubber parts and plastic materials. In these cases, the compatibility of the material with the cleaning compounds must also be considered. 

The physical state of the cleaning compound (solid or liquid) influences the convenience of cleaning operations and can have an influence on costs. Liquid materials are frequently more hazardous to handle, but lend themselves to better and more uniform concentration control through liquid feed devices. Powdered materials are more frequently over-used; and, where feasible, pre-weighing of standard amounts of powdered detergents can improve cleaning efficiencies and reduce waste. 

Water quality cannot be overemphasized in cleaning operations. If the water is heavily loaded with scale forming minerals (calcium, magnesium, iron or sulphate), the cleaning compound must be adjusted to eliminate the depositing minerals or the water must be treated to reduce the mineral content. The efficiency of post-cleaning rinses is related directly to water quality. Magnesium calcium, iron and manganese salts in rinse water will precipitate more readily from alkaline solution than from acid solution. Therefore, the conditioning of rinse water with acid (to Ph of 6.5 or less) will minimize the deposition of mineral water salts on cleaned equipment surfaces. 

The amount and reliability of the service provided by the manufacturer and/or supplier of cleaning materials is extremely important. However, knowledge of the fundamentals of cleaning on the part of dairy plant personnel is useful in evaluation of reliability of available services. 

In the final analysis, however, the true test in cleaning compound selection is a measure of its effectiveness in actual application under the commercial conditions being used. Emphasis is placed on the need to make sure that any surface to be tested is "technically clean" before initiating the evaluation of a cleaning compound. The surface should be dried to visualize any mineral "stone" deposits and heated to visualize protein films. A 150-watt exterior flood-light held 12-15" away from the surface will dry the surface and help to visualize deposits. Protein films give the appearance of aluminum that has been exposed to weather. Protein films can be differentiated from mineral "stone" deposits by scrubbing adjacent dried surfaces with undiluted milk stone remover and a 4-fold concentrated solution of chlorinated alkali. Acid will remove the mineral stone and the chlorinated alkali will remove the protein film. This method is effective unless the build-up is massive or consists of alternating layers of protein and mineral. 

Generally, cleaning compounds are classified as on of two groups: the alkaline cleaners and the acid cleaners.  The alkaline cleaners are typically comprised of basic alkalies, polyphosphates and wetting agents. 
 
Alkaline Type Cleaners 

None of the basic alkalies, higher phosphates or wetting agents can meet all the requirements of a good cleaner when used alone. Blends of mixtures of these chemicals can be made, however, which bring several of these properties together in one product. 

Basic Alkalies: The basic alkalies, such as soda ash, caustic soda, tri-sodium phosphate and sodium metasilicate, form the bulk of most of the common cleaners. Two or more of them are used in combination as a rule to give certain properties to the blended product. In addition to providing alkalinity for the cleaning process, they have other properties which effect the cleaning process in various degrees. 

Caustic soda is high in germicidal action and dissolving action, but it lacks deflocculating and emulsifying power as compared with other alkalies. In addition, caustic is objectionable in jobs requiring hand cleaning because of hand burning. It also is the most corrosive alkali on metals. 

Soda ash which was once the principal component of washing powders, is gradually being replaced by other alkalies. It is, however, the most common constituent of detergents today and is the most inexpensive form of alkali. It is a poor water softener and has only fair deflocculating and emulsifying action. It has the advantage of being a good buffer. This makes it useful in solutions which are used over extended periods as in hand washing. When soda ash is used in hard water, calcium carbonate is precipitated and this precipitate causes hard water spotting and helps develop milkstone deposits on equipment. This may be prevented in products containing soda ash by the addition of the higher phosphates in quantities large enough to sequester (or tie-up) the water hardness.  It is obvious that soda ash cannot be used in large proportions in cleaners to be used in extremely hard water. 

Trisodium phosphate has become a very popular constituent in cleaners because of its ready solubility and high deflocculating and emulsifying powers.  It is a fair water softener because of the flocculent character and insolubility of the calcium and magnesium phosphates formed. It is relatively expensive as a source of alkalinity in washing powders. When compared with metasilicate or soda ash, trisodium phosphate is also relatively corrosive on tin unless metasilicate is present as a protective agent in the mixture. 

