Our grandmothers did things differently. But that was before they knew what we know now. If you’re new to canning, throw out most of what your grandmother taught you and read up on the newest rules of water bath canning.

The Jars

Though cheaper jars exist, Ball and Kerr are tried-and-true brands that can last (and have lasted) over a century. A good-quality canning and pickling jar withstands the heat and processing necessary for water bath canning to kill microorganisms. Never reuse commercial containers such as spaghetti sauce or pickle jars. Don’t buy your jars at the dollar store unless they are embossed with the logo of a trusted canning company.

Always check your jars by running a fingertip along the rim. Discard any jars with chips or nicks in the glass because they will not seal correctly. Sorry, but these are now only good for dry goods or displaying on a shelf.

Lids are single use only. Reuse only for storing foods short-term in the refrigerator or for non-food items. When in doubt, throw the lid out and get a new one from the box.

You do not need to buy a canning pot to water bath. Make sure jars do not touch the bottom of the pan and that the water covers the tops of the jars by at least one inch. To create a makeshift rack to keep jars off the bottom of the pot, twist-tie extra canning rings together to fit the bottom of the pan.

Always sterilize jars before filling. This may be done in a dishwasher with no soap. Or you may simmer the jars in scalding water within the canner, removing to fill, then placing back in the canner to process. Do not sterilize jars in the oven.

The Acidity

Because certain acidity deters bacterial growth, foods with low acidity must be pressure-canned. High-acid foods can undergo a water bath, but it may be necessary to add more acid.

Additional acid includes lemon juice, citric acid, vinegar or sugar. Juices are extremely high in sugar so canned fruit recipes in 100% juice are safe. Though oil is also acidic, it is not safe to water bath any recipe containing oil due to dangers from rancidity.

Always follow the recipe. This is crucial. A marinara recipe may be perfectly safe as it is published within a canning book but adding more garlic or herbs upsets the acidity and allows microorganisms to grow. Never decrease the amount of sugar, vinegar, citric acid, or lemon juice. If you want lower sugar, search for a new but approved recipe. Reduced sugar jam recipes for canning usually involve a different type of pectin.

Peppers are interchangeable as long as you use the exact same amount. If you wish to make your salsa hotter, switch mild peppers for jalapenos or habaneros. Do not add more peppers.

Always use vinegar with at least 5% acidity. Be diligent about checking before you buy, because some generic or store brands have 4% or lower acidity. Never use homemade vinegars for canning recipes because actual acidity is undependable.

The Processing

To avoid burning yourself or dropping hot jars, invest in tools such as jar lifters, canning funnels, and magnetic lid-lifting wands. Look for nonmetallic or coated products, since metal can damage the jars.

Have all tools, rings and lids ready so you don’t waste time. Delays could cool the jars or food to an unsafe level. When filling hot jars, place on a protected surface such as on a towel or a wooden cutting board. This prevents thermal shock from a cold counter and also keeps the jar from slipping as you fill it. Always fill canning and pickling jars to within specified headspace. This prevents seeping as the food expands during processing.

Heat-processing is not optional. All home-canned foods must undergo a certain amount of time to kill microorganisms and stop the enzymatic process which would cause food to spoil. Using correct canning jars and lids creates a hermetic seal that prevents other microorganisms from entering the jar.

At 212 degrees Fahrenheit (at sea level,) molds, yeasts and some bacteria die within high-acid foods. Bacterial spores within low-acid foods die at 240 degrees F, which is only achievable with a pressure canner.

The safest method is “hot/hot/hot.” Boil the food or the acidic liquid (like juice or pickling liquid) as the first safeguard. Fill hot jars with hot liquid…the hotter the better. Place hot jars within hot water in the canner. Begin processing immediately. Placing hot jars in cool water (or cool jars in hot water) could break the jars due to thermal shock. Filling jars with cool liquid then raising the temperature might not give it enough processing time to kill microorganisms.

