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Drying or dehydration is one of the oldest ways of preserving agricultural
products. It is a process of separating a certain amount of water from fresh
fruits, in order to enable its long-term storage in natural conditions without
spoilage. With dehydration (reduction of moisture), the activities of
microorganisms in the fruit are reduced. Self-produced dry food is just another
form of fresh food, without chemical preservatives. One of the advantages of
drying vegetables over other canning methods is that dehydrated products can be
rehydrated and reused fresh without compromising quality. Dried products are
easier to store, pack and transport.
Application of renewable energy sources and energy efficiency
Our company aims at greater application of renewable energy sources in
agriculture. Several experts in this field were involved in the calculations and
design of the dryer. The basic drying parameters are: Temperature, Relative
humidity, drying time and air circulation speed for drying.
Digitization
Our company additionally installs in larger dryers Wi-Fi devices for monitoring
energy consumption and Wi-Fi data loggers for monitoring relative humidity and
temperature. The client from home, through the Android platform can follow the
drying process.
Rules for drying vegetables and fruits
The technological process of drying vegetables includes two basic stages:
preparation of the drying product and the drying procedure and quality control
of the dry product (percentage of moisture in it).
Preparation before drying: Do not crush the fruits. After harvesting, transport
should be done as soon as possible to prevent spoilage. Primary fruit processing
involves washing, controlling, cutting and sorting. Each culture has a special
way of preparation. Dried fruits must:
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To be healthy, fresh and in the stage of
technological maturity;
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No foreign smell and taste;
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To be free from impurities from plant
protection products above the maximum allowed quantities.
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Handles and seeds must be removed from some
fruits before drying
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Fruits intended for drying should never be
stacked on top of each other, but next to each other
Recommended technology for drying certain types of fruit.
Note: Each manufacturer determines the drying technology depending on
the fruit and the requirements of the market or the end buyer. Consult a
technologist about this! A very important detail is the way of packaging the
dried product.
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Plum: The initial drying temperature of 75ºC,
and the final from 60 to 65ºC. Drying lasts from 16-18 hours. Dried plums
should contain 22 to 26% moisture, which will depend on the method of
further processing. Cool the plums before storing.
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Apples Drying temperature should be between
30 and 70º C. Too long drying at low temperature can create mold. Apples
should not be dried too fast at high temperatures, because dried fruit will
be less tasty. Drying time depends on air temperature and the amount of
water apples. Most often, the drying time at a temperature of 50-60ºC is 6 ÷
8 hours
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Apricot. Preparation: Sulfurization takes
place by burning pure sulfur. This should prevent the fruit from darkening.
It lasts from 2-3 hours. The required amount is 2.3 kg of sulfur per 1000 kg
of fruit. Immersion in sucrose solution can vary from 70-85% Drying
temperature of 45-55ºC. Duration 18-24 hours.
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Grapes. White seedless varieties are mostly
used for drying grapes, but colored varieties can also be successfully
dried. The seedless varieties are Sultanija, Sultanina and the new Belgrade
seedless variety. Drying is from 50 to 70 ºC, duration 15 - 17 hours. The
grapes are dried to a water content of 10-15%
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Fig. Drying temperature is 45-50ºC, duration
30-40 hours, or 65-75 ºC with drying time about 5 hours (depending on the
type of dryer). The water content in the dried fig is 12-22%. Dried figs
should be stored at 10ºC in well-ventilated conditions
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Aronia. Drying lasts 66 hours, takes place at
a temperature of 45˚C to a moisture content of 10%. The basic aspect of the
drying process is related to the amount of water in the fruit.
The technology is obtained from the University Goce Delchev Stip. Only a
shortened and general version of fruit drying is given above.
Recommended technology for drying certain
types of vegetables.
Note: Each manufacturer determines the drying technology depending on the fruit
and the requirements of the market or the end buyer. Consult a technologist
about this! A very important detail is the way of packaging the dried product.
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Tomato: The drying temperature at the
beginning is 65-70 ºC, and at the end of the process it should not be above
45 .C. The drying process takes 6-7 hours. The moisture content in the dry
product should not exceed 4-5%. After drying, the product is checked, it is
done manually in order to remove the pieces that do not match in color, dark
or damaged. Due to the hygroscopicity, it should be packed in an airtight
container immediately.
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Onion: Drying is carried out with an initial
temperature of about 70ºC. The temperature should gradually decrease (drop),
so in the final stage it should be around 55ºC. Drying takes 3.5-5.5 hours,
and the moisture content of the dry product should be 8%
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Leek. The length of the leek is 30-40 cm, and
the diameter 3-5 cm, depending on the variety. The white part of the stem is
cut into pieces 5-7 mm thick, the green and white part 6-8 mm, and the
leaves into pieces 8-10 mm thick. Drying is at a temperature of 70ºC at the
beginning and at the end at about 50ºC.
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Carrots. Preparation: Cut the carrots into
circles (thickness 3mm) or cubes (10x10x10mm). The drying air temperature at
the beginning of the process is 71ºC for 7 hours and then decreases to 60ºC
for the next seven hours. It is dried with initial 95% and final 3.5-4.5%
humidity.
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Mushrooms: The temperature in the first four
hours should be 43 ºC, and then increase to 75 ºC for 1 hour. During this
time the humidity decreases from 87% to 3%. The final product to have good
taste and color, dried mushrooms should not be blanched, but immediately
after drying are packed in a hermetically sealed package
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Pepper: The initial temperature should not be
above 75ºC, and in the later phase 55ºC to 60ºC. The moisture content in the
dry product should not be more than 9%, Dried peppers should have a uniform
red color and appearance.
Properties that affect the quality of the
final dry product are the following:
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Structural properties: Density, porosity,
pore size, specific volume
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Optical properties: Color, appearance
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Mechanical properties: Resistance to pressure
and tension
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Thermal properties: Glass, crystalline or
rubber state of the product
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Curly properties: Smell, taste and aroma;
Nutritional properties: Vitamins, proteins
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Rehydration properties: Rehydration,
rehydration capacity
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Quality characteristics are related to drying
temperature and air flow
The technology is obtained from the University Goce Delchev Stip. Only a
shortened and general version of fruit drying is given above.
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