Sodium metasilicate has high active alkalinity and excellent deflocculating and emulsifying properties. It, like trisodium phosphate, is only a fair water softener. The calcium and magnesium silicates formed in hard water are flocculent and insoluble in solutions. Although it is the strongest alkali next to caustic, it is relatively non-corrosive and has the property of protecting metals against corrosion by other alkalies. Metasilicate is very effective in holding the soil in suspension during the washing operation so that complete cleaning is possible. 

In addition to their water conditioning properties, the complex phosphates are valuable with respect to emulsification, dispersion, protein peptizing and prevention of soil redeposition. However, the pyrophosphates have the lowest effectiveness regarding these properties. 

Tetrasodium Pyrophosphate is most widely used and is lowest in price. It lacks calcium sequestering power as compared with the higher phosphates but has the advantage of being more stable under high temperature and high alkalinity conditions. Pyrophosphate has the disadvantage of being slow to dissolve as compared with the common alkalies. This is of importance in general cleaners where anhydrous pyrophosphate is a component of a dry mixture. 

Tripolyphosphate and Tetraphosphate are substantially superior to pyrophosphate in sequestering power on calcium hardness, which is the form present to the greatest extent in natural waters. Sodium tetraphosphate, also known as Quadrafos, ranks just above tripolyphosphate in this respect and is somewhat higher in price. Both products are readily soluble in warm water. They are unstable in hot solutions, however, and revert to the lower forms in the presence of high temperature and alkali. 

Hexamethaphosphate, also known as Calgon, is the most effective sequestering agent when calcium hardness alone is considered. It is the highest priced member of the group. In comparison with the other phosphates it lacks sequestering power on calcium in the presence of magnesium hardness, and this may be a limiting factor in some areas. Hexamethaphosphate is unstable under high temperatures and alkaline conditions. 

Wetting Agents: Wetting agents are used in many phases of cleaning, but in most instances they are used in relatively low percentages. Wetting agents are soluble in cold water and in the usual concentrations are not affected by water hardness. This permits better rinsing in hard water with the result that equipment is cleaner and brighter in appearance. Wetting agents are effective over a wide range of acid and alkaline conditions which permits their use in acid type cleaners as well as in alkaline washing powders. When added to these cleaners, the wetting agents improve the wetting or penetrating power of the product. Even in low concentrations such as 0.15%, they reduce the surface tension of water to half of its original value. It is important to note that increased concentrations typically fail to give any additional lowering of surface tension, and therefore, the amounts used in cleaners are usually small. 

Wetting agents also contribute to some emulsifying and deflocculating properties to cleaning solutions, but these properties can be provided more economically through the use of metasilicate or phosphate compounds. 

CIP cleaners generally contain no wetting agents as these additives cause substantial foam development during the recirculation process.  Some sanitizing materials which depend on wetting agents to enhance the "kill" are used on a once through basis, the acid sanitizer being metered into the water enroute to the vessel or line circuit, thence to drain. 

Chelating Compounds: The use of the organic type sequestering agents is widespread throughout the detergent industry. These materials perform similar functions of preventing water hardness precipitation that are normally performed by the polyphosphates. The chelation agents are, however, stable to heat and are also compounds. 

Chlorinated Alkalies:  Chlorine reacts strongly with proteins and markedly increases the effectiveness of alkaline components. Utilization of from 50 to 200/mil chlorine increases the peptizing efficiency of alkaline detergents and also minimizes the development of mineral deposits. Observations suggest that the elimination of protein films eliminates binding sights for the build-up of mineral deposits. Chlorinated tri-sodium-phosphate, hypochlorides, and chloroisocuranic are commonly utilized chlorine components. The compatibility of the chlorine with the basic alkali is a necessary consideration. Improper alkaline, chlorine combinations will result to the development of white deposits upon the equipment. 

Chlorinated alkalies do not function as bactericidal agents because of the high pH. The high pH minimizes the corrosive activity of the chlorine component. 

Acid Type Cleaners 

Acid cleaners have long been used in the dairy field for milkstone removal and also as part of the cleaning process on high-temperature heat exchange equipment. Such equipment as HTST pasteurizers, tubular heaters and all high temperature machines now are cleaned most effectively by a two-phase recirculation system, using acid type cleaner as one phase. Burned-on deposits are more easily removed and milkstone is prevented. 

