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Boiling Water Bath or Pressure Canning, which to use?

If you are new to food preservation, you might ask why there are two different processes for canning food: boiling water bath and pressure canning. What is the difference between them? This question often arises as individuals begin growing and preserving their own food. The decision process can seem intimidating, especially with the many differing viewpoints found on social media or stories of traditional methods passed down through generations. Fortunately, science can help us understand which methods are most effective to ensure our food is safely preserved.

The National Center for Home Food Preservation and the USDA can help take the guesswork out of your project. Their recipes have all been rigorously tested, taking into account factors such as food density, pH, and heat penetration in the jar. That’s why their guidelines are considered reliable and “approved”.

Returning to the original question: Why are some foods preserved using a water bath while others require pressure canning? The answer lies in the acidity, or pH, of the food. A basic understanding of the pH scale, often introduced in high school science classes, is helpful here. This scale measures the acidity or alkalinity of a substance, with 1 being highly acidic and 14 being highly alkaline. Water is at the center of the range with a neutral pH of approximately 7.

Understanding pH is crucial in food preservation because it directly affects food safety. The pH level determines how well spoilage microorganisms can grow and multiply in food. These microorganisms thrive in foods with a neutral pH. A higher acidity level creates an environment that inhibits their survival. The critical threshold for microbial growth in food is a pH of 4.6. Foods with a pH below 4.6 are classified as high-acid foods, while those with a pH of 4.6 or higher are considered low-acid foods. This distinction determines which canning method can be used.

From the USDA Guide to Home CanningHigh-acid foods and acidified foods are safely preserved using the boiling water bath method. High-acid foods, like berries, are naturally well below pH 4.6, so need no additional acid when combined with boiling water processing to safely prevent microbial growth. Acidified foods are naturally low-acid foods that have been preserved using a solution such as lemon or vinegar to reduce their pH below 4.6. A common example is pickling. This process involves submerging low acid foods, such as cucumbers or beans, in an acidic solution before canning. The combination of acidity and the boiling water bath process, which heats food to 212°F, prevents the growth of spoilage microorganisms.

Master Food Preserver volunteers hot filling jars of strawberry jam to be processed using a water bath canner.

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Growing Food Preservation Education

Do you have some experience with food preservation and would like to be part of helping others gain confidence in the kitchen?

I’m excited to announce an upcoming training to grow our Master Food Preserver volunteer base. Applications are open throughout the month of March to participate in the May training. I have the privilege of being the coordinator for this delightful program, and the group is curious, fun and capable. Their experience varies widely, from homesteaders who have been growing their own food for decades to others who are newer to the scene and have insights about how to lessen the learning curve for other newbies.

The food preservation methods covered in the program include water bath canning, pressure canning, fermentation, dehydration and freezing. Volunteers are not required to teach classes. Some prefer planning programs, answering questions 1-1, assisting at workshops, tabling at events and strengthening the program in other ways.

Here’s some goodies to help you decide if joining the Master Food Preserver Volunteer Program is a good fit for you.

  • Below is a photo slideshow of preservation activities over the past three years showcasing our great volunteers and the many types of programs we’ve offered.
  • Join me tomorrow, Friday, March 21st, for a free 30 minute webinar starting at noon for folks to ask questions and learn more about the program and training.
  • Here’s a 5-minute radio interview I just did with Jody Tosti of B99.3 Community Connections.
  • The event page for the training has all the written material about the program including a recruitment brochure, a volunteer position description and the application.

Read more Growing Food Preservation Education

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Celebrating our Volunteers with tamales

Our volunteers make it all possible here at the Extension Learning Farm. We recently gathered to celebrate the dedication and year’s accomplishments of all three Ag and Food System volunteer programs (Master Food Preserver, Energy Navigator and Master Gardener). From teaching classes, answering 1-1 questions, attending events for outreach and more- these are active, capable folks! For a change of pace, it was fun to simply gather and enjoy time together. Extension organized a tamale-making activity in the Harvest Kitchen for any volunteer who thought that would be an enjoyable treat, then a larger group came together for a shared potluck lunch and conversation. Check out the slideshow below for a few shots of the action.

At our 2nd annual Volunteer Appreciation event, we recognized Ken Kogut with the Fruition Service award for his spirited contributions, his continuous learning, and his 30+ hours spent helping us build a new High Tunnel last fall. Thank you, Ken!

  • Linda mixing the dough for the meat tamales, a mixture of corn masa, lard, salt and water.

We look forward to widening the circle of volunteers. There is a new group of Master Gardeners whose training will finish in April, and openings for Energy Navigators trainings starting in mid-February and mid-April, find more here. The Master Food Preservers just secured May 13-15, 2025 for a training too so keep your eyes peeled for registration opening!