414 THE SPKIVGING OF TINS OF PRESERVED FRUIT. 



The experimental evidence shows that the duration and tem- 

 peiature of the processing are suflBcient to absolutely free the 

 contents from active yeasts. Their entry into the containers is 

 most likely to occur while the tins are cooling down or shortly 

 after. It is reasonable to suppose that the original air of the 

 tin has been partly or entirely expelled during processing, and 

 the vacuum created during cooling draws in the air of the factory 

 with its suspended yeasts and other organisms. It is entirely a 

 matter of chance as to the number of organisms and the activity 

 of the organisms that may be in the indrawn air. There 

 may be none, or they may be inactive, and the tin will not leak. 

 There may be one or more, and, if these are active gas-producers, 

 the tin will " spring. ' It is quite possible that some of the tins 

 might be so imperfectly closed that they would leak under any 

 circumstances, but the scarcity of leaks and springers among the 

 tins of stone-fruits shows that this is of very rare occurrence. 



The behaviour of the pears and plums, as compared with 

 apricots and peaches, points to the use of a more insoluble luting 

 material, and, failing this method of overcoming the trouble, 

 there is the alternative and probably better plan of allowing the 

 tins to cool after processing in a current of filtered, sterile air, 

 and, when cold, painting the joints with a lacquer- varnish. Thus 

 the entry of yeasts into the tins would be prevented during the 

 cooling, and the varnish would make them germ-tight and germ- 

 proof. 



