Food Preservation: Fruits and Vegetables
Fruit Specific Preservation Technologies
“Preparation”
PREPARATION
Fruits and vegetables should be prepared for preservation as soon as possible after
harvesting, in any case within 4 to 48 hours. The likelihood of spoilage increases rapidly as time
passes.
1.1 Cleaning and washing
First, the fruits or vegetables must be thoroughly cleaned to remove any dirt or insecticide
residues. The outer layers of onions also must be removed. This cleaning process usually involves
washing the products under a faucet with running drinking-water or in a bucket with clean water
that is regularly refreshed. When cleaning leafy vegetables, it is best to first remove the stems.
Some types of fruit, such as cherries, strawberries and mushrooms are not washed, because this
would increase the spread of micro-organisms. It is also not advisable to wash cucumbers, because
this shortens their shelf-life.
1.2 Lye dip
Some products, such as plums and grapes, are immersed for 5-15 seconds in a pan of hot,
almost boiling, lye (NaOH; 10-20g lye/liter water) to make the peel rough and to thereby speed up
the general drying process. The peel then also separates more readily from the fruit, which makes
it easier to remove. After such a treatment, the fruit must be rinsed vigorously with cold water to
remove the lye residues. Lemon juice can also be used to neutralize any remaining lye residues.
The preparation method described above is ecologically harmful because alkaline is transported
by the wastewater into the environment. Other disadvantages of using lye are that the food can
become discolored and the metal pan could become corroded. The use of too-high concentrations
of lye is also unhealthy for the people working with it.
1.3 Sorting
To achieve a uniformly sized product, fruits and vegetables are sorted immediately after
cleaning according to their size, shape, weight or color. Sorting by size is especially important if
the products are to be dried or heated, because their size will determine how much time will be
needed for these processes.
1.4 Peeling
Many types of fruits and vegetables must be peeled to be preserved. This can easily be
done with a stainless-steel knife. It is extremely important that the knife be made of stainless steel
because this will prevent the discoloration of the plant tissues. It is best to first submerge citrus
fruits, tomatoes and peaches, whose peels are all securely connected to the fruit, in hot water for 1
½ to 3 minutes. The softened peel can then be removed without too much effort.
1.5 Cutting
Cutting is important because you will need approximately uniform pieces for the heating,
drying, and packing stages. Fruits and vegetables are usually cut into cubes, thin slices, rings, or
shreds. The cutting utensils must be sharp and clean to prevent micro-organisms from entering the
food. From the moment they are cut, the quality of the products decreases due to the release of
enzymes and nutrients for micro-organisms. A decrease in quality is also caused by the damage
Fruit Specific Preservation Technologies
“Preparation”
PREPARATION
Fruits and vegetables should be prepared for preservation as soon as possible after
harvesting, in any case within 4 to 48 hours. The likelihood of spoilage increases rapidly as time
passes.
1.1 Cleaning and washing
First, the fruits or vegetables must be thoroughly cleaned to remove any dirt or insecticide
residues. The outer layers of onions also must be removed. This cleaning process usually involves
washing the products under a faucet with running drinking-water or in a bucket with clean water
that is regularly refreshed. When cleaning leafy vegetables, it is best to first remove the stems.
Some types of fruit, such as cherries, strawberries and mushrooms are not washed, because this
would increase the spread of micro-organisms. It is also not advisable to wash cucumbers, because
this shortens their shelf-life.
1.2 Lye dip
Some products, such as plums and grapes, are immersed for 5-15 seconds in a pan of hot,
almost boiling, lye (NaOH; 10-20g lye/liter water) to make the peel rough and to thereby speed up
the general drying process. The peel then also separates more readily from the fruit, which makes
it easier to remove. After such a treatment, the fruit must be rinsed vigorously with cold water to
remove the lye residues. Lemon juice can also be used to neutralize any remaining lye residues.
The preparation method described above is ecologically harmful because alkaline is transported
by the wastewater into the environment. Other disadvantages of using lye are that the food can
become discolored and the metal pan could become corroded. The use of too-high concentrations
of lye is also unhealthy for the people working with it.
1.3 Sorting
To achieve a uniformly sized product, fruits and vegetables are sorted immediately after
cleaning according to their size, shape, weight or color. Sorting by size is especially important if
the products are to be dried or heated, because their size will determine how much time will be
needed for these processes.
1.4 Peeling
Many types of fruits and vegetables must be peeled to be preserved. This can easily be
done with a stainless-steel knife. It is extremely important that the knife be made of stainless steel
because this will prevent the discoloration of the plant tissues. It is best to first submerge citrus
fruits, tomatoes and peaches, whose peels are all securely connected to the fruit, in hot water for 1
½ to 3 minutes. The softened peel can then be removed without too much effort.
1.5 Cutting
Cutting is important because you will need approximately uniform pieces for the heating,
drying, and packing stages. Fruits and vegetables are usually cut into cubes, thin slices, rings, or
shreds. The cutting utensils must be sharp and clean to prevent micro-organisms from entering the
food. From the moment they are cut, the quality of the products decreases due to the release of
enzymes and nutrients for micro-organisms. A decrease in quality is also caused by the damage
