Paraffin or wax sealing of jars is no longer considered an equally acceptable choice for any sweet spread, including jellies. Any pinholes, shrinkage or cracks in the wax paraffin allow airborne molds to contaminate and grow on the product. In addition, leaks or holes in the paraffin can allow product to seep out during storage and once on the surface, it will provide nutrients for molds to grow on the surface and enter into the jam or jelly in the jar.

Follow These Steps in Making Jam or Jelly at Home:

1. Wash Mason canning jars (half-pint or pint size) in hot water with detergent and rinse well by hand, or wash in a dishwasher. Presterilize the clean jars by submerging them 10 minutes in boiling water. The easiest way is to stand the empty jars upright on a rack in a boiling water canner filled with clean water. There should be enough water to fill the jars and still come to a level 1-2 inches above the tops of the jars. Bring the water to a boil and boil for 10 minutes. Jars can remain in the hot water until they are ready to be filled.

2. Prepare two-piece canning lids according to the manufacturer's recommendations.

3. Prepare jam or jelly according to recipe directions. Boil for the recommended time in the recipe and then quickly skim off foam (if needed or desired).

4. Remove presterilized jars from the hot water one at a time, tilting them to quickly empty them into the canner. To make sure they are completely drained, they may be turned upside down on a clean towel on the countertop. Fill quickly with the hot jelly or jam mixture, leaving 1/4 inch headspace. Wipe the sealing surface of the jars with a clean paper towel, dampened with hot water, to remove any jelly, jam or sugar crystals. Adjust lids.

   Work quickly to insure that the filled jars stay as hot as possible until all are filled and ready to load into the canner for processing. However, remember the jam or jelly mixture is very hot and take precautions not to burn yourself.

5. Load the filled jars, fitted with lids, into the canner one at a time, using a jar lifter. Keep the jar upright at all times. Tilting the jar could cause the hot jelly or jam mixture to spill into the sealing area of the lid, which should remain clean and undisturbed. The water in the canner can be close to boiling when the jars are added, if you have made sure the filled product has remained very hot until the canner load is ready.

6. Turn the heat under the canner to its highest setting, cover the canner with its lid and heat until the water boils vigorously. Process the jars for 5 minutes after the water boils. The water level in the canner should be 1-2 inches above the tops of the jars. The water in the canner must remain boiling during the entire 5 minutes, so keep the heat source on high and a tight lid on the canner.

7. Remove jars from canner after the process time is up; use a jar lifter and keep jars upright. Carefully place them directly onto a towel or cake cooling rack, leaving at least one inch of space between the jars during cooling. Avoid placing the jars on a cold surface or in a cold draft.

8. Cool jars upright for 12-24 hours while vacuum seal is drawn and jam or jelly sets up. Let the jars sit undisturbed while they cool. Do not tighten ring bands on the lids or push down on the center of the flat metal lid until the jar is completely cooled.

9. Remove ring bands from sealed jars. Put any unsealed jars in the refrigerator and use first.

10. Wash jars and lids to remove all residues. Label and store in a cool, dry place out of direct light.

Do I have to pre-sterilize the jars?

If the jars are not presterilized, the process time in the boiling water canner is 10 minutes. Jars should still be washed in hot water with detergent and rinsed well by hand, or washed in a dishwasher, and kept warm until they are ready to be filled.

Presterilization of jars (and thus the five minute process time) is preferred when the fruits may not be naturally high in pectin, since the longer process time in the canner without presterilized jars may weaken these gels.

Are there other methods of sealing jars?

Some other methods of sealing jars call for inverting a closed, filled jar of hot product for anywhere from thirty seconds to one hour. (Inverting is turning the filled jar upside down on its lid.) While this inversion process can be successful in producing a sealed jar, it works best with very hot product. Individual variation in practicing this process or unexpected interruptions can result in delays between filling jars, getting lids screwed on, and inverting the jars. If the product cools down too much, the temperature of the product can become low enough to no longer be effective in sealing jars or preventing spoilage.

When the inversion process does work, the vacuum seals of filled jars still tend to be weaker than those produced by a short boiling water canning process. A weak seal is more likely to fail during storage. In addition, the headspace of the jar may retain enough oxygen to allow some mold growth if airborne molds contaminated the surface of the product as the jar was filled and closed. More complete removal of oxygen from the headspace also offers some longer protection from undesirable color and flavor changes with some types of fruit products.

The canning process is therefore a more foolproof method of making jams and jellies that will not spoil. In addition, although no cases of burning have been reported in the news media, experience has shown that some people will experience leaking of the hot product from the jar when it is turned over if the lid wasn't put on just right. If hot enough, someone could get burned. Even if it doesn’t cause burns, leaking means product is lost.

Should I worry about mold?

But is there a safety hazard in some molding of a jam or jelly? The best answer is that there is a potential risk. However, we want to make a recommendation that minimizes all potential problems and hazards. Some molds growing on fruit products made at home have been shown to produce "mycotoxins", or mold poisons. The danger to humans from consuming mycotoxins, as well as the actual expected incidence of mycotoxins from moldy jars of jams, are issues with no easy answers. But, animal studies indicate there is the potential for poisonous effects of some mycotoxins in humans. Patulin is one mycotoxin detected in a few tested jars of homemade apple jam and juice. Patulin has been shown to be carcinogenic in animals, but its role in causing human disease is not all that clear. It is also difficult to assess the actual health risk from consuming moldy jam or jelly because not all molds produce mycotoxins, and molds which do produce them vary in consistency of production when conditions change some.

Summary

Because we are interested in recommending jam and jelly making procedures that offer the highest quality, the least health and safety risks, and the lowest chance of losing product, all Extension recommendations for jams and jellies include a boiling water canning process for room temperature storage of sealed jars. Standard canning jars used with self-sealing flat metal lids and screw bands, presterilization of clean canning jars, hot filling of product into the jars, and processing for 5 minutes in a boiling water canner are recommended for highest quality and to prevent mold growth.