FRUIT JUICE PROCESSING
Introduction
A wide range of drinks can be made using extracted fruit juice or fruit pulp as the base material. Many are drunk as a pure juice without the addition of any other ingredients, but some are diluted with sugar syrup. The types of drink made from fruit can be separated into two basic types; - those that are drunk straight after opening - those that are used little by little from bottles which are stored between use. The former groups should not require any preservative if they are processed and packaged properly. However, the latter group must contain a certain amount of permitted preservatives to have a long shelf-life after opening. The different types of drink are classified according to the following criteria: Type Juices Nectars Squashes Cordials Syrups Description Pure fruit juice with nothing added Normally contain 30% fruit solids and are drunk immediately after opening Normally contain at least 25% fruit pulp mixed with sugar syrup. They are diluted to taste with water and may contain preservatives Are crystal-clear squashes Are concentrated clear juices. They normally have a high sugar content
Each of the above products is preserved by a combination of natural acidity, pasteurisation and packaging in sealed containers. Some drinks (syrups and squashes) also contain a high concentration of sugar which helps to preserve them. Equipment required Measuring cylinder Peeler Capping machine Knives (stainless steel) Wooden spoons Cutting boards Plastic funnels Juice extractor Plastic buckets Thermometer Strainers Analytical balance Stainless steel saucepan 10kg scales Cleaning equipment (brushes, scourers, cloths, hosepipes etc) 2 gas cylinders, 2- or 3- ring burners. Building with large preparation table, smaller table for gas burners, shelves for products, sink, draining board, taps, cupboard for labels and dry ingredients. The total capital for equipment and furnishings is likely to be £500-800 ($US900-1440), working capital for fruit purchase, packaging and other materials is likely to be around £600 ($US1080). The cost of a building is not included, but it should have the following features: • Sloping concrete floor and proper drainage for washing down each day • A potable water supply • Preferably electricity
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Fruit juice processing
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Screened windows and doors to reduce insects No horizontal ledges, window sills, or rafters where dust, insects and bird droppings can collect.
This technical brief outlines the basics of fruit juice processing. It does not give specific details or recipes for individual fruits. These can be found in the individual technical briefs (lime cordial, mixed fruit juice manufacture, passion fruit juice).
Method of production
For all the fruit based beverages, the first stage is the extraction of juice or pulp from the fruit. The following are the key manufacturing stages: Selection and preparation of raw material Juice extraction Filtration (optional) Batch preparation Pasteurisation Filling and bottling. Any fruit can be used to make fruit juice, but the most common ones include pineapple, orange, grapefruit, mango and passion fruit. Some juices, such as guava juice, are not filtered after extraction and are sold as fruit nectars.
Preparation of raw material
Select mature, undamaged fruits. Any fruits that are mouldy or under-ripe should be sorted and removed. Wash the fruit in clean water. It may be necessary to chlorinate the water by adding 1 tablespoon of bleach to 5 litres of water. Peel the fruit and remove stones or seeds. If necessary, chop the fruit into pieces that will fit into the liquidiser or pulper. Remember that at this stage, you are exposing the clean flesh of the fruit to the external environment. Make sure that the utensils are clean. Do not leave the cut surfaces exposed to the air for long periods of time or they may start to turn brown and this will discolour the juice. The fruit pieces can be placed in water that contains lemon juice (250ml lemon juice per litre of water) to stop them browning.
Juice extraction
There are several methods to extract juice depending on the type of fruit you use. For citrus fruits which are naturally juicy, the best option is to use a hand presser (see figure 1) or a revolving citrus 'rose'. Some fruits such as melon and papaya are steamed to release the juice. Apples are pressed and fruits such as mango, guava, soursop, pineapple, strawberry must be pulped to extract the juice. The fruit pieces are pushed through a perforated metal plate that crushes and turns them into a pulp. Some fruits can be pulped in a liquidiser and then filtered to remove the fruit pieces. There is a range of equipment available that varies in size and in the type of power supply (some are manual while the larger ones require electricity). For the small scale processor, the Mouli Legume or a hand-powered pulper/sieve which force the fruit pulp down through interchangeable metal strainers (figures 2 and 3) is sufficient.
