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4.1 Types of soil

Before planning a cleaning programme one of the essentials is to know which types of soil are present in the area to be cleaned. Fat and protein are the most common types of soil in the meat industry. Characteristics of soil types are shown in Table 1.

Table 1

Soil characteristics

Component on surface Solubility characteristics Ease of removal and changes induced by heating soiled surfaces
Carbohydrate &ldquosugars&rdquo Water soluble Easy to remove, but more difficult to clean when caramelized
Fat Water insoluble
Alkali soluble
Difficult to remove
Protein * Water insoluble Alkali soluble Slight acid soluble Very difficult to remove and even more difficult when denaturated
Salts Water soluble Acid soluble Some salts are easy and some difficult to remove. If interaction occurs with other constituents these substances will be more difficult to remove
Polyvalent Water insoluble Acid soluble  

* See Table 2

4.1.1 Carbohydrates

Carbohydrates are not a usual type of soil in slaughterhouses, but may occur in meat processing plants (sausage production). Normally carbohydrates are easily removed with water. Detergents may increase the cleaning effects.

4.1.2 Fat

Fat can be removed to give an optically clean surface using water at a temperature of more than 50°C for pork fat and more than 55°C for beef fat. The efficiency can be improved by adding a detergent.

4.1.3 Protein

Removal of protein depends on the treatment the proteinaceous soil has been exposed to before the cleaning procedure. Protein will coagulate and be difficult to remove when exposed to hot water (more than 60°C) for a long time. A short exposure to hot water may not cause coagulation of protein. The surfaces soiled with protein should be kept wet until the cleaning procedure can start.

Table 2. Characteristics of proteinaceous soil types

Type of soil Cleaning technique Cleanliness achieved
not dried on surface Remove with water (manually or mechanically) Sensorily clean
dried on surface Soften with water and detergent and remove with mechanical force (pressure, manually) Adhesive layer often left behind
dried on and/or Soften with water and detergent Crusts, coatings
burnt in surface and remove with mechanical force (pressure, manually) and adhesive layer often left behind

4.1.4 Mixed types of soil

Often the soil type is a mixture of protein and fat. The fat may be removed when using hot water, but hot water may coagulate the protein. The water temperature must therefore not exceed 60°C. A reasonably good effect will be obtained using a detergent and water with a temperature between 45–55°C or even cold water with a suitable detergent. If cold water is used, the dosage of detergent must be larger for most detergents than when used with hot water.

Besides protein and fat, smears are often blended with mineral salts from water, especially calcium and magnesium and to a lesser extent iron.

Mineral salts are best removed with acids or acidic detergents. The acidic detergents have a reduced cleaning effect and have a corrosive effect against some types of surfaces. They must therefore be used carefully with regular frequency when the water has a large content of mineral salts.

Another type of smear may be described as “a waxy mass”. This kind of smear consists of an undefined mixture of fat, protein, mineral salts and residues of detergents. This type of smear will often be found where the cleaning procedure has been irregular, for example wrong working routines, wrong dosage of detergents or wrong detergents. This waxy mass will not be alkali or acid-soluble. The only way to remove this smear type is by using mechanical force. Often scrubbing by hand and scrubbing brushes or scrubbing tools (nylon pads etc.) will be the only way to remove this kind of deposit.

It is important to be aware of the difference between deposits of mineral salts and those of a waxy mass.

4.2 Detergents

Any substance which, either alone or in a mixture, substitutes physicochemical energy for some of the mechanical energy required for removing dirt can be classified as a detergent. Detergents influence the amount of energy or work that must be applied to a cleaning system.

Increasing one kind of energy can compensate for shortage of other kinds of energy. For example manual power will often be used as compensation for shortage of detergents or hot water.

Water alone is not a very efficient cleaning agent because of its high surface tension. Adding of detergent to water facilitates the contact between water and surface soil because detergents enable water to penetrate soil by lowering the surface tension. If water is used as the sole cleaning agent a considerable amount of mechanical energy is required.

A good detergent should have the following properties. It should be:

  1. able to soften water completely

  2. completely soluble in water

  3. non-corrosive to surfaces (metals and buildings)

  4. non-toxic and biodegradable

  5. economical in use

It should have:

  1. good wetting or penetrating ability

  2. emulsifying ability on fat

  3. dissolving ability on food solids

  4. deflocculating, dispersing or suspending ability

  5. good rinsing properties

  6. scale and rust removing properties

No detergent or cleaning compound can be called an all-purpose detergent. None of the alkalis, acids or surface-active agents fulfil the requirements of a good detergent when used alone.

Certain mixtures of these chemicals will combine several properties in one product which will be effective for a particular cleaning operation.

The types of chemical compounds used to achieve the functions of cleaning described above are:

  1. Alkalis and alkaline salts

  2. Surface active agents

  3. Sequestering agents

  4. Inhibitors (anti-corrosive agents)

  5. Acids

  6. Fillers

4.2.1 Alkalis and alkaline salts

Sodium hydroxide (caustic soda) is a common ingredient in detergents for the food industry. It is a powerful detergent and is used to suspend protein and to convert fats to soap, and it is cheap. However it corrodes aluminium and galvanized iron, strips paints, and presents a hazard to personnel using it. It is available in most geographical areas.

