T h r e e means of cooling are available: ( 1 ) cold air; ( 2 ) ice; and ( 3 ) chilled w a t e r or brine.
A . C O L D A I R
T h e rate of cooling in cold air is very low. F i g u r e 7 shows the dif
ference b e t w e e n chilling of fillets immersed in w a t e r at 2 ° C . / 3 5 . 6 ° F . and c°
12 10 8 6 L 2 0
1 2 3 U 5 H o u r s
FIG. 7. Cooling curves for medium-size cod fillets, one lot immersed in cold water, the other lot wrapped in parchment in 2-lb. packages and exposed to slowly circulated cold air (Fisheries Technological Laboratory, Copenhagen).
kept in air at — 1 ° C . / 3 0 ° F . Moreover, in experiments w h e r e fish h a v e b e e n kept in cold air at the same temperature ( a b o u t — 0 . 5 ° C . / 3 1 ° F . ) as that of iced control fish, the i c e d fish h a v e k e p t several days longer t h a n the fish without ice. T h i s difference has b e e n shown b y taste panel work as well as b y bacterial counts or b y measurements of c h e m i c a l
spoilage products. I t appears to b e due to t h e washing away of bacteria and the leaching of some of the spoilage products caused b y the melting water from the ice ( N o t e v a r p and Hjorth-Hansen, 1 9 3 3 ; Anonymous, 1 9 5 6 a ) .
B . F R E S H - W A T E R I C E
Normal ice will cool fish to the temperature of melting ice, 0 ° C . / 3 2 ° F . , if used properly and in sufficient quantities. F r o m measurements in fish landed from large trawlers in G r i m s b y and from small North S e a cutters in E s b j e r g it appears that even temperatures around — 0 . 5 ° C . / 3 1 ° F . (i.e., near the freezing point of the fish) are c o m m o n in well-iced shiploads of fish.
1. Cooling Rates
I f insufficient ice is used, or if the ice is not mixed thoroughly with the fish, the fish will r e a c h desirable temperature levels either very slowly
A / / / / / / / /
LL
/ / /
, - · " " / D / ο
5 6 0
-<υ
/ / /
/ / / s s
• / /
>f fish 1
/
/ I
I ι
40 50 60 Hours after icing
FIG. 8 . Cooling curves for gutted cod iced aboard a schooner. Fish under in
vestigation were located in the pen as shown in the diagram (MacCallum et al.,
1 9 4 9 ) .
or not at all. F i g u r e 8 ( M a c C a l l u m et al., 1 9 4 9 ) indicates h o w b a d things m a y b e . Curve A shows t h e cooling rate of a fish situated at t h e top of a p e n in an insulated fish hold on b o a r d a vessel. T h a t this fish was buried in ice w h e n it was stored is evident from the rapid cooling rate.
It dropped from about 1 0 ° C . / 5 0 ° F . to 1 . 7 ° C . / 3 5 ° F . in approximately 3 hr. At the end of this period t h e i c e was gone, and 2 days later the temperature of the fish h a d risen to well over 4 . 4 ° C . / 4 0 ° F . as a result of warm air and insufficient i c e near the deck. Curve Β shows the cool
ing rate of a fish next to the pen boards at the front of a pen in an uninsulated vessel. I n this case the fish was not adequately iced, since it took almost 2 0 hr. to bring it down to 1 . 7 ° C . / 3 5 ° F . I t never got cooler.
Curves C and D show cooling rates along the b a c k wall of the same pen, but within about 3 hr. most of the ice was gone and it took almost a day for the fish to r e a c h 1 ° C . / 3 4 ° F . B y that time the i c e must have b e e n completely melted, b e c a u s e the fish w a r m e d up to 4 . 4 ° C . / 4 0 ° F . Curve D shows the same thing in a m u c h more pronounced form. T h e ice was gone in a couple of hours and the fish did not cool to lower than 5 . 5 ° C . / 4 2 ° F .
T h e normal practice in t h e b o a t w h e r e t h e temperatures w e r e mea
sured was to stow the fish in layers as m u c h as 15 i n c h e s / 3 0 cm. thick.
