Canning Basics: Step One Science

Canning Basics: Step One Science

By Chef D | Published 8/19/2011


So you’ve considered home canning. There are lots of good reasons for home canning – from avoiding chemical preservatives, to creating homemade gifts, to making it a part of your survival plan.


Before embarking on this endeavor, it is important to know how to do it safely. Our concern with food is that we’re not the only ones that need it. There is a multitude of bacteria and fungi living on our kitchen surfaces, in the air that we breathe, and yes, in our food. In small amounts, most of these bacteria and fungi are not harmful but when we’re putting our food into glass jars and setting them on the shelf, we’re giving these little guys one of their primary needs: time. Time to breed. Time to digest and pass their waste back into our food. So our fundamental task, when canning, is to make sure these little creatures are good and dead before we put that lid on.


Perhaps your grandmother canned. Or your great-grandmother. They probably never hear the words “food microbiology”. This is the study of microorganisms that share our food and how they can result in various food-borne illnesses. If our great canning ancestors had had access to the information we have today we would not be educating people now about the dangerous canning methods of yesteryear such as simply ladling hot food in the jar and then turning the jars upside down to create a seal. Or putting filled jars in the dishwasher to heat them. Yes, the cooling will create a seal but just sealing something doesn’t make it germ-free. Botulism is a rare but deadly disease that is primarily contracted through home-canned goods but fortunately is avoidable.


In part, to understand how to can food safely, we need to understand the life of the microorganism. These guys aren’t very smart, and they’re not very demanding. Besides food and water (moisture), they only really need 3 things to get their party started. First, an environment with low acidity. You’re not going to want to hang out in a jacuzzi tub full of acid, and neither are they. Second and and third, time and temperature. Warm cozy temperatures and plenty of time for them to breed, eat, digest, and pass their waste back into our food. Luckily, we can control these last three things. Food-borne illnesses are largely preventable with a little knowledge and following the directions.


There are two types of canners: water bath canners and pressure canners. Water bath canners are safe to use only if the items being canned are high in acidity. Botulism can survive well in low-acidity environments and is only killed in temperatures exceeding 250F. Water bath canners only heat a jar’s contents to about 210F. Therefore water bath canners have limited uses, primarily for canning fruit, pie fillings and jams which are highly acidic as it will kill of other bacteria, molds and yeasts (as well as halt the enzyme action of fruit which contributes to spoilage). Please note that many old recipes did not take food safety into account the way it is now and are no longer considered safe. Many new recipes add acids such as lemon juice or vinegar to increase acidity. 



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Canning: Step 2, The Equipment


Canning Basics: Step Two: Choosing a Canning Method

By Chef D | Published 8/19/2011


Now that we’ve gotten the not so fun task of talking bacteria out of the way, it’s time to roll up our sleeves and start our investigation into the different types of canners out there, and which one we should plunk our money down on.


As discussed above, there are two types of canners: water bath and pressure canners. Actually, there are three if we include the steam canner. However at this time the USDA does not recommend this method as they have not conducted enough research as to its safety. Until the steam method is judged safe, I prefer not to spend time looking into them.


Water bath canners have limited uses as the food item must be acidic enough to stop the growth of the Botulism bacteria as it will not be killed from the lower temperature of approximately 210F that we can hope to reach. But if our goal is to stick to fruits, pie fillings, and jams, then a water bath canner can work just fine and might be a good way to start to determine if it’s something you’re going to find worthwhile.


Examples ohigh-acid foods (pH less than 4.6) that we can safely processing the water-bath method include fruits such as Apples, Applesauce, Apricots, Berries, Cherries, Cranberries, Peaches, Pears, Pickles, Pickled Beets, Plums, Rhubarb, and acidified Tomatoes as well as Fruit Juices and Tomato Juice. (Just remember, many older recipes were made before we became more knowledgeable about microorganisms and food-borne illnesses and therefore may not be appropriate for safe canning.)


Low-acidic foods would include vegetables and meats. These are NOT safe for the water-canning method.

So let’s take a look at waterbath canners. First, what is the benefit to water-bath canning as opposed to pressure canning? Speed. Jars can be processed in about half the time in a water-bath compared to a pressure canner. To a certain extent, any large metal container can potentially be a water-bath canner. But there are limits. First, it needs to have room for a rack in the bottom that keeps the jars at least ½ inch above the bottom of the pot (you want the water to be able to circulate underneath the jars. It also needs to be deep enough that the jars are covered with 1-2 inches of briskly boiling water. I

Take a look at the stove you will using to boil your jars. If it is an electric range, you’re going to want a flat-bottomed pot. If you have gas, a ridged bottom will be OK but the flat-bottomed will definitely be more versatile. You also don’t want your pot to be a lot larger than the burner as it will not heat the water well if there is a large discrepancy. Also, many canner brands include a disclaimer that they are not meant for flat-top ranges due to the size and weight. This is something to take into account too… for those of you with flat top ranges, you may want to pick something of a smaller size though it means you can do fewer cans at a time.

Choosing a stainless steel brand has the benefit of being used as a stock pot or tamale steamer or the like when canning season is over.

Next, we’ll be looking into pressure canners.


Pressure Canners

As mentioned above, pressure canning is for low-acid foods such as vegetables, meats, and tomatoes. Without the acid, we cannot be sure the microorganisms are killed unless we can get the temperature of our product above 240 degrees Farenheit. Because of water only being able to reach 212F before turning into steam, we cannot do this without putting that steam under pressure. Using pressure canning for fruits is not recommended as the higher temperatures break down the flesh of the fruit. Your pressure canner may be used as a water bath canner, however.

