T h e racks of cooled tuna are n o w rolled into the cleaning room, w h e r e a c r e w of cleaners (usually w o m e n ) , standing on b o t h sides of the cleaning table, start the task of separating skin, bones, fins, b l o o d meat, etc., from the light loin meat. T h e cleaning tables are long tables, usually covered with stainless steel, in t h e middle of w h i c h an elevated con
veyor belt, also of stainless steel, is provided to receive the loin m e a t and carry it to the cutting m a c h i n e on its w a y to the canning equipment.
U n d e r the cleaning t a b l e runs a steel conveyor b e l t which, through holes a n d chutes in t h e cleaning table, receives the offal from the tuna clean
ing, a n d transports it to a cart in w h i c h it is transported to the fish m e a l plant.
T h e previous cooking and cooling of the tuna have firmed the m u s c l e tissue to such a n extent that t h e fish c a n b e handled b y the cleaners without crumbling. T h e dorsal, ventral, a n d pectoral fins are first re
moved, after w h i c h the skin is scraped off the flesh ( o f the t u n a ) with a knife, without cutting too deeply into the m u s c l e meat. N e x t the tuna is cleaved b y h a n d into four longitudinal parts, e a c h containing one of t h e dorsal or ventral loin muscles w h i c h surround the spinal column of the fish from h e a d to tail and w h i c h form the m a i n substance of t h e tuna.
As the tuna is b r o k e n into these four sections, the m e a t falls readily a w a y from t h e b o n y structure, thus aiding in a c o m p l e t e separation of fish m u s c l e from t h e bones. T h e dark vascular b l o o d meat, w h i c h separates the dorsal and ventral loins and is in part e m b e d d e d in t h e m , is scraped off, and the c l e a n e d loins are p l a c e d on t h e conveyor b e l t w h i c h carries t h e m to t h e canning equipment. T h e procedure w h i c h is followed from h e r e on depends u p o n the style of p a c k w h i c h is desired. T h e T u n a Standards that h a v e recently b e e n set, w h i c h will b e discussed in m o r e detail later, recognize four styles of pack. T h e s e are ( 1 ) solid pack, ( 2 ) chunk pack, ( 3 ) flake pack, a n d ( 4 ) grated pack. T h e solid p a c k m a y b e p a c k e d b y h a n d or b y m a c h i n e . I n c a s e a h a n d p a c k is used, the tuna loin meat, u p o n leaving t h e cleaning tables, is passed through a guillotine
like cutting m a c h i n e w h i c h cuts t h e loins into proper lengths to fit the depth of t h e can. T h e individual loin pieces which, generally speaking, h a v e the shape of a sector, are p l a c e d neatly, side b y side, in the c a n b y
2 3 0 SVEN L A S S E N
the cannery worker until it is filled completely. After this, the c a n is placed b a c k on the moving conveyor line w h e r e the required amounts of salt, oil, or other flavoring ingredients are added automatically. F r o m there the cans m o v e either into an exhaust b o x before they finally enter the closing m a c h i n e , or, if an exhaust b o x is dispensed with, through a closing m a c h i n e provided with a steam-jet v a c u u m mechanism. T h e m o r e expensive hand packing is fast b e i n g replaced b y the m o r e practical m a c h i n e pack. T h e introduction of the modern closing m a c h i n e in w h i c h a v a c u u m is pulled on the filled can immediately before closing has largely eliminated the n e e d for exhaust boxes.
I f m a c h i n e packing is used for solid packs, the loin meat, on leaving the cleaning tables, is formed into a cylindrically shaped continuous ex
trusion, b y passing through a m a c h i n e called t h e pack-shaper. At the point w h e r e the e m p t y c a n passes the discharge end of the pack-shaper, the cylindrically shaped tuna loins are pushed into the can and cut b y a reciprocating knife, t h e r e b y filling t h e c a n with a solid plug of tuna meat. T h e c a n is subsequently passed through a tapping m a c h i n e which, b y means of a revolving, reciprocating plunger, presses the tuna m e a t further down in the can, t h e r e b y leaving room for the subsequent addi
tion of salt, oil, or other flavoring ingredients. F r o m there the can is sent to the v a c u u m closing m a c h i n e .
