170 



THE COMMERCIAL CANNING INDUSTRY 



the ends of the cans and should always be present 

 in sound cans. If, however, putrefaction or fer- 

 mentative changes take place, in which gases are 

 produced, the ends bulge out, owing to the pres- 

 sure of the gas within, and so may be easily de- 

 tected. Even in case no swelling of the cans takes 

 place, skilful inspectors can distinguish between 

 good and bad cans by the sound when the cans are 

 struck on the ends. The vacuum is generally pro- 

 duced by filling the cans with the material in a 

 hot condition and sealing them immediately. When 

 water-bath sterilization is employed, the cans are 

 sometimes unsealed or punched while hot and the 

 steam allowed to escape, the aperture being closed 

 again at once. 



Principles involved in canning specific crops. 



In the canning of fresh vegetables, the raw 

 materials are substances high in their percentage 

 of water and relatively high in carbohydrates, but 

 relatively low in proteid matter. Because of dif- 

 ferences in texture and composition, no hard and 

 fast rules of procedure can be laid down. The 

 details of the processes for various kinds of canned 

 goods cannot be given here, but the general prin- 

 ciples involved in the different classes may be 

 mentioned. 



In the preparation and preservation of all kinds 

 of canned goods the necessity for cleanliness is 

 evident, since the entire operation is one in which 

 the aim is to prevent bacterial action. Although 

 in the final process absolute sterilization is to be 

 brought about, the length of time necessary to 

 produce this end may be much shortened if care is 



added in sufficient amount to fill the cans. Unless 

 the freshly cut plant is used, a poor product is 

 obtained, as, on standing, it rapidly becomes with- 

 ered and tough. If not sufficiently " processed " it 



Fig. 250. A steam apple-butter cooker. 



taken to exclude the organisms from external 

 sources. Owing to the preponderance of carbohy- 

 drates, fermentations taking place are most likely 

 to give rise to acids, lactic acid, probably, being 

 the one most frequently found. Putrefactive fer- 

 mentations sometimes occur, especially in those 

 vegetables having considerable nitrogenous sub- 

 stances, as beans, peas and asparagus. 



Asparagus is packed in large quantities in Cali- 

 fornia and the middle Atlantic states. After plac-; 

 ing the stems in the cans, a dilute salt solution is 



Fig. 251. WUrlpool blanclier for use in canning factories. 



undergoes fermentation, losing color and assuming 

 a rather bitter, acid taste. If too highly heated, it 

 is darkened and has an overcooked taste. 



Peffis.^In packing peas, the peas are first 

 removed from the pods by a machine, either a 

 " viner"or a "podder." In construction the " viner " 

 consists of a large hollow cylinder, enclosing a 

 wire cylinder, within which a paddle wheel revolves 

 rapidly. The vines are fed in at one end of the 

 cylinder, and as they are struck by the paddles the 

 pods are burst open and the peas dislodged, the 

 bruised vines being delivered at the other end of the 

 cylinder. The peas and fragments of leaves, pods 

 and the like, fall on a broad endless rubber belt 

 which travels up an inclined plane, where separa- 

 tion by gravity takes place, the peas rolling down 

 into a trough while the lighter impurities are 

 carried away by the belt. 



In the " podder " the mechanism is still simpler. 

 Instead of passing the whole vines into the 

 machine, the pods are picked off by hand and these 

 are fed into the machine through a hopper. The 

 removal of the peas from the pods is effected in the 

 same way as in the viner, and the peas and pods 

 delivered by chutes. 



From a bacteriological point of view, the latter 

 process is the more desirable, as it leaves the peas 

 clean and dry, while in the case of the " viner " 

 they become wet and sticky with the juice of the 

 bruised vines, and consequently more or less con- 

 taminated with dirt and dust. 



After grading, i. e., separation by sieves into 

 peas of different sizes, and further removal of 

 fragments and poor peas, washing and blanching 

 or scalding takes place. In this process much of 

 the adherent dust and other contamination is 

 removed, and the peas pass to the "filler" where 

 they are delivered into cans, then to the " briner," 

 where a boiling hot solution of sugar and salt is 

 added. The cans are then sealed and are ready for 

 the final cooking process or sterilization. This is 

 done by steam under pressure, the length of time 

 being determined by the age and quality of the 

 peas. The temperature and time given varies with 

 different manufacturers, ranging from 230° to 240° 

 for thirty to forty minutes. 



The fermentations which are likely to take 

 place in case of insufficient sterilization are numer- 



