DRIED FRUIT Food and Agriculture Organization

Dried Fruit Food And Agriculture Organization-Free PDF

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DRIED FRUIT,1 General information,Dried Fruit general information. Drying is one of the oldest methods of food preservation It is still used widely to preserve. foods for home consumption and for sale Dried fruits are one of the most popular products. made by small scale processors, Drying removes the water from foods so that the growth of micro organisms is inhibited It. also reduces the weight and bulk of foods which cuts down on transport and storage costs. Sun drying is the simplest and cheapest method of drying It is used for high volume foods. such as grain rice sultanas and raisins The disadvantage of sun drying is that the processor. has very little control over the drying conditions and the quality of the dried fruit. There are two main forms of dried fruit semi moist and dried fruits Semi moist fruits such as. grapes contain naturally high levels of sugar which means they can be preserved with a higher. moisture content than most other dried fruits Semi moist fruits can have a moisture content. as high as 25 and are consumed as they are without rehydration The sugar content of other. fruits can be increased by soaking the fruits in sugar solution prior to drying These fruits are. known as osmotically dried fruits, To make higher quality products processors use an artificial dryer There are several types of. dryer available solar diesel electric biomass powered according to the different needs of. 2 Processing details for dried fruit production,A Preparation of the fruit. All fruit to be dried should be hand picked and not shaken from the tree. To obtain maximum yields of top quality dried product all fruit should be ripe and free from. bruising Any rotten or bruised fruit should be thrown away. For maximum profitability the dryer should be loaded to maximum capacity as often as. possible therefore it is advisable to buy more fruit than is required. Bananas have a low level of acidity and turn brown very rapidly after peeling and cutting To. prevent this they should be immersed in water containing sodium metabisulphite 400 parts. per million of sulphur dioxide immediately after peeling. Unpeeled fruits should be washed in a mild disinfectant solution made from one part of bleach. to 50 parts of water Care must be taken not to break the skin of the fruits as this will. contaminate the flesh, Gloves and aprons must be worn to protect the workers hands and clothes Ten litres of.
treated water will be sufficient for about 20kg fruit. The wash water should be changed after this amount has been washed as it becomes. contaminated by the fruit, Soft fruit such as berries and apricots are delicate and should be handled carefully to avoid. bruising Washed fruits are carefully peeled to remove all the peel and any damaged parts of. the flesh Fruits are cut into slices of varying thickness depending on the type of fruit and the. dryer The following points are useful to consider thick pieces dry at a slower rate than thiner. ones very thin pieces tend to stick to the drying trays and may be difficult to remove thicker. pieces may not dry fully in the centre and will not store well packets of mixed thick and thin. pieces do not look attractive,Recommended slice thickness for various fruits. Food Chain 31 Ref 36,Pineapple 2 3mm,Mango 6 8mm,Banana 5mm. Tomato 3 5mm, Only stainless steel knives should be used to peel and chop the fruit. Other metals will discolour the fruit flesh,B Blanching or sugaring.
This stage is optional but some processors choose to soak fruits in a sugar syrup prior to. drying There are several benefits of including this process There are also constraints to. Fruit pieces are immersed in a concentrated sugar solution for up to 18 hours They are rinsed. in clean water to remove any excess syrup before drying. Most vegetables and some fruits are blanched before drying to inhibit enzyme activity and to. help preserve the colour, The material is cut into appropriate sized pieces and plunged into boiling water for up to 5. minutes They should be blanched in small batches to ensure that each piece is properly. heated through, If too many pieces are put into the water at one time the water temperature will drop and. prolong the blanching time After blanching for the required time vegetables are rapidly cooled. by plunging into cold or iced water,C Sulphuring, Sulphuring or sulphiting is an optional stage of processing The main benefit of sulphuring is to. preserve the fruit colour Some consumers object to chemical preservatives and prefer. naturally dried fruits, Sulphur dioxide gas SO2 is applied to the fruit pieces by placing them in a cabinet or tent in. which sulphur is burned The gas is absorbed by the fruit For most fruits 5 6g sulphur per kg. food is adequate The gas given off is toxic and corrosive Therefore sulphuring should be. carried out in a well ventilated place using appropriate equipment See the information on. sulphuring for more details Sulphite can be included in the sugar syrup as sodium or. potassium metabisulphite, Fruit pieces are arranged on mesh bottom trays so that they are not touching or overlapping.
The fruit should be loaded into the trays as soon as it is cut This prevents the pieces from. sticking together and allows the drying process to start as soon as possible. The trays should be brushed clean to remove any old fruit pieces. The trays should be loaded into the dryer as soon as they are ready The dryer doors should be. closed after each tray is loaded, Direct sunlight should be avoided as this bleaches the colour and reduces the level of vitamins. A and C The drying temperature should be controlled to avoid over heating and spoilage of. the fruit Most fruits are dried at about 60 70 deg C. Fruits are dried until they have the desired final moisture content 15 for conventionally. dried fruits 20 25 for osmotically dried sugar treated fruits. E Packaging, Dried fruits should be packaged immediately after drying to prevent them absorbing moisture. from the surrounding air After drying fruits can be packed in bulk in sealed moisture proof. polyethylene bags then packed into smaller packets at a later date. All equipment must be thoroughly cleaned each day to prevent contamination by insects and. micro organisms,3 Information on drying,A Principles of drying. The following gives basic information about drying Although it seems a simple technique. drying is quite technical and requires a certain amount of knowledge to ensure it is carried out. efficiently and safely More detailed information about the principles of drying can be found in. the references,Axtell 2002, Foods are dried when the water contained within them is removed into the surrounding air It. first moves to the surface of the food and then evaporates as water vapour. Fellows 2000, For effective drying the air should be hot dry and moving The three factors are all inter.