F o r chunk pack, the tuna loin m e a t is machine-cut into suitable pieces b y a cutting device similar to t h e o n e just m e n t i o n e d and passed through a so-called pack-former, an ingenious m a c h i n e w h i c h fills the cans loosely, and subsequently b y means of a tapping m a c h i n e presses the content of the loosely filled cans down to proper volume before the cans return to the line w h e r e salt, oil, or other ingredients are added, then on to the conventional v a c u u m closing m a c h i n e ( s e e further Anonymous, 1 9 3 9 ) . F l a k e p a c k is manufactured in a m a n n e r m u c h like chunk pack. T h e size of the individual pieces of tuna m e a t is m u c h smaller than chunk pack. T h e relative content of large and smaller pieces is regulated b y t h e standards covering this style of pack. T h e individual p i e c e of flake must, however, b e of such a size that "the muscular structure of the flesh is retained." T h e standards covering the manufacture of canned tuna will b e dealt with in m o r e detail later in this chapter.
T h e grated p a c k is produced b y passing t h e tuna m e a t from the cleaning tables through a grating m a c h i n e , in w h i c h the tuna m e a t is c h o p p e d up and passed through a screen to give a product of uniform size. I t is p a c k e d into the cans b y passing it through the pack-former, w h i c h is equally well suited for filling the cans with chunk, flake, or grated tuna. L e a v i n g the pack-former, the cans containing the grated tuna are passed through the tapping m a c h i n e , then b a c k to t h e packing
4. T U N A CANNING AND P R E S E R V A T I O N O F R A W M A T E R I A L 2 3 1
line to have salt, oil, and other optional flavoring ingredients added, after w h i c h they are closed in the steam-jet closing m a c h i n e .
After leaving the closing m a c h i n e , the tuna cans are usually passed through a m a c h i n e or device in w h i c h the cans are c l e a n e d of any oil or other organic matter w h i c h has stuck to t h e surface of the cans, before they are d u m p e d into cylindrical, perforated metal baskets in w h i c h they are transported to t h e retorts.
T h e canning operations and the e q u i p m e n t described here are illus
trative of methods and e q u i p m e n t used in t h e large tuna-canning centers located on the Pacific Coast of t h e U n i t e d States. I t is b e l i e v e d that the methods and the canning e q u i p m e n t used in other countries for similar purposes do not vary essentially in principle from those used in the United States. I n countries w h e r e labor costs are lower and skilled oper
ators harder to get, there will naturally b e less incentive to install the expensive and highly complicated packing machines, w h i c h in this coun
try have b e e n found so useful for high quality mass production; in that instance, hand-packing or semiautomatic packing is used ( s e e also Jarvis, 1944, 1 9 5 2 ) .
F o r a discussion of standards of identity, fill of container require-and other optional flavoring ingredients used in tuna canning operations, ments for c a n n e d tuna, and of quality specifications for salt, salad oil, the reader is referred to Section I X of this chapter.
VIII. Retorting
T h e retorting or autoclaving w h i c h follows the filling and closing of the tuna c a n consists of heating t h e c a n and its contents to such a tem
perature that all microbial life inside t h e c a n is destroyed. T h i s is t h e most critical step in t h e whole canning operation and has, therefore, b e e n the subject of considerable study. T h e minimum time required to destroy the spores of the most heat-resistant organisms at various temperatures must naturally b e k n o w n for any size and type of p a c k b e f o r e recom
mendations on retorting temperature and time can b e made. T h e funda
mental work b y B i g e l o w et al. ( 1 9 2 0 ) on h e a t penetration in processing canned food, and the establishment b y B i g e l o w ( 1 9 2 1 ) of the logarith
m i c nature of t h e thermal death-time curve for microorganisms did m u c h to advance safe canning practice. I n the study on the heat resistance of sixteen different botulinum strains, W e i s s e ( 1 9 2 1 ) found that under best conditions of survival, t h e most heat-resistant spores of Clostridium botu
linum w e r e destroyed in 5 hr. at 1 0 0 ° C , within 4 0 min. at 1 0 5 ° C , and within 6 min. at 1 2 0 ° C . E s t y and M e y e r ( 1 9 2 2 ) also m a d e extensive studies on the h e a t resistance of Clostridium botulinum. T h i s last work h a d a profound influence upon the formulation of t h e cannery code in
2 3 2 SVEN L A S S E N
California and elsewhere. A very comprehensive study of the bacteri
ology of the thermal processes for canned marine products has b e e n reported b y L a n g ( 1 9 3 5 ) .
