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Edible oils are extracted from a wide range of raw materials. Common types include coconut, oil palm, sunflower, groundnut and mustard seeds. The process of oil extraction is often referred to as oil milling and a range of technical options are used from very simple hot water extraction, manual screw presses to large scale solvent extraction. The term oil milling is however generally connected with the use of mechanical oil expellers, a typical example being shown in Fig. 15 (see Figure 15: Small continuous oil expeller).
Cooking oils are considered as low risk products. Their very low moisture content and the heat applied during processing means that microbiological hazards are minimized. A major risk to consumers however can arise from toxins that are produced by moulds that attack oilseeds in store. These are known as mycotoxins and are produced by microorganisms to which the Aspergillus flavus species belongs. Aflatoxin producing moulds can grow on raw material that has been inadequately dried or has absorbed moisture in storage. It is particularly associated with groundnuts although it has been detected in other products. Although chemical tests for aflatoxins are commonly used, the equipment and skills required put them beyond the capacity of small rural oil processors. Fortunately the presence of aflatoxin producing moulds is usually evident due to the presence of stained, darkened and discoloured seeds.
The first step in developing a quality assurance system when producing edible oils, is to set a system in place that ensures that incoming raw material has been properly dried and shows no sign of mould growth thus minimising a consumer hazard. It should be noted that aflatoxins, if present, tend to be concentrated in the oil-cake that remains after oil extraction rather than in the oil. Samples from a selected number of bags of seed should be taken using a thief sampler (Fig. 34) and wherever possible, examined prior to purchase of seed. In some cases it may be possible to purchase raw materials from a large supplier or para-statal body that has efficient drying and storage systems. Oilseed stocks held by the miller should be stored in a well-ventilated store, off the ground and protected from birds, insects and rodents.
Some oilseeds, for example sunflower, groundnuts and coconuts, require de-husking prior to oil extraction. Others, such as mustard seed, require no pre-treatment.
Prior to oil extraction, larger oilseeds are milled and then in most cases heated in a scorcher or cooker. This treatment breaks oil-bearing cells and assists in the release of oil as the material passes through the expeller. In the expeller, oil is pressed out and flows from the cage and the fibrous residue or cake exits from the expeller 'throat'.
This crude oil contains some moisture, natural flavourings and colours, dirt, vitamins and natural gums. It is not acceptable for direct use and has to be refined, or cleaned, prior to sale. The extent of refining required, depends upon the type of oil being extracted and the intended market. From the quality point of view it should not be assumed that customers prefer the typical bland, crystal clear oil of the type that is manufactured by very large oil mills. In fact the reverse may be true; for example, many consumers prefer a coconut oil that tastes of coconut and has a slightly rancid flavour.
As part of the total quality assurance system, the miller should thus investigate the consumers' preferred quality requirements and carry out refining to meet these demands. Most small rural millers limit refining to clearing and filtering, or sell the crude oil to a larger processor for more sophisticated refining.
In larger companies, a wide range of refining methods may be applied such as filtering, neutralisation, winterising, bleaching, deodourisation and de-gumming. Those used depend on the type of oil to be processed and the market specification.
Typically in a small mill the crude oil is allowed to stand in large, closed drums for a few days, during which time the majority of suspended matter settles. The cleared oil is then carefully removed by syphoning or decanting. Final clarification is achieved by passing the oil through a fine filter cloth (Figure 16: A simple oil filter).
The main quality tests that need to be applied to oils are for an unpleasant flavour caused by rancidity and the presence of free fatty acids. The rate of rancidity development is speeded up by light, heat, moisture in the oil, moulds, enzymes and some types of metals, particularly copper and iron. For a long shelf life, oils should be heated to remove any moisture and destroy enzymes and micro-organisms. It should then be stored in sealed airtight tins or bottles, protected from the light and in a cool place. Although chemical tests are available, the equipment is expensive and an experienced miller can simply control the process by the taste and odour of the oil. The presence of higher than normal levels of rancidity and free fatty acids can often be traced to stale raw materials. Millers should therefore check for such faults in their stocks by taste and smell.
2.2 Baked products
Bread production using the bulk fermentation method is used as an example of a common baked product in the process flow diagram (Figure 17: Bakery process flow diagram). The accompanying table (Table 10) describes the process steps involved and the main process control points. These are then analysed and discussed in relation to developing a quality assurance system in a small bakery in the following chapter.
Table 6: Process flow chart for the production of bread
Baking is a long established traditional process and the basic principle of cooking by dry heat in an oven has changed little with time. Traditionally the dough was heated over open fires and hot stones. This progressed to ovens of various shapes and sizes and simple static ovens have been designed and used successfully at village level in many countries (Figure 18: A simple beehive oven). Heat may be derived from a variety of energy sources, ranging from burning coconut husks or camel dung, to heating by electricity or gas.
