how to tell if canned food is bad

Home Canning – Signs of Spoiled Food

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Home canning has really made a comeback and if you do a lot of it, chances are you’ll run into the situation at least once, where you question the edibility of something you’ve just pulled out of the pantry.  Whether it’s because it didn’t seal correctly to begin with, or that it came unsealed while in storage, if you know what to look (and smell) for it makes decision making easier.  I tend to err on the side of caution if I find myself questioning a jar of something that I’ve canned, but most of the time the signs your canned food has gone bad are pretty obvious.  The one exception to that is if a home canned product has developed botulism.  You can’t taste or see botulism but you’ll become quite sure about it real quick if you consume a jar of food that has botulism spores growing in it.  Botulism sickness, also known as food poisoning, begins with weakness in the face that then spreads downward to the rest of the body.  Other symptoms, according to WebMD, are blurred vision, difficulty speaking and swallowing, shortness of breath and nausea and/or diarrhea.  Because it is technically a neurotoxin traveling through your body, if left unchecked, botulism poisoning may be fatal.  Using correct canning methods for the food and keeping all supplies and work areas sterile is the key to botulism free home canning.  Any of the home canning books will walk you through the process and give you the correct methods, but my favorite is the Ball Blue Book – Guide To PreservingThe Ball Blue Book has recipes but also gives information on equipment and easy to follow step-by step instructions for which method to use (water bath or pressure canner).  The method used varies by food type and using the correct method ensures your jars have been processed with sufficient heat to kill botulism spores and other bacteria that could cause all your hard work to be wasted.   Follow the guidelines and you’ll have few worries.

For spoilage that you can see and taste, look for the following clues:

  • Bubbling in the jar.
  • Bulging lids.
  • A lid that spews when you open it, indicating the contents have been developing pressure or gas inside the jar.
  • A lid that has lost its seal.
  • A jar that has had visible seepage (on the outside of the jar coming from the lid).
  • Food that has an odd color.
  • Food that has an odd smell.
  • Any kind of film or slime covering the top of the food.
  • A lid that moves when you press on the top.  Canning lids have small indented “buttons” that will be completely concave when they are properly sealed.  A “button” that moves is not sealed.

A few handy tricks to have up your sleeve:

  • Don’t store your jars with the rings on.  If pressure develops inside the jar, an unseal will be forced by the pressure.  A lost seal makes your decision easier as it is a clear sign of spoilage.  To bring that point home even more, a jar with a ring still on it may actually lose its seal and then re-seal.  When this happens it’s called a false seal.  Albeit lightly resealed, it may make it less clear that there has been a problem taking place.
  • Before you put your jars in storage, take the rings off and give the lids a trial lift with your fingernail.  If the seal is not good, you’ll be able to lift it off.  If the seal is good, you won’t.
  • If you’ve taken the advise above and are storing your jars without the rings, put foods that are more prone to building pressure (tomatoes, etc.) under a shelf that will at least help contain the mess if one pops the seal and lid.
  • If you’ve just finished processing and discover a jar that has not sealed properly, just stick that jar in the fridge and use it within a few days.  Generally the rule of thumb is no more than 24 hours after processing, but use your judgement if it already looks “off” or if it has been subjected to excessive heat while sitting out waiting to seal.
  • Store your jars in a dark, cool place that is not subject to large temperature swings. (another thing that can cause an unseal and reseal.)

Canning is an important part of being self-sufficient and is extremely rewarding.  Follow sanitary methods and the guidelines in a well-respected canning publication and know what to look for.  Then follow golden rule #2; If in doubt, throw it out!  Happy canning:)

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4 thoughts on “Home Canning – Signs of Spoiled Food

  1. Pingback: Strawberry Picking 2017 Part 2: Jam Making – Oscoey

  2. Great tips. I’m new to canning and need all the information I can get. So far I’ve only done water bath items. Maybe this year I’ll try my pressure canner for the first time. – Margy

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