Food Chemistry

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. Refriger-
ation 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 ungut-
ted, 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 .5to− 5 ◦C is rapidly passed over. Apart

Fig. 13.5.Temperature course during fish fillet freezing

process

from air and contact freezing processes, cryo-

gen frosters are being increasingly used, espe-

cially for sensitive and high quality product (crus-

taceans).

In air freezing, freezing takes place in a cold cur-

rent of air in differently arranged, usually con-

tinuously 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