I am often asked, “what keeps us safe when home canning”?

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In a nutshell, understanding how time, temperature and acidic value play a vital role in the creation and processing of recipes keeps our home canned goods safe for consumption and long-term storage.  Although the answer is quite straightforward, it deserves a bit more explanation so we may further understand the “whys” behind the logic.  Personally, I believe many more individuals would home can if they understood the three main elements to safe canning practices.

The below information is an excerpt from my cookbook, Canning Full Circle.  If you intend to reference or site my works, please be sure to include “The Canning Diva” and my website at www.canningdiva.com.

Three Key Players

Throughout my years of teaching canning classes, I begin every class with the basics.  Whether you are a veteran canner or a beginner, I make it my job to teach everyone the reasons why we are able to do what we do in our home kitchens.  At the forefront are Time, Temperature and Acidic Value.  Let’s break it down…

Let me ask you, what do you think has more acidity; a sweet strawberry or a hot habanero pepper?

Acidic Value

Food naturally has a pH value.  Sometimes that value is neutral, meaning alkaline, other times a food’s value can be highly acidic.  On the pH scale, numbers demonstrate the acidic value – the higher the number on the scale, the lower the acidic value whereas the lower the number, the higher the acidic value.  For those of you who maintain pools or hot tubs, it is the same pH scale of acid and alkalinity.

Adapted from USDA Complete Guide to Home Canning 2009 (Bulletin No. 539)

When it comes to the acidic value of food, please do not confuse pH acidic value with flavor.  Let me ask you, what do you think has more acidity; a sweet strawberry or a hot habanero pepper?  The answer, a strawberry (3.5 pH) has a higher acidic pH value than a hot habanero pepper (5.8 pH).  Spicy or hot tasting foods do not mean a higher acidic value on the pH scale.

The reason we must understand a foods acidic value is without the presence of acid, harmful bacteria will grow.  Such bacteria will continue to grow in an anaerobic environment, which means a sealed jar in absence of free oxygen[1].  Botulism, a well-known bacteria in canning, can only grow in an anaerobic environment.  But did you know potatoes naturally have botulism bacteria on their skin because they grow underground without the presence of free oxygen?

Canning doesn’t produce botulism.  Botulism naturally exists throughout the earth, however, educated canners know how to prevent botulism from inhabiting their food in jars because they understand time, temperature and acidic value and follow tried-and-true recipes.

Another major factor with respect to acidic pH value is to consider the sum of all foods in one recipe, not just the main ingredient.  Take, for instance, salsa.  Although the main ingredient is tomatoes, which have, on average, a mid-grade level of pH acidity, it is the sum of all ingredients which count most in home canning.  Once you start adding onions, jalapenos, cilantro, corn and black beans, you now have diluted, or neutralized, the salsa’s overall acidic value.  So what do you do when a recipe is lacking acidity?  You add acid.

Acid can be in the form of lemon juice, lime juice, vinegar and often wine.  The key however is to ensure when shopping for these products the label clearly states a minimum of 5% acidity to be considered safe for home canning.  If it is not 5% acidity or higher, do not use it for home canning.  Save diluted vinegars for fresh recipes, vinaigrettes or cleaning and drink the wine…okay, or cook with it!

Time & Temperature

Time and temperature refer to the second stage of canning called, processing.  The recipe’s overall acidic value dictates the proper processing method.  There are two processing methods, water bathing and pressure canning.  Each method is defined by its temperature output.  Water bathing temperature is 212°F while pressure canning is upwards of 250°F.  The length of time in which foods process is dictated by the foods acidic value and the temperature required to process.

In my water bath recipes throughout Canning Full Circle, you will note not to start the timer until the water is at a full rolling boil.  A full rolling boil is the only way to visually ensure the water temperature is at 212°F, the required temperature to kill bacteria in acidic foods.  An overall recipe with a high acid content of 4.6 pH or less can be safely water bathed because the temperature in combination with the bacteria killing acid are sufficient for long-term storage.

Foods such as root crops and meat do not have a high acid content, 4.6 pH or higher, so we must rely on time and temperature to safely kill harmful bacteria during processing.  Bacteria, yeast and mold grow fastest between temperatures of 40°F and 140°F.  When canning low acidic foods, the temperature required to kill harmful bacteria, yeast and mold is 240°F to 250°F.  Such high temperatures can only be achieved when using a pressure canner, not a water bather.  Pressure canning is the only method of processing home canned foods which get foods hot enough for long enough making them safe for long-term storage.

So how will you know which method to use?  A tried-and-true recipe will always have the method and the length of time required for processing.  If the recipe does not give you this information, get a different recipe from a reliable source.  Each of my recipes have been tested in triplicate using a commercial food grade pH tester, stored, then retested to ensure the pH did not deviate.  This method of testing is especially important when canning tomatoes and foods which hover around the 4.6 pH mark.  For this reason I have often changed the method of processing or added additional acid to the recipe to ensure its safety.  A prime example of this is my Basil Diced Tomatoes recipe on page XX.  Because it hovered too closely to 4.7pH, it was safest to quickly pressure can this recipe rather than water bath.

[1] living, active, occurring, or existing in the absence of free oxygen <anaerobic bacteria> Merriam-Webster Dictionary

The above information is an excerpt from my cookbook, Canning Full Circle.  So you may learn more about Food Preservation Basics, pick up your copy today!  Be sure to follow me on Facebook, Pinterest and Twitter.  If you intend to reference or site my works above, please be sure to include “The Canning Diva” and my website at www.canningdiva.com.

From the Garden to the Jar,

Diane, The Canning Diva®