Curve F shows the cooling rate in a pen, w h e r e the layers of fish w e r e restricted to the depth of one fish, i.e., about 3 i n c h e s / 7 . 5 c m . T h e tem
perature of the fish investigated r e a c h e d 0 ° C . / 3 2 ° F . in about 7 hr.
I n t h e case of fish or fillets p a c k e d with ice in boxes, t h e rate of cooling depends also on the thickness of the fish layer and on whether it is iced on one side only or on b o t h sides. I n Figs. 9 - 1 1 are shown examples with fillets and whole fish iced in boxes (Nicol, 1 9 5 8 a ) . T h e s e measurements have more relation to subsequent material concerning the handling of fish on shore ( s e e Section V I , B ) . However, they are men
tioned here for practical reasons.
2. Influence of Ambient Temperature
T h e temperature of the air in t h e room around i c e d fish—the ambient temperature—influences t h e storage life of the fish. R e c e n t repeated ex
periments with well-iced fish in individual boxes have shown that, within normal limits, the higher t h e temperature of the air around iced fish the b e t t e r the fish keep, despite the fact that the temperature of the fish in all cases was very near 0 ° C . / 3 2 ° F . (Anonymous, 1 9 5 6 b ) . It is doubt
ful whether this effect, w h i c h presumably is due to removal of bacteria and leaching out of decomposition products, would b e completely re
produced in a fully stowed pen of fish. However, it is a widespread ex
perience among fishermen that a fair rate of melting of i c e — a n ambient temperature of about 5 ° C . / 4 0 ° F . — i s beneficial to the bloom of the fish and to quality as a whole. T h e influence of a m b i e n t temperature on t h e rate of cooling in fish stored in ice has b e e n examined several times.
L u m l e y et al. ( 1 9 2 9 ) found that fish buried in crushed ice took twice as
' ' S S S S ' S s s//// s SSS /
FIG. 9. Curves showing the temperature of fillets in a 28-lb. wooden box at various times after icing on one side only (Nicol, 1958a).
FIG. 10. Curves showing the temperature of fillets in a 28-lb. wooden box at various times after icing on both sides (Nicol, 1958a).
t ° c 1 2 Γ
FIG. 11. Curves showing temperatures in medium-size cod iced in one case on top only. In the other case ice was used underneath the fish as well. The fish were packed one layer deep in wooden boxes. The fish used for measurements were not in contact with the vertical sides of the boxes (Fisheries Technological Laboratory, Copenhagen).
long to cool in a refrigerator at 0 ° C . than in a room at about 8 ° C . / 4 6 ° F . Similar findings w e r e recorded later (Anonymous, 1 9 5 3 b ) . I f this w e r e true, refrigeration of fish rooms on b o a r d trawlers would actually delay cooling.
This conclusion is criticized b y Heiss ( 1 9 3 7 ) , w h o points out that t h e transfer of h e a t b e t w e e n air a n d i c e is m u c h slower t h a n b e t w e e n fish and ice, and that furthermore the influence of the temperature of the air on the rate of cooling in fish completely i m b e d d e d in i c e c a n only b e of secondary importance. T h i s was confirmed b y Osoling ( 1 9 3 7 ) and Cutting ( 1 9 4 9 b ) , b o t h o f w h o m experimentally found that t h e tem
perature of the air surrounding iced fish h a d no effect on the rate of cooling.
C. C H I L L E D F R E S H W A T E R
T h e use of chilled water with a temperature near 0 ° C . / 3 2 F . is a quick m e t h o d of cooling fish and fillets ( s e e F i g . 7 ) . S o m e canners use this m e t h o d for chilling raw fish. T h e w a t e r c a n b e chilled either b y cir
culation through a cooler similar to that used for chilling sea w a t e r ( s e e Section V , E ) , or simply b y adding crushed i c e to the water. I f the latter m e t h o d is used, a reserve of i c e m a y b e stored up to m e e t p e a k loads, so that this m e t h o d therefore does not require as b i g a re
frigeration c a p a c i t y as that of direct w a t e r cooling (Anonymous, 1 9 5 5 c ) . Tanks containing refrigerating pipes have b e e n in use, b u t cooling of the water and consequently of the fish b y this m e t h o d is generally slow. F u r t h e r m o r e , such tanks are difficult to clean.
