How Do You Know If A Canning Jar Is Safe?

Canning is a food preservation method that uses glass jars to extend the shelf life of fruits, vegetables, meats, and other foods. During the canning process, food is placed into sterile jars and heated to kill microorganisms and enzymes that cause spoilage.

The distinct purpose of canning jars is to provide an air-tight seal that prevents recontamination while keeping food shelf-stable for 1-5 years or longer. This allows people to stock up on produce when it is in-season and enjoy homegrown flavors year-round.

Home canning remains popular today with an estimated 30 million Americans canning foods each year. Ensuring canning jars provide a safe and effective seal is critical to avoid food spoilage and foodborne botulism, which can have serious health consequences.

Identifying Safe Jars

When canning, it’s important to use jars specifically designed for home canning. The most common and reliable brands for safe canning jars include:

– Mason jars – First invented in 1858 by John L. Mason, Mason jars are one of the most popular types of canning jars. They come in wide-mouth and regular mouth versions and are recognizable by their threaded metal screw lids and bands. Popular brands for Mason jars include Ball, Kerr, and Golden Harvest.

– Ball/Kerr jars – Ball and Kerr are two leading brands of Mason jars produced in the U.S. All of their jars are designed specifically for home canning and go through rigorous testing and quality control. Kerr is owned by the Newell Brands corporation along with Ball and Golden Harvest.

– Weck jars – Weck jars are another type of safe canning jar, though they use glass lids and rubber rings instead of metal lids. Weck jars must be used with special Weck accessories and tools for canning. They allow for a vacuum seal but have a steeper learning curve than regular Mason jars. Weck jars received top ratings from TechGearLab for canning.

Inspecting Jars

When inspecting jars for safety, it’s important to check for any cracks, chips or dents in the glass or lid. Even small cracks can allow air to enter the jar, leading to spoilage or contamination. Make sure to turn the jar around and inspect all sides and the underside of the lid for defects. According to the CDC, discarded jars with cracks or chips, which can prevent proper sealing (CDC).

Also examine the rim of the jar, as any small dents or imperfections can affect the seal. Run your finger along the rim to feel for any unevenness or sharp edges. The rim should be completely smooth all the way around to ensure a tight seal with the lid. The National Center for Home Food Preservation recommends rejecting any jars with flaws around the shoulder or rim area when canning (NCHFP).

Testing the Seal

After closing the jars and allowing them to cool completely, it’s important to test that each lid has properly sealed. According to the National Center for Home Food Preservation, there are two main ways to check jar seals:

Press the center of the lid. If the lid pops up when you release your finger, then it did not seal properly. A properly sealed lid will remain dipped and not pop up when pressed.¹

Try removing the band around the lid. If you can easily twist off the band, the jar did not seal. The band on a properly sealed jar will be difficult to remove, since the vacuum created inside the jar will hold the band tightly in place.²

Testing the seals ensures no air can get into the jar and contaminate the preserved food. Jars that did not seal properly should be refrigerated and consumed quickly, reprocessed, or discarded if spoilage is suspected.

Checking for Spoilage

When opening a previously canned jar, it is important to check for signs of spoilage before consuming the contents. Look for the following possible signs:

• Mold growth – Examine the food surfaces and underside of the lid. Cotton-like mold in white, black, blue or green colors indicates the food has spoiled and should be discarded (Source).

• Bubbles – Bubbles indicate gasses produced by the growth of microorganisms and is a telltale sign of spoilage.

• Cloudiness – Cloudy or murky liquid is unhealthy. The liquid should look clear.

• Sliminess – A slippery or slimy texture on food surfaces or the jar interior indicates microbial growth.

• Unnatural odors – Take note of any unnatural or unpleasant odors when opening the jar, which can indicate spoilage.

If any of these signs of spoilage exist, the contents should be discarded. When in doubt, throw it out. Don’t taste food that shows signs of spoilage.

Proper Canning Procedure

To ensure food safety, it is critical to follow proper canning procedures. According to the USDA, there are three safe methods of home canning: boiling water, steam, and pressure canning (https://extension.missouri.edu/publications/gh1451). The recommended method depends on the acidity level of the food being preserved.

