100 U. §. BUREAU OF FISHERIES 
of frying in oil by developing a substitute method of preparing the 
fish for canning. These subjects are discussed below in the light of 
the experimental results. 
Minimizing undesirable changes.—The changes that take place in 
frying oil have been shown to be due largely to the action of the 
oxygen of the air upon the heated oil. Fish oil is affected more by 
oxidation than cottonseed oil. It darkens quickly, becomes viscous 
more rapidly, and when oxidized is more unpleasant as to taste and 
odor. It would be advantageous, therefore, to keep the fish-oil con- 
tent of the frying oil as low as possible and to do whatever is prac- 
ticable to prevent oxidation of the frying oil. Fish oil can not be 
kept out of the frying oil, and oxidation changes probably can not 
be prevented in a practical manner, so the difficulties can not be 
completely eliminated. There are ways, however, in which improve- 
ments can be made. 
In a typical fry bath, for example, a layer of oil 6 inches deep 
may be spread out in a vat 50 by 3 feet. With such a large surface 
of heated oil exposed to the air in proportion to the amount of oil 
in the vat, it is no wonder that oxidation takes place so rapidly. 
These changes can be lessened considerably by placing an inexpensive, 
removable cover on the vat, leaving the ends open where the baskets 
of fish enter and leave the oil. Steam coming from the fish will 
collect in the inclosed space, excluding air. One canner agreed to 
try this and found that the oil remained in better condition when 
the cover was used. The blanket of confined steam over the oil 
also minimized temperature variations in the oil and lowered the 
amount of steam used in running the vat. In order to further con- 
serve steam, the whole exposed surface of the cooking vat should be 
well insulated. 
It is important in constructing a fry bath to build it so that the 
smallest possible amount of oil can be used. The vat should be but 
slightly wider than the baskets that pass through it, and they should 
move as close together and as near to the steam coils as possible. 
The coils should be placed so as to aid in permitting the use of the 
minimum amount of oil. Only enough oil should be used to cover 
the fish as they pass through the vat. Had these precautions been 
taken in constructing many of the fry baths now in use it would be 
possible to use as much as 1 to 3 barrels of oil less in filling them, 
with a saving at the time of filling of possibly $50 to $150. By 
taking these precautions, too, the oil in the vat that gets into the 
canned product will, in the long run, be in better condition than 
otherwise. The main reason for this follows: A given lot of fish will 
mechanically carry away a certain amount of oil, which has to be 
replaced either by oil from the fish or by adding oil, no matter how 
much there is in the vat. The amount removed, however, will be a 
greater part of the total oil the less oil there is in the vat. It is an 
advantage for the oil replacements to be as large a part of the total 
oil as possible, because the more rapidly it is replaced the better the 
quality of the oil in the vat and the longer the time before it will 
have to be discarded entirely. 
Using the minimum amount of oil also keeps the fish-oil content 
of the frying oil from increasing as rapidly as it would otherwise. 
Calculations show this to be true for all cases except where the oil 
content of the bath is increasing, as it does when very fat fish are 

otros hajaet. 
INS EDPA 
