No. 2 (1921) REMARKS ON CANNING 97 



cold water so as to reduce the internal pressure as soon as possible 

 and to prevent overcooking. 



As regards overcooking ; this is not so important in the matter 

 of fish as in the case of fruits, which are easily spoiled by undue 

 processing either in the degree of temperature or length of process. 



128. Where sporing organisms are found or suspected in the 

 goods, it is the practice to minimise danger to the goods by 

 fractional sterilisation; the cans are processed on two or even 

 three successive occasions at 24-hour intervals ; the first processing 

 kills the existing mature bacteria, and the second kills those which 

 mature from the spores of the previous day. But it is not a satis- 

 factory method, as the goods are apt to be overcooked; in the 

 case of mackerel, canned plain or marinated (in spiced vinegar), 

 the flesh may become unduly dry and insipid, the natural fluids 

 having been boiled out and remaining in the fluid found on 

 opening the tin. 



129. It appears that for small canneries where the output does 

 not warrant the expenses of steam processing, viz., an expensive 

 boiler, retorts, and autoclaves, and skilled boiler attendants who 

 are necessary even for pressure autoclaves, the open pan method 

 is preferable to pressure processing, owing to the advantages 

 mentioned previously, such as cheapness of first cost, simplicity, 

 cheap running charges, absence of danger of explosion, ease of 

 operation by the combination of testing, exhausting, processing, 

 and retesting in the same pan as an almost continuous operation 

 (see paragraph 115), absence of strain on the soldered seams, etc. 

 The main disadvantages are slowness of operation, which does 

 not always matter, and inability to obtain temperatures higher 

 than 212^ F. ; even this can be got over by using calcium chloride 

 or oil baths. 



Final testing. — This is mainly necessary after pressure process- 

 ing because, as has been explained above, there are heavy strains 

 internal and external on the seams, especially dangerous to them 

 when soldered; hence pressure processed cans should be again 

 tested. This is readily done by placing them in trays and lower- 

 ing them into an open vat of hot water, just below boiling point, 

 when any leaks can be detected by streams of bubbles ; this, of 

 course, is still more simple when processing is effected in an open 

 vat; see paragraph 1 1 5. Such cans may be re-sealed at once and 

 re-processed, being of course as safe as any other can. 