Baking involves heating a dough or batter in an oven to produce the shape and colour of the crust and to set the internal structure. The baker can control and modify the process to produce a wide variety of products such as buns, biscuits and cakes with different shapes, colours, flavours and sizes (Figure 19: Examples of baked products).
Baked products may be unleavened, or leavened (raised) by yeast, by chemicals, by air or water vapour. The action of the yeast in the fermentation stage may be replaced by chemicals or by mechanical mixing for some products.
Customers expect bread to have an adequate volume, an attractive shape and colour, a crumb that is finely and evenly distributed and is soft enough to chew but firm enough to slice. These quality characteristics can only be achieved through a combination of careful selection of ingredients and control of the manufacturing process. These customer-needs must be documented and agreed, as this will enable the producer to select the ingredients and define the control points within the process. Control of the process must occur during all stages, from selection of the ingredients and packaging materials through to delivery of the finished product and labelling information.
Raw materials and their testing
In contrast to fruits, herbs and spices, where raw materials may come from many small scale growers the ingredients used in breadmaking such as flour, fats, salt and yeast, are normally supplied by large scale producers. Many small bakers are therefore faced with problems of an assured supply when their custom may be of little importance to the supplier. Small companies may be better advised to co-operate with other small bakers and as a group, purchase and store certain raw materials in bulk. On receiving the raw materials small scale bakers may be faced with problems of controlling their quality with only limited facilities for testing. The correct choice and specification of the main raw materials for baked products is essential to ensure good quality products.
Flour provides the major functional ingredients (starch and protein) which give strength and structure to baked products. Starch has a number of roles in baked products: in bread it produces sugars for yeasts to ferment and gives a framework for the gluten to bond to.
When starch is gelatinised by heat during baking it provides a rigid structure to the finished product. The characteristics of the flour can be controlled by the blend of wheat grains used in flour manufacture or by variations in milling techniques (see also Chapter 2.1).
Small producers do not normally have facilities for flour analysis and must rely on the information supplied by the miller. However useful information can be obtained from simple tests which are described in detail in Chapter 3 (flour infestation, gluten measurement, sieving tests, filth test, water absorption measurement and moisture content).
It is important that the baker buys the correct type of flour. For breadmaking it should be 'strong' (that is, made from hard wheats having a medium protein content), have high protein and water absorption levels and a good colour. For other products 'weak' soft wheat flours are normally used. These are lower in gluten and are therefore weaker (the dough extends more) than hard wheats (Figure 20: Assessing gluten quality, weak flour on left, strong flour on right).
Gluten is the protein which gives the unique elastic properties to bread dough and some other baked products. It can be measured by simply washing out the starch from a small ball of dough under running water and the remaining gluten proteins will be left. The quantity can be measured by removing excess water and weighing. The quality can be assessed by pulling the gluten piece apart and noting how much it stretches and its breaking point (Chapter 3: gluten measurement). This is a quick test which with experience, provides much useful information to the baker.
Water absorption should be consistent to allow production of a uniform finished product. Bakers should know the capability of the flour to absorb water and adjust the process accordingly - too much absorbed water can give a sticky dough and too little can produce a tough, poorly risen product.
A good quality bread flour absorbs water to 60-65% of the flour weight whereas a biscuit flour may hold 55 %. A simple test is to measure how much water by weight can be absorbed by 100g flour to make an extensible dough (Chapter 3: water absorption measurement).
Starch gelatinisation is the swelling of starch due to heat and moisture and this begins when the temperature rises above 56°C for wheat starch. With further heating there is a marked increase in viscosity. At very high temperatures the starch granules burst and the viscosity falls.
The baker may control the nature of the starch in different baked products. For example the starch can be totally broken down, as in wafer biscuits, there can be no breakdown as in shortbread biscuits, or there can be a range of swollen and dispersed starches as in bread. This range of products is achieved by adding ingredients which prevent starch breakdown, by preventing the starch from absorbing water or by adding insufficient water for the starch to swell.
Enzymes present in the flour can attack the starch to produce the necessary sugars for fermentation. However, if the grain has germinated before harvest, an excess of these enzymes can cause problems to the baker by producing too much sugar and giving a sticky dough. A common test that is used for flour quality is based on gelatinisation and is named the 'falling number' test. The viscosity of gelatinised flour is assessed by counting the number of seconds that a steel plunger takes to drop through a standard gelatinised solution. This number is used to decide whether the enzyme activity is in excess or insufficient and allows the baker to adjust the recipe. A simple modification of the test is described in Chapter 3 (starch gelatinisation).
