Introduction

This note explains briefly what is meant by cleaning, why it is necessary in the fish industry, and what cleaning materials and equipment are available for different jobs. The main types of detergents and sterilizers are described, and some advice is given on the selection and use of cleaning agents for the removal of the many kinds of dirt that are typically encountered in fish processing.

In the food industry, cleaning is one of the commonest, and certainly one of the most important, operations. In the fish industry, cleaning in the past has almost always been done by scrubbing by hand and hosing with cold water; hot water has often not been available, and there is in any event probably some truth in the belief that fish slime is more difficult to remove with hot water than with cold. Cleaning agents are now available in bewildering variety, and many that are designed for a particular operation are of little value when used for any other purpose. For example, a cleaning agent that successfully removes dried fish slime from aluminium fish boxes may be completely ineffective in removing fat from plastic trays. This note is intended to help the processor to choose the correct cleaning agent for the job.

Mechanical cleaning equipment can be used to do some cleaning jobs more quickly and efficiently; the main types available and their use in the processing factory are also briefly discussed in this note.

What is cleaning?

Very simply cleaning means removal of dirt from soiled surfaces. Ideally, thorough cleaning should remove all bacteria with the dirt, but in practice this is difficult to achieve.

Cleaning, therefore, differs from sterilizing in that a clean surface is not necessarily sterile, that is free from bacteria. Sterilizing agents will render bacteria harmless and, in some instances, will have a residual effect which delays further growth of bacteria for a time, but obviously a sterilized surface does not necessarily look clean. Since sterilizing agents do not work very effectively in the presence of large amounts of dirt, it is therefore usual first to clean a dirty surface and then to sterilize it to destroy any remaining bacteria.

Why is cleaning necessary?

Cleaning is important for two main reasons, the prevention of food poisoning and the reduction of spoilage.

Bacteria that cause food poisoning are for the most part transferred to the fish, mainly from human beings, during processing, but occasionally some may be present on the fish when caught. Most food-poisoning bacteria do not grow in fish at temperatures below 10°C, and the few that do will not grow much below 4°C. Therefore when fish is kept chilled the risk of food poisoning of microbial origin is not very great. Nevertheless, food-poisoning bacteria can survive at chill temperatures, and food processed under unhygienic conditions can act as a carrier, even when refrigerated. The danger is greatest when higher temperatures are used during processing, for example during the manufacture of cooked or partly cooked products like fish fingers and fish cakes. The bacteria will grow rapidly, not only in the warm product but also in dirt on the equipment. Cleaning of equipment and premises is therefore essential to obviate the risk of contamination.

Unfrozen protein foodstuff’s deteriorate mainly because of the action of bacteria. Fresh food coming in contact with a dirty surface is quickly contaminated and spoilage is accelerated. In the fish industry, this can happen just as much in the trawler fishroom as in the processing factory or the retail shop. For example, stinker fish, which are fairly common, are produced when fish are in close contact with a dirty surface in the trawler fishroom, as a result of the growth of certain bacteria that flourish in the absence of air. Spoilage bacteria can grow at 0°C and even lower. Therefore it is important to keep down the numbers of bacteria in fishrooms and factories in order to reduce spoilage of the product.

What is the difference between detergents and sterilizers?

The prime function of a detergent is to assist in the removal of dirt from soiled surfaces, whereas that of a sterilizer is the killing of bacteria. There is always some overlap between the functions of detergents and sterilizers; for example most detergents have some effect on bacteria. For some light cleaning duties it is possible to remove dirt and kill bacteria in one operation by using specially prepared detergent-sterilizers, but for most factory cleaning jobs it is advisable to use a detergent first and a sterilizer afterwards.

What types of cleaning agent are available?

The term cleaning agent is used loosely to describe a whole range of liquids, powders and jellies that makes cleaning easier; the most important types for the fish industry are the detergents and sterilizers and, to a lesser extent, some of the jellies and abrasive powders.

Detergents

The detergents are the most important type of cleaning agent, and are usually mixed with water before use. They can be divided into three broad groups, dependent on the kind of solution they form, whether acidic, neutral or alkaline.