D . S A L T - W A T E R I C E
B y proper icing of fish with fresh-water i c e it is normal to attain tem
peratures just a b o v e the freezing point of the fish ( a b o u t — 0 . 5 ° C . / 3 1 ° F . ) . I n m a n y cases at sea and on shore, however, fish are not iced properly, with the c o n s e q u e n c e that t h e temperature in t h e fish is sev
eral degrees a b o v e what it should b e . T h i s fact is perhaps (intentionally or unintentionally), t h e b a c k g r o u n d for the m a n y experiments with ice m a d e from w e a k brine or sea water, usually called salt-water ice.
"Klondyking" is a m e t h o d of preserving u n g u t t e d herring b y sprin
kling t h e m with ice and salt and packing t h e m in boxes. S i n c e about 1880 this m e t h o d has b e e n used in t h e British export o f herring for North G e r m a n marinating factories. T h e preservation is p r o b a b l y due to t h e low temperature and partial freezing that result from mixing i c e and salt.
Production o f salt-water i c e is technically possible. I n F r a n c e , w h e r e experiments with this kind of i c e have b e e n going on since a b o u t 1 9 2 0 ,
a m a c h i n e has recently b e e n constructed ( L e Danois, 1 9 5 2 ) with w h i c h the salt-water i c e is formed in tubes. I t is in use on an island w h e r e fresh w a t e r is not available for ice-making.
T h e primary disadvantages o f such installations are corrosion and the fact that the i c e is not homogeneous in temperature. I n some places it m a y b e too low so that the fish is partially frozen ( D a v a l , 1 9 5 5 ) . However, t h e salt disappears with the melting water during storage. In the experiment shown in F i g . 1 2 the final temperature of the salt-water ice corresponds to that of fresh-water ice.
10 15 20 D a y s of s t o r a g e
FIG. 12. Average temperatures in codling thoroughly iced in wooden boxes with flake ice made from ( I ) tap water, (II) tap water containing 1% sea salts, and (III) tap water containing 3% sea salts (Hansen, 1960b).
O n t h e other hand, it is claimed that, b e c a u s e of its softness, salt
water ice is less injurious to the fish, that it does not c a k e as does fresh
w a t e r ice, and, as already mentioned, that it preserves t h e fish better.
Another aspect of salt-water i c e is t h e possibility of producing it on b o a r d instead of taking ice from t h e port. Suggestions h a v e b e e n ad
v a n c e d for such an installation ( L e Danois, 1 9 5 4 ; Anonymous, 1 9 5 5 d ) . Several experiments indicate that a slightly b e t t e r keeping quality of fish is o b t a i n a b l e with salt-water i c e than with conventional ice. Fields ( 1 9 5 3 ) and T a y l o r ( 1 9 5 3 ) , reporting on t h e same experiments, found that 3 % salt-water-iced fish ( r e d snappers, skipjack, and s h r i m p ) w e r e superior in appearance, color, brightness of eyes, and firmness of flesh to fish stored in ordinary crushed fresh-water i c e . T h e temperature in t h e con
trols was 3 ° - 50C . / 3 70- 4 1 ° F . against a b o u t — 0 . 5 ° C . / 3 1 ° F . in the salt
water-iced fish. T h i s temperature difference m a y explain these findings.
Hansen ( 1 9 6 0 b ) i c e d t h e control fish to such an extent that t h e lowest
possible temperature with fresh-water ice was attained ( s e e F i g . 1 2 ) . Using a trained taste panel h e found that the over-all quality of codlings stored in i c e m a d e from tap water containing 3 % sea salt gained more from the delay in spoilage than it lost through partial freezing and salt uptake. H e remarks that experiments on a m o r e practical scale are nec
essary before it c a n b e seen whether salt-water ice m a y b e o f commer
cial value. A r e c e n t large-scale American trial showed no significant difference in the storage life o f h a d d o c k stowed in the two kinds of i c e in a trawler's hold. I n salt-water ice the fish w e r e cooled somewhat faster than w e r e the fish in fresh-water ice. T h e difference in temperature dur
ing the first 6 days was from 0.5° to 1 ° F . in favor of the salt-water-iced fish. However, b e c a u s e of a faster rate of melting and a consequent greater loss o f i c e , t h e temperature of the fish stored in salt-water ice rose at t h e end of the experiment to a higher point than did that of t h e fish stored in fresh-water ice. No definite conclusion, therefore, can b e drawn from these experiments ( P e t e r s and Slavin, 1 9 5 8 ) .
