A STUDY OF THE METHODS OF CANNING MEATS, WITH REFERENCE TO THE PROPER DISPOSAL OF DEFECTIVE CANS.

By C. N. MCBRYDE, M. D.

Bacteriologist, Biochemic Division.

OBJECT OF INVESTIGATION.

In the canning of meat food products the cans are subjected to various processes, in the course of which they are inspected from time to time for leaks or defects in the tins. In spite of all precautions a certain number of defective or leaking cans are nearly always detected during the process of canning, and these cans, unless they be reprocessed, may constitute quite a loss to the packer. The regulations governing meat inspection permit the reprocessing of these defective cans, but require that this be done within a short interval after the original processing. This requirement is made in order to obviate all danger from the possible development of putrefactive changes within such cans as are to be reprocessed.

In the case of certain cans known as "slow leakers," where the defects or leaks are not detected as a rule until several days after the cans have been processed, the regulations require that the contents shall be condemned and tanked, or rendered into inedible fat and tankage. Prior to the issuance of the regulations, however, at one of the larger packing centers the question came up in connection with the canning of corned beef as to whether the contents of these slow-leaking cans might not be "worked over " with safety-that is, chopped or ground and mixed with other products of unquestioned soundness—and it was with a view to determining whether such a procedure should be allowed that the present investigation was undertaken.

To insure a better understanding of the experiments which were carried out in the course of the investigation it would seem desirable first to describe somewhat in detail the method of canning corned beef and also to define some of the terms used in the canning industry.

METHOD OF CANNING CORNED BEEF.

The fresh meat is first chilled, and then cut and boned, after which it is put in pickle for twenty-five to thirty days. After the meat has been properly cured it is removed from the pickling vats, placed in open kettles with sufficient water to cover it, and cooked for twenty

to forty-five minutes. The chief object of this preliminary cooking or parboiling is to secure the shrinkage, which always occurs on heating, before the meat is placed in the cans.

The meat is next trimmed, the gristle and superfluous fat being removed. After that it is run through a cutting machine and cut to the desired size, which varies for different-sized cans.

The meat is next fed into an automatic stuffing machine, the amount put into each can being roughly measured in a scoop. A small quantity of a liquid preparation known as "soup stock" is then added to each can. This soup stock, prepared by digesting fresh meat and bones, is simply a clear soup or consommé, and is added to fill up any spaces which may exist between the pieces of meat.

After it leaves the stuffing machine the can goes to a weigher, who weighs it and adds or takes off according to the weight. If the man who feeds the stuffing machine feeds in too much meat an "overstuffed" can results, and if too little meat is put in, as sometimes happens, the can is liable to collapse under the vacuum, giving rise to what is known as a "collapsed " can.

After the can has been weighed and any necessary correction made in the weight, the top is wiped and the cap put in place and soldered under a rotary soldering machine. The can is next inspected for cap leaks, and these are repaired by hand. The can then goes to the vacuum machine, where it is exhausted of air, and the vent is sealed while the can is in this machine and in a vacuum. If, as sometimes happens, the air in the can is not all exhausted, a short-vacuum can results.

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From the vacuum machine the cans are run out on a table and again inspected for leaks. The inspector examines the vent and feels the can for loose tin, and all cans found to be defective are thrown out. All body, cap, and seam leaks in the defective cans are now repaired, the vents are opened, the cans are put back in the vacuum machine and the vents resealed under vacuum. If the can is a vent leaker it is not necessary, of course, to reopen the vent, and the can is simply replaced in the vacuum machine, the air exhausted, and the vent resealed.

The cans are next "processed" or heated to a sufficiently high temperature to insure the preservation of their contents. Two methods of processing are employed, known as the retort process and the water process.

In the retort method the cans are placed in strong iron or steel boilers, known as "retorts," which may be securely closed by means of bolts. In these retorts the cans are subjected to the action of steam under pressure. The temperature of the retorts varies from 215° to 250° F., and the cans are held in the retorts for varying lengths of

time, depending on the nature of the product and the size of the

cans.

In the water process the cans are placed in large open kettles or tanks filled with water, which is maintained at the boiling point by means of steam pipes. The cans are kept in the boiling water for varying lengths of time, as in the retort method, depending upon the size of the can and the nature of the product.

After processing, the cans are placed in a spraying machine and sprayed with cold water. The cans are now inspected again, and all leakers found on this inspection are classed as "do-overs," which in some establishments are repaired and reprocessed.

The cans are next passed through the washing machine, where they are immersed for several minutes in a strong solution of sodium hydrate (caustic soda) in order to remove the fat and grease from the outside, and are then passed on through a bath of hot water to remove the alkali. They now undergo another inspection, the inspector tapping the end of each can with a small brass or wooden mallet. If the can emits a hollow sound it is thrown aside. All leakers found on this inspection are tanked. The cans are next painted and labeled. This part of the work is done by girls, who are quite expert in detecting leakers, so the cans really get another inspection while they are being painted and labeled.

