122 U. S. BUREAU OF FISHERIES 
TEMPERATURE OF THE FISH AS A FACTOR IN DRYING 
The temperature of the raw fish is an important factor in drying. 
It is of importance from the very beginning of the operation. The 
fact that higher fish temperatures increase the drying rate by hasten- 
ing moisture diffusion has already been noted. Acting against this 
favorable result are the undesirable changes that take place in the 
fish if they are heated too much. In such a case the flesh softens, 
and if the fish are fat oil is rendered. Even partial cooking may 
take place. It is necessary, then, to know something concerning 
the conditions under which these changes take place if they are to 
be avoided. 
Effect of air temperature upon the condition of the fish.—Raw fish 
usually have about the temperature of outdoor air when placed in the 
drier. In the drier warm air strikes them and gradually raises their 
temperature almost to that of the drying air. Evaporation of water 
retards this heating by using much of the heat taken up by the fish. 
In Table 8 are given data that illustrate changes in temperature 
when large pilchards are dried at different temperatures and the 
effect of heat upon the fish.* 
In actual practice the fish behave quite similarly to the way they 
did in the experiments covered by Table 8. Most canners do not 
want the fish to soften much or become oily during drying, conse- 
quently they seldom employ a drying temperature greater than 110°. 
A few, however, shorten the drying time to about 30 minutes and use 
air at slightly higher temperatures. 
Experiments indicate that the undesirable changes take place 
rapidly only after the fish attain a temperature of 95° to 100°. Good- 
quality, large, fat pilchards can be dried with air having a temperature 
up to 95° for at least 3 hours without bad effects. An hour at 105° 
to 110° and 30 minutes at 115° to 120° are about as long as the fish 
can be heated at these temperatures without much change. These 
statements should be approximately true for air velocities of about 
500 to 1,500 feet per minute. 
TABLE 8.—Temperature rise in large, fat, California pilchards, and the effect of 
heat on the condition of the fish 











Ai Air Temperature of fish, ° F.1 sas 
Experi- nd ae (time in minutes) Condition of fish 
ment pera- lity, feet 
No. ture, per 
°F. |minute|Start|} 30 | 60 | 90 | 120 End of 1 hour End of 2 hours 
1O2bes >= 95 634022 ia ep 0 ee ee eee in = 2222 1s) ee ea Firm; very little oil 
rendered. 
MW3ales 2 95 602 60 80 90 92 (15 | eae! dow. EES aoe oO. 
103 p= 105 616 Glatt 100 | 102 | 103 | Good condition_________ Softened somewhat; 
some oil rendered. 
104cerges 105 602 63 SANE TOZR LOS TES 22 Goeet eet Ae RS 0. 
1025 ees 115 G02 2c. oe ie ee a Softened somewhat; | Soft; oil rendered. 
some oil rendered. 
LOsd ee === 115 580 62; 100, ||) 109.4) 242 heat ee 0:23. 2343-33 3352 Do. 
| 


1 Taken about 14 inch under the skin at thickest part of bobdy—‘‘cut’’ fish used. 
The softening that takes place probably is brought about mainly 
by autolytic changes in the flesh of the fish. 


6 More complete data on changes in temperature are given in the Appendix (p. 203). 