A wide choice of acid-type cleaners is available. They are blends of organic acids, inorganic acids, or acid salts usually with the addition of wetting agents. To be effective and acid type detergent should produce a pH 2.5 or lower in final use solution. It should work well in hard as well as soft water and should show a minimum of corrosion on metals. 

CONCENTRATION 

Where cleaning is done by hand, it is evident that strong acids and alkali cannot be used, since man's skin is never as inert as the surface being cleaned. Therefore, detergent strength is generally reduced and greater reliance is made on external energy. Generally, superior results can be achieved by use of circulation cleaning ... either in or out of place. In circulation techniques, optimum concentrations of cleaning compounds can be more readily utilized. 

EXTERNAL ENERGY FACTORS 

The cleaning process can be improved by increasing the "external energy" applied, either by increasing the temperature or the force applied. In this discussion the effective time will be considered as an external factor. Each of these can be varied independently to adjust a cleaning operation to a particular problem or plant operating practice. The conditions generally are selected so as to permit the best cleaning job at the least cost. The significance of the various factors will vary with the method of cleaning used or with the type of condition of the soil to be removed. 

Temperature:  Temperature is extremely significant in cleaning operations. Increasing the temperature has the following effects: (a) decreases the strength of bonds between the soil and the surface, (b) decreases viscosity and increases turbulent action, (c) increases the solubility of soluble materials, and (d) increases chemical reaction rates. For milk products within a temperature range from 90? to 185?, an increase in temperature of 18? F., will approximately double the efficiency of the cleaning operation. Below 90? F., milk fat remains in a solid state and above 185? F. heat-induced interactions bind the protein more tightly to the surface and decrease cleaning efficiency. 

For any food soil, the minimum effective temperature will be about 5? higher than the melting point of the fat. The maximum temperature will depend upon the temperature at which the protein in the system is denatured. Temperatures above the denaturation point can increase the adhesion of the protein to the surface faster than the cleaning efficiency is increased. 

Time: All other factors remaining constant, the cleaning can be increased by utilizing longer times. However, increasing the time beyond a given value provides little additional increase in effectiveness. As previously discussed for concentration, there is only minimum time for effective cleaning and a practical maximum time for achieving desired results economically. 

Physical Action: In hand-cleaning, force is applied by "elbow-grease", whereas fluid-flow is utilized in the application of force in CIP or COP systems. Originally, the utilization of velocity as a means of measuring the fluid flow force was employed with the "thumbrule" of 5 ft./second being employed by Regulatory Agencies. Although this value is still in the regulations, effective cleaning can be achieved frequently by velocities lower than 5 ft./second. This is because velocity and turbulence, which is the actual cleaning force, are not equally related under all conditions of flow. To be effective, fluid flow must be turbulent (Reynold's number greater than 3000 in pipeline systems and greater than 200 in free-falling films over storage vats and similar containers). Generally, the values above 30,000 (for pipeline systems) give greatest effectiveness. 

Detergency: Consideration must be given to the type of cleaner to be used ... its strength ... and in certain instances where two or more cleaning materials are used, the proper sequence of application. 

METHOD OF APPLICATION 

The cleaning agents, in solution, and in the proper sequence, may be applied : 

Manually:  By clean-up personnel, using  (1) buckets and brushes, and hoses for pre-rinsing and post-rinsing, (2) HPLV Systems (High Pressure Low Volume) via spray wands supplied from portable or fixed central systems to apply the wash and rinse solutions to the surface, or  by (3) Foaming, agin via permanent or portable systems which deliver foam through a nozzle to the surface, allowing the rate of breakdown of the foam to control the time of contact, cleaning being primarily by chemical action. 

Mechanically:  By COP or CIP systems.  The COP (Cleaned Out of Place) System uses a heavily agitated tank to clean components disassembled and placed in the tank, often in special baskets or racks.  The COP tank is often used only to apply the chemical (and control time, temperature and concentration), and rinsing is by hand, though COP tanks have been combined with CIP Units to accomplish fully automated COP cleaning.  CIP (Clean In Place) involves spray washing of processing and storage tanks and pressure recirculation washing of piping systems and integrated equipment by use of permanently installed CIP Systems to deliver, heat and re-circulate the flush, wash and rinse solutions for controlled periods of time, at the desired temperatures and concentration.  All components in the system must be of CIPable design. 

