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The process flow chart for selected fruit products is shown in Fig. 23 (see Figure 23: Process flow diagram for fruit products) and a summary of the main quality assurance procedures for fruit processing is shown in Table 7 (see Table 7: Quality assurance procedures for fruit processing) below. The quality assurance procedures in the table are discussed in more detail in the following chapter.
Processing of fruits
Heat (1) = Pasteurization
Heat (2) = Concentration
Introduction
Fruit products are commonly produced by small scale rural producers as the technologies are relatively simple and producers are often close to the source of supply. The main quality factors associated with fruit products are the characteristic flavour and colour of the fruit, the absence of contamination, and in some products, a characteristic texture. However few quality characteristics of fruit products can be measured objectively and fewer still can be measured by machines. Therefore reliance should be placed on subjective assessment by operators and the more operators that examine the raw materials, ingredients, process and product, the greater will be the level of control. The importance of proper staff training and involvement in production, as stressed in Chapter 1.1, are particularly important in fruit processing.
In general fruits and fruit products are considered to have a low risk of causing food poisoning. This is because they contain natural acids which prevent the growth of food poisoning bacteria. For fruits having a medium acid level, citric acid is usually added to bring the pH down below 4.5. Processing, either by drying, heating (such as pasteurisation of juices) or by adding salt, (in pickles), or high levels of sugar (in jams and crystallised fruits), also reduces the risk of contaminating bacteria.
However fruits can be infected with moulds and yeasts and processors should use good quality raw materials and have strict control over hygiene and handling. The main areas for the application of quality assurance and control are:
Raw material harvesting, transport and inspection
There are a number of specific problems with fruits that are not found to the same extent with other foods:
A further problem facing manufacturers in many developing countries is the large number of different varieties of a particular fruit. It is common for example to see four or five different varieties of mango or banana on sale in local markets, but not all varieties are suitable for processing and many have very different tastes. For a processor to be able to make a uniform product, there must be either control over the variety of fruit that is used, or a standard system of blending raw materials to give a consistent product.
Unfortunately this is not always easy to achieve as fruits are often grown in small quantities by individual farmers. It is usually the case that farmers have a few fruit trees on their land to provide a little extra income in addition to their main crops and to provide shade around their houses or in the fields. Planted orchards or fruit estates in which the variety is selected and cultivation is managed, are the exception. For the manufacturer there is therefore a problem in obtaining enough fruit of the required variety and quality to allow proper production planning and quality assurance of the raw materials. Some of the options that are available to processors are described below.
Buying fruit from markets
Many small scale producers buy fruits from local markets, particularly when they first start a business. Because fruits are often seen as a low-value food, they are handled without care by farmers and traders. They may be piled into heaps on the ground and then thrown into trucks for transportation, without protective crates or boxes.
The system of payment and distribution of fruits frequently causes problems of poor quality and high levels of spoilage losses. In some countries, traders or 'middlemen' tour a farming area and buy all of the fruit that a farmer produces, regardless of its condition. They then transport the fruits to central markets where it is sorted into different quality grades. Higher quality goes to more expensive retail markets and lower quality to cheaper markets. Because the system of payment to traders does not rely on supplying high quality fruit there is little incentive to protect the fruit during transport. In fact the use of fruit boxes adds weight to a load and reduces the space available for carrying larger quantities. There is also little incentive to return empty boxes to farmers as the carriers do not receive payment for this.
Similarly, the farmers have little control over the treatment of their crops by traders and because the traders are willing to buy all of the crop and often offer informal credit and loans to farmers, the farmers may become indebted and are unable or unwilling to change the system by which they sell their crops.
For the processor to achieve higher quality raw materials it is better to avoid buying from markets with their attendant problems of variable quality and uncontrolled prices. There is a limited range of other options, each with its associated costs and benefits.
Agreements with farmers
To avoid the variations in quality and price that are found in markets, it may be possible for processors to reach agreements with a number of farmers in an area to supply fruit of a specified variety and quality. Typically the specifications would include details of the variety to be grown, the degree of ripeness (often described by the colour or firmness of the fruit) and the minimum size of each fruit. The price is guaranteed provided that the quality is met and there may be a part of the agreement that specifies the maximum amount that will be bought. In this type of agreement it may also be possible for the processor to both offer training to the farmers in how to achieve the required quality and to employ a field worker to advise the farmer throughout the growing season.
