36 REPORTS OF THE DEPARTMENT OF COMMERCE. 
of the commercial canner. In this manner she may practice a meas- 
ure of economy and provide a supply of palatable and nutritious food 
in seasons of the year when fish are abundant for use in periods of 
scarcity. 
The primary object of “ processing” fish, or cooking them under 
steam pressure, is to sterilize them to prevent spoiling. An addi- 
tional advantage of the method is that if the heating is continued 
for a sufficient length of time, the organic matter in the bones is dis- 
solved, leaving only a soft, friable, mineral matter that can be eaten 
along with the meat. With the bones thus softened the fish is much 
more acceptable as food. Thus, small bony fishes that would other- 
wise be useless, or fishes of small market value, may be saved, and the 
larger staple fishes made more attractive. 
The time required to soften the bones of fishes varies with the 
species, the size of the fish, and the pressure and temperature em- 
ployed. In domestic canning, unless the required time is known, 
time and fuel may be wasted by overcooking, or by insufficient cook- 
ing the bones may not be properly softened. 
A recent journal article calls attention to the small amounts of 
calcium present in most of the common foods and presents a table 
showing that comparatively large amounts of the ordinary foods are 
required to yield four-tenths gram of calcium oxide per day, which 
is about one-half the daily requirement of the average adult. The 
bones of fish, properly softened as they are by domestic or commer- 
cial canning, render available an abundant amount of calcium in ac- 
ceptable form, not encountered in such amounts in any other common 
food. In addition to this they supply phosphoric acid and other 
valuable minerals. It is, therefore, not only good housekeeping, but 
good dietetics, to can fish for home use. 
The Bureau has conducted experiments to determine the time re- 
quired to soften the bones of about 30 common marine and fresh- 
water fishes of different sizes. In the table which follows the time 
given is that determined experimentally for the sizes mentioned. It 
will be a simple matter to interpolate the time periods required to 
soften the bones of fishes of the same species but of sizes different 
from those represented. The term “softening,” as here used, means 
the point in cooking when the small bones, ribs, etc., are soft, but when 
the large vertebre are not yet sufficiently soft to be consumed along 
with the muscle. In some of the larger fishes whose large bones 
could scarcely be eaten, even if they were softened, it would appear 
to be a waste of time and fuel to carry them to the point of complete 
cooking, and in such cases it ought to be sufficient to soften the small 
bones and sterilize the contents of the can. For such a purpose the 
“ softening ” rather than the “ soft ” point may be used. 
These experiments refer to fish cooked in Mason glass jars of quart 
size. The time periods are measured from the, point when the given 
pressure and temperature are reached (at the top of the cooker) to 
the time when the heat is shut off. The heating-up and cooling-off 
periods of time are thus not included. The fish were salted, but no 
water was added. Samples of fish canned during the course of these 
experiments were kept six weeks at room temperature (about 68° F.) 
and were then incubated at 98° for 48 hours. All were sterile. 