Acid detergents are generally based on phosphoric or sulphuric acid, and their use is rather limited. They are extremely effective in removing salts precipitated from water in hard water areas, and in cleaning aluminium where the acids readily remove the white scale that forms on the surface of the metal.

Neutral detergents comprise a wide range of materials that are mainly suitable for light duty cleaning. They are generally similar to household detergents, and their good wetting ability makes them ideal for the dispersal of grease and oil.

Alkaline detergents can vary in strength from those that are only a little stronger than the neutral types to ones that are strongly alkaline, consisting almost entirely of caustic soda, and requiring extreme care in use.

Sterilizers

Chlorine is the most common sterilizing agent. It is used in solid form either as a powder of ‘chloride of lime’, or in tablet form for making solutions containing a fixed concentration of chlorine, and in liquid form, like the domestic bleaches, containing up to 15 per cent chlorine. Chlorine-based sterilizers are cheap, but their main disadvantage is that the chlorine is easily freed and will fairly quickly disappear.

Quaternary ammonium compounds, QUATS, are more expensive than chlorine, but they have the advantage of possessing a residual action. They not only kill the bacteria they come in contact with, but remain active on the cleaned surface for a day or so, thus discouraging further bacterial growth. They are more stable than chlorine and under normal storage conditions show no loss of activity. In general the products are easy to handle and working solutions are odourless, noncorrosive and nonirritant.

Hydrogen peroxide is more expensive than chlorine but has the advantage of being odour free. It breaks down into oxygen and water and leaves no residual contamination. Its present use in the food industry is as a sterilizer for packages and machinery which come into constant and direct contact with foodstuffs, for example the sterilization of long life milk cartons or fermentation vessels. Although the uses of hydrogen peroxide in the fish industry may be rather limited, its action might be suitable for some specific operations.

Many sterilizers, particularly those based on phenols, have strong odours, which are likely to taint foodstuffs; they should therefore be used with caution.

Detergent-Sterilizers

A number of detergent-sterilizers are now marketed that will clean and sterilize in one operation; these are often based on quaternary ammonium or chlorine compounds, and are most suitable for light cleaning duties.

Abrasive cleaners

These consist of powders of varying degrees of hardness and particle size. Although of limited use, they can be of value in some operations, particularly where the cleaning is done by hand.

Jellies

A number of jellies are available of the kind used for cleaning the ovens of domestic cookers. These are often based on caustic soda, and have the advantage that they can be applied to vertical surfaces and will stick there long enough for the active constituent to soften the dirt.

Foam cleaners

See foam cleaning machines.

How do detergents work?

There are three main steps in any wet cleaning process:

1. wetting the soiled surface; when grease or oil is present, a detergent with good wetting properties makes this easier.

2. softening of the dirt and its removal from the surface in dissolved or dispersed form; mechanical action and the use of a hot detergent solution both help this process.

3. suspension of the dirt particles in solution for subsequent removal by rinsing with clean water.

A good detergent, therefore, should have good wetting ability, a good softening action, and be capable of holding the dirt removed in solution or suspension.

Choosing and using detergents and sterilizers

Buy detergent from a reputable manufacturer, and let him know the cleaning task it is wanted for. Additional information about the method of application can help the manufacturer to supply exactly what is wanted; for example a low-foaming detergent can be supplied for use in mechanical washing equipment, and water-softening constituents can be added to cleaning agents for use in areas where the water is hard.

It is always possible to buy detergents and sterilizers that appear to be cheaper than others on the market, but they may be cheap only because they contain less of the active constituent or are made of inferior materials. The cost of cleaning is not very high in relation to its importance, and the purchase of cheap cleaning materials may prove to be false economy.

Always follow the manufacturer’s instructions when using detergents or sterilizers. Twice the recommended concentration will not give results twice as good; indeed, the results may well be less satisfactory. Solution strengths of 1-2 per cent are usually adequate; excessively strong solutions may not only damage the surface being cleaned but may also result in injury to the operator.