The advantages to the processor are a greater control over the variety and quality of the raw materials, some control over the amounts supplied and an indication of likely raw material costs. This is helpful in production planning and maintaining a positive cash-flow in the business.
The advantage to the farmer is less clear if traders normally buy all of the crop. If however the farmer usually sells directly in local markets, the security of having agreed sales to the processor at a known price may be an incentive. However, it is difficult to persuade farmers to reduce their sales to traders. The local power of traders may include a refusal to offer loans to farmers, a threat not to buy the crop again if sales are made directly to processors and possible indebtedness by farmers who may be threatened to repay loans immediately.
Contract farming
This approach has been tried in many countries with varying degrees of success. A processor specifies the types of fruit to be grown, often supplying seeds or grafting new varieties onto existing trees and sometimes supplying all other inputs including fertilizer, pesticides and even labour. In effect the farmer is simply being paid for the use of his or her land.
The price paid for the crop is often set between the mid-season lowest point and the end-of-season high point. The advantages to the producer are an assured supply of the required variety at a cost that is known in advance and can therefore be planned into the production costs. For the farmer there is a guaranteed sale of the crop with a known income. The risks to the processor are that the farmer will sell on the open market once the price rises above that agreed in advance, resulting in less fruit available than planned.
There is also a higher risk and more planning involved when processors supply all of the inputs to farmers.
The risk to the farmer is that the processor will not honour the agreement or payment will be delayed. For such a system to operate effectively and benefit both farmers and processors, a level of trust has to be built up by honest dealing over several seasons.
Manufacturer's farms (Nucleus farming)
Here a processor buys land and hires labour to produce the fruits required for the range of products being made. In effect the farm becomes another department of the factory and is totally within the control of the processor. Because of the higher costs associated with this option it is usually only attempted by larger companies and is therefore beyond the scope of this book.
Good practice in harvesting and transporting fruits
Fruits are usually harvested by cutting them from the tree or plant, by hand picking or by mechanical systems in large plantations. It is important to leave the stem of the fruit in place and not to pull it out when harvesting. This reduces the risk of moulds and yeasts infecting the fruit through the open hole. Where it is not possible to hand pick fruit (for example from tall trees) a net or cloth should be stretched below the tree to catch the fruit as it is shaken down and prevent it being damaged by hitting the ground.
Some fruits such as wood-apple and orange have a strong outer skin which resists puncturing, but most have a thinner skin that is easily damaged by poor handling, especially when fruits are ripe and soft. The following suggestions can result in improved fruit quality:
Fruits are easily damaged by vibration and bumping when they are carried on trucks, especially on unmade rural roads. Where possible transport by train or by riverboat is a better option for protecting fruit because of the reduced vibration. Although this is often not available, there are many examples in the authors' experience where this type of transport exists but has never been considered or evaluated.
Raw material inspection
Once the fruit has been transported to the processing unit it is within the control of the manufacturer and more systematic quality assurance procedures can be adopted. As resources for quality assurance are usually limited they should be focused on the parts of the process that are most effective in ensuring that the products meet customer specifications. The HACCP approach should be used as a means of achieving maximum results from the resources available for quality control. Examples include regular monitoring of the cleanliness of the production area and checking to ensure that there is no animal or insect infestation, maintaining good operator hygiene by regular inspection and training, making sure that wastes are disposed of properly and regularly.
When raw materials arrive each batch should be recorded in an Incoming Materials Test Book, noting the number of the batch, the name of the supplier and useful observations (Figure 25: Incoming materials test book). This information should also be recorded for other ingredients and packaging materials used in the process.
The first series of checks are made on the raw materials as they arrive at the processing unit. These usually involve spreading the fruits on sorting tables and inspecting them for quality and suitability for processing. Maturity of raw materials is usually assessed by looking at the fruit or sometimes by handling them as there are few objective tests that can be applied to incoming fruit in small processing plants. Similarly, other ingredients should be checked to make sure that they are of the right type and have not been adulterated. Packaging should be inspected on arrival to make sure that it is the correct type and is not damaged m any way.
