Choose the Right Cookware
It is necessary to maintain a constant even temperature throughout the canning process to safely preserve your food. These high temperatures for long periods of time pose a risk to glass cooking surfaces. If the heating element overheats the glass, it will crack. Choosing the right cookware will minimize the chance that the glass on your range will break. If the heat is distributed evenly across the pan your risk is reduced. This makes it necessary to use flat-bottom pans when you can on a glass top stove.
Metal pans facilitate the best heat transfer and will also help distribute heat properly. Aluminum or stainless steal pans are recommended. Older processors made from stoneware or cast iron are not recommended as they might reflect the heat back to the stove and crack the glass during processing.
Choose cookware with a diameter of no more than an inch larger than the heating element. Using a pan which is too large for the element could cause a burnout on the element.
The final criteria in choosing cookware is to make sure the maximum weight of the fully loaded canner does not exceed 50 pounds. Weight in excess of 50 pounds can cause the surface to crack.
Minimize Cooking Time
As it is not recommended to use your surface elements all day for canning purposes, try to minimize the amount of time your elements are heating. This will help to reduce wear and tear to your elements and reduce the amount of heat on your glass surface. Start with hot water and use a lid on your pan as you bring the water bath to a boil to help bring the water to boil in less time.
Using the proper sized element also reduces cooking time. If the element you are using is too small for the canner, it may take too long to boil the water and over heat your glass surface causing it to break.
Know Your Stove
Many glass top ranges have built in limiters on them. This is what enables your heating elements to cycle on and off when the temperature gets to the point where it could break the glass. Don't confuse this with no heat on your processor. Most pressure canners don't register the difference in heat (pressure) when the element cycles down to prevent the glass from breaking. As long as the minimum temperature/pressure is maintained for the required time, your food should be safe to eat.
Follow Recommended Canning Techniques
It is important to follow cleanliness and food safe practices for all canning. Be sure you follow all directions on your recipe relating to cook times and processing times. These are necessary to eliminate bacteria in the food and to preserve it for its designated shelf life.