O n the basis of carefully conducted studies on heat penetration and distribution in packs of a given style and fill, and the establishment of the thermal death time for spores of a heat-resistant organism (usually Clostridium botulinum) in a pack, it is possible to calculate the time and temperature at w h i c h a given c a n size containing a given style of p a c k must b e heated to obtain total destruction of microbial life inside the can. I t is on the basis of such measurements that t h e California Depart
ment of P u b l i c Health, B u r e a u of F o o d and D r u g Inspection, C a n n e r y Inspection Section issues instructions regarding the temperature and the time at w h i c h it must b e maintained during retorting (Natl. Canners' Assoc., 1 9 3 1 ) . F o r further details on process calculations of and general bacteriological and c h e m i c a l examination of c a n n e d food, the reader is referred to C a m e r o n and E s t y ( 1 9 2 6 ) and T o w n s e n d et al. ( 1 9 5 4 ) .
T h e retorts used in the tuna canning industry are, with a few excep
tions, batch-type retorts, consisting of long, horizontal, cylindrical pres
sure vessels, m a d e of j4 hi-? or thicker steel plate, with ends dished for safety. At one end is a hinged door of the same diameter as the shell.
T o secure a safe and airtight closure during retorting, the door is usually secured b y a large n u m b e r of eye-bolts, attached to the shell, which m a y b e swung into the recesses in the perimeter of t h e door, and secured b y nuts. I n some retorts, the so-called spider closure m e c h a n i s m is used for securing the retort door.
T h e retort is provided with a track w h i c h allows the cylindrical baskets filled with cans from the canning machines to b e rolled into the retort. I n a 4-ft.-diameter retort, the cylindrical baskets on wheels will have a 42-in. diameter so that at least a 3-in. c l e a r a n c e is left b e t w e e n the perforated m e t a l basket and t h e wall of the retort. W i t h a 32-in.
length of basket, a 24-ft.-long retort will b e a b l e to hold eight baskets of cans and still have ample room to spare for the important steam and water circulation. T h e retort has steam, water, and compressed air con
nections, and is provided with air vents, bleeders, a w a t e r and steam distribution system, relief valves, pressure gauges, temperature measur
ing and recording instruments, etc.
I n order to give the public m a x i m u m protection against t h e danger of inadequate retorting, the California State D e p a r t m e n t of Public Health has, as already mentioned, imposed upon the canners of California very strict specifications, with regard to the time and temperature at w h i c h c a n n e d tuna must b e held in the retort. I t also has issued specifications with regard to the design of the retorts to b e used. T h e s e r e c o m m e n d e d
4 . t u n a c a n n i n g a n d p r e s e r v a t i o n o f r a w m a t e r i a l 2 3 3
specifications on retort design pertain mainly to such m e c h a n i c a l features as t h e methods of introduction of steam a n d w a t e r into the retort, t h e n u m b e r o f vents, bleeders, thermometers, etc., all of w h i c h have for their purpose to secure proper and uniform heating, cooling, a n d venting of the retorts. Details of these specifications m a y b e found under the head
ing "Retort E q u i p m e n t and Operation," Sections 1 2 7 2 5 - 1 2 7 8 5 of Article 8, entitled " C a n n e r y Inspection Regulations," S u b c h a p t e r 2, C h a p t e r 5, T i t l e 17 ( P u b l i c H e a l t h of California Administrative C o d e ) . T h e follow
ing is a general description of the p r o c e d u r e followed during retorting operations in a tuna cannery.
After t h e retort has b e e n loaded, the retort door is closed and bolted, and a c h e c k is m a d e to see that all vents and bleeders are open, and drain and overflow closed. S t e a m is then admitted gradually through the steam control valve as well as through its by-pass valve, into t h e perfo
rated steam spreader w h i c h runs through t h e entire length along the inside b o t t o m o f t h e retort. W h e n t h e t e m p e r a t u r e has c o m e up close to t h e processing temperature, t h e by-pass valve is gradually closed and the temperature is b r o u g h t up to t h e final processing temperature b y the steam control valve alone. H a v i n g finally arrived at the processing tem
perature, t h e recording t h e r m o m e t e r and pressure g a u g e are c h e c k e d , and time, temperature, and pressure are entered in t h e production record. T h e t i m e it takes to b r i n g a retort up to t h e required processing temperature is t h e "lag" or "come-up time." D u r i n g the processing period, the tem
perature must b e k e p t constant, and frequent temperature checks must b e m a d e to m a k e certain that no fluctuation in temperature occurs. I t is important to see to it that all bleeders are k e p t open during the entire processing period. W h e n the processing t i m e has c o m e to an end, the steam is turned off, and all bleeders are closed, after w h i c h compressed air is introduced into t h e retort, increasing the pressure a b o u t 2 l b . p e r square i n c h a b o v e the processing pressure w h i c h existed in t h e retort during processing. W a t e r is n o w introduced into the retort through the perforated top inlet pipe w h i c h runs inside the retort along its entire length. A constant pressure is maintained in the retort during the intro
duction o f t h e cooling w a t e r b y manipulating the compressed air valve.