Checks on incoming fruit should include the following:
Any fruits that do not meet the required standard are removed together with foreign matter such as leaves, stones, etc. and taken outside to a disposal site well away from the processing room. Regular removal is important to prevent the waste from attracting flies to the processing area and to avoid the risk of contaminating good quality fruit.
Careful inspection at this stage can save a lot of time and money later in the process. Good training for inspection staff is important and possibly a bonus scheme should be considered, as proper sorting is one of the most cost-effective ways of improving the value of a raw material. It should be remembered that it is not possible to improve the quality of a raw material by processing it. Poor quality raw materials produce poor quality finished products.
Processing
Resources allocated to testing the finished product should be relatively small compared to those used to monitor the process, because mistakes in the finished product are often too late to correct. It is better to have control of the process to prevent the mistakes from occurring in the first place. This is the basis of the HACCP approach. Management systems should encourage operators to quickly report faults in the product or process. An incentive or bonus scheme may help and any form of penalty should be avoided.
Preparation
The fruit is washed in clean potable water, chlorinated if necessary, as quickly as possible after inspection (details of chlorinating systems are given in Chapter 1). It is important to inspect the fruit and remove any that are spoiled or damaged before washing as these would otherwise quickly contaminate the wash-water. That in turn would increase the risk of contaminating the other fruit and increase the risk of later problems.
Operators should be trained to inspect fruits for faults, for example, they should check the following:
Part-processing (intermediate storage)
Two of the main problems facing the processor are the need to process the fruit quickly to prevent further ripening and spoilage, and the need to handle the large amounts of fruit that arrive in the short harvest season.
To avoid investment in large capacity processing equipment which is only used for a few weeks of the season, it is possible to part-process fruits. This prevents further ripening or spoilage and maintains the fruit near its original condition until it is required for final processing. Although it is possible to preserve many fruits by freezing, this is an expensive option and generally not affordable by small scale producers. A more viable alternative is to preserve the fruit with salt, sugar or a chemical preservative. The method selected depends on the finished product to be made (Table 8: Methods for intermediate storage of fruits).
Details of methods to measure the concentration of salt and sugar are given in Chapter 3.
Raw material preparation
Four basic steps are involved in preparing fruits for processing: peeling, slicing, pulping and filtering or straining.
Peeling is usually done by hand with sharp, stainless steel knives although small manual peeling machines are available for some types of fruit (Figure 26: Small fruit peeling machine). The quality check at this stage in the process is to ensure that all peel is removed with a minimum loss of fruit flesh.
Slicing is also often done using knives and this is acceptable if the uniformity of slices is not too important (for example when making chutneys, pickles or bottled fruit). However, a uniform size is essential for products such as banana chips, dried and crystallised fruits and shreds for marmalade. For these products it is recommended that a small slicing or dicing machine is used to obtain uniform sized pieces. A quality check at this stage is to inspect sliced fruit to ensure that pieces are uniform in size and any over-sized pieces are removed or re-sliced.
When making fruit leathers, sauces, jams, marmalades and the many types of fruit drinks (juices, squashes, cordials and nectars), it is necessary to pulp the fruit. In all but the smallest scale of operation, this is best done using a pulper/finisher machine (Figure 27: A pulper-finisher for making fruit pulps).
These are available in a range of different sizes or they may be fabricated by local metal workshops.
Fruit pulps are filtered when a clear product such as squash, jelly or juice is required. This is usually done using a nylon mesh or cloth bag. A quality check at this stage is to ensure that bags are thoroughly cleaned and boiled for at least 10 minutes before each use.
Processing
Batch preparation
Mixing of ingredients to prepare a batch for processing is one of the most important stages in a process. When done properly it results in a uniform product from every batch and can save money by not using excessive amounts of expensive ingredients every time. However, any mistakes that are made at this stage cannot be easily corrected later and may result in non-uniform finished products or having to throw the whole batch away. A record book should be kept in which the batch number is noted and the correct amount of ingredients are ticked off as they are added to each batch (Figure 28: Ingredient record book).
Good quality scales are required for batch preparation and two sets may be necessary; one for heavier weights (for example 50 kg in divisions of 250 g) and one for smaller weights (for example 1 kg in divisions of 2 g). Although scales are generally expensive, especially for accurate types, they can save money in the long term by ensuring that excess ingredients are not added.