E . C H I L L E D S E A W A T E R OR B R I N E
Refrigerated sea w a t e r or diluted brine with a salt content of up to about 8 % are widely used in some areas in canning plants for storing sardines, herring, pilchards, mackerel, salmon, and similar fish prior to processing. C o m m o n temperatures of the liquid are — 1 ° C . / 3 0 ° F . to
— 2 ° C . / 2 8 ° F .
In F r a n c e , such a practice was advocated about 1 9 2 0 ( L e Danois, 1920; Monvoisin, 1 9 4 6 ) . Huntsman ( 1 9 3 1 ) showed that fish could b e held in a tank with circulating sea water chilled b y large blocks of ice and suggested that m e c h a n i c a l refrigeration could replace ice in such a system. Davis et al. ( 1 9 4 5 ) , continuing some earlier laboratory experi
ments b y L a n g , experimented with commercial-size tanks for California sardines, w h i c h w e r e kept in chilled brine awaiting canning operations.
W i t h circulating brine at 0 ° C . / 3 2 ° F . , the temperature of fish at 1 7 ° C . / 6 3 ° F . was lowered to 1 0oC . / 5 0 ° F . in 1τ/2 hr. Among t h e advantages gained w e r e a higher over-all case p a c k per ton of fish received and a resultant firmness of fish from chilling that speeds up the cutting opera
tion and minimizes t h e tearing and losses that normally occur in cutting soft fish.
Sigurdsson ( 1 9 4 5 ) found that herring stored in refrigerated brine showed keeping qualities superior to those of herring held in ice. Kono-kotin ( 1 9 4 9 ) cooled sprats intended for smoking and held t h e m for 3 6 hr. in rigor mortis in brines chilled to — 2 ° C . / 2 8 ° F . or — 1 ° C . / 3 0 ° F . H e stated that this m e t h o d of storage is preferable to that of holding the fish in ice.
T h e possible difference in temperatures b e t w e e n those obtained in fresh-water i c e and in w e a k brines does not in t h e beginning seem to have b e e n the m a i n reason for preferring brine-cooling to packing in ice.
B e t t e r a p p e a r a n c e and easier handling of fish are considered important advantages.
T h e rate at w h i c h t h e fish are cooled down can b e very slow in inefficient installations. F ä r b e r ( 1 9 6 0 ) described a r e c o m m e n d a b l e cool
ing system consisting of a tank with a m m o n i a coils to cool t h e brine, a brine-circulating pump, and fish-holding tanks. I n a typical run, 17 tons
2 3 U 5 6 1 10
FIG. 1 3 . Technological diagram of sprat cooling. ( 1 ) Fish pump; ( 2 ) diffuser;
( 3 ) water separator; ( 4 ) feeder; ( 5 ) reception funnel; ( 6 ) sprat cooler; ( 7 ) diffuser;
( 8 ) filter-water separator; ( 9 ) box; ( 1 0 ) deck, ( a ) Water thrown overboard; (b) water in filter for accumulating scales; ( c ) cold water; (d) water for cooling; (e) water to filters for accumulating scales and for cooling (Gakichko et al., 1 9 5 8 ) . of sardines—starting at 1 7 ° C . / 6 3 ° F . — w e r e chilled to 4 . 4 ° C . / 4 0 ° F . within 8 5 minutes. T h i s r a t e is of t h e same order as that obtained w h e n fish are p a c k e d with ample ice ( s e e F i g s . 8 a n d 1 1 ) .
