The thermocouple sensing element of the first of three controller systems is inserted in the fish flesh near the surface; it regulates the tem
perature of the air circulating over the fish in the dryer. The controller is adjusted to 8 0 ° F . , thus there is no danger of overheating the product.
The air is always at the highest permissible temperature. At the begin
ning of the operation, when the surface of the product is still wet, the temperature of the air is very high, but the temperature of the product approaches the wet bulb temperature of the air, because the rapidly proceeding evaporation exerts a cooling effect on the fish. As evapora
tion proceeds further, the surface gradually dries out and the cooling effect decreases correspondingly. Consequently, the temperature of the air is automatically and gradually lowered to 8 0 ° F . , until the surface is completely dry. The second (dry bulb temperature) and third (relative humidity) controllers are adjusted to 8 0 ° F . and 6 0 % , respectively. These regulate the operation automatically and according to the conditions required at temperatures above and below 8 0 ° F . If the temperature of the air is higher than 8 0 ° F . , as long as the surface of the product is still wet or partly wet, the relative humidity controller shuts off and the relative humidity of the air is kept at the lowest possible level by the action of the dry bulb temperature controller. When the air temperature reaches 8 0 ° F . and when the surface of the product is completely dry, the dry bulb temperature controller stops dehumidifying and the relative humidity of the air is gradually increased to 6 0 % , where it is maintained by the relative humidity controller as long as the temperature does not exceed 8 0 ° F .
2. Advantages
The system outlined in the previous lines has several advantages over the conventional method. The improvement in performance is found under favorable and unfavorable conditions, with light as well as with heavy salted fish.
a. FAVORABLE ATMOSPHERIC CONDITIONS
When atmospheric conditions are favorable for artificial drying, an increase in rate is obtained at the beginning of each stage. The initial drying rate is about twice as great with thermocouple control as with ordinary control. This is very important not only because the drying time is reduced, but also because the danger of bacterial contamination is practically eliminated. Moreover, the system permits an increase in relative humidity as soon as the surface of the fish becomes dry, conse
quently the production of choice quality light or heavy salted fish is
comparatively easy. The possibilities of overdrying the surface or cook
ing are avoided automatically. With light salted fish it is even possible to save one drying stage. Experiments with Gaspe-cured fish have shown that only three drying stages are required, compared with the four necessary with the conventional method. Time and labor for loading, unloading, and cross-piling are saved.
A striking advantage of thermocouple control for the artificial drying of heavy salted fish consists in reducing the possibility of formation of an impervious salt-protein crust on the fish surface. This crust is usually encountered when conditions giving high drying potentials are used with ordinary control. Therefore the use of thermocouple control renders it comparatively easy to obtain a product of good quality, in spite of its high drying rate.
b. UNFAVORABLE A T M O S P H E R I C CONDITIONS
It has already been shown that, with ordinary control, perfect dry
ing conditions are obtainable only when the outside temperature is below 8 0 ° F . and the dew point below 5 5 ° F . However, the thermocouple system of control maintains conditions in the dryer permitting perfect operation at much higher dew points. As long as the surface of the fish is still wet, there are practically no limits as regard temperature, and good results can be obtained as long as the dew point does not exceed 7 2 ° F . When the surface is dry, the temperature must be below 8 0 ° F . and the dew point in the vicinity of 65 ° F . However, since there is no moisture at the surface, sliming is not encountered and drying is still possible, although at a reduced rate, with dew points up to 6 8 ° F .
This has been confirmed by drying experiments made under unfavor
able atmospheric conditions, that is, when artificial drying would have been impossible with ordinary control. The drying rates obtained with the new method and without an external dehumidifier were of the same order as with ordinary control if used under favorable atmospheric conditions.
The method is based on the general theory of drying and can there
fore be used for the artificial drying of any other product, provided the highest temperature that the material tolerates and the lowest relative humidity that will give a product a good quality are known. The con
trols need only be adjusted for these limits and ideal drying conditions will automatically b e maintained at each instant of the operation.
R E F E R E N C E S
Arnesen, G. ( 1 9 5 4 ) . T r a c e s of c o p p e r in fishery salt c a u s e b r o w n discoloration in w e t - s t a c k e d salted fish. ( I n N o r w e g i a n . ) JEgir 4 7 ( 6 ) , 9 8 - 1 0 4 .
