How to can foods

I grew up in a family committed to canning and preserving. We ate food fresh in season and preserved our garden’s goodness for later, too. My family would make gallons and gallons of preserves in all-day marathons, both at home and at the community canning centers. That kind of time and volume can be daunting, but canning and preserving can be a part of modern life even for the busiest cooks with small-batch recipes and refrigerator or freezer jams, jellies, and pickles. It can feel overwhelming, but the truth is anyone who can boil a pot of water can make a pickle or a jar of jam. Here’s how to get started.

Canning and preserving is not necessarily hard, but it does take pre-planning and organization. First, choose your recipe. It’s important to choose a recipe from a reliable source that meets USDA safety guidelines and trustworthy recipes with good ratings. The National Center for Home Preservation is my go-to for the final answer on safety. Food safety is very important with canning and preserving; you don’t want to introduce any potentially harmful bacteria. It’s also important to follow the recipe; don’t make substitutions or changes. Yes, it will seem like an awful lot of sugar, but a lot of sugar is needed to transform fruit into jam and jelly.

You will want to purchase or harvest your produce as close to the time of canning as possible. Don’t use frozen or defrosted ingredients. Freezing affects the pectin and retards the gelling of the jam or jelly. Make sure the fruits or vegetables are not overly bruised or moldy.

You will notice that some jam and jelly recipes call for store-bought pectin and some do not. Pectin is a soluble plant fiber found in fruit such as apple and citrus. In correct balance with fruit, sugar and acid, pectin assists in forming the gel structure in jams, jellies and other soft spreads. Commercial pectin is available in both powdered and liquid form. Powdered pectin is more consistent in regards to quantity and measurements than liquid pectin, from brand to brand. But liquid pectin works even faster than powdered pectin, resulting in a shorter cooking time and a super fresh fruit taste. Use whatever your recipe recommends, and when in doubt of amounts or ratios, always consult the manufacturer and package ingredients.

It’s possible to make jams and jellies such as Blueberry Lemon Drop Jam and Strawberry Bourbon Vanilla Preserves without store-bought pectin. For it to come together and gel, it is necessary to cook the fruit, sugar and acid to 220 degrees F. But this can take up to an hour! Adding store-bought pectin can allow for far less cooking. This works brilliantly in the recipe we’ll be highlighting in this guide, Fresh Strawberry Jam for Canning. The strawberries are lightly cooked and taste fresh and vibrant.

Once you’ve decided on your recipe, it’s time to assemble your equipment and utensils and supplies. These tools will make your home canning easier and safer. Perhaps the most important piece of equipment is the boiling water canner (aka canning kettle or just canner). The iconic canning kettle is the Granite Ware Porcelain Canner, but you can also simply use a large heavy duty pot.

A boiling water canner is indispensable for preparing high-acid foods to be shelf stable. Foods such as fruits, pickles, sauerkraut, jams, jellies, marmalades and fruit butters, are high acid with a pH level of 4.6 or lower, so they can be preserved by boiling water canning, which ensures the safety of the preserved produce by destroying harmful molds, yeasts, and some bacteria. Low acid foods such as meats, seafood and non-brined vegetables like green beans, carrots, asparagus and beets require a pressure canner or pressure cooker. In this beginner’s guide, we’re focusing on boiling water canning.

Before we continue, a note about acid and pH. pH means the "potential of Hydrogen." It is a system of measuring in chemistry for determining the acidity or alkalinity of a solution. In canning, foods are categorized as high-acid or low-acid. It can be confusing — tart tomatoes may seem like they would be a high-acid ingredient, but they are not. They are not low enough in acid to require a pressure cooker as with meat and seafood, but it is necessary to add acid (like lemon juice) to lower the pH. You will also notice some recipes call for bottled lemon juice instead of fresh. This is because a commercially bottled lemon juice will always have a specific pH.

Boiling water canning consists of a large pot, tall enough to fully submerge the canning jars with an inch or two of water over top. (You don’t have to have the traditional Granite Ware Porcelain Canner with a rack, you can simply use a deep pot that will allow you to cover the jars by at least 1-inch.) The pot is used for both the sterilization of jars prior to filling and also for boiling the jars once they are filled.

Canning jars, sometimes called mason jars, are available in all shapes and sizes. It’s important to use modern canning jars. Do not use vintage jars for canning; they may not work well with a modern lid and ring closure. Also, do not reuse commercial jars such as old spaghetti or mayonnaise jars; they may not be able to withstand the temperatures required for home canning.

Home canning lids and rings are actually a two-piece vacuum cap. The lid consists of a flat metal disc with a sealing compound on the bottom and a threaded metal screw band or ring that fits over the rim of the jar. Vintage lids and rings should not be used as they may no longer effectively seal. Rings can be reused if they are in good condition, but lids are a one-and-done.

The rings and rubber-lined lids must be sterilized, too. Place the new lids in a small saucepan, cover with water and bring to a gentle simmer. Very gently simmer for 10 minutes, taking care not to boil — boiling can cause the sealing compound on the lids to deteriorate. Turn off the heat and keep the lids in the water until ready to use.

Some European jar companies such as Weck and Le Parfait rely on a jar rubber plus cooking the jars in a boiling water canner for sealing. Yes, they look very pretty, but can be a bit more complicated. You will need to follow the manufacturer’s instructions exactly.

The following tools are specifically designed for home canning and will make the canning process easier and safer.

Canning or Wide-Mouth Funnel

This funnel fits most standard and wide-mouth mason jars and has an extra-wide mouth. This allows for the transfer of large quantities of liquids or dry ingredients with less spills and mess.

