There are various ways of canning or sterilising vegetables, but the two methods principally adopted here are the "Intermittent or Two or Three-day" method and the "One period or Continuous" method. The former methods are the most reliable for such vegetables as Peas, Beans, and Maize, as they contain nitrogenous substances, and are particularly favoured by heat-resistant germs or bacteria. The difference between these methods is that in the "Continuous"
Method food is cooked for several hours and the work finished in one day, while in the first two processes the sterilisation is repeated on two or three successive days, as follows: -
1. After the food is canned, boiled, and sealed, it is allowed to stand for 24 hours in a warm place. This gives the spores time to develop.
2. The canned food is then cooked a second time, in order to destroy the spores which have had time to change to the vegetative form.
3. If done by the "Two-day" process the food is sterilised the first two days for 2 hours, and repeated the second day. If done by the "Three-day" method, it is sterilised for one hour the first day, and repeated on two successive days.