124 U. §. BUREAU OF FISHERIES 
content of the drying air and slacken drying still further. Most of 
the time such conditions do not prevail and it is possible to use part 
of the air again. 
It is safe to return to the fan and through the drier a little less 
air than an amount that, when added to fresh air, will cause con- 
densation on the fish. In practice it is easy to regulate recirculation 
by. observing the fish and cutting down the amount of air returned 
to the fan if there is any slackening in the drying. Although recircu- 
lation increases the humidity of the air, it will have little effect on 
the drying. Partial drying of the fish can be carried out about as 
well in air having a high humidity as in drier air, providing no con- 
densation of moisture takes place on the fish. 
Rapid drying has been shown to depend on vigorous circulation of 
as warm air as possible through the drier. In order to keep the 
temperature from falling much through the drier, a large excess of 
heated air is used. In the case of most driers now in use for partially 
drying fish for canning as sardines (and undoubtedly the same will 
be true for future installations), the air leaving the drier is still quite 
warm and has absorbed only a part of the moisture that it is able to 
take up. Operating costs can be lowered by recirculating as much 
of this air as possible. 
COMMERCIAL SARDINE DRIERS 
In the California industry accurate operating data were collected 
on most of the commercial sardine driers in use during the 1922-23 
season. Many of these data are givenin Table 9. It will be observed 
that drying conditions varied greatly and that temperatures from 
75° to 120° and air velocities from 339 to 1,676 feet per minute were 
used. The drying time varied from 28 minutes to about 2 hours, with 
moisture losses on large fish running from 3.8 to 10.7 per cent. In 
all cases raw fish were being dried for cooking in oil, brine, or steam, 
and in each instance the skins were so conditioned that the fish 
cooked satisfactorily without undue breakage. These observations 
again call attention to the fact already discussed—that to prepare fish 
for ceoking it is necessary only to toughen the skins of the fish and 
to remove a little water from them. 
