The National Center for Home Food Preservation suggests following the manufacturer’s advice because styles of smooth top cooktops being manufactured differ in ways that influence suitability for canning.
Some smooth cooktop manufacturers say do not can on them, while others who say it is OK but still put stipulations on the diameter of the canner compared to the diameter of the burner.
Boiling water or pressure canners may not be available that meet the maximum diameter pot they allow.
There are several issues:
1. There can be damage to the cooktop from the excessive heat that reflects back down on the surface, especially if the canners used are too large of a diameter than is intended for the burner being used.
The damage can range from discoloration of white tops to actual burner damage to cracking of the glass tops to fusion of the metal to the glass top.
Another tip to remember. Even if the manufacturer says a burner/cooktop can be used for canning, people should also be aware the scratching can occur if the aluminum canner is slid or pulled across the cooktop.
This often happens with large, heavy canners, so we need to be careful.
2. Many of these cooktops have automatic cut-offs on their burner when heat gets excessive. If that option is built in, and the burner under a canner shuts off during the process time, then the product will be underprocessed and cannot be salvaged as a canned food.
The process time must be continuous at the intended temperature, or microorganisms may survive. Also, if the pressure drops quickly, most likely liquid maybe food will be lost from the jar (It will spill from the area of higher pressure inside the jar to the lower pressure now in the canner around the jar).
3. Even if boiling water canning is approved by the manufacturer, it may be necessary to fashion your own canner out of a flat-bottomed stockpot with a bottom rack inserted.
Many canners do not have flat enough bottoms to work well on a smooth cooktop to be able to maintain a full boil over the tops of the jars. The pot used as a canner must also be large enough to have lots of water boiling freely around the jars, and at least 1 inch over the tops of jars.
If the canner is too small, then it starts boiling faster than expected and the total required heat the jars receive in the canner even before the process time begins can be too short.
One recommendation from the national Center for Home Food preservation is to contact the manufacturer of your smooth cooktop before making your decision to can (or not) on it.
The manufacturers are the recommended source of this information and may also have up-to-date alternatives or suggestions for equipment that you can use. They would also need understand how large your boiling water or pressure canner is, how long it must be heated at high heat, how long the hot canner may stay on the burner until it cools after the process time, and that the canner is make from aluminum (If it is).
Happy Canning and as always let me know if I can answer any questions (728-7001).