TYPICAL CIP CLEANING PROGRAMS  

There is no single "best way" to handle any particular cleaning program, for, as observed in the previous section, the effectiveness of mechanical/chemical cleaning is related to a number of variables including time, temperature, concentration and physical action. More importantly, exact or specific numbers (as part of the recommendation) are of no value if the equipment is still dirty upon completing a cleaning cycle. The first objective must be to "do what is necessary to get the equipment clean" after which further adjustments giving consideration to limitations of temperature, time, or cleaning chemical cost may be completed. 

Four decades of experience have demonstrated that the product soil encountered in all fluid and semi-fluid processes for food products can be removed by one or a combination of several of the following treatments: 

Chlorinated Alkalies: In its simplest form this detergent solution may be nothing more than a mild solution of caustic soda supplemented with laundry bleach. More commonly a chelated caustic is used to provide some control of water hardness. Chemical concentrations may vary from as low as 800-1200 ppm of chlorine for lightly soiled equipment to a maximum of 5,000 ppm. Cleaning temperatures are normally in the range of 135?-160? F., and exposure time (recirculation at temperature) may vary from 5 to 20 minutes. 

Acidified Rinse: A minimum post-rinse using fresh water to drain will be used to remove the major portion of the chlorinated alkaline solutions from the equipment surfaces. Then, to minimize water requirements for rinsing the final treatment will be a recirculated solution lightly acidified to produce a pH of 5.5 - 6.0 (just slightly on the acid side of neutral). This solution recirculated at the water supply temperature, will neutralize all traces of alkali residual films on the equipment surfaces. It has the further benefit of providing an equipment surface which will drain and dry free of spots. Finally, though not a sanitizing agent, a mild acid solution is bacteria-static and its use as the final treatment reduces or slows down the growth of any bacteria that may be present as a result of the water supply or that may remain due to improper cleaning. 

Strong Alkalies:  Chelated caustic may be used alone at higher concentrations and temperatures to handle heavy fat and coating soils. Chemical concentrations may range from 0.5% (5,000 ppm) to as much as 50.000 ppm. Recirculating temperatures may be increased to 180?-190? recirculating period may be extended to 45-60 minutes. This is typical of the treatment used for cleaning a milk High-Temperature Short-Time pasteurizing system, a beer kettle, or a cheese whey evaporator. 

Strong Acids:  The above treatment may be either preceded or followed by recirculation of a strong acid solution, phosphoric acid being the most common. Acid will be added to produce a pH as low as 2.0 and the recirculating temperatures may be in the 170-190 degree F. range though the time will generally be shorter than for the caustic product (20-30 minutes maximum). 

The decision as to which to use first will depend upon the predominance of fat or protein in the soil. High-fat soils are most easily attacked by strong alkaline products, followed by the acid to handle the remaining mineral deposits and the deposition of any hardness from the water used for preparing the cleaning solution. Soils which are heavy in mineral will be more responsive to the acid first, followed by caustic for protein removal. 

Sanitizing: All equipment used in producing products sold in the "fresh" form (such as fluid milk, cottage cheese and ice cream) must,  by regulation, be sanitized following the cleaning and before being again used for processing. Sodium Hypochlorite is the most common sanitizing agent, being applied in cold solutions at concentrations ranging from 55 ppm to 200 ppm for periods of only a couple of minutes. Acid sanitizers now available can be applied to accomplish the "Ácidified Rinse" described above and comply with the requirements for a legal sanitizing solution. 

SUMMARY 

It is possible to design and apply equipment and programs which can produce food contact surfaces that are physically clean and essentially free of all bacterial contamination. Standard swab tests on CIP-cleaned equipment should yield no growth plates in 75-80% of all samples and plates showing not more than 2 to 10 colonies for the remaining samples, when swab sampling is done immediately following cleaning and before sanitizing. If equipment is properly handled, there will be no positive coliform counts on any swab taken from surfaces cleaned by in-place cleaning procedures.  Re-contamination during the re-connect process following CIP cleaning is a major source of spoilage organism in the products subsequently processed in the subject system. 

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