Use hot detergent solutions wherever possible. As a rough guide, a solution at a temperature of 55-60°C is twice as effective as one at 5°C.

Wherever possible, soak dirty equipment in a tank of detergent solution; even the hardest dirt can be softened by a prolonged soak in the right solution.

What precautions are necessary when cleaning?

Following the introduction of the ‘Health and Safety at Work Act’, manufacturers and users became more conscious of the hazards that might arise from the use of certain chemical cleaning agents, and some companies now circulate customers with safety instructions on relevant products. Information on any risks associated with a product, handling instructions for it and first aid procedures in the event of an accident may be included.

Do not make mixtures of detergents or of detergents and sterilizers; they may neutralize one another, as when an acid product is mixed with an alkaline one, or may even produce dangerous fumes, as when a product containing hypochlorite is mixed with an acid.

When using strongly acid or alkaline cleaning agents the operator should wear suitable protective clothing of rubber or plastics. Most detergents and sterilizers are undesirable in food; all traces should be removed after cleaning by using plenty of clean rinsing water.

Take care that the detergent or sterilizer is safe on the surface being cleaned; the advice of the maker of the cleaning agent is the best guide here. For example, acid cleaners attack galvanized surfaces, while strong alkalis are harmful to aluminium. A more complete list of the precautions necessary with certain surface materials is given in the table below.

Precautions when cleaning surface materials

Surface material	Precautions to be taken
aluminium	Some alkalis and acids attack aluminium. If alkalis are used they should be of low alkalinity and incorporate silicates.
aluminium bronze	Safe with alkalis, but avoid use of acids.
brick, concrete	Rough, porous surfaces should be given a smooth, impervious finish to make them cleanable. Avoid strong acids.
bronze, gunmetal	Some alkalis attack these metals. Non-caustic detergents based on silicates, phosphates and carbonates are suitable.
galvanized metal	Acids and some alkalis attack zinc. Where the surface is in contact with brine over a long period, some reaction will take place, particularly where the galvanized coating is broken.
glass	Any detergent may be used.
mild steel	Any alkali may be used. Where acid solutions have to be used to remove hard water scale, they should be inhibited against corrosive action.
nickel alloys	Any alkali may be used.
plastics	Keep the cleaning temperature below the softening point of the material. Pay special attention to badly scratched containers, and discard cracked ones. Do not use abrasive cleaners, or solvents such as carbon tetrachloride or white spirit. When in doubt obtain the advice of the plastics manufacturer.
rubber	Strong alkalis may be used, particularly for removing fats and oils which may be harmful to rubber. Do not use solvents like carbon tetrachloride or white spirit.
stainless steel	Any alkali may be used. Acids should be chosen and used with care. Many abrasive cleaners are likely to scratch the surface.
tinned steel and tinned copper	Some alkalis corrode the coatings. Corrosion may be reduced by using low-alkai detergents, based on silicates, phosphates and carbonates, with the equivalent of at least 2-5 g/litre of anhydrous sodium sulphite in the detergent solution.
vitreous enamel	Caustic alkalis and many acids attack vitreous enamel. Detergents of low alkalinity and high silicate content are suitable.
wicker baskets	Wickerwork is extremely difficult to clean, and its use is not recommended. Avoid strong acids and alkalis.
wood	Wood is very porous and difficult to clean, and its use is not recommended. Avoid strong acids and alkalis.

Mechanical cleaning equipment

The main purpose of mechanical equipment is to make cleaning easier. Unfortunately there is no universal cleaning machine; operations like vacuum cleaning, scrubbing and pressure washing each require different machines.

Vacuum cleaners

There is great variety in size, capacity and design. Although some pick up only dry materials, most industrial machines are suitable for both wet and dry dirt. Vacuum cleaners normally operate on mains electricity, but a few models work from batteries or petrol engines. Some petrol-driven types are fitted with a seat and steering wheel.

Vacuum cleaners are of limited use in the fish industry, but some smaller hand types are useful for special cleaning jobs such as removing dust and dirt from roof trusses and girders.