An even faster rate c a n apparently b e achieved. T h e apparatus in F i g . 13 is installed on a Soviet fishing vessel in t h e Caspian Sea. I n a trial run, sprats w e r e cooled from 1 7 ° C . / 6 3 ° F . to 3 ° C . / 3 7 . 4 ° F . b y b e i n g in c o n t a c t for 1 minute with a flume of chilled brine ( G a k i c h k o et al., 1 9 5 8 ) . I n t h e case o f soft, "feedy" fish, such fast cooling m a y b e decisive for the use o f such fish as raw material for h u m a n consumption.
I n recent years, it has b e e n suggested that advantages m a y b e gained b y stowing fish on b o a r d ship either in sea w a t e r or in brine chilled to
— 1 ° C . / 3 0 ° F . as c o m p a r e d w i t h stowage in i c e ( T a r r , 1 9 4 7 ) . M a n y ex
periments have b e e n carried out, particularly on t h e Canadian Pacific coast, with salmon and halibut to determine w h e t h e r this is so. Salmon
stored in this w a y for from 8 to 19 days w e r e preferred to normally i c e d fish ( L a n t z , 1 9 5 3 ) .
L a n t z and Gunasekera ( 1 9 5 5 b ) tried this m e t h o d with various trop
ical fishes in Ceylon at — 1 ° C . / 3 0 ° F . in 2 % brine; they found, for in
stance, that ungutted sardines kept chilled this w a y up to 8 days did not differ in a p p e a r a n c e or flavor from freshly caught fish. T h e s e results sound very promising for future practice in w a r m climates. Stern and D a s s o w ( 1 9 5 8 ) twice compared E n g l i s h sole in refrigerated 3 % brine at 0 ° C . / 3 2 ° F . to 1 ^ ° C . / 3 5 ° F . with the same fish heavily iced, and found that both lots remained edible for an equal length of time. T h e y add that the advantages of refrigerated brine appear to b e that the brine temperature can b e lowered to — 1 ° C . / 3 0 ° F . , that pressures upon fish can b e reduced, and that greater e c o n o m y in handling the fish can b e attained.
British laboratory-scale trials w e r e m a d e in w h i c h codling, stored in chilled sea w a t e r at 0 ° C . / 3 2 ° F . to — 1 ° C . / 3 0 ° F . for periods ranging from 13 to 18 days with or without aeration of the sea w a t e r and with or with
out antibiotics ( 2 p.p.m. Chlortetracycline [ C T C ] ) , w e r e c o m p a r e d with codling stowed in i c e (Anonymous, 1 9 5 8 a ) . E x c l u d i n g the experiment with antibiotics, little difference could b e d e t e c t e d on cooking b e t w e e n the two lots of fish, apart from the distinct b u t not unpleasant saltiness of the fish stored in sea water. T h e fish stored in sea w a t e r with C T C remained edible about 5 days longer than t h e fish stored in ordinary ice.
Several crude trials of sea-water stowage of c o d on b o a r d a commercial trawler, w h e n the tank was aerated, also resulted in the same quality for sea-water-chilled fish and those shallow-bulked in ordinary ice, al
though it was observed that the bacterial counts w e r e significantly lower in the sea-water-chilled samples. I f practical problems o f construction can b e overcome, the sea-water m e t h o d m a y show definite advantages, such as ease of stowage and unloading, uniformity of the treatment of the fish, and ease of applying antibiotics if the latter are ever introduced (Anonymous, 1 9 5 9 ) . T h e experiments with aeration h a v e shown that where there is no aeration, white fish develop odors associated with bilgy
( a n a e r o b i c ) spoilage, b u t a very m o d e r a t e aeration apparently sup
presses this kind of deterioration. F o a m i n g c a n b e controlled b y antifoam agents (Anonymous, 1 9 6 0 b ) . W h e n herring w e r e stored for up to 6 days, no difference could b e d e t e c t e d b e t w e e n aerated and nonaerated speci
mens. T h i s is in a c c o r d a n c e with Pacific W e s t Coast experience, w h i c h has not indicated that aeration leads to quality improvement ( S o u t h c o t t et al, 1 9 5 7 ) .
D u t c h experiments have given particularly good results with herring, mackerel, and shrimp in refrigerated sea water. Advantages are lower
temperature and easy discharge b y pumps. Important types of round ( w h i t e ) fish, however, are not considered suitable for this kind of stow
age, b e c a u s e they a b s o r b w a t e r a n d consequently b e c o m e less attractive from a c o m m e r c i a l point of view ( v a n M a m e r e n , 1 9 6 1 ) .
