Canning Methods to Avoid
Because older canning methods are unreliable, they are no longer recommended for home canning. Occasionally, these methods are revived as being faster and easier than the water bath (water boiling) or pressure (steam pressure) canning, but using any of these methods is risking your family to unsafe food.
For this method, filled jars are placed in a hot oven. In oven canning, food temperatures never exceed the boiling point which destroys bacteria, and uniform heat penetration cannot be assured. Also, there's no guarantee that the food in the jars will reach the temperature you set your oven. Don't be fooled if your jars seal, this does not guarantee the bacteria has been destroyed. There is also a chance that your jars may explode from the sudden temperature change when your oven door is opened. Canning jars are not designed for intense dry heat.
Open Kettle Method
For this method, food is cooked in an open pot and transferred to sterilized jars. The two-piece caps are quickly added hoping that the jars will seal as the food cools. Sometimes recipes indicate to turn the jars upside down (inversion method). This process produces a low vacuum seal that may be broken when gas builds and escapes as the food spoils. In this method food isn't heated high or long enough to destroy microorganisms. There's also a chance for the food to be contaminated by airborne bacteria when transferring to the jars since the jars and food are not further processed.
For this method, a shallow, covered pan with a rack in the bottom is used. Filled jars are placed in the pan with a small amount of water in the bottom of the pan. The water is heated causing steam to circulated around the jars. This method is unsafe because the jars aren't evenly heated (underprocessed) and the steam isn't pressurized to superheat the food and destroy microorganisms. Don't confuse this method with pressure canning. Using this method with low acid foods can produce the poison that causes botulism, or high acid foods can spoil.
Microwave Oven Method
All microwave ovens heat differently. As a result, there's no way to set standards for processing times that achieve a uniform high temperature to penetrate the jars and destroy microorganisms that cause food storage. There's also a danger of the jars exploding within the microwave oven or as the jars are being removed from the oven.
For this method filled jars are run through the dishwasher cycle. Since there isn't a way to know the exact temperature of the different dishwashers and the temperature fluctuates throughout the cleaning cycle, processing times cannot be assured for all dishwashers. You cannot rely that the food has been properly process to kill microorganism and produce a safe product.
You can use the dishwater to wash and sanitize the jars. The dishwasher is hot enough to sanitize an empty jar especially if you have a "sanitize" cycle. After sanitizing the jars, you can leave them in the unopened dishwasher until you're ready to fill them.
Aspirin or salicylic acid at one time were considered canning powders that were claimed to be preservatives that replaced the need for heat processing. Food was heated in pots, aspirin or salicylic acid was added then the food was placed in jars without further processing. While aspirin does contain a germicidal agent that acts as a preservative, it doesn't destroy the enzyme that causes food spoilage.
Wax or Paraffin Seal Method
Using wax or paraffin was once thought safe to use for sealing jars. This method was used 50 years ago and has been proven unreliable and unsafe. Jams, jellies and preserves were once sealed using this method. The two-piece cap (lid and ring) method with a boiling water bath (usually 5 minutes for jams and jellies) is much safer. Dangerous botulism spores can still develop sealing jars containing low acid foods with wax or paraffin instead of the two-piece cap.
The heat generated from captured sunlight is not a reliable method to process foods since uniform heat penetration cannot be assured to kill microorganisms. It should never be used to can low-acid foods.