Sodium carbonate (soda ash) is not as efficient a cleaning agent as sodium hydroxide, but it is a cheap source of alkalinity and is used as a detergent filler. It is corrosive to aluminium and galvanized iron, and forms a scale of calcium carbonate and other insoluble salts in hard water. It is available in all geographical areas.

Sodium metasilicate is an effective detergent for many purposes. It is an excellent emulsifying and suspending agent and has reasonable wetting and rinsing properties. It possesses anticorrosive properties but will deposit on stainless steel. It may also deposit with soil as a grey-white coating if used in water above 70°C.

4.2.2 Surface active agent

This kind of agent is employed in a variety of cleaning applications such as wetting, emulsifying and penetrating agents. The main function is to lower the surface tension.

Anionic surface active agents dissociate in solution to give a negatively charged surface active ion and a small inactive action. Most commercial surface active detergents belong to this group. Several agents of this type are available but the alkyl aryl sulphonates are the most common surface active agents.

Nonionic surface active agents do not yield ions in aqueous solutions and are compatible with either cationic or anionic materials. Mixtures of anionic and nonionic surface active agents in a ration of 2:1 in detergent formulations appear to be suitable for the food industry. It is not common to use nonionic surface active agents alone because they are more expensive than anionic surface active agents.

Cationic surface active agents dissociate in a solution to yield a positively charged surface active ion and a small inactive anion.

Their performance as detergents is only fair but they exhibit anti-microbial activity and can be used as disinfectants or in mixed detergent-disinfecting agent mixtures.

4.2.3 Sequestering agents

Sequestering agents are used to bind calcium and magnesium and prevent the formation of insoluble calcium and magnesium salts by the interaction of hard water or dirt with the detergent. The amount of sequestering agents needed depends on the hardness of the water, the composition of the detergent and the composition of the soil.

Different chemicals have the ability to be effective as sequestering agents. Common in use are EDTA (ethylenediamintetraacetate), NTA (nitrilotriacetic acid) and different phosphates.

Sodium tripolyphosphate, sodium tetraphosphate and sodium hexametaphosphate are phosphates mainly used in detergent formulations. In addition to removing the minerals causing water hardness, they have varying functions in emulsification, protein peptization and dispersion.

4.2.4 Inhibitors

Inhibitors neutralize the corrosive effect of some chemicals. The use of inhibitors is dependent on the composition of the detergent and the materials which will be cleaned.

Silicates may be used as anti-corrosive agents in alkaline detergents but will deposit on stainless steel and it is therefore important to know on which materials they will be used.

4.2.5 Acids

Acids are used to remove mineral deposits but they have reduced cleaning effects and are corrosive to different materials (especially galvanized iron and aluminium). The inorganic acids are principally more corrosive than the organic acids.

Acidic detergents are mixtures of one or more acids and surface active agents, and may be inhibitors too. These detergents have a reasonable cleaning effect. If the mineral deposits are removed by acids alone, the cleaning effect will be minimal and it may be necessary to remove fat and protein with an alkaline detergent before removing the deposits with acid.

The inorganic acids used are phosphoric acid, nitric acid, sulphuric acid and hydrochloric acid.

The organic acids used are gluconic acid, tartaric acid, citric acid, acetic acid and sulphamic acid.

4.2.6 Fillers

The purpose of fillers is to make detergents fluid or to turn fluidized detergents into powders. As fillers sodium chloride or sodium sulphate may be used. The last mentioned is cheap and has some cleaning effect, especially when mixed with chemicals with a better cleaning effect.

4.3 Examples of formulas for detergents

4.3.1 Alkaline detergents

  1. Strong alkaline detergent

    69% Sodium carbonate
    25% Sodium hydroxide
    6% Nonylphenol (surface active agent)

  2. Alkaline detergent

    59% Sodium carbonate
    35% Sodium triphosphate
    6% Nonylphenol (surface active agent)

  3. Alkaline detergent

    37% Sodium carbonate
    37% Sodium metasilicate (anti-corrosive effect when used on aluminium and galvanized iron) 20% Sodium tripolyphosphate
    6% Nonylphenol (surface active agent)

4.3.2 Acidic detergents

  1. Strong acidic detergent

    Phosphoric acid (50%)
    Sulphuric acid
    Thio-urea (anticorrosive agent)
    Nonylphenol (surface active agent)

  2. E. Acidic detergent

    Sulphamic acid
    Sodium sulphate
    Thio-urea (anticorrosive agent)
    Nonylphenol (surface active agent)

4.4 Choice of detergent

The type of metal and building materials (including paint) used in the area to be cleaned severely limits the choice of detergent. Aluminium and galvanized iron, which are frequently used, corrode rapidly in strongly alkaline or acid detergents. Although detergents can be formulated so that they do not corrode these metals, their effectiveness as cleaning agents is usually reduced.

Where it is suitable to clean by hand only mild detergents should be used. Automatic cleaning techniques enable the use of stronger detergents.

Depending on the actual conditions (i.e. detergent supply, economics, etc.) it is recommended to use a single cleaning chemical (e.g. sodium carbonate) if the alternative is no cleaning agent. In most instances the choice of a suitable detergent must be a compromise between the efficiency of the detergent, the need to protect metals, building materials and personnel, the cleaning methods, the frequency of cleaning and economics.

The cost of the detergent is not a guide to its efficiency. Only actual tests with a particular detergent during a specific cleaning operation will give some indication of its efficiency.

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