M a c C a l l u m a n d C h a n ( 1 9 6 1 ) also found disadvantages with white fish w h e n t h e y stored E a s t C a n a d i a n c o d in refrigerated sea-water. T h e y stored the fish in 3 % salty sea w a t e r at 0 ° C . / 3 2 ° F . a n d in sea water fortified to 5% salt at — 1 ° C . / 3 0 ° F . in quite extensive tests on land.
T h e taste panel thought that the saltiness of the fish was too strong and found it o b j e c t i o n a b l e w h e n the salt r e a c h e d 0 . 9 % after 9 days in t h e 5 % brine. T h e sea water:fish ratio in this case was 1.3:1. T h e authors add that t h e high salt content m a y b e detrimental to the use of the fillet offal in fish m e a l production. Sharp seaweedy and rancid odors w e r e found in t h e older sea-water-chilled fish m o r e often than in t h e i c e d fish.
T h e s e flavors decreased somewhat w h e n antibiotics ( 1 0 p.p.m.) w e r e used. T h e eyes of t h e sea-water-stored fish b e c a m e o p a q u e a n d t h e gills b l e a c h e d earlier than those of the i c e d fish. T h i s was also observed in t h e British experiment. Apart from this, the general a p p e a r a n c e and firmness of t h e sea-water-chilled fish w e r e preferred.
C o h e n and Peters ( 1 9 6 1 ) w e r e m o r e successful in their experiments with A m e r i c a n E a s t Coast whiting. T h e organoleptic evaluation of t h e r a w fish showed little difference b e t w e e n those stored in refrigerated sea w a t e r at — 1 ° C . / 3 0 ° F . and those stored in ice. T h e ratings o f t h e cooked fish showed a consistent preference of the panel for the whiting in refrigerated sea water.
T h e results of investigations so far seem somewhat conflicting. R o a c h et al. ( 1 9 6 1 ) have published an interesting survey in w h i c h they stress the n e e d for proper application of the m e t h o d and emphasize that re
frigerated sea-water-holding of fish in any fishery must b e carefully as
sessed before large-scale applications are effected. F a c t o r s such as salt penetration a n d control of bacterial contamination must b e studied, and standards ( s u c h as limits for h o l d i n g s ) carefully adhered to. I f this is done, then t h e authors think that this general m e t h o d m a y not only simplify handling b u t will improve the quality of fish landed in m a n y areas. T h e i r survey contains detailed information regarding practical in
stallations on b o a r d and also mentions a great m a n y c o m m e r c i a l appli
cations on t h e Pacific W e s t Coast, w h e r e t h e m e t h o d has already found fairly widespread a c c e p t a n c e .
A question that is often raised is that of the fish storage capacity of sea-water holds. R o a c h et al. ( 1 9 6 1 ) state that the capacity of m e d i u m or large vessels using refrigerated sea-water tanks approximately equals that of similar vessels using ice in uninsulated holds. F i g u r e s run about
4 5 5 0 lbs. of fish per c u b i c foot of tank, which corresponds to about 5 9 0 -6 4 0 kg. fish per c u b i c meter.
Certain bacteriological difficulties have occurred in the experiments b e c a u s e the liquid in the tank, despite its low temperature, is a substrate favorable to bacterial growth. T h e addition of antibiotics seems helpful ( S t e i n e r and Tarr, 1 9 5 5 ) . I t was expected that the anaerobic environ
ment in such a tank, in contrast to the aerobic conditions in normally iced fish, would appreciably c h a n g e the bacterial flora. Present British evidence suggests that during stowage in chilled sea water, ecological conditions are such that they favor the early development and predom
inance of the nonpigmented Pseudomonas species and h e n c e , although the total viable counts m a y b e lower for the sea-water fish, as mentioned earlier, more spoilage types are present than in the ordinary iced controls (Anonymous, 1 9 5 9 ) .
Concerning the sustained significance of nonprocessed raw fish in the landings of world fish catches, see V o l u m e I I , C h a p t e r 19.