If the size of the business does not justify expenditure on scales, it is possible to use calibrated cups, spoons or jugs to measure out ingredients, provided that the same amount is added in every batch. Concentrations of sugar used in syrups or salt used in brines should be checked for each batch (Chapter 3: sugar measurement, salt measurement). In some preparations the amount of acid added to a syrup or brine is important and should be checked by titration, not by pH (see Chapter 3: acidity measurement).
Process control
Most fruit products are heated to pasteurise them (to destroy enzymes and microorganisms and therefore achieve preservation). However some pickles and chutneys are not heated and preservation is achieved by a careful combination of acids, salt and sugar. In the following section, the three basic methods of processing (drying, heating and pickling) are described in outline, together with the relevant control procedures. More details of the processes for individual products are described in publications listed in Appendix 1.
In all types of process, records should be kept of the amount and type of ingredients used, the process conditions (ea. drying temperatures, heating times etc), the raw material batch numbers and the product code numbers that are printed on the labels. This allows the processor to trace any subsequent faults in a batch of product back to the process or to the raw materials.
Drying
Dried fruits are often pre-treated with sulphur dioxide to maintain their colour, reduce browning and reduce the number of contaminating micro-organisms. This may be done by either dipping the fruit into a solution of sodium metabisulphite or placing the fruit in a cabinet containing burning sulphur. The level of sulphur dioxide is controlled by law in most countries and careful measurement is needed to correctly weigh out sodium metabisulphite when making up a solution or when weighing out sulphur for burning in the cabinet. For this reason the producer should take great care to weigh out sodium metabisulphite correctly when making up the solution. Similarly the weight of sulphur for burning in the cabinet and the time of sulphuring should be carefully controlled. Details of the permitted levels of sulphur dioxide can be obtained from a local office of the Bureau of Standards, or Ministry of Health, Agriculture, or Trade and Industry, depending on the country.
Crystallized fruits and fruit leathers are pre-treated with sugar syrup and then dried. The amount of sugar added to the soaking solution and the temperature to which the fruit is heated are controlled by careful weighing and the use of a thermometer respectively. Again sulphur dioxide, usually in the form of sodium metabisulphite, is added to help maintain a fresh colour and inhibit mould growth during drying.
Due to their high sugar content,- fruits tend to dry slowly. For this reason the use of artificial dryers is preferred in order to reduce drying times. However, under suitable climatic conditions, solar dryers can perform well. Drying conditions also need to be carefully controlled to ensure that the fruit is fully dried to a sufficiently low moisture content without mould growth. Further details on drying are given in the chapter on Herbs and Spices (Chapter 2.4) and further reading is suggested in Appendix 1.
The shelf life of dried and crystallised fruit depends mostly on the 'equilibrium relative humidity' (ERM) of the product under the expected storage conditions. This is a measure of the amount of water that is available within the product that can support the growth of contaminating micro-organisms. This is usually found by measuring the moisture content of the product (Chapter 3: moisture content measurement, fruits), but the relationship between moisture content and ERH varies with different foods and so it is necessary to find out by experiment what is the highest moisture content that will allow the food to be stored without spoiling. In practical terms this can be done by removing samples at different times during a drying test, packaging them and checking to see which ones develop mould after a few weeks of storage. Moisture checks are then made on samples that do not show mould growth and this is used to find the highest moisture content that can keep the food stable.
Heat processing
Products such as sauces, preserves (jams, jellies, marmalades), fruit drinks, fruit toffees and bottled fruits are each heated during processing. This is usually done by heating the food in boiling pans and then hot-filling into pre-sterilised jars or bottles. Alternatively the product can be filled first and then heated in the container. In both cases the time and temperature of heating is an important quality control measure. Too much heat reduces the quality of the food by excessive softening, loss of the colour or flavours. Too little heat results in survival of enzymes and contaminating micro-organisms, which could lead to mould growth and loss of texture or colour during storage, and in the case of drinks, separation of pulp forming a sediment in the bottom of the bottle.
It is essential that the correct temperature and time of heating are carefully determined for each product and that operators are trained to ensure that these conditions are maintained for every batch. Normally a clock and a thermometer are sufficient to control the process, but for preserves, toffees and sauces, this is not sufficiently accurate and a refractometer is used to check the final solids concentration (see Chapter 3: sugar measurement).