Incoming flour should have a moisture content of not more than 14% to reduce the risk that moulds, insect infestation and rancidity do not develop during storage (see also Chapter 2.1). Samples should be taken from each batch and tested for moisture using accurate scales and an oven (Chapter 3: moisture content measurement, grains)
Yeast acts on natural sugars in the flour to produce carbon dioxide gas which raises the dough. The level of yeast used is normally 1% of flour weight for a 2 to 3 hour fermentation process. The activity of yeast is crucial to a successful fermentation. The baker must ensure that the yeast is active (alive) and is stored in a cool dry place.
A simple method to test yeast activity involves placing a standard ball of dough in water and timing how long it takes to float to the surface. This is related to the yeast activity by assessing gas production or the power of the yeast to inflate the dough (Chapter 3: yeast activity).
Salt gives flavour, strengthens the gluten, controls the action of yeast and therefore controls the loaf volume. Traditionally salt is added between 1.8% and 2.2% of flour weight and if the salt is above this level the taste of the bread is adversely affected. Salt generally requires little testing.
Fat is an optional ingredient in bread but can improve the appearance of the crumb and contribute to product flavour and the ability of the dough to retain gas. Fat also improves the keeping quality, softness, moistness and contributes to the texture of the bread. The melting temperature of the fat must be above the temperature of the dough otherwise a sticky dough will be produced.
The main problem encountered with fat is rancidity which can best be detected by smell and taste. Any rancid fat should be rejected. The dough temperature and the melting point of the fat can each be checked using a thermometer.
Sugars are normally present in bread flour at a level of 1-2% and these are acted upon by yeast during the early stages of fermentation. Later the action of enzymes in the flour releases further sugar for gas production. Extra sugar may be added to increase gas production, to improve the crust colour and to sweeten the bread. The main quality problem with sugar is the presence of dirt which can be checked by dissolving a quantity of the sugar in hot water and allowing any dirt to settle.
Storage of ingredients
Flour is normally delivered and stored in hessian or jute sacks, although woven polypropylene is becoming more commonly used. The sack material provides some protection against dust, insects and birds but offers little protection against rodents or a humid atmosphere. It is therefore important that the conditions in the store-room are suitable for the correct storage of flour.
The main reasons for spoilage of flour are an increase in its moisture content which can lead to mould growth, development of rancidity over a period of time and attack by insects, birds and rodents. It is a common sight to see sacks piled on the floor of a store-room or even in a corner of the bakery. Under these conditions the flour can absorb moisture from the floor or from a humid environment and it is easily attacked by pests.
Details of correct construction and use of food processing buildings are described in Chapter 1.3 and in particular relation to bakery store-rooms the following points should be emphasised:
Figure 21: A well managed flour store
Before use, the flour should be checked by workers to ensure that it is free of insects and moulds and that it does not have a rancid smell. Simple tests for insects are described in Chapter 3 (flour infestation, sieving tests and filth test).
Sugar and salt are also delivered and stored in sacks and require the same storage conditions as flour. In particular these ingredients can pick up moisture from the atmosphere and the store-room temperature and humidity should not be allowed to fluctuate.
Fats and oils are usually delivered and stored in tins which protect the oil from air and the development of rancidity. Provided the tins are kept sealed until they are used and the store is reasonably cool, there should be few storage problems. If the oil is stored in any other containers rancidity can quickly develop. As heat accelerates the development of rancidity cool storage areas should be used. Solid shortenings (fats) are often supplied in a simple paper or plastic wrapping which offers little protection against rodents, insects or birds. In addition, the fat can rapidly develop rancidity if it is exposed to heat or sunlight. As expensive ingredients fats and shortenings should therefore be very carefully stored. If available a refrigerator is ideal. They should also be used as quickly as possible and strict stock rotation should be enforced.
Good quality water is required to form the dough and wash equipment. Details of how to ensure that potable water is available are described in Chapter 1.
Manufacture of bread
The manufacture of bread has four main stages: the first involves mixing the ingredients to form a dough, at the same time entrapping air. In the second stage the gluten structure develops and the yeast acts on damaged starch granules to release sugars. After dividing and moulding, the proving stage allows gas produced by the yeast action to inflate and expand the dough. Finally the inflated structure is baked and set in the oven.
In this chapter the traditional or 'bulk fermentation' method of bread production is described but mechanical mixing, chemical additives, or a combination of both may be used to shorten the dough development time and produce a more consistent product. Details of such chemical and mechanical methods are given in references in Appendix 1.
The baker can determine the type and quality of the finished product by careful attention to the main process control points which have been summarised in Table 6 at the beginning of this section. They involve accurate weighing, temperature and humidity control, timing and handling procedures.
This systematic approach to quality control and quality assurance requires the baker to understand and modify the recipe or the process to suit natural variations in raw material quality.