The cans are now usually packed in cases and placed in stock. The men who do the packing, like the girls who do the labeling, are quite expert in detecting defective or leaking cans, so the cans undergo another inspection while they are being packed. The cases as a rule are not nailed up, and before shipment the cans are usually removed from the cases and given a final inspection before they are sent out on the market. The operations of painting, labeling, wrapping, and packing occupy several days, so that after the cans have been processed and washed it requires ordinarily from three to seven days to get them ready for shipment. The leakers which develop during this time are known as "slow leakers," and it is these cans with which we are especially concerned in the present investigation.

DEFINITION OF TERMS USED IN THE CANNING INDUSTRY.

Overstuffed can. This is a can which has had too much meat forced into it by the stuffing machine, causing the can to bulge. Although the excess of meat is removed from these cans before they are capped and sealed, they do not regain normal shape, because the tin has been stretched and strained. These cans present a bulged appearance, usually on the sides near the top, and may resemble a swelled can, but the sides of the can are not tight as in a "sweller," and there is usually a little loose tin at the sides of the can. These cans

will not become "swellers" and their contents will remain good, provided the tin has not been broken by the extra strain to which it has been subjected.

Collapsed can. This is a can which has collapsed or buckled in the vacuum machine because it was not properly filled-that is, because it did not receive a sufficient quantity of meat. If the tin is not broken these cans will not develop into "swellers" and the contents will remain good. They are discarded, however, because of their unsightly appearance.

Short vacuum can.-A can which has not been completely exhausted of air is known as a short-vacuum can. Such a can shows a little loose tin, usually at the bottom. When this loose tin is pressed down with the fingers it either springs back into place of itself or it may be sprung back by squeezing the sides of the can. These cans will not develop into "swellers" and their contents will remain good, provided the processing was properly carried out and there are no defects or leaks in the tins.

Do-over can.-This is a defective can which is discovered after processing and before the can goes to the washing machine. In some establishments these cans are repaired and reprocessed or done over, hence the term "do-over" can.

Slow leaker.-A can which has a small leak through which the air gains entrance is called a slow leaker. The leak is often very hard to locate. It may be an opening the size of a hair in the solder filling the vent, or it may be a small opening in the solder holding the cap, the top, or the bottom. The leak may also be due to defects in the seam, the band, or the crimp, or it may be due to a bruise resulting from rough handling. If the top of the can is not properly wiped before the cap is put on a small particle of meat may project between the can and the cap and prevent the solder around the cap from taking hold at that point. Slow leaking cans always show loose tin, that is, the sides of these cans are not concaved and tight as in a normal can, because air has gained entrance and there is no longer a vacuum within the can. By squeezing the sides of these cans the contents may often be forced through the leaks, and this is one way of examining for slow leakers. Another way of testing for slow leakers is to place the can in hot water for a few minutes in order to dissolve the fat or gelatin which sometimes plugs the leak, and then by squeezing the can under water the air contained in the can may be made to bubble out through the water. Perhaps the best test for slow leakers, however, is to place the cans in a room heated to 100° to 110° F. and keep them there for a week or ten days, during which time all slow leakers should develop into "swellers." Even at ordinary room temperature a slow leaker will, after a time, usually develop into a sweller. Sometimes a slow leaker will swell sufficiently to open the leak and allow

the air and gases to escape, and if the leak does not become sealed by the contents of the can the gases formed in the interior will continue to escape and the can will not develop into a sweller; in this case, however, the contents of the can will be seen exuding through the leak or else may be forced through the leak by squeezing the sides of the can, and in this way the leak may be readily detected. As a rule, however, the leak becomes sealed by the contents of the can as a result of the solidification of the gelatin or fat, which prevents the escape of the air and gases, and the can develops into a sweller.

Sweller. This is a can the contents of which have undergone fermentative or putrefactive changes resulting in the formation of gas which causes the can to swell or bulge. A swelled can is, as a rule, a further development of the slow leaker, as explained above. Swellers also sometimes occur where cans have not been properly processed, but this is a comparatively rare occurrence, as in most canning establishments the methods of processing are carefully watched.

LOCATION AND DESCRIPTION OF LEAKS.

Leaks may be located in the vent, in the cap, or in the body of the

can.

Vent leaks. These are leaks in the solder filling the vent. Oftentimes these leaks are very minute, no larger than a hair, and can only be detected by whittling away the solder with a knife; at other times, when the opening is larger, the contents may exude and solidify about the leak.

Cap leaks.—Leaks in the solder holding the cap are known as cap leaks. These are often due to small particles of meat projecting from the interior of the can, or to particles of meat left on the top of the can, which was not properly wiped before the cap was put on. The particles of meat prevent the solder from taking hold and a leak results.

Body leaks. These are leaks in the body of the can. They may occur in the solder holding the top or bottom and may also occur in the seam, in the band, or in the crimp. They are designated according to their location as follows: (1) Top-float leaks, (2) bottom-float leaks, (3) seam leaks, (4) band leaks, (5) crimp leaks.

Body leaks are due to defects in manufacture, and on the books of a packing establishment, where a record is kept of all leaks, they are charged to the tin shop which supplies the cans. All vent and cap leaks result from faulty sealing of the cans, and are very properly charged to the canning room.

The location of the different leaks described above may be better understood, perhaps, by reference to the accompanying diagram (fig. 46).