Catching
Maintenance of freshness
1. Processing on board ship
1.1 Processing in small
vessels
After squid are caught, the concern is how to maintain
the freshness. If squid are brought back to port by small
fishing vessels, which operate primarily in coastal waters,
they are: 1) arranged in baskets 2) packed in crushed ice
3) surrounded by ice-water, 4) placed in crates or stacked.
During the first step, the body temperature fluctuates by
4-5oC. Although the ice-water section exhibits quick cooling,
the temperature rises during transit due to insufficient ice.
The ice water is comparatively superior in terms of cooling
and maintenance of low temperatures.
The chromatophores in the epidermis open
immediately after capture, and the entire surface assumes
a semi-transparent, dark brown color. As time elapses, the
chromatophores contract and the surface become white-transparent,
but as the freshness declines, the amount of volatile basic
nitrogen in the epidermis increases, causing alkalinity. As
a result, the pigment is eluted and the body surface changes
to red, depending on the processing and storage conditions.
Bringing squid back in chilled sea water
(0-2 C) immediately after capture is good for preserving squid
in a form suitable for sashimi. However, processing with ice
water is not usually employed, since this method cannot be
used in vessels that do not have freezing equipment.
1.2 Freezing on-board
The 'fresh' color can be preserved by quick freezing of
fresh squid below –20 C to prevent drying. However, the body
color is readily tinged with red in moderate freezing, and
further discoloration occurs when the temperature subsequently
rises. Quick freezing of fresh squid is important to avoid
such changes in body colors.
Many modern squid vessels can meet such
requirements. Caught squid are transferred to the working
area by trough, slipway or conveyor. Water washing drainage
at the working areas is followed by sorting. There are also
vessels that are equipped to carry out water washing during
transit. The sorted squid are weighted and packed in 7.5 kilogram
or more.
The squid are frozen in a freezing chamber.
Freezing is based on the contact plate freezer method or semi-air
blast method. After freezing, the squid are immersed in cold
water for 5 to 6 seconds to prevent oxidation during storage
and increased weight. Squid are then placed in a corrugated
box and kept in cold storage at –25 to –35 C.
2. Processing on land
2.1 Ice storage processing
The freshness would naturally decline if the treatment
on shore is poor, regardless of how carefully the freshness
is maintained on-board. In maintaining freshness on land,
the requirements in terms of appearance vary, depending on
whether the squid are to be shipped as fresh. The first requirement
of fresh squid is that the epidermis be clear.
When squid have been processed with cold
seawater on board and on land, their appear fresh even after
one full day. However, those squid that are processed with
ice water after transport to land become tinged white and
opaque. Even after two days, squid processed with cold seawater
are superior to those processed in ice water on board.
These results indicate that squid must
be placed in cold seawater immediately after capture and on
land in order to ship them as fresh squid. Conversely, on-board
processing with ice water, or sprinkling of ice, is sufficient
for squid used in processed foods. The temperature need only
be maintained at a low level by ice water, ice treatment or
refrigerated storage after return to shore.
The effects of using crushed ice vary
under different conditions, including the mode of pretreatment,
the ratio of squid to ice, and the temperature at the storage
site. In general, the tentative criteria used in cold storage
of fish are as follows 1) the weight ratio of fish to crushed
ice in the summer should be 1: 3 for three days of cold storage,
1:2 for two days of storage, and 1:1 for one day of storage.
2) The ratios in the spring and fall should be 1:2 for three
days of storage, 1:1 for two days of storage and 2:1 of one
day of storage 3) The ratios in the winter should be 3:1 for
three days of storage, 4:1 for two days of storage and 5:1
for one day of storage.
2.2 Freezer processing
Freezing must be conducted for long-term storage of squid.
The freezing method was outlined in the discussion concerning
on–board processing, but the freshness of squid on land is
not always good.
The primary condition in freezing squid
is to freeze fresh squid. However, the moisture content in
the meat produces large ice crystals, which can destroy the
meat if the temperature is high and moderate freezing is carried
out, even if the freshness is good. This increases the amount
of drip during thawing. However, if the temperature during
storage is high, ice crystals in the tissue enlarge and the
quality decreases. Thus, the storage temperature should be
as low as possible.
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