Home canning: Why it matters that you do it right

By Diane Wright Hirsch, MPH, RD - Extension Educator/Food Safety
Featured Article - posted Wed., Sep. 4, 2013
- Contributed Photo

They say that what is old is new again, and canning food at home food is certainly experiencing a resurgence. It goes hand in hand with the trend toward buying locally-grown fruits and vegetables, shopping at the farmers’ market, joining community supported agriculture (CSA) farms, and even greater interest in backyard vegetable gardens. If you are at all successful, and your garden is producing more tomatoes than you could ever eat before they start rotting, you pretty much have to turn to canning, freezing or using other methods of preserving food at home.

If canning is your method of choice, it is important to know that at least for some foods, doing it right may make allow you to enjoy those tomatoes on a cold winter’s day. At best, doing it wrong may be a waste of hard labor and good produce when the food in those jars you managed to put up on a hot day in August start to explode or mold. At worst, you could make someone very sick.

It just doesn’t make much sense to fool around with questionable canning (or other types of home food preservation for that matter) practices. And these unsafe methods can be found just about anywhere you look these days. Even though, for years, the prudent advice has been to follow recipes tested by USDA or some reputable food scientist, it is easy to be drawn to the latest YouTube video or blog and leave your laptop thinking, “Wow, I’m going to try that!”

Here are just a few pieces of potentially unsafe advice that I found during a recent trip through internet land…

• A video showing a home cook pressure canning in a pressure cooker rather than a canner (yes, there is a difference)

• A series of instructional pictures using a steam canner (equipment not recommended for safe canning)

• Using a pressure canner without properly venting it for 10 minutes

• A blog stating that you must sterilize all jars for foods processed in a water bath canner (you only need to sterilize products that will be processed 15 minutes or less)

• A video telling viewers to process quarts of tomato puree for only 30 minutes (USDA doesn’t even recommend canning puree in quarts, but pints should be processed for 35 minutes)

• A blog post stating, “I usually find that the best way to get my jars to seal (any recipe) is to invert them onto a towel on my counter for five minutes after tightening the bands.”

• Another blog post, “I cook my tomatoes, fill the jars, invert them and let them cool - I never water bath can them…”

• Bunches of recipes for half-sour or partially fermented pickles - no vinegar.

This is the result of a short review. I am pretty sure that the list could easily grow and grow with even just a few more hours spent browsing. In other words, there is a lot of bad advice out there, prettied up with homey pictures and personal tips that could lead you down the path of no return - literally!

So what is a home canner to do?

First, understand that while canning has been a late-summer chore for decades, it is best to ditch the family heirloom canning books and get up-to-date information from a reputable source.  Reputable sources understand that the science of safe canning has changed over the years.

For example, the current science of safe home canning takes into account that the bugs have changed: Listeria monocytogenes, a possible concern in partially fermented pickles, wasn’t even in the human food chain until the last third of the last century. Our grandmothers did not have to worry about it. And, research has shown that the mold that often graces the tops of a paraffin covered jelly is not all that harmless. Mycotoxins, produced by filaments that may not even be seen by the naked eye, well below the surface of the jelly, may be cancer-causing or promoting, may cause gastrointestinal distress, or have other health consequences.

Tomatoes are especially problematic. For years, consumers have been complaining that tomatoes were too acidic. So, scientists developed tomato varieties that are somewhat less acidic. This puts them in a pH range that leaves little wiggle room for the overripe tomato (the pH increases with ripeness). This also means that if you add even a small amount of low acid ingredients to a canned tomato product, such as peppers, onions, or garlic, you can bring the pH of the entire mixture up to a range that can no longer be safely canned in a water bath canner.

Hence the development of new recommendations for canning tomatoes sometime in the 1990s.  Processing times were increased, acidification by lemon juice (one tablespoon for pints, two for quarts) or citric acid was added, and the requirement to water bath process was emphasized in revised canning publications of that time. A canner batch of quart jarred tomatoes will take about 45 minutes to process adequately.

All foods should be processed either in a water bath canner (acid foods such as fruits, pickles, and acidified tomatoes) or a pressure canner (low-acid food such as all other vegetables, meats, fish). Some folks may still insist that they do not need to process high-acid foods. Simply fill the jar with hot food and turn it over, several bloggers said!

First, when you do that, you run the risk of seal failure as food seeps under the jar and compromises the sealing surface. Also, why risk it? After cultivating perfect berries or tomatoes, or cucumbers through a long hot summer, preparing them and carefully stuffing them into jars, why would you want to risk spoilage (what a waste of food!) or food-borne illness? Jams and jellies need only five minutes in the water bath; pickles need about 10; applesauce about 20 minutes.

So with the exception perhaps for recipes for jams, jellies, and preserves - as long as you promise to process them in a boiling water bath to prevent mold - it really makes sense to make sure that the canning methods you are using are up to date. Canning is not difficult, and if done right, it is perfectly safe. Start with the National Center for Home Food Preservation at www.uga.edu/nchfp. From there, you can visit other sites that are considered safe and reputable, offering science-based, tested recipes for safe home canning.

For more information on safe home canning, contact the Home and Garden Education Center at ladybug@uconn.edu or 1-877-486-6271.

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