8. At the end of the sterilizing period cool the jars quickly after sealing completely. The tin cans may be cooled by immersing them in cold water.
9. Store for future use.
SOFTENING OF BONES IN FISH
This can be done satisfactorily under pressure. The bones of fish are composed of large quantities of harmless lime, bound by a matrix of collagen, which is insoluble under ordinary conditions. When subjected to a high temperature under pressure this collagen is converted into gelatin and dissolved, leaving the bones soft and friable and even edible. Bony fish, such as herring and shad, which are too small to use otherwise are greatly improved when subjected to steam under pressure.
The bones in herring are softened in 37 minutes at a temperature of 240 degrees; shad in 1 hour; flounder 1 hour. Other fish are fully cooked and the bones softened in times approximately proportionate to the size of the bones.
The following table was made after many experiments and gives the time required to soften the bones in many common species of fish.
The term "softening" means the point in cooking when the small bones, ribs, etc., are soft, but when the large vertebrae are not yet sufficiently soft to be consumed along with the meat. In some of the larger fishes where the 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 a 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.
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 period of time are therefore 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° F. for 48 hrs. All were sterile.
TIME REQUIRED TO SOFTEN THE BONES OF VARIOUS SPECIES OF FISH IN QUART JARS OR NO. 3 TIN CANS, 10 LBS. PRESSURE, 240° F.