Figure 1: Hand presser
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At slightly higher production levels, it is necessary to use a power source to achieve a higher throughput of juice. The multi-purpose Kenwood Chef food mixer, is strongly recommended. This has a pulping attachment that is similar to the Mouli Legume and it can also be used for other operations such as liquidising and mixing.
Figure 2: Hand powered pulper
Figure 3: Hand powered pulper
For large-scale production, an industrial pulper-sieving machine is necessary. This also acts by forcing the fruit pulp through a fine cylindrical mesh. However, these cost in excess of £2,500.
Filtering
To make a clear juice, the extracted juice or pulp is filtered through a muslin cloth or a stainless steel filter. Some of the larger filter presses have a filter included. Although juice is naturally cloudy, some consumers prefer a clear product. It may be necessary to use pectic enzymes to break down the pectin and to help clear the juice. Pectic enzymes may be difficult to find and expensive and therefore should only be used if really necessary and readily available.
Batch preparation
When the juice or pulp has been collected, it is necessary to prepare the batch according to the chosen recipe. This is very much a matter of choice and judgement, and must be done carefully to suit local tastes. Juices are sold either pure or sweetened. Fruit squashes would normally contain about 25% fruit material mixed with a sugar syrup to give a final sugar concentration of about 40%. Squashes are diluted with water prior to use and, as the bottle is opened, partly used and then stored, it is necessary to add a preservative (for example 800ppm sodium benzoate). Another popular product is fruit nectar, which is a sweet mixture of fruit pulp, sugar and water which is consumed on a 'one shot' basis. Essentially, these consist of a 30% mix of fruit pulp and sugar syrup to give a final sugar level of about 12-14%. All fruits contain sugar, usually around 8-10%. The actual levels vary from fruit to fruit and with the stage of ripeness of the fruit. They also vary within the same fruit grown in different parts of the world. The addition of sugar to the fruit pulp to achieve the recommended levels for preservation must take into account the amount of sugar already present in the juice. It is important to achieve the minimum level that will prevent the growth of bacteria, however, once that level has been achieved, it is possible to add more if the consumers require a sweeter product. The amount of sugar added in practice is usually decided by what the purchasers actually want. The Pearson Square is a useful tool to use to help with batch formulation (see the appendix) and to calculate the amount of sugar to be added for preservation.
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In all cases, sugar should be added to the fruit juice as a sugar syrup. The syrup should be filtered through a muslin cloth prior to mixing to remove particles of dirt which are always present. This gives a clearer, higher quality product.
Pasteurisation
All the products mentioned above need to be pasteurised at 80-95°C for 1-10 minutes prior to hot-filling into bottles. At the simplest level, this may be carried out in a stainless steel, enamelled or aluminium saucepan over a gas flame, but this can result in localised overheating at the base of the pan, with consequent flavour changes. Care is needed when producing pineapple juice due to a heat resistant enzyme in the juice. The enzyme damages skin after prolonged contact and workers should therefore wear gloves to protect their hands. The juice must be heated to a higher temperature for a longer time to destroy the enzyme (eg boiling for 20 minutes). It is best to use stainless steel pans to heat fruit juice as the acidity of the juice can react with aluminium in aluminium pans during prolonged heating. However, large stainless steel pans are very expensive and may not be affordable by the small scale processors. To get round this problem, it is possible to use a large aluminium pan to boil the sugar syrup. The boiling syrup can then be added to a given amount of fruit juice in a small stainless steel pan. This increases the temperature of the juice to 60-70°C. The juice/syrup mixture is then quickly heated to pasteurising temperature. Bottle size (litres) 0.33 0.5 0.75 Pasteurisation time at 80°C (minutes) 10 15 20
Table 1: Pasteurisation times at 80°C for different bottle sizes Another option is to pasteurise the juices once they have been bottled. The bottles are placed in a hot water bath which is heated to 80°C. The bottles are held in the hot water for the given amount of time until the contents reach the desired temperature. The length of time required in the water bath depends on the size and volume of the bottles (see table 1). A thermometer should be placed in one of the bottles, which is used as a test bottle per batch, to monitor the temperature and to ensure that the correct temperature has been reached. This method of pasteurisation has benefits but also has problems. Benefits Juice is pasteurised within the bottle so the chance for re-contamination of the juice is reduced No need for large stainless steel pans for pasteurisation Problems Difficult to ensure the internal temperature of the bottles reaches the desired pasteurising temperature Require glass bottles for pasteurising
Table 2: The pros and cons of pasteurising within after bottling The next industrial jump in pasteurisation is an expensive option that involves the purchase of a double-jacketed steam kettle in stainless steel and a small boiler. The total cost is likely to be in the region of £5-10,000, which is only viable for larger scale operations.
