Mastering Food Preservation: Freezing & Canning Low-Acid Vegetables

As a general rule, it’s the acidity of an ingredient that determines the method of canning that should be used. Low acid foods (ph greater than 4.6), such as vegetables and meat, require processing in a pressure canner in order to be preserved safely at home. Unless you have unlimited freezer space, learning to use a pressure canner expands the options for the winter pantry.

With 18 pounds of green beans from Fairwinds Farm in Bowdoinham, ME, on hand, the fourth class in the Master Food Preserver Program focused on several different ways of preserving this low acid vegetable — through freezing, pressure canning (raw and hot pack), and pickling.

The raw pack process, also known as cold pack is just what it sounds like — packing the jars with uncooked beans  — and goes quickly. Simply wash the beans, trim and cut, and pack the jars tightly until you run out of beans or jars, whichever comes first.

A quarter teaspoon of canning salt was added to each pint-sized jar for flavor, with boiling water following, and leaving a 1 inch headspace. Once the jars were covered, they were placed in the pressure canner. Above, you can see the pressure canner being loaded with a second tier, another canning rack placed in between to keep the two levels separate. These raw-packed green beans were then processed at 10 pounds of pressure for 20 minutes.

Our teacher, Kathy Savoie, brought in two different types of weighted-gauge pressure canners for us to use. The one above is from Presto and is designed to rock gently, while the one below is from Mirro and “jiggles” several times a minute once they’re up to pressure. It can be mystifying what these terms mean and, as both these canners came up to pressure, we appreciated the opportunity to experience firsthand what “rocking gently” and “jiggling” sounds like.

Another way to regulate the pressure in a canner is through a dial gauge. I use what’s called a dual-gauge canner, which has both a dial and weighted gauges, and allows the user to track pressure visually as well as by sound.

These are the hot-packed green beans being carefully removed from the canner and set aside to cool. Notice how Kathy is lifting the jar straight up from the pot before setting it down; the liquid in the jars was still boiling inside, and tilting the jars may interfere with the vacuum seal as it forms.

Rather than packing the jars raw, these hot-packed beans were covered with boiling water and left to boil for 5 minutes before transferring to jars. The extra step preshrinks the beans, allowing more to fit in the jar; it also helps to prevent floating once the jars of beans are processed. Hot-packing as a technique also improves shelf life, further preserving color and flavor, especially with foods that are processed with a boiling water canner.

After processing, these jars were left to cool undisturbed for at least 12 to 24 hours. The two jars of raw-packed beans on the left seem indistinguishable from the hot-packed one to the right. Once the rings were removed, the hot-packed jars were noticeably more full than the raw-packed ones; the raw-packed beans had shrunk more during processing.

Also known as the “olive of Maine,” dilly beans are another way of preserving green beans, especially if you don’t have access to a pressure canner. The inclusion of vinegar brings up the amount of acidity, allowing these spicy pickles to be processed safely with a boiling water canner.

There seem to be two distinct camps when it comes to preserving green beans — some prefer them canned, while others prefer them frozen. In a side by side comparison, there didn’t seem much difference between the raw-packed (left) and hot-packed (middle) beans, while the frozen ones had retained both more color, flavor and texture. The closest in texture to fresh were the dilly beans, which were raw-packed and processed for only 5 minutes, compared to 20 minutes for the pressure-canned ones.

– Preserving Food: Freezing Vegetables
Preserving Food: Canning Vegetables
– USDA Canning Guide: Selecting, Preparing and Canning Vegetables

This is one in a series of posts following the Master Food Preserver Program offered by the University of Maine Cooperative Extension.

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12 Responses to Mastering Food Preservation: Freezing & Canning Low-Acid Vegetables

  1. Again a fascinating post-especially for someone on the ‘other side’ of the pond and not at all familiar with canning. All our beans are just blanched and frozen.

    Look forward to hearing more!

    • leduesorelle says:

      I’m equally fascinated by the practices there! Is it true that people in the UK use waxed cellophane to seal jams and jellies? Saw it in a movie once…

  2. Patsy says:

    Thank you for this post! I am considering getting a pressure canner one of these days to do beans. My husband only likes them frozen, but I do like them out of a can once in awhile and it would free up some freezer space for sure!

    • leduesorelle says:

      Getting a pressure canner completely opened up what I can preserve! The canned green beans definitely have their own charm…

  3. GrafixMuse says:

    I am loving this series of “Mastering Food Preservation” that you are sharing. The classes sound very interesting. I learned something from this post. I tend to tilt the jars when lifting them out of the canner so as not to hit the stove hood above. I didn’t know it could affect the seal. I will be more careful in the future.

    • leduesorelle says:

      Glad you’re finding new things here! Since you’re in Maine, you’d be eligible to apply. I have previous experience with most methods of preserving but am learning lots of new things nonetheless. it’s definitely making me a better and more conscientious canner.

  4. kate @ bbf. says:

    great review, debra! i love the side-by-side comparison of the different methods.

  5. azita says:

    Time beautifully spent! Love this inspiring series.

  6. Christina says:

    Thank you for showing and explaining everything. I signed up for a pickling class and can’t wait! I will be trying all these recipes out.

    • leduesorelle says:

      I highly recommend getting some hands-on experience when you can, and I hope this series helps to demystify some of the process. I remember how overwhelming it all seemed at first. Pickling is a great place to start — hope you enjoy it, Christina!

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