50
from the pre-cooker (blancher) into cold water. The shrimps pass from the coldwater boiler onto a drying belt and the excess water is removed. Steam pre-cooking
is done at 95–100 °C for 8–10 min depending on shrimp size. While the shrimp
colour changes from pink to white during pre-cooking, the texture changes into firm
and the shrimp gets its typical curl appearance. They then come to the grader, which
can be separated into five categories (tiny, small, medium, large, and jumbo). Then
they are visually inspected to correct grader’s mistakes and foreign matter and
crushed shrimps are removed (Featherstone 2016a).
Shrimps are filled into suitable containers. These containers can be tin cans and
glass jars. However, the containers to be used must have properties such as hermetic
sealing, heat resistance, and non-reactivity with the product. It is more common to
use tin cans because of their advantages such as sterile preservation of the product,
resistance to sterilization temperatures, ease of distribution, storage, and stacking.
However, in the case of use of cans, there is a risk of corrosion (Horner 1992;
Gokoglu 2002). In fact, flexible bags, which have been started to be used in 1960s,
have been used more widely in recent years. These are robust polymer laminates
consisting of a heavy-duty outer polymer layer which then binds to the heat sealable
inner polymer layer. Of course, flexible bags also have some disadvantages. They
are more expensive than tin cans; they require specially designed retorts and leak
detection is more difficult (Horner 1992). In addition, retort pouches have several
advantages, resulting in more quality, such as shelf stability, low weight and less
storage space, ease of opening and preparation, and low temperature exposure.
Because of the faster penetration of food into the food, there are also advantages
such as cooking time and decreasing energy consumption. In a study compared the
cooking process of shrimp in retortable pouches and cans, retort pouches showed
37% less thermal processing time than the canned product (Chiar et al. 2006).
In another study, 35% reduction in processing time in kuruma shrimp processed in
retortable pouches compared to aluminium can was observed (Mohan et al. 2006).
Pouched foods are reported to have a better texture and flavour. Most retort pouches
are made from a four-layer laminate consisting of a polyester outer layer, a nylon
second layer, a third layer of aluminium foil and a polypropylene inner layer.
Polypropylene polymers have a melting point of about 138 °C, which is higher than
the commercial sterilization temperature of 121 °C. It has been reported that
improved texture and flavour are observed in freshwater shrimp (Macrobrachium
rosenbergii) packed with laminated flexible pouches in a curry medium (Majumdar
et al. 2017).
Shrimps are placed by hand in the cans and carefully weighed. The can weight
depends on the type and size of the shrimp. Because of the cans are contaminated
during the transportation and storage stages before filling the canning containers
must be washed. The cleaning of the cans is usually done by pressurized water or
steam (Gokoglu 2002). The filled cans come to the sealing machine via conveyor
belts. Hot saline solution is added to the shrimp cans. The product produced in this
way is called “wet-pack”.
The filled cans are placed in the autoclave with the metal baskets. Heat treatment
is carried out under pressure. The processing time depends on the size of the can. At
2 Crustacean Shellfish
from the pre-cooker (blancher) into cold water. The shrimps pass from the coldwater boiler onto a drying belt and the excess water is removed. Steam pre-cooking
is done at 95–100 °C for 8–10 min depending on shrimp size. While the shrimp
colour changes from pink to white during pre-cooking, the texture changes into firm
and the shrimp gets its typical curl appearance. They then come to the grader, which
can be separated into five categories (tiny, small, medium, large, and jumbo). Then
they are visually inspected to correct grader’s mistakes and foreign matter and
crushed shrimps are removed (Featherstone 2016a).
Shrimps are filled into suitable containers. These containers can be tin cans and
glass jars. However, the containers to be used must have properties such as hermetic
sealing, heat resistance, and non-reactivity with the product. It is more common to
use tin cans because of their advantages such as sterile preservation of the product,
resistance to sterilization temperatures, ease of distribution, storage, and stacking.
However, in the case of use of cans, there is a risk of corrosion (Horner 1992;
Gokoglu 2002). In fact, flexible bags, which have been started to be used in 1960s,
have been used more widely in recent years. These are robust polymer laminates
consisting of a heavy-duty outer polymer layer which then binds to the heat sealable
inner polymer layer. Of course, flexible bags also have some disadvantages. They
are more expensive than tin cans; they require specially designed retorts and leak
detection is more difficult (Horner 1992). In addition, retort pouches have several
advantages, resulting in more quality, such as shelf stability, low weight and less
storage space, ease of opening and preparation, and low temperature exposure.
Because of the faster penetration of food into the food, there are also advantages
such as cooking time and decreasing energy consumption. In a study compared the
cooking process of shrimp in retortable pouches and cans, retort pouches showed
37% less thermal processing time than the canned product (Chiar et al. 2006).
In another study, 35% reduction in processing time in kuruma shrimp processed in
retortable pouches compared to aluminium can was observed (Mohan et al. 2006).
Pouched foods are reported to have a better texture and flavour. Most retort pouches
are made from a four-layer laminate consisting of a polyester outer layer, a nylon
second layer, a third layer of aluminium foil and a polypropylene inner layer.
Polypropylene polymers have a melting point of about 138 °C, which is higher than
the commercial sterilization temperature of 121 °C. It has been reported that
improved texture and flavour are observed in freshwater shrimp (Macrobrachium
rosenbergii) packed with laminated flexible pouches in a curry medium (Majumdar
et al. 2017).
Shrimps are placed by hand in the cans and carefully weighed. The can weight
depends on the type and size of the shrimp. Because of the cans are contaminated
during the transportation and storage stages before filling the canning containers
must be washed. The cleaning of the cans is usually done by pressurized water or
steam (Gokoglu 2002). The filled cans come to the sealing machine via conveyor
belts. Hot saline solution is added to the shrimp cans. The product produced in this
way is called “wet-pack”.
The filled cans are placed in the autoclave with the metal baskets. Heat treatment
is carried out under pressure. The processing time depends on the size of the can. At
2 Crustacean Shellfish