As t h e w a t e r level in t h e retort rises, the pressure in t h e retort should b e closely w a t c h e d and k e p t constant. W h e n t h e w a t e r level is n e a r the top o f t h e retort, t h e overflow or drain is o p e n e d slightly and then o p e n e d rapidly the m o m e n t t h e retort is filled with water, to avoid pressure fluctuations w h i c h m a y d a m a g e the cans in t h e retort. Cooling of the cans b y t h e w a t e r is n o w continued for some time, during w h i c h the pressure in t h e retort should b e k e p t up until t h e cans h a v e cooled down so that a lower pressure in t h e retort will not subject the c a n lids to
2 3 4 SVEN L A S S E N
any excessive strain. T h e final step is now to close all valves, except the drain valve, open all vents and bleeders, thereby releasing all pressure in the retort, after w h i c h the door m a y b e unbolted. T h e w a t e r cooling should b e continued so that the retorted cans w h e n removed from the retort do not have a temperature of a b o v e 1 0 0 ° to 1 1 0 ° F . T h e baskets containing the retorted cans are now rolled out of t h e retort and placed in a cooling room w h e r e they remain until released b y the State B o a r d of Health, C a n n i n g Inspection Service, upon submission of evidence b y t h e canner that the cans involved have b e e n retorted at the temperature and for the length of time prescribed. Section 12470, Article 8, of the California Administrative C o d e ( P u b l i c H e a l t h ) C a n n e r y Inspection Regulation, details the nature of this evidence as follows: " E a c h licensed retort oper
ator shall k e e p a record of the cooks as required b y the State B o a r d of P u b l i c Health.
" a ) T h e original and duplicate of t h e production record must b e kept b y filling in accurately in complete detail the form approved b y the D e p a r t m e n t of P u b l i c Health. E a c h entry in the record must b e m a d e b y the operator at the time the specific retort operation is observed and not copied afterwards. I t must b e in legible handwriting and b e signed b y the operator or operators.
" b ) Charts of recording thermometer must show full time and temperature as required, otherwise the product will b e restrained.
" c ) E a c h production record and recording thermometer chart shall b e stamped, initialed and n u m b e r e d b y a State C a n n e r y Inspector before use and must b e accounted for.
" d ) T h e cook or b a t c h n u m b e r and size of cans involved must b e recorded b y t h e c a n n e r in e a c h respective curve of all temperature charts.
" e ) Production records and charts must b e scrutinized and c h e c k e d b y a State C a n n e r y Inspector before product is released for shipment."
All cans must naturally b e coded. T h e regulations covering coding of tuna cans are contained in Section 12475 of the above mentioned C a n n e r y Inspection Regulation, as follows:
" E a c h plant must submit and have approved a code to appear legibly on the cover of e a c h container. This c o d e will show the plant w h e r e packed, year packed, the product contained therein, b a t c h n u m b e r or day code. It is understood b y the packer that w h e r e a day c o d e is used, the entire day's output shall b e considered as one b a t c h in case of question."
After the retorted cans have b e e n released b y t h e State C a n n e r y Inspector, the cans are brought b a c k into the canning line b y emptying the baskets into a hopper to w h i c h is attached a so-called "unscrambler,"
4 . T U N A CANNING AND P R E S E R V A T I O N O F R A W M A T E R I A L 2 3 5
an ingenious d e v i c e which, b y passing the cans over a d o m e or letting t h e m slide down a tray reciprocating at a right angle to the c a n motion, arranges the cans in such a w a y that they can b e fed b a c k into t h e conveyor line. O n this line t h e cans are passed to the labeling machines, after w h i c h they are p a c k e d in corrugated cardboard cartons and sent to the warehouse.