3. CIP TECHNOLOGY
3.1 Different
It is important to know the composition of the soil when designing a CIP sequence.
The composition of soil will vary depending on the type of product being processed.
Simply changing the fat content of milk can result in a change in the composition of the soil, which makes it more difficult to remove. Tetra Pak process equipment is used for different food applications, ranging from juices to prepared food such as rice pudding and Béchamel sauce. Table 1 shows a schematic overview of the different types of soil that need to be removed from equipment surfaces during CIP.
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Table 1.
Table 1. Different types of soil (according to Guthrie, 1972). From the Handbook of Hygiene Control in the Food Industry (Ed. Lelieveld, H. L. M., Mostert, M. A. &
Holah, J., CRC Press, 2005) Type
Type of of soil soil Solubility Solubility Ease Ease of of removalremoval Low/medium
pasteurisation
High
pasteurisation/UHT
Sugar Soluble in water Easy Caramelisation,
more difficult to clean
Fat Not soluble in
water, soluble in alkali
Difficult Film formation, more difficult to clean
Protein Not soluble in water, soluble in alkali, slightly soluble in acid
Very difficult Very difficult
Mineral salts Solubility in water varies, most salts soluble in acid
Varies Varies
Starch Soluble in water
and alkali
Easy to moderate Glue-like
formation, difficult to remove
Two examples are given below of the fouling that can be found in Tetra Pak processing equipment, srcinating from milk production and tomato paste production. Both products represent typical soil situations, but also serve to
illustrate the differences in the CIP cycles.
Milk fouling
During the processing of milk, either pasteurised or UHT milk, the heating equipment is fouled. There are two main types of fouling (see Table 2). Low-temperature pasteurisation (maximum Low-temperature 72-75 °C) creates a kind of fouling with a high content of protein, mainly β-lactoglobulin. This type of fouling is denoted type A, and is dominant in the temperature range 70 to 105 °C. During the production of UHT milk, another type of fouling besides type A fouling, denoted type B, arises. Type B fouling is created in the high-temperature range starting at 110 °C. This type of fouling contains a higher level of minerals than type A fouling, mainly calcium phosphate.
Table 2.
Table 2. Composition of soil in dairy applications.
Type
Protein 50-60 15-20
Minerals (calcium phosphate) 30-50 70-80
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Tomato paste fouling
When cleaning a protein deposit, e.g. milk fouling, the detergent solution will cause swelling of the soil. Deposits resulting from the processing of tomato paste are cohesive, and can be removed in large chunks by hydration of the deposit–substrate interface. Fouling deposits form as a result of both adhesion of material to the equipment surface and cohesion between elements of the material.
3.2 Water Chemistry and Quality
Two main issues are of importance regarding water quality, namely microbiological status and water hardness. The microbiological status is the more important one in food processing. The other issue, water hardness, concerns the amount of metal ions in the water. Water hardness and inadequate pre-rinsing are two major factors causing failure in CIP operations, apart from inadequate flow rates. Calcium and magnesium ions are considered in the context of water hardness, but other polyvalent cations may also be of importance. The European standard for water
hardness is German degrees (°dH).
Three problems causing failure of CIP:
• water hardness
• inadequate pre-rinsing
• too low flow rate (Sect. 3.8)
Water hardness can be discussed in terms of carbonate hardness (temporary hardness) or non-carbonate hardness (permanent hardness). The salts causing permanent hardness are Ca and Mg sulphates or chlorides. Temporary hardness is
remedied by heating the water. The total water hardness is defined as the sum of the calcium and magnesium concentrations, expressed as equivalent calcium carbonate, according to:
mg equivalent CaCO3/l = 2.4797 ⋅ [Ca, mg/l] + 4.118 ⋅ [Mg, mg/l]
When referring to water hardness, it is essential to make it clear whether one is referring to temporary, permanent or total hardness.
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Table 3.
Table 3. Water hardness according to The Orange Book.
Hardness CaCO
Moderately hard 100-200 5.6-11 2-4
Hard 200-400 11-22 4-8
Very hard >400 >22 >8
Table 4.
Table 4. Conversion table for water hardness units (The Orange Book).
1 °dH = 17.9 mg CaCO3 / l
1 meq/l = 50.0 mg CaCO3 / l
1 °f = 10.0 mg CaCO3 / l
1 ° Clark = 14.3 mg CaCO3 / l
1 grain/US gal = 17.1 mg CaCO3 / l
Water quality can vary depending not only on the source, but also the time of day.
