The following are questions that Penn State Extension educators frequently receive about food preservation and canning. Perhaps you have wondered about them too.

How long will home-canned food keep?

Food that has been properly canned and stored under ideal conditions will maintain its quality for a year. It will be safe to use as long as it is sealed, but the quality begins to deteriorate after a year. Canned food stored in a warm place near hot pipes, a range, a furnace or in direct sunlight may lose some of its eating quality in a few weeks or months depending on the temperature.

What if some jars have not sealed when you remove them from the canner. When is it safe to re-can food if the lid does not seal?

Canned food can be safely re-canned if the unsealed jar is discovered within 24 hours of processing. To re-can, remove the lid and check the jar sealing surface for any cracks. Change the jar if necessary, add a new prepared lid and reprocess using the same processing time.

When is it necessary to sterilize jars before canning?

Jars do not need to be sterilized before canning if they will be filled with food and processed for 10 minutes or more. Jars that will be processed less than 10 minutes need to be sterilized first by boiling them in hot water for 10 minutes. That means most foods only need to be put into clean hot jars.

Is it safe to can vegetables and meats without salt?

Yes. Salt is used for flavor only and is not necessary to prevent spoilage.

What is canning salt?

Canning salt, also called pickling salt, is a pure salt without additional additives or minerals. Regular table salt usually contains an anti-caking ingredient so that it pours easily. Table salt may have added iodine, a necessary nutrient, which can discolor light-colored vegetables and pickles. Sea salt contains minerals that can discolor food. Kosher salt is a pure salt, but the crystals are larger and measure differently than canning salt.

Is it safe to can fruits without sugar?

Yes. Sugar is added to improve flavor, help stabilize color, and retain the shape of the fruit. It is not added as a preservative.

What causes jars to break in a canner?

Breakage occurs for several reasons: using commercial food jars instead of the jars manufactured for home canning, using jars that have hairline cracks, and putting jars directly on the bottom of the canner instead of on a rack.

What causes liquid to be lost immediately after processing?

Liquid can be lost when jars have been removed from the canner before the internal temperature has stabilized to room temperature. For a boiling water canner or an atmospheric steam canner, when the processing time is complete, turn off the heat and remove the cover. Wait 5 minutes before removing jars. For a pressure canner, follow the manufacturer’s instructions for cooling the canner and remove the cover. Do not force-cool a pressure canner. Wait 10 minutes before removing the jars.

Should liquid lost during processing be replaced?

No. Loss of liquid doesn’t cause food to spoil. However, the food above the liquid may darken from exposure to air. If the liquid loss is excessive (for example, if at least half of the liquid is lost), refrigerate the jar(s) and use within two to three days.

What causes a jar to lose its seal (the jars seals and then unseals)?

Minimum or inadequate vacuum is caused by under-processing of the filled jar. Tiny particles of food might be on the sealing surface. A tiny chip or crack might be on the jar rim. Excess air may have been left in the jar because of too much headspace or air bubbles may not have been removed before processing.

What causes the lid to buckle or to warp or budge upward?

When the buckling occurs immediately after heat processing, the band may have been applied too tightly. Adjust the band using only your fingertips. When buckling occurs during storage, the cause is food spoilage. The heat processing has been inadequate to destroy all spoilage microorganisms, which then produce gases inside the jar.

If you have food preservation questions, a home economist is available to answer questions on Wednesdays from 10 a.m.-2 p.m., by calling 717-394-6851 or writing to Penn State Extension, Lancaster County, 1383 Arcadia Road, Rm. 140, Lancaster, PA 17601.

The Well Preserved news column is prepared by Penn State Extension.