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Canning and Preserving
(article, Ashley English)
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h3. From Chapter 3: Canning Concepts
Knowing whether a food is low or high in acid is crucial to canning safety. This is because relative acidity determines the temperature at which microorganisms present on a food will be killed. The pH scale is used for measuring acidity. Those foods with a pH of 4.6 or lower are considered high acid, whereas those whose pH is above 4.6 are considered low acid.
Microorganisms on high-acid foods will be killed at 212 degrees, the temperature achieved by a boiling-water bath. Microorganisms on lower-acid foods can survive at temperatures up to 240 degrees, so a boiling-water bath cannot guarantee that pathogens on such foods will be destroyed. Pressure canning is an absolute must to ensure safety when canning low-acid foods.
h1. About the book and author
Ashley English farms and preserves in North Carolina. She has written a series of DIY homesteading books, including Canning and Preserving.
Reprinted by permission of Lark Books (2010).
Jams, jellies, chutneys, marmalades, butters, and most fruit spreads are generally higher in acid, and therefore may be processed in a boiling-water bath. Some fruits, however, straddle the high/low acidity fence. For example, tomatoes can have variable acidity, and on occasion may have a pH higher than 4.6. Unless you plan on putting all your tomatoes to a litmus test, adding an acidifying agent like vinegar, lemon juice, or citric acid will provide enough acidity to allow tomatoes to be safely boiling-water-bath processed.
Otherwise, if you are intending to preserve any vegetable, meat, seafood, or poultry products through canning, they must be pressure-canned. The steps for pressure canning are similar to water-bath canning, but with a few unique twists.
[%image featurette-image float=right width=400 caption="If you purchased your pressure canner at a garage sale and it didn't come with a manual, you'll want to obtain one from the manufacturer or online."]Pressure canners come in either weighted- or dial-gauge versions. While the following directions apply to both models, always consult the manufacturer's directions provided with your model to ensure proper and safe use.
If you picked up your pressure canner at a yard sale or via a no-longer-canning relative, write or email the canner's manufacturer and request a manual, or simply check the manufacturer's website for an online version. Read the manual thoroughly before firing up your pressure canner for the first time.
Here are eight steps for successful pressure canning.
#(clear n1). Assemble all your equipment. Gather up jars, lids, and ring bands, canner and rack, jar lifter, funnel, spatula, recipe ingredients — everything you'll need to concoct your recipe, bottle it up, and process it. Read through your recipe. Know what you're getting into, how many jars it yields, and how much time you should be prepared to spend on the entire process.
#(clear n2). Prep your pressure canner. Put about 2 to 3 inches of water in the bottom of your pressure canner. Place the rack in the bottom of the canner. Begin warming the water over medium heat with the lid off.
#(clear n3). Prep everything else. Clean and heat your jars and lids, prepare your recipe, fill the jars, clean the rims, and put on the lids and ring bands. See the recipe Whole, Crushed, or Quartered Tomatoes for detailed instructions.
#(clear n4). Exhaust the vent. Take your filled jars and, using a jar lifter or tongs, place them one at a time into the pressure canner. Be certain they are sitting on top of the rack and aren't touching each other. Once all of your jars are in, place the lid on the canner and lock it into place according to the manufacturer's directions for your model. If using a dial-gauge canner, be sure the petcock (the small tube sticking out of the lid) is open. If using a weighted-gauge canner, leave the weight off of the vent pipe. Bring water to a boil over medium-high heat. Once you see steam coming out of the vent pipe, set a timer for 10 minutes. This process is known as exhausting. Its purpose is to force all the air inside of the canner out. You will want to time this to be certain that you have allotted 10 minutes and no less, as failure to do so could alter temperatures inside the canner and result in improperly sealed jars. Exhausting is necessary every time you use a pressure canner.
#(clear n5). Process the jars. After you have exhausted the vent for 10 minutes, close the petcock on dial-gauge canners by putting the counterweight on it. For weighted-gauge canners, close the vent by placing the weight over the vent pipe. If you are at sea level up to 1,000 feet of elevation, position the weight at the number (5, 10, or 15) indicated by your recipe. If you are at more than 1,000 feet above sea level, amend your canner setting accordingly: 15 on weighted-gauge canners, 11 through 15 for every 2,000 feet of elevation gain on dial-gauge canners.
Depending on the model you are using, you will either watch the dial until it reaches the desired pressure (dial-gauge) or listen and watch for the weight to begin to jiggle and sputter and rock (weighted-gauge), indicating pressure has been reached. Once that level is achieved, set a timer for the number of minutes listed in your recipe.
It is essential that the pressure in your canner remain constant during processing. Significant fluctuations can cause food inside the jars to leak out, ruining the seals in the process. You will therefore need to keep an eye on your canner for the entire duration of the processing time. Dial-gauge models should read at the same number the entire time, and weighted-gauge models should continue to emit a hissing sound and jiggle one to four times per minute. If something takes you away from the stovetop and you return to find a reduction in pressure, you will have to start timing from the beginning. The only way to ensure food safety, and prevent the dreaded botulism, is to guarantee that you have processed your items at the correct pressure for the full duration of the suggested time.
#(clear n6). Cool down the canner. Once you are absolutely certain that your canner has continually remained at the correct pressure and your processing time is complete, turn off the heat and allow the canner to cool. When the pressure gauge returns to zero (consult the instructions included with your model to determine when this occurs), it is then safe to remove the weight from the vent. Do not remove the weight, however, before the pressure returns to zero. Depending on your model, it could take between 15 minutes and one hour for the canner to cool completely and pressure to reach zero.
After you take off the vent, wait another few minutes (again, refer to your model's instructions) before removing the lid. As you take the lid off, be certain to tip the steamy side up away from you, as the steam that will rise out of the canner, along with any water droplets accumulated on the underside of the lid, will be very hot.
#(clear n7). Remove the jars. Using a jar lifter or tongs, remove the jars one at a time. Try to avoid tilting the jars as you remove them from the canner. Place the jars on a towel and allow them to cool, untouched, for 24 hours. You might want to drape a cloth over your jars to keep them from catching drafts, as cooling too quickly can cause jars to crack.
#(clear n8). Check the seals and tidy up. Press on each jar lid with a fingertip; if the lid flexes, the jar isn't sealed. You can reprocess unsealed jars in a boiling-water bath or simply store the unsealed jars in the fridge. Label and date each jar before storing them in a cool, dark, dry location.
p(bio). The photo used here (which does not appear in the book) is by Kathie N. Lapcevic; it appears on the Cans Across America flickr pool.