Some naturally soft water can cause corrosion due to its acidic pH. Mineral salts make water more basic (pH above 7) and corrosion increases, leading to a high risk of damage to pipelines, heat exchangers and boilers.
Table 5.
Table 5. Water quality recommendations for minimum corrosion (ppm or mg/l).
Hardness 4 – 7 °dH
Alkalinity > 0.6 meq/l
Chloride ions < 30 ppm Cl
-Chlorine < 0.2 ppm Cl2
pH 7.0 – 8.5
Sulphate ions < 100 ppm
Aluminium < 0.1 ppm
Iron < 0.2 ppm
Manganese < 0.05 ppm
KMnOconsumption 4 < 20
Aggressive carbon acid 0 ppm CO2
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3.3 CIP Theor y
Cleaning of processing equipment is a necessity for all food producers. CIP should be planned in such way that it intrudes as little as possible on production time. In
order to reduce CIP times it is important to consider the process as a whole.
Cleaning is not an isolated event, and product recovery preceding CIP can be performed in an intelligent way. In many UHT applications, production starts
immediately after cleaning, and thus the sterilisation of the process equipment must also be considered as part of the cleaning cycle.
The factors influencing the cleaning of processing plants are mechanical design, process design and cleaning process. The interrelationships between these is
illustrated in the figure below (Fig. 5). It can be seen how the process design is related to the cleaning process through the type and amount of fouling on the equipment surface. The type of detergent and concentration must be chosen so as to be appropriate for the type of fouling. The mechanical design then governs both the process design and the cleaning process. Designing and managing cleaning
processes is extremely important, but before all else – processing equipment must be designed for hygiene.
Mechanical design - materials, surface finish
- equipment design and installation - geometry
Process design - quantity and type of soiling
- age/moisture of soiling - composition of soiling
Cleaning process
- detergent type and concentration - temperature
- flow rate - water hardness
Fig. 5.
Fig. 5. The relations between the factors affecting the cleaning of a food processing plant.
Designing and managing cleaning processes is extremely important, but before all else – processing equipment must be designed for hygiene.
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The cleaning steps after pre-rinsing can be described in the following steps, which are illustrated schematically in Fig. 6.
1. The cleaning solution is transported to the fouling layer by the fluid flow (turbulence).
2. The detergent reacts with the surface of the fouling layer and the chemicals start to penetrate the layer. Proteinaceous fouling starts to swell.
3. The dissolved fouling layer is then transferred to the bulk solution. It is possible to prevent the soil from aggregating and re-attaching to the fouling
layer by using additives.
Fig. 6.
Fig. 6. Illustration of the cleaning mechanism.
(from Jeurnink and Brinkman) .
Rinsing water
Alkaline cleaning solution
Alkaline cleaning solution
Alkaline cleaning solution
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Fig. 7 illustrates Zinner’s circle consisting of the four main process parameters that can be controlled during CIP: the concentration of the cleaning agent, temperature, time and flow. Zinner’s circle is surrounded by a circle representing the production time. A longer production time usually results in a longer cleaning period. This in turn may result in a longer down time. Therefore, production time must be considered as well as the specific product being processed.
Fig. 7.
Fig. 7. The parameters that affect the cleaning result.
Time
Flow
Concentration
Temperature
It is important to know which of these four parameters is the most important. In order to reduce costs and energy consumption it is important to optimise the CIP sequence. The cost of the energy required to heat the CIP solutions, the energy needed to pump the CIP solutions and the price of the CIP solutions should thus be compared. In the broader perspective CIP must be included in the total production scenario.
In the following sections the different aspects of cleaning will be considered in more detail, starting with the chemistry of cleaning.
3.4 Detergent Chemistry
Many dairy producers today use lye (sodium hydroxide solution) and an acid as cleaning agents. This is sufficient for many applications and results in adequate
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chelating agents and acids, and it is important to choose the most suitable component or components based on:
• the kind of fouling to be removed
• the detergent
• the concentration, temperature and contact time
• the quality of the water
The function and effectiveness of various detergent compounds are summarised in Table 6, on a scale from 1 to 5, where 5 indicates excellent functionality.
Table 6.
Table 6. The effectiveness of various cleaning compounds (from the Handbook of Hygiene Control in the Food Industry, Ed. Lelieveld, H. L. M., Mostert, M. A. &
Holah, J., CRC Press, 2005) Cleaning
If the fouling consists of proteins an alkali is the best cleaning agent. The most frequently used alkali detergents are sodium hydroxide (NaOH), potassium hydroxide (KOH) and sodium carbonate (Na2CO3). Alkalis cause the proteins to swell, facilitating their removal. In order to reduce the cleaning time the pH of alkali solutions should be between 12 and 13 (Table 7).
