14 BULLETIN 106, U. S. DEPAETMEXT OF AGRICULTURE. 



processing may have been insufficient to kill the vegetative forms or spores, but may 

 have injured them to such an extent that time was necessary for recovery and subse- 

 quent development. A microscopic examination of the material a few days after 

 processing, or of the incubating cans dm-ing a short period, might not show anything 

 wrong. It is only by incubating samples for a number of days that early recognition 

 can be made of some cases of spoilage or possible spoilage. The canner often sends 

 his goods from the factory with full confidence in their condition, and it is not until 

 after they have been in the broker's warehouse or upon the grocer's shelves many weeks 

 or even months that he becomes aware that anything is \vrong. The spoilage may 

 amount to only one can to the case, or the percentage may be high; but in either event 

 the goods are rejected with loss. 



Spoilage from the use of improper material — i. e., material which has been allowed 

 to stand until fermentation has begun — is generally more or less sour to the smell and 

 taste, but is sterile, the heat of processing having killed the bacteria. 



Can leaks may occur along the side, "seam leaks"; at either end, "end leaks"; at 

 the cap, "cap leaks"; at the tip, "tip leaks"; or may be due to defective tin plate. 

 Can making has reached such a point of perfection that manufacturers guarantee all 

 above two to the thousand. These imperfect cans are usually due to the solder not 

 making a perfect union or to defects in crimping or double seaming. With the use of 

 the automatic capping and tipping machines there are fewer leaks than formerly 

 occurred when the work was done by hand; leaks in sanitary cans are generally due 

 to poor adjustment of the rollers. Leakers are recognized, as a rule, by inspection in 

 the hot bath, few getting into the wareroom. Leaks may be very small, even micro- 

 scopic in size, and, therefore, difficult to detect, or pieces of the can content may be 

 driven into the opening and seal it for the time. Leaks invariably cause swells. A 

 check on spoilage can be kept by placing a few cans from each day's run in a room 

 kept at a high temperature (98°), as these will incubate much more rapidly than if 

 kept in a storeroom. In the laboratory this is done in the ordinary incubator. Since 

 1903 the writer has used refrigerators in which water tanks are placed in the ice com- 

 partment and a heater connected to the outside, the temperature being controlled 

 by a thermo-regulator similar to that used on a chicken incubator. This gives large 

 capacity at low cost and is suitable for small canners. A large chicken incubator 

 has also been used with success. 



There are two conditions known to the trade as "springers" and "flippers." A 

 springer is a can the end of which will bulge slightly after a time, but on opening there 

 is found neither gas nor spoilage, though the cans have the appearance of being swells. 

 This condition has been found to be due to overfilling or to packing cold. Such goods 

 when placed in a warm grocery will bulge, owing to the temperature. A flipper is a 

 springer of such mild character that the head may be drawn in by striking the can on a 

 hard object. It is always possible to tell a swell from a springer by the use of a micro- 

 scope, as in the former there will be large numbers of organisms while in the latter 

 there will be very few. 



While a spoiled can of food should never be eaten, the danger of poisoning from fruits 

 and most vegetables is very remote. Ptomain or other poisons may form in meat, 

 milk, and fish, but rarely, if ever, in vegetables. 



EFFECT OF HEAT AND COLD. 



Canned foods may be injured by an excess of either heat or cold. Some products 

 are injm-ed more than others. The effect of prolonged heating is to cook the contents 

 to a pulp. This is seen at times, in the case of peas and tomatoes in particular, when 

 the cans have been stacked tightly before being fully cooled. The liquor will become 

 cloudy from short heating, thick and heavy from prolonged heating, and the peas 