Process according to altitude. Because water boils at lower temperatures in higher altitudes, it may not be high enough to kill bacteria. Based on your location, add the following times to the specified processing time in the recipe:

• 1,001-3,000 feet above sea level: 5 minutes
• 3,001-6,000 feet: 10 minutes
• 6,001-8,000 feet: 15 minutes
• 8,001 to 10,000 feet: 20 minutes

When processing is complete, turn off the heat and let the canner sit for five minutes. Carefully remove the jars, without tilting them, and place on a towel within a draft-free location. Do not wipe off the tops or disturb the jars; water will evaporate on its own. Let cool for 24 hours then check seals by pressing on the dome lids. If the lids are concave and fit tightly across the top, your jars are sealed. If they wiggle up and down, the food must be reheated/resealed using a new lid or stored in the refrigerator or used within a few days.

Store jars at 57-70 degrees F, to deter growth of bacteria which may still exist within the food. Consume within a year for best quality; afterward traits such as color, texture, or nutritional value may decline. Discard any food that smells alcoholic, spoiled, or “off.” Do not use food if the seal has broken or comes off with little effort. Throw away any food with visible mold, slime, yeast, or cloudiness in a recipe that was clear to begin with. Only reuse the jar after washing in soapy water then sanitizing.

If low-acid food has spoiled, the jar must be thrown away.

The Safe List

These high-acid foods may be water-canned: citrus, 100% fruit juice, berries, and tree fruits such as apples, peaches, pears, and plums. Other foods are safe with added acid, such as pickles, relishes, jams and jellies, conserves/preserves, fruit butter, and sauces which follow a specific canning recipe.

Do not can any food that is overripe, diseased, moldy, or insect-damaged as it is higher in microorganisms. Processing times are calculated for fruits at optimal ripeness and a given time may not be enough to kill bacteria within overripe fruit.

What about tomatoes? Our grandmothers canned their tomatoes without additional acid but the rules have changed. New lower-acid tomato varieties upset the safe balance. To be sure you’re not endangering your family, always can tomatoes with additional acid such as lemon juice, vinegar or citric acid. Refer to a trusted canning recipe for correct measures.

The Banned List

Low-acid foods which must be pressure-canned include meats and broths, squash/pumpkins, carrots, beets and turnips, green beans, leafy greens, asparagus, shelling beans, peas and corn. Tomato sauces and marinara which does not follow a specific recipe approved for water bath canning must also be pressure canned. Most of these foods are safe within pickles but meats can never be water bath canned. Also, some concoctions such as pumpkin butter are so thick the heat does not penetrate within processing time. If you want to preserve any of these foods and do not know how to pressure can, consider freezing instead.

Incorrectly processing low-acid foods could cause growth of botulism, a deadly bacteria. If you’re unsure if your food is acidic enough, pressure-can or freeze.

Archaic Practices

Our grandmothers used paraffin to seal jars of jelly, pouring the wax into the hot liquid. As everything cooled, the wax would rise to the top and seal the jar as the jelly solidified. This is no longer an approved method. Do not use it.

If a jar did not immediately seal, my mother would turn the jars upside down to reheat the sealing compound. A correctly-filled jar will seal. If your jars fail to seal, rebottle it and use a new lid. Process again.

Pickling lime crisps cucumbers nicely but is extremely alkaline. This can compromise even the safest pickling jars. Some recipes advise you to rinse limed food at least four times before pickling. Others advise you use salt instead and avoid the lime.

When searching for a recipe, do not use someone’s random recipe for water bath canning. Often these were written before we knew about acidic balance, were altered since then, or were created without knowledge of safe canning practices. Jam recipes for canning or canned fruit recipes are more likely to be safe with failure to gel as the most common flaw. When in doubt, search for a recipe in a book published by a canning company.

For additional information regarding safe water bath canning and other techniques, refer to trusted sources such as publications by Ball or Kerr, government sites, or university agricultural extensions.