2009_Book_FoodChemistry

13.1 Fish 631
Fig. 13.4. Fish processing on board (a) and on land (b)
ered fully preserved, canned or semi-preserved
products. Semi-preserves may contain additives
against microbial spoilage. The compositions of
some fish products are given in Table 13.12.
13.1.6.2 Cooling and Freezing
Preservation of freshness by refrigeration is the
most modern and effective way to retain the
wholesomeness and nutritional value of food.
Refrigeration also enables fishing fleets to range
the oceans for months in search of fish. Refrigeration
permits stockpiling of fish, thus making fish
processing plants more economical and better
able to respond to market demand and supply.
Fish deteriorates rapidly at temperatures only
slightly above 0 ◦ C. Therefore, immediately after
catching fish are packed in ice on board the ship.
The ice used may be sprinkled with a bactericidal
substance. Freezing, which may also be used on
ships, is suitable for whole fish (gutted or ungutted,
with or without head or skin removal), as is
the case with flat fish, tuna, mackerel or herring,
or for fish fillets (cod, haddock, saithe, red fish).
Only quick freezing is used (−30 to −40 ◦ C;
cf. Fig. 13.5), so the critical temperature range
of −0.5 to−5 ◦ C is rapidly passed over. Apart
Fig. 13.5. Temperature course during fish fillet freezing
process
from air and contact freezing processes, cryogen
frosters are being increasingly used, especially
for sensitive and high quality product (crustaceans).
In air freezing, freezing takes place in a cold current
of air in differently arranged, usually continuously
operated systems (tunnel, spiral band
etc.). In the contact freezing processes used, the
fish are pressed and frosted between two contact
plates that are cooled by a flow of coolant. The
blocks obtained by this process can be portioned
into slabs or sticks using band saws. They can
be sold to the consumer as such or breaded and
prefried (170 ◦ C, 20 s). Waste pieces (8–12%) are