Fat is also removed by alkali. At high temperatures fat is saponified, i.e. soap is formed. Soaps also lower the surface tension of solutions thus improving the emulsification of fat and the wetting effect.
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Sodium hydroxide (NaOH) has excellent detergent properties but corrodes
aluminium, galvanised metal and tin. Its rinsing and wetting properties are poor, and divalent metal ions (Ca2+ and Mg2+) are precipitated in alkaline solutions. If hard water is used for rinsing and/or preparation of the cleaning solutions, this will add to the mineral-based fouling of the equipment.
Table 7.
Table 7. pH as a function of concentration for two alkali detergents.
Concentration
Concentration 0.25 0.25 0.5 0.5 1.0 1.0 2.02.0
NaOH 12.5 12.8 13.0 13.3
Na2CO3 11.3 11.4 11.6 11.7
The use of NaOH with hard water will add to the mineral-based fouling of the processing equipment.
Acids
The hydrogen ion (H+) in acids reacts with the fouling causing it to break down and dissolve. The most frequently used inorganic acids are nitric acid (HNO3) and phosphoric acid (H3PO4). The former is most frequently used in Europe, while the
latter is the first choice in the USA. Nitric acid is a stronger acid, having a higher coefficient of dissociation than phosphoric acid, and is thus more efficient, but it is also more corrosive to stainless steel. Among the organic acids, acetic acid, lactic acid, citric acid and gluconic acid are the most frequently used. These acids are weaker than, and not as corrosive as, nitric acid but expensive compared with the above mentioned inorganic acids. Hydrochloric acid (HCl) must not be used due to its corrosive properties on stainless steel. However, chlorine detergents are
commonly used in membrane cleaning applications due to their high oxidising capability.
In many applications alkali CIP is followed by acid CIP. However, inorganic acids have strong dissolving effects on protein fouling and can thus be used before alkali CIP in order to facilitate cleaning with an alkali detergent. Due to the passivating effect of acids on stainless steel, acid detergents are used after alkali CIP. In the cleaning of UHT milk processing equipment, especially in high-temperature parts of the steriliser, minerals and the white deposit called milk stone are removed by acid cleaners.
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thus making cleaning more efficient. They also prevent re-deposition of fouling material on the surface through electrostatic interactions or steric hindrance.
As can be seen in Table 6, the function of these compounds in CIP detergents is to improve the physical dispersion, emulsification, foaming and wetting of the fouling layer. Surfactants may be ionic or non-ionic. The ionic surfactants are divided into three sub-classes: anionic (negatively charged in water), cationic (positively charged in water) and amphoteric (charge is pH dependent). Amphoteric surfactants are cationic under acidic conditions and anionic under alkaline conditions. The active components in these substances are tensides, which means they have a hydrophilic part (from the Greek for water-loving) and a hydrophobic part (from the Greek
water-rejecting). This enables them to act as a binder between the hydrophilic water and the hydrophobic fat.
Ionic surfactants
Anionic wetting agents can be classified into five groups: sulphated alcohols, sulphated hydrocarbons, aryl alkyl polyether sulphates, sulphonated amides and alkyl aryl sulphonates, which have good to excellent detergency. Both the removed foulant and the equipment surface become negatively charged, thus preventing re-deposition. However, in the presence of Ca2+ or Mg2+ ions the effect will be the opposite, and therefore sequestering agents should be added to these detergent solutions.
Cationic wetting agents consist of quaternary ammonium compounds. This group of wetting agents exhibits lower cleaning efficiency than anionic and non-ionic wetting agents, and is not used for the cleaning of food processing equipment.
Amphoteric wetting agents act by loosening and softening protein- and carbohydrate-rich soil, and are widely used in the food processing industry.
Non-ionic surfactants
These surfactants are best employed when removing soil consisting of oil, and are affected little by water hardness. The working principle is to sterically prevent the removed soil from returning to the equipment surface or aggregating in the bulk solution.
Sequestering Agents (chelating agents)
The function of sequestering agents is to bind to calcium and magnesium ions in order to soften water. The ions are bound so securely that they can no longer react to form so-called milk stone or calcium soaps. Common sequestering agents are orthophosphate, orthosilicate and phosphates. It is important to bear in mind that the waste water evacuated to the drain contains phosphates, which can be an
environmental problem.
