448 MARINE PRODUCTS OF COMMERCE 



does not command as high a price as white meat. A machine for molding blocks 

 of tuna meat the exact size for the can is in operation in some canneries. 



In order to heat the cans and get a better vacuum after sealing they are first 

 passed through an "exhaust box," an enclosed steam chamber through which a 

 conveyor runs, and then sealed. 



Closed horizontal retorts are generally used for "processing" or sterilizing the 

 canned tuna, the usual process temperature being 240° F (116° C). The time 

 averages 50 minutes for No. % cans, 55 minutes for No. /2 cans, and 70 minutes for 

 No. 1 cans. 



To prevent the cans from being damaged by too sudden a release of external 

 pressure when the retorts are opened, the cans are usually cooled under pressure 

 by introducing compressed air and water into the retorts before opening. 



Methods of canning yellowtail and bonito are very similar to those followed for 

 tuna. 



Recently there has been considerable demand for California tuna packed 

 Italian style. Bluefin tuna (or striped tuna) is used for this product, which is more 

 heavily salted than the regular canned tuna and is packed in olive oil. 



Grades of Tuna. About 80 per cent of the pack of tuna is placed in /2-size 

 (7-ounce) flat cans. Other size containers used are M and 1 pound. The following 

 4 grades are ordinarily packed: 



Solid pack— Fancy, contains only the choicest cuts of meat. 



Standard pack— 75 per cent of the pieces is small. 



Flake— Consists of small pieces left over from the other packs. 



Shredded or grated— Light meat treated so that the pieces are of uniformly 

 small size. 



Other Fish-Canning Industries 



Mackerel. In Maine the mackerel, after delivery to the cannery, are dressed 

 by splitting, by removing heads, tails, fins, and viscera, and by washing. The 

 fish are next held in strong brine until the desired saltiness is secured, and are 

 then packed and sealed in oval cans, usually with a little vinegar and spices 

 added. The sealed cans are cooked and sterilized in boiling water. 



In 1948 57,653,640 pounds of mackerel valued at $9,850,843 were packed on 

 the Atlantic Coast; this includes Jack mackerel. There were 68 canneries in opera- 

 tion making this pack. The cases of this product contain 45 pounds, which indi- 

 cates that 1,281,192 cases were packed. 



A few packers prepare "fillets of salt mackerel." In the preparation of this pack 

 the mackerel are first brined and then filleted. The fillets are packed with brine 

 and a small amount of vinegar in 1-pound, oval "C" enamel cans. The cans are 

 sealed and processed after the usual method. The can size used is that known as 

 the 1-pound oval and contains 12 ounces of fish. 



The canning of the chub mackerel (S. japonicus) on the coast of California has 

 developed to considerable importance, having first been canned experimentally 

 by the tuna canners of southern California. 



The method of canning consists of the following steps: The fish are scaled and 

 eviscerated, the head and fins being removed by a specially developed mechanical 

 apparatus. The dressed fish are put into 75° Sal. brine until blood is extracted, 

 and then rinsed in fresh water and packed tightly in No. 1 tall cans. The full 