The USDA recommends using a pressure canner large enough to hold at least 4 quart jars. We also suggest that you use only pressure canners that have the Underwriter’s Laboratory Approval (UL) to ensure further safety. We also recommend that you use pressure canners with dial gauges to ensure accuracy. Every year, before starting canning, check the dial. Gauges that are reading too high can cause under-processing which means that we may not have reached high enough temperatures to ensure that our product is safe. If it reads too low it could result in over-processing. Presto tests gauges at no charge. You can reach them at 1-800-877-0441 to find out where they are in your area. You can also use the Cooperative Extension Office of the USDA. (

In the case that you end up in a survivalist situation, it is not going to likely be possible to drive somewhere and have the gauge checked. My understanding is that there are some brands, All American, in particular, that have both. My thought is that it would be best to buy something like that, and while using the gauge, make note of the action of the weighted gauge so that should the time come, you’ll feel more comfortable not relying on the dial gauge.

Your pressure canner
Before canning, also go over the canner each year. Check the lid gaskets and make sure they’re clean. Make sure the vent pipes are clear as well with no trapped food particles or mineral deposits.

Be sure, also, to make adjustments for altitude. The pressure in your canner will be lower when you are at higher altitudes. Your manufacturer’s instructions should have instructions as to how to adjust.

– To begin canning center the canner over the burner. The burner and the range must be level. Also check your manufacturer instructions about the proper types of burners. Usually outdoor gas burners or anything that puts out more than 12,000 BTU’s is not acceptable.

– Put the rack and hot water into the canner. If the food is being put into the jars already hot, you can heat the water up to 180 degrees Fahrenheit before processing. If starting with uncooked items, only bring the water up to 140 degrees F. The recipe should tell you the correct amount of water. If it does not, put in between 2-3 inches. If the recipe requires more time, it will need more water than shorter-timed recipes. Some recipes will require more water than this. If unsure, check with the USDA for specific foods.

– Place your filled jars, with lids and ring bands fitted, onto the rack inside the canner. Use the jar lifter as either they or the water may be hot. Be sure that the jar lifter is positioned securely below the ring band of the lid. Do not tilt the jar. You do not want food on the sealing area of the lid.

– Put the lid on the canner and fasten securely. Depending on your model, either leave the weight off of the vent pipe, or open the petcock.

– Turn the heat on your burner to its highest position. Heat until steam flows freely in a funnel shape from the open vent or petcock. The USDA recommends that all pressure canners must be vented 10 minutes before they are pressurized so at this point we will let the steam escape for 10 minutes.

– At this point, put the counterweight or weighted gauge on the vent pipe or close the petcock. It will take several minutes for the canner to pressurize. When the dial gauge indicates that the desired pressure has been reached, start your timer based on the recommendations of the recipe. If using a weighted gauge, the gauge should jiggle or rock, to show it’s maintaining a steady temperature. Read your manufacturer instructions regarding how your weighted gauge should behave and how to read it.

– Adjust the heat as needed to maintain a steady pressure at or just above the desired gauge pressure. Any increases or reductions in heat should be done gradually. A loss of pressure at any time can lead to under-processed and therefore unsafe food. To remedy this, if the pressure goes below the recommended pressure level at any time during processing, bring the canner back up to the desired level and start the timing process over again from the beginning. Another reason to make heat adjustments slowly is that large and quick variations in pressure can cause liquid losses from the jars.

– Once the time for processing has been reached, turn the heat off and carefully remove the canner from the burner if possible. Place on a safe and heat-resistant surface and allow to cool naturally. If you are not comfortable moving the canner due to weight or heat, leave on the burner as I do. It is not worth the risk of tilting the jars inside or hurting yourself.

– As the canner cools, it will de-pressurize. Recipes take into account the amount of time it takes to cool naturally so trying to rush it is rushing the canning process and therefore may result in unsafe food. Examples of rushing cooling would be running under cool water in the sink or opening the vent pipe before the canner has completely de-pressurized. Not only may this result in unsafe food but it can damage your jar lids resulting in loss of liquid, seal failures, and even warpage of your canner lid – especially older models.

– When the dial has reached zero or nudging the weighted gauge doesn’t seem to produce steam, tilt the weight slightly with a utensil to protect your skin from any steam. (Steam burns are the worst, ouch!) to make sure no steam escapes. Check your manufacturer instructions as to how to open the lid after cooling. Be sure the lid is facing away from you so any residual steam will not escape towards you and burn your face.

– Take the jar lifter and gently remove each jar. Take care to keep the jars upright and not tilted. Place them onto a towel, or a sturdy cake cooling rack. Leave space between each jar for air to circulate and cool the jars, at least one inch of space if not more. Don’t place jars on a cold surface and don’t place in a cold draft such as under the AC vent or by an open window if the weather is cool.

– Leave the jars to cool. This could take from half a day to a full 24 hours. Do not fiddle with the ring bands, try to tighten them, nor push down on the center of the lids until the jars are completely cooled. Once cooled, then remove the ring bands from the sealed canning jars. If any jars did not seal properly, place these in the refrigerator immediately and use them first. Wash the outside of the remaining jars to remove any food particles, and store in a dry and cool area and out of direct light.

– Wash ring bands and canner, removing any food particles and mineral deposits.

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