

CANNING SARDINES 123 
Cause of slow drying on rainy days.—Driers handling raw fish at 
times show a marked diminution in their ability to dry the fish satis- 
factorily. This usually takes place on a rainy day, and the claim is 
always made that there is too much water in the air for good drying. 
This is not a logical explanation, because the experiments have 
shown that the amount of moisture in the drying air has little effect 
upon the drying rate of fish that are being partially dehydrated 
when there is no condensation on the fish. Further investigation 
showed that the slackening in drying referred to here is brought 
about by fish entering the drier at a lower temperature than the 
dew point of the drying air. The dew point of the air in the drier 
ean be no higher (and it may be lower) than that of the air outdoors 
when it may be raining and the temperature is at, say, 60°. This 
outside air is saturated with moisture at this temperature; its dew 
point is 60°. This air may be heated, but its dew point will still 
remain at 60°. Now, if this air strikes fish that have a temperature 
of 50° it will not remove water from them; in fact, some small part 
of the air will be cooled to a temperature below its dew point, and 
water will condense upon the fish. In a few minutes, however, the 
warm air striking the fish will raise their temperature above 60°, and 
then evaporation will commence. 
Where the drying time is short (say, 30 to 45 minutes) and the 
temperature of the drying air is low (95° to 100°), and where perhaps 
the velocity also is low (500 feet per minute), the slackening in drying 
is considerable. Under such conditions (they prevail in many com- 
mercial installations) it takes a good many minutes to heat the fish 
to a temperature where drying can take place. 
When confronted by such circumstances as these, the operator 
usually raises the temperature of the drying air until he gets the 
results ordinarily attained in the usual length of time. This works 
quite well, because the higher temperature heats the fish quickly and 
tends to cause more rapid drying. Another way to-get around this 
difficulty is to see that the fish that enter the drier have a tem- 
perature high enough to prevent moisture from condensing upon 
them. The temperature of the fish can be raised easily, when they 
are brined, by warming the brine before it is placed on the fish. 
This worked nicely in small-scale experiments and should do likewise 
with large quantities of fish. The temperature of the brine must not 
be too high, however, because this tends to soften the fish; nor should 
the fish enter the drier at too high a temperature. In this case 
additional heating by the air causes the fish to soften too much. 
This difficulty was encountered when an attempt was made to hasten 
drying by first heating the fish with warm brine, so that moisture 
diffusion would be rapid from the very beginning of the drying 
period. The more rapid diffusion brought about in this way, how- 
ever, caused greater moisture loss from the heated fish. 
Recirculation of the drying air.—The amount of air leaving the 
drier, which may be used again, depends largely upon the tem- 
perature of the entering fish themselves. It has just been shown 
that when the temperature of the fish entering the drier is below the 
condensation point (dew point) of the water vapor in the drying air 
drying is delayed. When this condition exists, it is inadvisable to 
recirculate any of the exhaust air, as it would increase the moisture 