Pickling
Chutneys and pickles may be pasteurised but usually they rely for their preservation on the correct balance of acids, salt and sugar in the finished product. The preservative action involves inhibiting enzymes and micro-organisms but they are not destroyed. Therefore strict control over hygiene is essential in the preparation and processing of fruits for these products (see Chapter 1.3). In particular, insects may carry moulds and yeasts into the product during the pickling process and these may later grow and cause fermentation or mould growth during storage. The product should therefore be protected from insects and covered at all times to stop dust and other contamination. A well-made pickle will remain useable for several months after opening without the use of preservatives and although many manufacturers use sodium benzoate, this is not strictly necessary.
The batch formulation needed to achieve the correct balance of salt, sugar and acids should be carefully calculated using the formula below to ensure a 'preservation index' above 3.6%.
Methods for measurement of acidity and total solids are given in Chapter 3 (acidity measurement, salt measurement, soluble solids content measurement by refractometer, moisture content).
Once a suitable recipe has been developed, it should be carefully controlled by accurate weighing of ingredients during the preparation of every batch. The concentration of salt, sugar, vinegar (acetic acid), other acids (ea. citric acid) or chemical preservatives such as sodium benzoate, should each be measured to ensure that the product will remain stable during storage (see Chapter 3: acidity measurement, salt and sugar measurement).
Packaging, storage and distribution
Packaging
Glass jars and bottles are commonly used to pack fruit products but other cheaper containers such as plastic pots and plastic bags are becoming increasingly common. There are a number of quality checks that must be done when using glass containers (see Chapter 3: glass container measurement) because of the risk of glass splinters entering the product and causing serious harm to consumers. Checks on plastic containers are less rigorous and these are also outlined in Chapter 3 (plastic container measurement).
All products should be carefully filled to ensure that the amount in the container is the same as the net weight described on the label. In most countries it is an offence in law to sell an under-weight product and over-filling means that the company is giving away product at a loss. Further details of labelling requirements are given in publications described in Appendix 1.
For liquid products such as drinks, sauces, hot filled chutneys and preserves, a piston filler (Figure 29: A piston filler for filling liquid foods) gives more accurate fill weights than manual filling. Solid products such as dried fruits, crystallised fruits, bottled fruit pieces and cold filled chutneys and pickles are usually filled by hand.
A check-weighing scale (Figure 30: A check-weighing scale in use) can be used to ensure that the correct weight is filled. This equipment is also used to check the weight of samples taken regularly from batches of liquid products. Control methods for fill-weights are described in more detail in Chapter 3 (fill-weight measurement).
Seals on lids of bottles and jars should have close and continuous contact with the glass rim. Plastic and glass seals should not be contaminated with product or else the seal will leak. Packs should be checked to ensure that the correct label is used for each product, that the date stamped onto the pack is correct and that code numbers are correct and are changed regularly (each batch of product or each day's production).
Storage and distribution
Once a fruit product has been processed and sealed into a container the risks of contamination by insects, dust and micro-organisms is reduced but further damage to the food is not eliminated. Incorrect storage conditions, such as exposure to sunlight, heat and water or incorrect stacking which causes crushing, can all result in spoilage of the processed fruit. This is particularly important because of the money that has already been spent on processing and packaging the food. Losses at this stage are financially very damaging.
Packaged foods should therefore be stored in cardboard (paperboard) boxes on pallets or shelves that keep the boxes off the floor of the store-room. Boxes can be stacked on top of each other provided that the combined weight of the stack does not crush the bottom box. The store-room should be cool and dark with a good ventilation to maintain a flow of air. Many manufacturers give careful attention to the construction of a processing area but forget about store-rooms. As a result they suffer financial losses because ingredients, packaging materials and finished products become damaged during storage. The details of building design and layout described in Chapter 1.2 should be applied equally to processing and storage rooms. In particular windows should be screened against insects and the structure of the roof and walls should prevent rats and birds from gaining entry.
An important aspect of storage and distribution is to develop a management system to monitor which products are in the store, to control stock rotation and record their destination for delivery. This is particularly important when a processor produces a range of products, as it is very easy for slower-selling products to be hidden at the back of a store and go beyond their 'sell-by' date. Simple records (Figure 31: Simple records for storekeepers) should be kept by storekeepers to show which products and materials are transferred into and out of the store-rooms.
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