Baxter, R. M . , a n d G i b b o n s , Ν. E . ( 1 9 5 4 ) . T h e glycerol d e h y d r o g e n a s e s of
Pseu-domonas salinaria, Vibrio costicolus a n d Escherichia coli in relation to bacterial p r o c e s s i n g of salt fish. Fisheries Research Board Can. Progr. Repts. Atlantic Coast Stas. 66, 16-17. Board Can. Progr. Repts. Athntic Coast Stas. 55, 3-4.
D u s s a u l t , H . P. ( 1 9 5 6 a ) . S t u d y of the r e d halophilic b a c t e r i a in solar salt and s a l t e d fish. I. Effect of bacto-oxgall. J. Fishenes Research Board Can. 13, 183-194.
D u s s a u l t , H . P. ( 1 9 5 6 b ) . S t u d y of r e d halophilic b a c t e r i a in solar salt a n d salted fish. I I . B a c t o - o x g a l l as a selective a g e n t for differentiation. / . Fisheries Research Board Can. 13, 1 9 5 - 1 9 9 .
D u s s a u l t , H . P. ( 1 9 5 7 ) . T h e microbiology of fish a n d m e a t curing brines. Proc Intern. Symposium Food Microbiol. (Cambridge, Engl.) 2, 13.
Dyer, W . J . , a n d G u n n a r s s o n , G . K . ( 1 9 5 4 ) . T r a c e elements a n d yellow coloration in salt fish. Fisheries Research Board Can. Progr. Repts. Atlantic Coast Stas.
60, 3-4.
D y e r , W . J . , F r a z e r , D . T . , a n d D i n g l e , J . R. ( 1 9 5 8 ) . W h i t e crystals of s o d i u m p h o s p h a t e on salt fish. Fisheries Research Board Can. Progr. Repts. Atlantic Coast Stas. 69, 2 8 - 3 2 .
F o u g £ r e , H . ( 1 9 4 8 ) . L e s e c h a g e artificiel d u c a p e l a n frais. / . Fisheries Research Board Can. 7, 2 0 0 - 2 1 1 .
F o u g e r e , H . ( 1 9 5 2 ) . S o m e considerations on h e a v y s a l t e d pickle fish. Fisheries Research Board Can. Progr. Repts. Atlantic Coast Stas. 52, 15-17.
F r a n k , M . , a n d H e s s , E . ( 1 9 4 1 a ) . S t u d i e s on salt fish. V. S t u d i e s on Sporendonema epizoum f r o m "dun" salt fish. / . Fisheries Research Board Can. 5, 2 7 6 - 2 8 6 .
F r a n k , M . , a n d H e s s , E . ( 1 9 4 1 b ) . S t u d i e s on salt fish. V I . Halophilic brown r e d halophilic bacteria. / . Fisheries Research Board Can. 6, 10-16.
J a r v i s , N. D . ( 1 9 5 0 ) . C u r i n g of fishery p r o d u c t s . U.S. Fish Wildlife Serv. Research Rept. 18, 2 7 1 p p .
J o n e s , N. R. ( 1 9 5 4 ) . T a u r i n e in fresh a n d iced skeletal m u s c l e of codling (Gadus calhrias). Biochem. J. 5 6 ( 4 ) , xxii.
L e g e n d r e , R. ( 1 9 5 3 ) . H o w to determine if atmospheric conditions are favorable for the artificial drying of salted codfish. Fisheries Research Board Can. Progr.
Repts. Atlantic Coast Stas. 5 6 , 2 3 - 2 7 .
Vaisey, Ε . B . ( 1 9 5 4 a ) . A note on the control of d u n . Fisheries Research Board Can. Progr. Repts. Atlantic Coast Stas. 5 8 , 3 2 .
Vaisey, Ε . B . ( 1 9 5 4 b ) . T h e control of d u n in salt fish plants. Fisheries Research Board Can. Progr. Repts. Atlantic Coast Stas. 60, 4-6.
Vaisey, Ε . B . ( 1 9 5 4 c ) . O s m o p h i l i s m of Sporendonema epizoum. J. Fisheries Re
search Board Can. 1 1 , 9 0 1 - 9 0 3 .
Wilson, Ε . M . C . ( 1 9 3 3 ) . In " S t u d i e s in E n g l i s h T r a d e in the 15th C e n t u r y "
( E . P o w e r a n d Μ . M . P o s t a n , e d s . ) , p . 1 5 5 . R o u t e l e d g e , L o n d o n .
W o o d , A. L . ( 1 9 4 7 ) . T h e artificial d r y i n g of salt fish. Fisheries Research Board Can. Progr. Repts. Atlantic Coast Stas. 3 7 , 18-19.