Canning Tongs or Jar Lifter

A canning jar lifter with a special non-slip coating holds canning jars securely for filling and lifting. It holds jars of all sizes securely to fill with hot foods, lifts them into and out of the canner, and transports them to a cooling rack.

Ladles or Glass Measuring Cups
It’s best to use metal ladles or heat-resistant glass for transferring hot liquids from the saucepan to the jars. Ladles work great, and I also find that large heat-resistant glass measuring cups are excellent for pouring, too.

Magnetic Lid Wand
This useful tool is a durable long, plastic handle with a magnet that allows you to easily remove canning lids from the hot water.

These tools aren’t essential to the job, but will make your life a little easier — and you are very likely to have them already on hand.

Cooling Racks
It’s best to not place the jars filled with hot liquid directly on the countertop, but to place them on a rack for faster, and safer, cooling. You can also use a folded towel or wooden cutting board as a heat buffer, especially if you have stone or tile counters, which can be too cold.

Rimmed Baking Sheets
These are not imperative but they are incredibly useful for moving jars from place to place. Also, I always place the cooling rack over a rimmed baking sheet as I fill the jars to catch any potential spills.

Electric Kettle
It may seem like a bit of glorious excess to buy a kettle just to heat the water, but you can buy a fairly inexpensive one, and it will save you lots of time. Instead of waiting for the proverbial “watched pot that never boils,” take the easy route and use an electric kettle to keep the canner hot.  

Canning and preserving is not hard, but there are key steps to follow. It’s definitely a time investment, but worth every minute once you’ve tasted your own homemade efforts! To demonstrate the process I’m sharing a recipe for Fresh Strawberry Jam for Canning — find the full instructions for making it here. Once you have your equipment and ingredients assembled, you want to read your recipe and make certain you understand the steps and process. It’s very important you have the specific type of pectin called for in the recipe.

When making jam, you need to go straight from sterilizing the jars to making the jam to filling the jars. Consider preparing the actual recipe, sterilizing the jars, and submerging the jars in the boiling water canner one continuous process. It’s all about timing. I love the focused, meditative process of it. Here’s how I do it:

Prep your ingredients so you’re ready to start cooking quickly after sterilizing the jars. In this case, we’ll prep the strawberries, and measure the sugar and lemon juice, and set aside.

Place clean canning jars on a rack in the bottom of the canning pot and add water to fill the jars and cover them by at least 1 inch. (Some kits come with a rack, or you can simply use a small metal cooling rack. Sometimes I use a kitchen towel.) Cover the pot and bring the water to a rolling boil over high heat. After the water reaches a boil, boil them for 10 minutes, then reduce the heat and maintain at a simmer until you’re ready to fill the jars. Jars must be hot when food goes into them. Once you remove the jars you can reduce the heat to a simmer and use the same water to prepare the lids and rings, by gently simmering for 10 minutes (taking care not to boil). Then turn off the heat and keep the lids in the water until ready to use. 

Line a rimmed baking sheet with a clean towel or a rack. Remove jars from the simmering water using a jar lifter, and carefully pour the water in the jars back into the pot. Place the jars upside-down on the prepared baking sheet to air dry.

Cook your recipe according to its instructions — in this case we’re making Fresh Strawberry Jam (here’s the full recipe). Combine strawberries, lemon juice, and sugar and stir well. Place on high heat and, stirring constantly, bring quickly to a full boil with bubbles over the entire surface. Boil for 1 minute, stirring constantly. Remove from the heat and stir in the liquid pectin.

Ladle or pour the jam (or whatever you’ve made) into the hot jars, using a widemouthed canning funnel to help keep the jar rims clean. Leave the recipe-specified amount of headspace (the space from the very top of the jar to the surface of the liquid or food inside). Repeat with the remaining jars, working quickly to ensure that hot mixtures go into the hot (or nearly hot) jars.

Place a lid and a ring onto each jar; screw just until fingertip-tight. Carefully lower the filled jars back onto the rack in the pot of simmering water using the jar lifter to keep them upright. Add more water, if needed, to bring the water level to at least one inch above the jar tops. Cover the pot, increase the heat, and return the water to a full rolling boil. After the water reaches a boil, set a timer, and boil for the amount of time specified in the recipe, adjusting if needed for your altitude (see the Cook’s Note here for instructions). Remove jars using the jar lifter, being careful to keep them upright.

Transfer jars to a towel-lined or wooden surface where they can rest undisturbed for 12 to 24 hours. Do not tighten or adjust rings. Lids may make a popping noise as the jars cool. It is the sound of winning! That’s one sign of an airtight seal — and the sound of canning success.

When the jars have cooled 12 to 24 hours, remove the rings and inspect the lids. Each lid should be concave in the middle and firmly attached at the edges. Press down on the center of each lid with your finger. If the lid doesn’t move, the jar is sealed and can be stored in a cool, dark place for up to 1 year (once opened, store in the refrigerator for up to 1 month). If the lid center depresses and pops up again, it means the jar isn’t sealed. Refrigerate immediately and use the contents within a week or so.

More than practical, the sights, smells, and sounds of canning are honest, simple pleasures. To see an array of deep red fresh strawberry jam jars with the sun shining through is delicious in more ways than one! I smile every time I hear the subtle “pop-pop-pop” of jar lids cooling on a wire rack, creating the dimple on the metal lid, the telltale sign of a successful seal. With this guide to canning, you are well on your way to enjoying these satisfying pleasures, too.