related and for optimum drying each one has to be correct The dryness of air is known as. relative humidity RH 0 100 Air with 0 RH is completely dry Air with 100 RH is. completely saturated with water vapour Air can only remove water from foods if it is not fully. saturated with water vapour, Humidity is affected by the air temperature At higher temperatures the humidity is reduced. and air can carry more water vapour, In solar dryers the air should be 10 15 C above room temperature In artificial dryers it should. be 60 70 C The RH of air entering a dryer should be below 60 Dryers are fitted with a fan. or exhaust to circulate air and remove the damp air. Axtell 2002, When a new food is to be dried processors must carry out a series of tests to find out the rate. of drying This information is used to find the optimum drying conditions for the particular. Fellows 2000, The rate of drying affects the quality of the dried food and the amount of fuel used for drying. and hence the cost, To find the drying rate the food is weighed placed in the dryer and left for 5 10 minutes It is.
removed and re weighed then put back in the dryer This is continued until the weight does. not change The rate of drying can then be calculated. Typical drying rates are 0 25kg per hour for solar dryers and 10 15kg per hour for artificial. dryers If the rate is lower than this either the temperature or air speed are too low or the. relative humidity is too high The test sample is left in an airtight container for one day then. re weighed to check if any more moisture has been lost If it has the fruit is likely to feel soft. or be mouldy, Case hardening is a condition that sometimes occurs during drying The outside layer of the. fruit dries too quickly and becomes quite hard This hard dry layer prevents any more moisture. from being lost from the fruit The centre of the fruit remains moist and is then prone to. spoilage during storage, The most common cause of case hardening is the use of drying temperatures that are too. high It can be prevented by using lower temperatures and controlling the rate of drying. especially during the early stages, The moisture content of the food can be measured with a moisture metre Alternatively a small. sample of the dried food is ground into small pieces weighed and placed in an oven at 100 C. for 4 hours It is reweighed and the moisture content calculated. Moisture content initial weight final weight 100,initial weight. The final moisture content of the dried food shows whether it will be stable during storage. Once a satisfactory product has been made the same drying routine should be used for all. batches of that particular fruit To ensure safe storage of dried foods they should have the. following final moisture contents,Fruit and meat,Vegetables.
Grains 10 15, The stability of a dried food during storage depends on its ability to pick up moisture from the. air Different foods have different susceptibilities but the risk is higher when the humidity is. high Dried foods should be packaged in moisture proof material to prevent spoilage Back to. dried fruit flow chart,B Practical aspects of food drying. B 1 Selection and preparation of fruit, To produce good quality dried fruit and vegetables that are acceptable for both export and. local consumption there are several factors to consider These include the following. NRI 1996 Ref 35,Purchase of good quality fresh produce. Careful transport and storage,Proficient preparation of produce.
Correct loading and operation of the dryer,Drying to the correct final moisture content. Proper packaging and storage of the dried product,Achieving good product quality. Efficient management of all operations to assure quality minimise losses and maximise. business profitability, All acitivities must be carried out with due dilligence at all times with regard to cleanliness. hygiene and food safety aspects,B 1 1 Location of dryer. The solar dryer should be positioned in a flat area out of the shade of buildings or trees so. that it is fully exposed to the sun throughout the day If the wind blows predominantly in one. direction for long periods the dryer should be placed end on to the wind This will reduce the. cooling effect of the wind blowing directly into the drying cabinet and lengthening the drying. times It will also reduce the chance of dust entering the cabinet. B 1 2 Drying, During the first few hours of drying particularly during hot and sunny weather the fruit may.
dry so quickly that moisture condenses on the inside of the plastic covers This can be avoided. by opening the door slightly 20mm to increase air circulation The gap should be covered. with mosquito mesh, This will only be necessary on the first day and during the sunniest part of the day The doors. should only be kept open for a minimum period of time and closed again as soon as the. weather becomes cloudy, The doors should never be left open overnight In poor weather drying will stop If it rains it. will rapidly cool the dryer and condensation may form on the plastic cover It will take some. time for the dryer to start working again once the rain stops Putting a portable thatched cover. over the dryer when it rains will help to reduce the impact In fine and sunny conditions the. fruit slices should be dry after two full days in the dryer It is essential to test the slices to. check they are dry, Judging dryness is an important skill Experienced processors will know when the fruits have. reached the desired level of dryness To check dryness several pieces of fruit should be. removed from the dryer and allowed to cool for a few minutes. A few simple tests can show if the fruit is dry Squeeze the fruit pieces If no moisture comes. out it is dry, Tear a piece of fruit in half There should be no moisture in the middle The slices should be. kneadable and pliable but do not stick together, If the slices are not fully dried they should be allowed to continue for one to two hours then.
checked again The final moisture content should be around 10 15. B 1 3 Unloading the dryer, When the fruit is dry it should be unloaded from the dryer as quickly at possible This should. not happen early in the morning since the overnight dew and high humidity may cause. condensation of moisture onto the fruit Take the trays out of the dryer and to a clean dry. area Remove the fruit from the trays and sort it on the basis of size and colour Discard any. over dried pieces Return any under dried pieces to the dryer This should all be done as. DRIED FRUIT 1 General information Dried Fruit general information Drying is one of the oldest methods of food preservation It is still used widely to preserve foods for home consumption and for sale Dried fruits are one of the most popular products made by small scale processors Drying removes the water from foods so that the growth of micro organisms is inhibited It also reduces

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