Just Because It Seals, Doesn’t Mean It’s Safe

— Written By Emily Troutman and last updated by
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We are well into canning season, and many people are looking for answers to their food preservation troubleshooting questions. A common assumption is that as long as the jar seals, it will be preserved and safe to consume. This is not always the case.

Although a good seal is important for a safe canned product, proper processing technique is arguably the most important step. Sealing without proper processing can lead to microorganism growth, spoilage, and possible harmful toxin formation.

The photo below shows canned carrots; the jars were hot packed the exact same way, but only the one on the right was properly processed at the correct time and pressure as directed by a tested canning recipe. Once the hot carrots and water were packed into the jar on the left, the jar sat at room temperature and sealed from the pressure change from the heat of the contents. In this instance, you can see the cloudy signs of spoilage in the jar that was not processed correctly, however, there are not always visual signs when a canned product is unsafe for consumption. Open kettle, oven canning, and other not-recommended forms of canning may give these, or similar unsafe results.

The pathogen of concern when canning is Clostridium botulinum, which could cause botulism- a potentially deadly form of food poisoning. These spore forming bacteria can survive harmlessly in soil and water and are very prevalent on the surface of most fresh food surfaces. As an anaerobic bacteria, Clostridium botulinum spores only become dangerous in environments with an absence of oxygen, making them harmless on fresh food surfaces.

In certain conditions, C. botulinum spores can produce vegetative cells that rapidly multiply and produce a deadly neurotoxin within 3 to 4 days of growth. Ideal conditions for C. botulinum growth consist of: a moist, low acid food, a temperature between 40℉ and 120℉, and less than 2 percent oxygen. You can see by these criteria that improperly processed home canned goods exhibit the perfect environment for C. bot growth!

While the jar on the left does not show growth of colorless, odorless C. bot spores, it does show strong evidence of spoilage organisms that may still be harmful if consumed. Don’t let the fear or inconvenience of proper processing of canned goods be a reason to compromise the safety of your friends and family. Just because it seals, doesn’t mean it’s safe!

For questions about proper canning methods and procedures, contact Emily Troutman at emily_troutman@ncsu.edu or 828-764-9480.

two jars of canned carrots

Canned Carrots