FUNDAMENTALS OF PRESSURE CANNING – WHAT IS IT, HOW DOES IT WORK AND WHY DO IT ?

We’ve had a lot of questions around pressure canning in recent months so I thought it was time to get back to the fundamentals and chat about the basics of pressure canning.  Let’s start with a definition:

Pressure canning is a technique of home food preservation that uses special equipment to process food at a higher temperature than ‘normal’ waterbath canning.  It is primarily used to can meat and vegetables without the need for adding high acid (like pickles).

We use a pressure canner (it’s similar but different from a pressure cooker) to can peas, asparagus, stock, soup and more.  The process makes these things shelf-stable so they produce homemade versions of canned vegetables and stocks found in the produce aisle.  The homemade version can be a superior product as you can choose the ingredients (including lowering or emitting salt and avoiding preservatives alltogether).

HOW DOES PRESSURE CANNING WORK?

Let’s start by discussing how water bath canning works: jars are covered in boiling water and processed for a certain amount of time.  Water can only reach 100 degrees Celsius (212 Fahrenheit); the boiling water raises the temperature of the ingredients within the jar to kill bacteria.  You use this technique for high-acid foods as they are safe to process at these temperatures.

Pressure canning uses less water (the jars aren’t covered) as it traps steam inside a pressurized container to raise temperatures beyond 240 degrees Fahrenheit.  This allows us to preserve food that otherwise would require acid to be added to it.

WHAT ARE THE ADVANTAGES OF PRESSURE CANNING?

There are several advantages to pressure canning, including:

• It maintains the flavor of the ingredients (peas and asparagus taste almost as fresh as they were canned).
• It uses less water and less energy (debatable) than water bath canning.
• It allows you to store items on the shelf without needing the space, budget or energy for a freezer or cold cellar.
• As mentioned above, you can control the ingredients that are added to your preserved foods.

WHAT ARE THE DISADVANTAGES OF PRESSURE CANNING?

• It requires specialized equipment that can be expensive (most canners are around $100) that can also be difficult to store.  I use my pressure canner (without the lid) as my pot for waterbath preserving so it sees lots of use.  We’ll share guidelines on what to look for when buying a canner later this week.
• It can be intimidating.  The equipment is more technical than most preserving equipment and there’s less people who do it which makes it a little more difficult to learn/ wrap your head around.  Once you do it a few times you’ll find it’s no more difficult that ‘normal’ canning.  If you’ve never used a waterbath (i.e. to preserve jam, pickles or tomato sauce), you may want to start there.
• The texture changes.  Vegetables will be softer as they are fully cooked (although every preserving method changes the texture of the original product in some way).
• Canners take maintenance (for example, a dial-gauge canner should be checked yearly for accuracy)

WHAT’S THE BASIC PROCESS?

I’m skipping a few details here (this isn’t a how-to) but it’s a good general overview:

1. A few quarts of water is added to the canner and turned on high.  You add enough water to ensure that it won’t run out when boiling during processing but not enough to cover the jars.
2. Vegetables/ product is heated and added to clean mason jars.
3. Rims of the jars are wiped clean, lids attached and placed in the canner (generally before boiling as you’ll see in the resource article below).
4. The lid is secured on the canner and it’s ‘brought up to pressure’ meaning that the water is brought to a full boil and the pressure accumulates within the pot until a certain temperature is met.  Canners let you know that temperature has happened by by a dial or a weight that wiggles in place.
5. Food is processed for a specific time (which has to be adjusted if you’re at extreme altitude).
6. Heat is turned off and the canner is allowed to cool before removing the lid and the jars.
7. Jars are cooled for 24 hours before being placed on a shelf or in a larder.

OTHER RESOURCES

There’s a great (and detailed) walk-through of pressure canning and pressure canning safety at the National Center for Home Food Preservation.

CLOSING

What questions do you have about pressure canning?  We’ll be sharing more about it this week as well as featuring a big round-up on pressure canning in the weekly newsletter this weekend (you can sign up here).