Patent GB-1056844-A (GB)
Title: Improvements in and relating to the drying of fish
IPC: A23B4/03
Filed: 1962-07-09
Abstract: A process for drying unsalted non-fatty fish having an initial water content greater than 350% (based on dry weight) comprises contacting the fish with heated air until the water content of the fish is less than 80% and in such manner that the temperature of the fish does not exceed the critical temperature (the maximum temperature at which drying can be carried out without thermal damage, which temperature increases as the water content of the fish falls during drying) and that the temperature of the fish exceeds 20 DEG C. until the water content has fallen to below 350%, so maintained within the range of from 25 DEG C. to 55 DEG C. while the water content is less than 350% but not less than 250%, is maintained within the range of from 30 DEG to 75 DEG C. while the water content is less than 250% but not less than 160%, is maintained within the range of from 45 DEG  to 100 DEG C. while the water content is less than 160% but not less than 80%, and is maintained within the range of from 65 DEG  to 120 DEG C. while the water content is less than 80% but not less than 25%. Thus, cod, tusk, saithe, hake, haddock, pollack and whiting, whole, split or cut into steaks, may be dried to water contents not exceeding 70%.  For satisfactory preservation over prolonged periods the final water content of the fish should not exceed 25%, but in certain cases some degree of fermentation may be thought desirable and a rather higher final water content may then be preferred.  The temperature of the fish during the drying should not fall below the initial critical temperature.  It may be progressively increased by maintaining it substantially equal to the critical temperature or so controlling the rate of transfer of water across the boundary surfaces between the fish and its surroundings that the rate remains substantially constant throughout the drying.  Otherwise, the temperature of the fish may be maintained substantially constant and increased alternately.  The drying may be effected as follows: (i) while the fish is stationary and the temperature of the air with which the fish is contacted is increased during the drying period (Figs. 4 to 6, not shown); (ii) by passing the fish in turn through regions wherein the temperature of the air increases from one region to the next in the direction of movement of the fish (Figs. 1 and 2, not shown); (iii) by passing air, heated to the maximum required temperature, through a tunnel in a direction opposite to the direction in which the fish is passed through the tunnel, the required temperature profile along the length of the tunnel being obtained by admitting cooler air into the tunnel e.g. through louvres at points spaced apart along the length of the tunnel, (Figs. 8 and 9, not shown); (iv) by passing the fish through a tunnel through which air is passed, a part of the air being heated to a temperature not exceeding the temperature required to heat the fish to the critical temperature at the commencement of drying and thereafter introduced into the tunnel at or close to the end at which the fish is introduced, the remainder of the air being heating to the maximum required temperature and thereafter introduced into the tunnel at or close to the end at which the fish is withdrawn, the air being withdrawn from the tunnel at a point towards, but spaced from, the end at which the fish is introduced, and cooler air being introduced into the tunnel e.g. through louvres at points spaced along the length of the tunnel, between the end at which the fish is withdrawn and the point at which the air is withdrawn to give the required temperature profile along the tunnel (Figs 9, 10 and 11, not shown).