Scrubbers and polishers

These are normally designed for use only on floors, since most models depend on the weight of the machine to keep a rotating brush, or brushes, in contact with the surface to be cleaned. They are most useful where large areas of floor require scrubbing but, for good results, a smooth and level floor is essential. Floors that are congested with machinery and equipment are obviously less readily cleaned mechanically than large uncluttered floor areas.

Steam cleaners

These machines are extremely useful for heavy duty cleaning. Some designs have built-in steam generators; others require a source of steam in the factory. These machines can be dangerous in the hands of untrained operators.

High pressure cold water cleaners

In these machines the pressure of cold water from the mains is boosted by a pump; the water is delivered at pressures ranging from about 1000 to 5000 kN/m², usually as a fine jet through a lance head, at rates from about 8 litres a minute upwards.

They are particularly suitable for cleaning fishworking machinery. The high-pressure jet can be directed into those parts of a machine where dirt accumulates, and is effective in areas normally inaccessible for hand cleaning. The low volume of water used can show considerable saving over conventional hoses.

Box washing machines

Where large numbers of similar containers require cleaning, washing machines are both effective and labour saving. They generally work on a sequence of rinsing and washing, and detergents suitable for the operation are obtainable. At least one step in the sequence involves the use of hot water. Such machines are most suitable for the cleaning of market containers in a box pool, or in large processing factories.

Foam cleaning machines

The technique of foam cleaning allows a detergent to be delivered by machine as a foam. It has the advantage of prolonging the time of contact between the detergent and the dirt and is equally suitable for horizontal, vertical or inverted surfaces. It is easy to see where the foam has not been applied and is suitable for cleaning parts of machinery not accessible by hand. Various types of detergent with the inclusion of a foaming agent are available. This technique is becoming increasingly used by the industry.

Wherever water or steam cleaners are used, all electrical equipment should be totally enclosed and waterproof.

Are there other advantages in cleaning?

It has already been stressed that where food is concerned clean equipment and a clean factory mean less bacterial contamination, which leads to a safer and better quality product that keeps longer. This is particularly true where a very perishable commodity like fish is concerned, but there are other advantages in cleaning.

The sales appeal of a product from a factory where housekeeping is obviously good is likely to be much greater than from a dirty-looking factory, and sales appeal means better business.

Staff morale is also very important, and clean working conditions make for a contented staff who take a pride in their surroundings. Where management are seen to be concerned about cleanliness, staff are also likely to take more care.

The fish industry has in the past accepted that a certain amount of dirt and discomfort was part and parcel of fish processing, but there is no reason whatever why today’s fishworking premises should not be clean and wholesome; it must not be forgotten that the fish industry is a food industry.

What can be done in the future?

The most important aim should be better design of factories and processing machinery. Most new factories are built on modern lines with tiled walls and smooth floors which are easily cleaned, and with vastly improved staff hygiene facilities. Unfortunately much of the equipment and machinery is still not easy to clean. Wooden boxes are becoming less common as they are replaced by plastics and aluminium and, at sea, the wooden fishroom is gradually disappearing; even the filleter’s block is sometimes of a synthetic easily cleaned material rather than wood. But the pace of change is often slow. Smoking kilns present cleaning problems; the mechanical kiln, although easier to clean than the traditional chimney kiln, still requires frequent and thorough attention. One possibility here is a modified design where parts could be removed for soaking or steam cleaning.

The vary nature of the job done by filleting, splitting and skinning machines makes them complex in design and thus awkward to clean, but modern design techniques, together with improved cleaning facilities, should make the processing line of the future much easier to tackle. Certainly, when buying new equipment, the processor should bear in mind the ease with which it can be cleaned.

Hygiene has improved tremendously in the fish industry over the past decade, and there is every reason to expect that, as fish becomes more obviously an integral part of the food industry, regulations will become more stringent, and processors will be more hygiene-conscious. The process of cleaning will be made easier by the continuous improvement in cleaning agents and by the development of new techniques.

