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It's been a few years since I published a Canning Q&A, but this year, with so many canning newbies out there, I think it's time to revive the tradition! (You can read my Canning Q&A posts from previous years here: 2010, 2011, 2012, 2013.)
Q: Please explain the difference between a water bath canner and a pressure canner. Do I need both?
A: A water bath canner (sometimes called a boiling water canner) is used for high acid foods such as fruit, jams/jellies, and pickles. It is really just a big pot (with a rack in it to prevent canning jars from touching the bottom) with a lid. Water bathing is an excellent place to begin when you're new to canning.
A pressure canner (which is different from a pressure cooker) is for low acid foods such as meat and non-pickled vegetables. These foods provide an ideal environment for botulism spores to grow and the temperature reached by boiling water cannot kill those spores; no matter how long you boil, the spores survive. A pressure canner reaches temperatures above boiling water, which is why low acid foods can only be safely canned in a pressure canner.
So...if you want to can low acid foods, you definitely need a pressure canner. However, it is possible to use a pressure canner as a water bath canner (learn more about that here) as long as the water in the canner can go a couple of inches over your jars. The downside to this method is that pressure canners tend to be heavy and take longer to reach a boil.
Q: Is it true that you shouldn't boil canning lids? My mother always boiled them.
A: New single use canning lids are made with a different sealing compound than they used to be. Boiling or simmering them will actually increase the risk of jars not sealing. Modern single use lids should not be heated before placing them on jars.
Q: Is it true that I don't have to sterilize jars for canning?
A: Yes, it's true! Once upon a time, some canning recipes called for processing times that were under 10 minutes. That is no longer the case (because now we know this increases the chances of food borne illness and mold that can cause botulism spores to grow). Nearly all tested safe canning recipes now call for at least10 minutes of processing time - and therefore sterilizing jars before filling them is no longer necessary. (If you do happen across the rare tested safe canning recipe that processes jars for under 10 minutes, then yes, you should sterilize jars by boiling them in water for 10 minutes before filling them.)
Q: How long will my home canned foods last?
A: A very, very long time! As long as you used a tested safe recipe and method and the seal on the jar remains intact, that food is safe to eat. After about a year, the food will slowly begin to lose nutrition and flavor...but I have to tell you, I've eaten decades old home canned food and could not tell it hadn't been canned yesterday! For more complete information on this topic, head over to my post on "How Long Do Home Canned Foods Last?"
Q: Does my canner have to be full?
A: If you don't have enough jars of food to fill your canner, you can definitely still process the jars. However, studies show that not having the canner full of jars can affect heat distribution, which in turn could potentially lead to pathogens not being killed. So in such instances, it's smart to go ahead and fill jars with water (no lids needed, unless you want canned water on hand) and add them to the canner before processing.
Q: I want to can jam in pint sized jars. How long should I process them?
A: Then you must find tested safe jam recipes that call for pint jars. The National Center for Home Food Preservation has a few...but most jam and jelly recipes call for smaller jars. The rule in home canning is that you may never put food in a jar that is larger than what the recipe calls for. This is because there is no way to know (without extensive lab testing) how long you'll need to process the jar so that all the pathogens that may make you ill are killed.
(On the other hand, you may go down on jar sizes. In other words, if the recipe calls for pint jars and you want to use half pint jars, that is fine. But you must use the same processing time as the pint sized jar called for. As you can imagine, in some instances, this may result in a loss of quality. For example, fruit may come out mushy.)
Q: I am trying to reduce sugar in my family's diet. Can I use the sweetener of my choice instead of the called-for sugar?
A: Not necessarily. The only artificial sweetener that is approved for canning is Splenda. For health reasons, I hope you will avoid man-made sweeteners. Of the natural low carb sweeteners, only Stevia is approved for canning. (EDIT 4/15/24: There are now some tested safe jam recipes that use allulose, as well.) I do know people who use, say, monk fruit or erythritol in canning, but it has not been tested as safe. You can learn more about why these sweetener may not be safe here. Also, if you are making jam/jelly, you will need to use a pectin that doesn't require sugar in order to gel; I recommend Pomona's Pectin. Learn more about low- or no-sugar canning here.
Q: I have a huge can of tomatoes that I bought from Costco. Can I re-can them in smaller jars?
A: It's important to understand that the density of food changes once it is canned.This means that if you re-can food, there may be spots in the jar that are not adequately heated through to kill pathogens. The food will also be lower quality because it will become more mushy and will lose more nutrients. In short, this is a "no."
Q: I know I can stack jars in my pressure canner, but can I stack jars in my water bath canner?
A: Yes. But remember that you're going to need a rack between the layers of jars. A water bath canner rack likely won't work, because the handles will get in the way of the canner lid. But a pressure canner rack will work as long as it fits inside your canner. Also bear in mind that the water must cover your jars by at least a couple of inches. Not all water bath canners are tall enough for a double stack of jars to fit.
A: First, for those who don't know, "rebel canners" (sometimes called "cowboy canners") basically don't follow any of the scientific rules for canning. They tend to water bath everything, sometimes for hours, and insist they are doing things the way our ancestors did.
However, home canning isn't centuries old. While canning was invented in 1795, it was almost never put into practice, and when it was, tin cans were used. In 1858, the mason jar was patented, but it wasn't until the 1880s that home canning become common...and even then, only high acid foods were canned at home. (I have a large collection of antique cookbooks and household guides that back this assertion up.) Pressure cookers were invented in 1679, but were extremely dangerous and not remotely common. Pressure canners were widely available by the early 1900s, and were always touted for home canning low acid foods.
I agree that our knowledge of science is always changing, but we are talking very basic stuff here: Did the process kill pathogens or not? There's nothing to get confused about there.
And for those who argue that "Grandma always did it and we never got sick:"
1. This is like saying, "I drive home drunk every night and have never gotten into an accident; therefore, drunk driving is safe."
2. You probably did get "the stomach flu" now and then. (Not every food borne illness is botulism, thank goodness.)
3. All the most recent cases of botulism poisoning from home canned food have been from reel-canned foods. Please don't risk the health of others; children and the elderly are most at risk.
To learn more about this topic, check out "When Home Canned Food Goes Bad" and "What You Need to Know about Home Canning and Botulism."
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