With the farmer’s markets and road stands bursting with juicy ripe produce, now is the perfect time to capture a bit of summer in a jar for the cooler months of winter. And one great way to do this is with home canning!
Invented in France by Nicolas Appert sometime around 1795, canning is a method to preserve food in an airtight container, giving it a shelf life ranging from one to five years and beyond. Today, this technique can be used in the comfort of one’s own kitchen, and is a pastime enjoyed by food lovers, chefs at Michelin star restaurants, hipsters, world apocalypse planners to food gift-givers alike.
With home canning, there are two major techniques that are based on whether the foods are considered high acid or low acid. For high acid foods with a pH of 4.6 or less, one can use the simple Water Bath Canning technique, which involves boiling the jars in water for a certain period of time. This is great for most fruits, pickled foods, jams/jellies, sauces and condiments. The reason the pH is so important in this technique is because while most bacteria are killed at boiling temperatures (100 C / 212 F), the bacteria Clostridium botulinum (which produces deadly toxins) actually can’t be killed by boiling. However, at a pH less than or equal to 4.6, it cannot survive, so the Water Bath Canning technique will work well for high acid foods.
For low acid foods with a pH higher than 4.6, one must use a more rigorous technique called Pressure Canning, which involves heating the jars up to temperatures well above boiling (about 116 C / 240 F) for a certain period of time to ensure all bacteria are killed, including your pal, Clostridium botulinum. Foods that fall into this category include meats, dairy and most vegetables.
Which foods are safe for the Water Bath Canning Method (have a pH of 4.6 or less)?
Since the easiest, low-cost canning method for the home is the Water Bath Canning technique, it’s a popular choice for most home chefs. But you may be wondering how you can determine which foods are naturally acidic. When in doubt, the best way is to look up which foods have a pH of 4.6 or less. One great online resource is the FDA’s published list of ingredients and their pH.
Common fruits like apples, cherries, berries, pears, and peaches are great, while most vegetables are not. And if you’re wanting to use tomatoes, use caution too – not all are created equal, and some actually hover above a pH of 4.6. This is where pickling comes in handy, since vinegar has a pH range of 2.0 – 3.4, which will allow for vegetables to be safely canned with the water bath method.
Another area to consider is the type of recipe you’ll use. I’m more partial to the “hot packing” technique, which means the recipe was fully cooked (and not raw) before immediate canning. This adds another layer of food safety to your recipe, as you’re essentially pasteurizing the food beforehand. If your food is in a solid state, it must also be suspended in a liquid with a pH of 4.6 or less (so fruit juices or vinegars should work well).
What kind of jars should you use?
One you’ve determined what you’d like to make, be sure to purchase the proper canning jars which are made for preserving. Typically, these involve a glass container with a two-piece lid made up of a sealing lid and screw top ring. I’m a fan of the Ball brand which is available in most grocery stores, and you can look up what kind of jar you’ll need at their website here.
How to use the Water Bath Canning Method
In a nutshell, water bath canning is quite easy. Once you’ve made your recipe (which, if not a sauce or spread should always have a liquid to suspend the solids in), just follow these easy steps.
1) Sterilize your jars (but NOT the sealing lids) in the dishwasher, and leave in the hot dishwasher until ready to use.
2) Put sealing lids in hot water (not boiling) until ready to use. Also, be sure to always use brand new sealing lids.
3) Fill the sterilized jars with your recipe. Be sure to allow for a bit of head space between the surface of the food and the lid, usually 1.5 cm / 0.5 inches for a typical mason jar. Gently tap the jar to remove any trapped air bubbles.
4) Wipe the rim with a clean paper towel, place the sealing lids on top, and the gently screw on the ring (do not tighten the ring too hard though. Go with finger tight only).
5) Place in a pot on top of a steamer rack or wet towels (you don’t want the jars to come in direct contact with the bottom of the pot). Fill the pot with enough water to cover the jars in 1 inch of water. Cover the pot with lid and bring to a boil.
6) Continue to gently boil in hot water bath for about 10-15 minutes (plus about 2 minutes for every 1,000 feet above sea level – for more information refer this High Altitude Canning Chart by Ball).
7) Turn off the heat, remove the pot’s lid, and let the jars sit in the bath for 5 more minutes before gently removing them to cool. Be careful to not disturb jars as much as possible.
8) Leave the jars to sit undisturbed for 24 hours.
Want more information on home canning and food safety? Here are some great resources!
- Fresh Preserving
- Boiling Water Canning by the Food Science and Technology Department at Virginia Tech