Other sources of advice

Some information on the design of fishworking premises is given in Torry Advisory Note 10. The following table has been taken from BS4259:1968, ‘Recommendations on Cleaning in the Fish Industry’; this is reproduced by permission of the British Standards Institution, 2 Park Street, London W1Y 4AA, from whom copies of the complete standard may be obtained.

Recommended types of detergent for removal of specific soils from different surfaces

Surface	Soil	Wet fish slime, blood, gut contents, scales, skin and oil	Air dried fish residues	Cooked and hardened fish residues	Tars	Starches and frying oil	Processing material, tomato puree and dyes, etc.	Common salt	Miscellaneous soils such as marine mud and fuel oil
Aluminium		Water or acidic. Scrub with neutral or mildly alkaline where necessary	Mildly alkaline or acidic. Strongly alkaline for mechanical cleaning plants	Mildly alkaline or acidic	Caustic alkaline detergents are the only really effective substances for removing tars. Steam lances and strongly alkaline solutions may be used with some success.	Neutral, mildly alkaline or acidic. Strongly alkaline may be necessary for charred residues	Neutral, mildly alkaline or acidic. Strongly alkaline may be necessary for hardened soil	No detergent is particularly effective in the presence of a high concentration of salt. Salt should therefore be washed away before application of detergent. Neutral or mildly alkaline based on polyphosphate are then adequate.	Neutral, mildly alkaline or acidic. In some instances water alone may be adequate
Stainless steel		Water. Scrub with neutral or mildly alkaline where necessary	Mildly alkaline. Strongly alkaline for use in soaking troughs	Mildly alkaline. Strongly alkaline for use in soaking troughs		Neutral or mildly alkaline. Strongly alkaline may be necessary for charred residues	Neutral or mildly alkaline. Strongly alkaline may be necessary for hardened soil		Neutral or mildly alkaline. In some instances water alone may be adequate
Mild steel		As stainless steel	As stainless steel	As stainless steel		As stainless steel	As stainless steel		As stainless steel
Galvanized iron		As stainless steel	As stainless steel	As stainless steel		As stainless steel	As stainless steel		As stainless steel
Glass		As stainless steel	As stainless steel	As stainless steel		As stainless steel	As stainless steel		As stainless steel
Vitreous enamel		As stainless steel	As above (care with strongly alkaline)	As above (care with strongly alkaline)		As above (care with strongly alkaline)	As above (care with strongly alkaline)		As stainless steel
Plastics		As stainless steel	As stainless steel	As stainless steel		As stainless steel	As stainless steel		As stainless steel
Bronze Gun metal		As stainless steel	As above (strongly alkaline should be based on silicate, phosphate or carbonate)	As above (strongly alkaline should be based on silicate, phosphate or carbonate)		As above (strongly alkaline should be based on silicate, phosphate or carbonate)	As above (strongly alkaline should be based on silicate, phosphate or carbonate)		As stainless steel
Rubber		As stainless steel	As stainless steel	As stainless steel		As stainless steel	As stainless steel		As stainless steel
Wood		As stainless steel	As stainless steel	As stainless steel		As stainless steel	As stainless steel		As stainless steel
Wicker		As stainless steel	As stainless steel	As stainless steel		As stainless steel	As stainless steel		As stainless steel
Concrete brick, etc.		Water or acidic. Scrub with neutral or mildly alkaline where necessary	Acidic, mildly alkaline or strongly alkaline	Acidic, mildly alkaline or strongly alkaline		As stainless steel	As stainless steel		As stainless steel
Tinned steel and tinned copper		Water. Scrub with neutral or mildly alkaline where necessary	Mildly alkaline. Strongly alkaline based on silicate, phosphate or carbonate with sodium sulphite for use in soaking troughs	Mildly alkaline. Strongly alkaline based on silicate, phosphate or carbonate with sodium sulphite for use in soaking troughs		Neutral or mildly alkaline. Strongly alkaline based on carbonate, phosphate or silicate with sodium sulphite may be necessary for charred residues	Neutral or mildly alkaline. Strongly alkaline based on carbonate, phosphate or silicate with sodium sulphite may be necessary for charred residues		As stainless steel