Sun Drying Of Fruits And Vegetables Pdf
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Log In Sign Up. Download Free PDF. Parvez Ali Ali. Download PDF. A short summary of this paper. SOLAR DRYINGDue to the current trends towards higher cost of fossil fuels and uncertainty regarding future cost and availability, use of solar energy in food processing will probably increase and become more economically feasible in the near future. Solar dryers have some advantages over sun drying when correctly designed.
They give faster drying rates by heating the air to ? C above ambient, which causes the air to move faster through the dryer, reduces its humidity and deters insects. The faster drying reduces the risk of spoilage, improves quality of the product and gives a higher throughput, so reducing the drying area that is needed.
However care is needed when drying fruits to prevent too rapid drying, which will prevent complete drying and would result in case hardening and subsequent mould growth. Solar dryers also protect foods form dust, insects, birds and animals. They can be constructed from locally available materials at a relatively low capital cost and there are no fuel costs. Thus, they can be useful in areas where fuel or electricity are expensive, land for sun drying is in short supply or expensive, sunshine is plentiful but the air humidity is high.
Moreover, they may be useful as a means of heating air for artificial dryers to reduce fuel costs 1 Solar food drying can be used in most areas but how quickly the food dries is affected by many variables, especially the amount of sunlight and relative humidity.
Typical drying times in solar dryers range from 1 to 3 days depending on sun, air movement, humidity and the type of food to be dried. The principle that lies behind the design of solar dryers is as follows: in drying relative and absolute humidity are of great importance. Air can take up moisture, but only up to a limit. This limit is the absolute maximum humidity, and it is temperature dependent. When air passes over a moist food it will take up moisture until it is virtually fully saturated, that is until absolute humidity has been reached.
But, the capacity of the air for taking up this moisture is dependent on its temperature. The higher the temperature, the higher the absolute humidity, and the larger the uptake of moisture. If air is warmed, the amount of moisture in it remains the same, but the relative humidity falls; and the air is therefore enabled to take up more moisture from it's surrounding.
To produce a high-quality product economically, it must be dried fast, but without using excessive heat, which could cause product degradation. Drying time can be shortened by two main procedures: one is to raise the product temperature so that the moisture can be readily vaporized, while at the same time the humid air is constantly being removed.
The second is to treat the product to be dried so that the moisture barriers, such as dense hydrophobic skin layers or long water migration paths, will be minimized 2. Types of Solar DryersThere are mainly three types of solar dryers 3 The absorption or hot box type dryers in which the product is directly heated by sun, 2.
The indirect or convection dryers in which the product is exposed to warm air which is heated by means of a solar absorber, or heat exchanger, 3. Dryers combining the principles of the above two, where the product is exposed to the sun and a stream of pre-heated air simultaneously. Direct Absorption DryersDirect drying consists of using incident radiation only, or incident radiation plus reflected radiation.
Most solar drying techniques that use only direct solar energy also use some means to reflect additional radiation onto the product to further increase its temperature. An example of direct absorption dryer is the hot box dryer as shown in Figure 1 3. The aim of this type of a dryer is mainly to improve product quality by reducing contamination by dust, insect infestation, and animal or human interference.
It consists of a hot box with a transparent top and blackened interior surfaces. Ventilation holes in the base and upper parts of slide walls maintained a natural air circulation. The main idea behind this type of a dryer is to obtain a low cost multi-product system. The leads to choose a drying chamber able to accommodate different kinds of trays and act in it self as a solar collector. The drying chamber has the shape of a parallelpiped with its longitudinal axes in the North-South direction.
A wooden frame supports a transparent polycarbonate hollow plate 4. The wooden skeleton and polycarbonate plates are screwed together allowing the whole chamber to be disassembled easily. The construction is modular to permit variations of the drying chamber capacity.
Trays have a shape that they can be piled easily without crushing the fruits and allow air circulation between them following the main axis. Four small windows located at the far ends of the chamber enable introduction of measuring devices and also control the air rene wal in the system. Eight fans placed inside the chamber produce and internal recycling, and cause the air flux to be uniform. The drying system has six solar collectors made of blackened iron plate, protected by a glass cover, which also helps to decrease heat losses 4.
The solar tunnel dryer Fig. To simplify construction and reduce costs, the solar col1ector is connected directly to the drying tunnel without any additional air ducts. Plastic foam sandwiched between two paral1el metal sheets is used as a back insulator for both the col1ector and drying tunnel. This insulator also functions as the structure of the dryer. The top surface of the insulator in the col1ector is painted black to absorb solar radiation.
The col1ector is covered with a transparent u. For the drying tunnel, a wire mesh is placed on top of the insulators. A sheet of plastic net, on which the product to be dried are spread, is placed on top of the wire mesh. This arrangement allows drying air to flow around the whole surface of the product being dried.
The drying tunnel is also covered with a u. One side of this sheet is fixed to the tunnel frame and the other side is fixed to a metal tube allowing the sheet to be rolled up and down for loading and unloading the dryer.
Fastening plastic profiles, as shown in Fig. This fixing method is designed to facilitate the replacement of the sheets. In general, the transparent sheet can be used for yr and the air bubble sheet lasts for years. Three small fans powered by a 53 W solar cell module are installed in the back of the collector to suck ambient air into the collector as shown in Fig.