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Fruit juice processing
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Filling and bottling In all cases, the products should be hot-filled into clean, sterilised bottles. A stainless steel bucket, drilled to accept a small outlet tap, is a very effective bottle filler. The output can be doubled quite simply by fitting a second tap on the other side of the bucket. This system has been used to produce 500-600 bottles of fruit juice per day in the West Indies. After filling hot, the bottles are capped and laid on their sides to cool prior to labelling.
Quality control
The freshness and quality of the expressed fruit juice is central to the quality of the final product. As soon as the juice is expressed from the fruit it starts to deteriorate, both as a result of chemical activity (enzyme action) and bacterial spoilage. It is important to move from the juice extraction stage to pasteurisation as quickly as possible to minimise any spoilage. Extracted fruit juice that is left to stand for long periods in the heat will start to ferment and may start to discolour due to enzyme activity. The juice should be stored in a refrigerator (if one is available) or in a cool place and away from the direct sunlight. It should be collected into a clean, sterile container (food grade plastic buckets is the best option) and covered to keep out dirt, dust and insects. For the best quality product ,it is essential to work quickly between the extraction of the juice and the bottling stage. The longer the juice is out of the bottles, the more chance there is of contamination. As in all food processing enterprises it is necessary to ensure that the fruit products are correctly formulated and priced to meet the customer's requirements, and that production costs are minimised to ensure that a profit is made. The quality of each day's production should be monitored and controlled to ensure that every bottle of juice has the correct keeping and drinking qualities. In particular the following points should be observed: • • • • • • • Only fresh, fully ripe fruit should be used; mouldy or insect damaged fruit should be thrown away. All unwanted parts (dirt, skins, stones etc) should be removed. All equipment, surfaces and floors should be thoroughly cleaned after each day's production. Water quality is critical. If in doubt use boiled water or add one tablespoon of bleach to 5 litres of water to sterilise it. If water is cloudy, a water filter should be used. Pay particular attention to the quality of re-usable bottles, check for cracks, chips etc and wash thoroughly before using. Always use new caps or lids. The concentration of preservative should be carefully controlled for correct preservation of squashes and cordials, and may be subject to local laws. Check first and use accurate scales to measure the preservative. The temperature and time of heating are critical for achieving both the correct shelf life of the drink and retaining a good colour and flavour. A thermometer and clock are therefore needed. The correct weight should be filled into the bottles each time.
These factors are important because a customer will stop buying the products if the quality varies with each purchase.
The use of chemical preservatives in fruit juices and fruit drinks
As the name suggests, pure fruit juice is solely the extracted juice of fruit and should not have any preservative, or any other ingredients (such as sugar) added. Fruit drinks that are not consumed in one go can have preservatives added to help prolong the shelf life once they have been opened. There are several chemical preservatives that can be added to fruit juices. Processors need to check with local authorities or standards agencies to find the maximum permitted levels.
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