Before canning, jars, lids and bands should be sterilized by submerging in boiling water for 10-15 minutes. This kills any bacteria or mold present. Only use jars specifically designed for home canning. Regular glass jars may crack or break under the heat and pressure of canning.

For high acid foods like fruit, tomatoes, pickles and jams, the boiling water bath method is recommended. Jars are filled with food, leaving headspace, then submerged in boiling water for a prescribed processing time to kill microorganisms. Follow an approved recipe for processing times based on the type of food being canned.

Low acid foods like vegetables, meat and seafood require pressure canning. The closed environment of a pressure canner allows the temperature to rise above the boiling point to kill heat-resistant bacteria. Carefully follow processing times and pressure levels indicated in USDA approved recipes.

It is critical to follow established, tested directions for canning methods, jar sterilization, headspace, processing time and pressure. Canning is a science, not an art, so do not make adjustments unless following approved guidelines.

Storing Canned Goods

Proper storage is important for maintaining the quality and safety of canned goods. According to the U.S. Department of Agriculture Food Safety and Inspection Service, canned goods should be stored in a cool, clean, dry place where temperatures are between 50-70°F [1]. Temperatures above 85°F can decrease quality over time.

For best quality, canned goods should also be used within 1 year of canning. The low oxygen environment and high heat processing enables canned food to last for years, but the quality slowly declines over time. Eating canned goods within 1 year ensures best flavor, texture, and nutrient retention [1].

Identifying Botulism Risk

When inspecting home canned goods, it’s important to check for signs of botulism contamination, which can have deadly consequences. Botulism is a serious illness caused by the botulinum toxin, which is produced by the bacteria Clostridium botulinum. This bacteria thrives in low-oxygen environments like improperly canned foods.

Look for the following signs that may indicate botulism contamination:

• Bulging lids or leaking jars – This can indicate the growth of gas-producing bacteria like Clostridium botulinum.
• Foul odor – Food contaminated with the botulism toxin can give off a foul, rotten smell.
• Never taste food that looks spoiled – Consuming even a small amount of food containing the botulinum toxin can be extremely dangerous and potentially fatal. If a jar looks compromised, do not open or taste it and discard it immediately.

Botulism is extremely toxic even in minuscule amounts. If you suspect a jar may be contaminated, do not open it or taste its contents. The CDC warns to immediately discard any jars with signs of spoilage.

Discarding Unsafe Jars

If you have any doubts about the safety of a jarred food, it is best to discard it. There are a few clear signs that a jar is unsafe and the contents should not be consumed:

• Bulging lids or leaking seals indicate bacteria growth and spoilage. Do not open or taste these jars – throw them away. As the University of Georgia Extension says, “Never use food from containers that leak or that spurt liquid when opening.” (Source)
• Any discoloration, mold, unpleasant odors, or spurting/bubbling indicates spoilage. Immediately discard the entire jar without tasting. (Source)
• When in doubt about the safety of a jar, apply the “when in doubt, throw it out” motto. The risk of foodborne botulism is not worth tasting potentially spoiled, low-acid foods. (Source)

Following proper home canning techniques reduces the chances of spoilage. However, if any signs of spoilage arise, it is essential to err on the side of caution and discard the food to avoid health risks.

Conclusion

In summary, there are several key steps you should take to identify and ensure the safety of your canning jars:

– Carefully inspect all jars before and after canning for any cracks, chips, rust spots, bulges or leaks. Damaged jars should be discarded.

– Check the seal on every jar by pressing down on the center of the lid. It should not flex up and down. Lids that improperly seal may allow bacteria to enter.

– Examine the contents of each jar. Look for signs of spoilage like mold, cloudiness, off odors or spurting liquid. If detected, do not use the food inside.

– Be sure to precisely follow proper canning procedures every time. Use up-to-date, trusted recipes and methods. Failing to properly sterilize jars or seal lids can lead to dangerous bacteria.

– Always store canned goods in a cool, dark place. Never consume food from a jar that was improperly processed or shows any evidence of contamination.

Safe home canning requires diligent care and precaution. But taking the time to carefully inspect jars, follow trusted procedures and watch for signs of spoilage will help ensure your canned goods stay safe to eat.