10. Have pet cock completely closed during the cooling.
11. Open pet cock before vacuum forms. This is evidenced by a rush of air into the canner when the pet cock is open. You can test this by placing the finger over the end of the pet cock. If a vacuum forms it will draw the flesh of the finger into the opening.
12. Remove jars from canner and tighten lids as soon as canner is opened.
BREAKAGE OF JARS
When breakage of jars occurs it is due to such causes as these:
1. Overpacking jars. Corn, pumpkin and sweet potatoes swell or expand in processing. Do not quite fill jars with these products.
2. Placing cold jars in hot water or vice versa. As soon as jars are filled with hot sirup or hot water, place immediately in the canner.
3. Having the wire bail of glass top jars too tight.
4. In steam canner, having too much water in the canner. The water should not come above the tray.
5. Cold draft striking the jars when they are removed from the canner.