Complex-forming agents form a sub-group of sequestering agents. The difference
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molecule in contrast to sequestering agents, which can bind to a number of metal ions. The most common complex-forming agents are EDTA (ethylene diamine tetra acetic acid), NTA (nitrilo-tri acetic acid), IDS (imido-disuccinic acid) and
gluconate.
Oxidation Agents
Formulated alkaline detergents produced by detergent manufacturers can contain oxidation agents to boost their cleaning effects. Examples of such substances are oxygen-releasing agents, active chlorine or active-chlorine carriers. These may be in a liquid form, such as sodium hypochlorite, hydrogen peroxide or potassium
hypochlorite, or in powder form, such as sodium perborate or sodium percarbonate.
They are added in a stabilised form, and active oxygen is cleaved off over a certain period of time. They create new sites for detergents to act.
Summary of the different detergents used in food Summary of the different detergents used in food equipment cleaning:
- Ionic (anionic, cationic and amphoteric) - Non-ionic
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Overview of Some Cleaners and Disinfectants
Below follows an overview of acid descalers and cleaners, neutral cleaners, alkaline cleaners and disinfectants.
Table 8.
Table 8. Acid descalers and cleaners (from the Handbook of Hygiene Control in the Food Industry).
Ingredient
Ingredient Substance Substance FunctionFunction
Inorganic acids Nitric acid Owing to its oxidising properties at high concentrations nitric acid cannot be used in complex formulations, e.g.
with surfactants. Its use is limited to descalers for removing inorganic residues such as water scale and milk stone from surfaces.
Phosphoric acid Sulphonic acids Sulphuric acid
These acids can be combined with surfactants, defoamers and other components in cleaning agents, and may be used in formulations designed to simultaneously remove inorganic and organic residues from food contact surfaces .
Organic acids Formic acid Citric acid Lactic acid Gluconic acid Sulphamic acid
See phosphoric acid
Inhibitors Phosphonic acids Protect materials against chemical attack.
Surfactants Non-ionic and anionic surfactants
Improve cleaning efficacy regarding organic soil; enhance scale-removing properties and are the choice for removing fat residues.
Defoamers Hydrophobic non-ionic substances
Suppress foam arising from formula components and/or removed soil.
Stabilisers Hydrotrophic substances
Stabilise liquid formulations at high and/or low temperatures.
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Table 9.
Table 9. Neutral cleaners (from the Handbook of Hygiene Control in the Food Industry).
Ingredient
Ingredient Substance Substance FunctionFunction Builders Phosphates
Phosphonates Citrates
Enhance soil-removal and suspension properties as well as the effects of surfactants.
Surfactants Non-ionic and anionic surfactants
Allow soil penetration and emulsification, and provide better surface wetting.
Defoamers Hydrophobic non-ionic substances
Suppress foam arising from formula components and/or removed soil.
Enzymes Proteases Improve protein removal at around neutral pH from sensitive surfaces.
Lipases Improve fat removal without using surfactants.
Specific enzymes Improve removal of recalcitrant substances from surfaces without using aggressive chemicals.
Stabilisers Hydrotrophic substances
Stabilise liquid formulations at high and/or low temperatures.
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Table 10.
Table 10. Alkaline cleaners (from the Handbook of Hygiene Control in the Food Industry).
Ingredient
Ingredient Substance Substance FunctionFunction Bases Sodium hydroxide
Potassium hydroxide
Solve, peptise, soften or decompose organic soil.
Chelates EDTA
NTA IDS Gluconate
Chelates not only reduce the negative effect of water hardness on cleaning efficacy and provide scale prevention, they can also remove fresh, thin layers of
inorganic deposits, attack inorganic soil and help in removing organic soil when combined with inorganic scale.
Builders Phosphates Phosphonates Citrates Silicates
By chemical nature most of the builders are chelates. They enhance soil-removal and suspension properties as well as the effects of surfactants.
Surfactants Non-ionic and anionic
Improve soil penetration and emulsification, as well as surface wetting.
Defoamers Hydrophobic non-ionic substances
Suppress foam arising from formula components and/or removed soil.
Sequestering agents
Polyphosphates Phosphonates
Prevent scaling, especially in rinsing stages.
Corrosion inhibitors
Silicates Protection of soft metals against chemical attack.
Oxidising cleaning boosters
Hypochlorites Assist in removal of recalcitrant and insoluble soil. They can break down larger molecules into smaller fractions by means of oxidation, or render soil soluble by introducing
Hypochlorites Assist in removal of recalcitrant and insoluble soil. They can break down larger molecules into smaller fractions by means of oxidation, or render soil soluble by introducing