Jumping into the world of canning food is exciting. By doing so, you are beginning a journey towards self-sufficiency and a fantastic hobby! But before starting your first recipe, it’s extremely important to arm yourself with knowledge of the basic science behind canning food.
You may ask- why is it so important to learn the basics of canning if there are so many recipes available online? The truth is that you have to take responsibility for your own safety when dealing with food preservation. Without an understanding of the processes and reasoning behind a recipe, you won’t be able to determine if it’s safe for the home canner.
So, let’s start with the basic and most important concept to understand in terms of canning. Specifically, what is the difference between high acid food and low acid food?
What is Acidity Anyways?
What determines whether a food is acidic or not? To fully understand this concept, we first need to understand what acidity is. A solution’s acid level is illustrated by its power of hydrogen, or pH. The value of a solution’s pH resides on a 14 point scale, where 0 is the most acidic and 14 is the least acidic (most basic).
The pH value of a solution is inversely proportional to the concentration of hydrogen ions that it contains, hence the name “power of hydrogen”. Water is the liquid of life, it’s neutral and has a pH of 7 – which is very close to the pH of our bodies. Water becomes more acidic when it comes into contact with molecules that easily give up hydrogen to it. Acidic water always has a pH less than 7. Conversely, chemicals that take hydrogen from water make it more basic, resulting in a pH higher than 7. Therefore, you can see that in chemistry, neutral water (pH 7) sets the baseline between where high acidity or low acidity occurs.
High Acid Food vs. Low Acid Food
The scientific explanation given above is an important first step towards understanding the principle of acidity in food. Food is harvested from living organisms, and these organisms are largely composed of water. However, there’s a lot more than just water in food. These extra molecules, which reside in our food are what determines its acidity. For example, lemons contain citric acid which easily gives up hydrogen to water making them acidic. Conversely, low acid foods contains less hydrogen-donating molecules than high acid foods, yielding a higher pH.
In chemistry, high acidity and low acidity is divided by a pH value of 7. However, in terms of canning, this dividing line occurs at a pH of 4.6. Any foods that exhibit a pH lower than 4.6 are considered high acid, while anything above is considered low acid.
Acidity in Nutrition
A common point of confusion when considering high acid food and low acid food is how you actually determine what constitutes acidity.
Nutritionists and food processors don’t always agree on what makes a food high or low acid. For a nutritionist, the determining stage comes once nutrients from food reach the kidneys. Here, the food will either produce ammonium or bicarbonate. If the food produces more ammonium, it’s considered acidic, and basic if it produces more bicarbonate. In fact, scientists have created a system to measure the nutritional acidity of food called the potential renal acid load (PRAL) score. The PRAL score method is very different from how we measure acidity in terms of canning- which is simply by determining the pH of the food itself.
As a result of these two differing methods, the nutritionist and home canner will often reach contrasting conclusions regarding a particular food’s acidity. For example, a lemon is considered a high acid food when canning due to the presence of hydrogen-rich citric acid. However, it’s PRAL score suggests that nutritionally, a lemon is alkaline (low acid). So, when researching the acidity of canned foods, make sure that it’s not based on their PRAL scores. Instead, consult a resource built for canning. Clemenson cooperative extension provides a basic list of canned food pH approximations here.
Canning High Acid Foods
In canning, a high acid food is one that has a pH less than 4.6. This environment of concentrated hydrogen ions effectively prevents the growth of most bacteria, fungi and yeast. These common spoilage agents do not thrive in an acidic environment, and killing them at the temperature of boiling water is an easy matter. For that reason, high acid foods can be safely processed in a water bath canner. Importantly, the acidity stops germination of Clostridium Botulinum, which prevents the release of it’s deadly neurotoxin. Therefore, mitigating the need to kill the spores during processing.
High acid foods are those that have a high concentration of hydrogen ions. Fruits, juices, pickled and fermented foods are all high acid, due to the presence of acetic or citric acid (very high concentration of hydrogen). Fruits, and anything that is derived from fruits are usually high-acid. However, mixing high and low acid foods can result in an overall mixture that has a pH greater than 4.6. For example, a common mantra states that adding 3 strips of bacon to a jar of strawberry jam changes that food from high to low acid, thus requiring the use of a pressure canner. Without knowledge of acid-base chemistry, it’s very difficult to know the pH of any particular mixture. That’s why it’s so important to only follow recipes that have been approved by a processing authority.
Canning Low Acid Foods
Complications arise when you get into canning low-acid foods (pH greater than 4.6), which include meat, fish and vegetables. Botulinum spores are unable to germinate in a high acid environment. However, canned low-acid food provides a perfect environment for the spore to germinate, grow and produce its toxin. Therefore, killing the spores is a necessity to safeguard against the risk of intoxicating your dinner guests with a paralytic disease. Unfortunately, Botulinum spores are fairly resistant to heating at boiling water temperatures. In fact, proper processing of low acid foods in a water-bath canner takes so long that doing so will significantly diminish the quality of your final product.
Instead, botulism can be prevented by processing low acid food in a pressure canner. This effectively raises the maximum temperature that you can reach during processing. Instead of maxing out at 100 degrees Celsius, a pressure canner can heat food up to 118 degrees. At this high temperature, Botulinum spores are rapidly killed and the processing time is significantly reduced.
Importance of Understanding Acidity
A home canner chooses their method of processing based on the pH of the food they are preserving. It all comes down to safety, and preventing the growth of C. Botulinum. This insistence on safety is what established the pH dividing line of 4.6, and provides a relatively simple way to know how to process your food.
Everyone knows that the internet is full of information that simply isn’t true. The same goes for home canning recipes. Recipe contributors are often qualified and go through proper processing protocols, though there are exceptions. Further, home canners frequently share recipes with each other. Most are great and the community is usually very responsible and experienced. However, arming yourself with the basic science of home canning will give you the ability to judge for yourself if a recipe is safe.
Empowering yourself with this knowledge will lead you to a mastery of home canning, never stop learning about your craft!
Please leave a comment and tell us your thoughts!