The fans are intentionally installed below the solar module to constantly reduce its temperature, thus maintaining its efficiency. Both the collector and the drying tunnel are installed on concrete block substructures. All parts of the dryer, including the back insulator and metal frames, are designed using a modular concept, which facilitates the transport and installation of the dryer.
This solar tunnel dryer uses solar energy both in the thermal form for the drying process and the electrical form for driving the fans, by means of the solar collector and solar module respectively. Therefore, the dryer could be used in rural areas where there is no supply of electricity. A rock-bed dryer is shown in Fig. In this dryer, air, drawn by natural convection through an air inlet A , circulates the heat collected by the p rimary solar energy collector B , throughout the drying chamber C which is packed with limestone rocks of relatively uniform diameter.
The heat would then stratify across the rock bed but, since rocks are poor thermal conductors, temperature differences would slowly disappear when air is not moving through the rock bed. Thus samples positioned above the rock-bed can continue drying during the night. This type of a solar dyer requires very little maintenance 6. Combined Direct and Indirect DryersMany types of drying systems utilize both direct and indirect solar radiation. In these types of systems, radiant energy from the sun falls directly onto the product being dried; however, in addition, a preheater also is used to raise the air temperature, which in turn, accelerates the drying rate.
Acceleration of drying rate can occur in two ways: hot air can transfer some of its heat to the product being dried, thus raising its vapour pressure causing a faster moisture loss; or as temperature of ai r mass increases, the water-holding capacity also increases 2, 3.
TomatoesDue to the increasing demand to dried tomatoes from the industry, especially from the soup manufacturers, interest in producing high quality dried tomatoes has been increasing.
Therefore, it is important to establish a drying method, which yields products with higher sensory and sanitary quality in a shorter drying time compared to the conventional sun-drying method. However, citric acid did not prevent the growth of moulds and yeasts effectively. Therefore, dipping into sodium metabisulfite solution for 3 minute is the best type of pretreatment. Red PepperRed peppers are deseeded, cut into small pieces, and washed before loading into the tunnel solar dryer.
Moreover, the drying temperature and piece size of red peppers affects the final product quality. Red peppers that are cut into bigger pieces needs a longer time period to dry and therefore the colour of the final product is darker. To increase the capacity of the solar dryer, a double layer system can be constructed, but with this system, drying needs a more careful control.
Final moisture content of dried red peppers which are pretreated with 2 Na 2 S 2 0 5 for 1 second is 3. Green PepperGreen peppers are used especially in the soup manufacturing.
Therefore, establishing an efficient and economic method for peppers is important for the food industry. Green peppers are washed, deseeded and cut into small pieces before loading into the dryer. Green peppers are very sensitive to high temperatures and light.
OnionA large part of the dehydrated onion production is used as seasoning in production of catsup, chilli sauce and meat casseroles, as well as cold cuts, sausages, potato chips, crackers and other snack items.
Food service outlets also use dehydrated onions because of its convenience in storage, preparation and use. Before drying, onions are peeled and sliced into desired shapes. Sodium metabisulfite dipping can be used to preserve colour. Naturally dried carrots loss their bright orange colour. The sodium metabisulfite treated ones preserve their colour to the largest extent 7. PrunesIt is known that certain treatments used to modify the waxy cuticle of the surface of various fruits prunes, grapes , cherries, etc.
Different olive oil concentrations combined with sodium or potassium carbonate or ethyl esters of fatty acids are used for this purpose.
Dry fruit business plan pdf
Solar drying of fruit and vegetables For thousands of years people have sundried fruit and vegetables to preserve for leaner times. New technologies brought changed techniques, but at present the increasing demand for healthy, low-cost natural foods and the need for sustainable income, are bringing solar drying to the fore as a useful alternative for surplus products. Save for tomorrow what you do not need today! This publication is about Preparation and pretreatment of different fruit and vegetable types for drying How to dry these using simple solar dryers Proper storage of dried fruit and vegetables Recipes for dried fruit and vegetables. Advantages of solar drying Food in the cupboard for later use increases household food security. It creates employment opportunities and a sustainable income.
PDF | Drying is one of the oldest preservation processes available to the Keywords: drying method; food; fruit; vegetable; sun drying; solar drying; osmotic.
Home Drying of Food
Food drying is a method of food preservation in which food is dried dehydrated or desiccated. Drying inhibits the growth of bacteria , yeasts , and mold through the removal of water. Dehydration has been used widely for this purpose since ancient times; the earliest known practice is 12, B.
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Просунув раскаленный паяльник сквозь проволочный лабиринт у себя над головой, он действовал с величайшей осмотрительностью: опалить защитную оболочку провода значило вывести аппарат из строя. Еще несколько сантиметров, подумал Джабба. Работа заняла намного больше времени, чем он рассчитывал. Когда он поднес раскаленный конец паяльника к последнему контакту, раздался резкий звонок мобильного телефона. Джабба вздрогнул, и на руку ему упала шипящая капля жидкого олова. - Черт возьми! - Он отшвырнул паяльник и едва не подавился портативным фонариком.
Кто-то рядом с ним попытался его приподнять.