Care and maintenance of weighing scales, thermometers and timers are essential for consistent and cost effective production. Quality checks are useful indicators of baking performance and play a significant role in assessing the quality of raw materials. Baking tests are important to modify recipes or processes or when evaluating a new supply of important raw materials. They are normally used to compare new raw materials (for example, fat, sugar and yeast) with a satisfactory flour that provides a good quality product. It is important that the recipe formulation and process control should be carefully standardised to achieve meaningful results from test baking. The products from test bakes can be assessed using a score sheet (see Appendix 2).
Packaging, storage and distribution of finished products
Baked products are packaged to protect them from contamination or deterioration due to moisture loss or pick-up and to enhance their presentation. Plastic film may be used but often baked goods can be wrapped in paper as they are expected to have only a short shelf life. Protection against crushing or dropping can be achieved by packing in cardboard boxes or loading onto trays for transport.
Most baked goods have a dry outer crust which inhibits contamination by microorganisms. However products such as cakes with cream fillings or pies that contain meat, fish or vegetables are a potential hazard to consumers if not packaged, stored and handled correctly. The danger zone for microbial growth is 5°C to 63°C and products should therefore be stored below 5°C or above 63°C. Storage refrigerators for creamed goods must be properly maintained at the correct temperature. The time that the products spend in the temperature danger zone during preparation and cooling must be minimised by proper handling and effective cooling. Problems can also occur if warm bread is packed into plastic bags. Condensation can occur which encourages mould growth on the bread surface. Bread should thus be cool before packing. Stores used for baked products should be cool, dry, regularly cleaned and protected against insects and rodents.
Safe storage and good stock rotation are helped by the use of mobile racks or steel shelving on adjustable supports, which are easy to inspect. Slotted trays made of high density polyethylene are easily cleaned and stacked and they can store a variety of different baked items. For ingredients, mobile storage bins made of plastic or stainless steel, can be wheeled to the point of use.
Undisturbed stock encourages rodent and insect infestation. The correct rotation of stock is necessary to maximise profits and prevent unnecessary wastage and contamination of materials. Daily checks should be made on short shelf-life products and weekly checks made on other products or raw materials in the store. The maintenance of correct stock levels by using the 'first in first out' (FIFO) system is good management practice. Stock rotation is easier with date coding but some products do not require a sell-by date and in these cases retailers should adopt their own code to identify the date of delivery. Colour codes have been successfully used (eg blue for Monday, red for Tuesday ).
Hazards associated with baked products
Baked products are rarely involved in food poisoning incidents because the heat during baking kills contaminating micro-organisms and reduces their numbers to safe levels. Stock control errors generally become obvious with staleness and mouldiness becoming quickly evident. Bread and most baked goods are not therefore classified as high risk foods. However, some of the fillings that are used in cakes, pies and biscuits such as cream, meat or fish pastes and vegetables are of high risk if they are not properly processed and stored. Appropriate care and attention to supplier assurance, good handling, temperature control, and cleaning are therefore essential with these products.
The time and temperature required to adequately cook a product vary with the product type, the types of micro-organisms present and the size of the food pieces. The baker must monitor the baking temperature to ensure that such micro-organisms are destroyed and the bread is not too moist as this will encourage bacterial growth. A common bacterial problem associated with bread is known as "rope", which results in the bread having a stringy consistency. The micro-organism that causes rope, Bacillus subtillis. has spores that can withstand the high temperatures of baking. The initial spoilage results in a fruity odour in the product but later, brown discoloured patches develop and the bread becomes sticky. It is this sticky material that can be pulled into strings or "rope" (Figure 22: "Rope" in bread). Consumption of the contaminated bread can cause illness.
Rope micro-organisms can be present in flour, water, salt and yeast. They can be controlled by specifying good quality ingredients and ensuring good handling practices in the supplier chain. This can be done by:
Another method of preventing rope is to add sodium propionate or more recently, acetic acid (vinegar) to the dough. Acetic acid may be added at 0.1 to 0.15 % of the flour weight. The higher level is normally used when rope problems are present or when the weather is very hot. Cleaning schedules and procedures should target important areas including equipment, water tanks, contact surfaces and attention to personal hygiene.
The application of HACCP principles to the manufacture of bread shows that the main hazards are physical contaminants, mould or rope. A small company may consist of the manager and a supervisor and they should identify the source of these contaminants and then implement methods which eliminate or prevent them. Contaminants identified in the incoming raw materials may be controlled by agreements with suppliers and sieving of dry ingredients. Sources of metal or wood contamination within a process can be identified and controlled. For example there should be no wood in contact with food products and machines should be checked before and after use to ensure that no parts are missing.
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