When considering food preservation methods, what do you think of? Do the terms sodium benzoate, butylated hydroxyanisole and butylated hydroxytoluene come to mind?
Probably not – but chemical preservatives like these (and around 40 others) are extremely common in many of the foods that we eat every day. A scary thought, made scarier by the fact that the use of some of these additives can pose serious health risks to humans (including cancer formation).
Erring on the side of caution and ridding your life of these chemicals just makes sense. Besides, there are plenty of ways that you can preserve your own local, additive-free food right at home!
Do you want a pantry, freezer and cellar stocked with locally-sourced, additive-free food for your family? Knowledge of these 12 home food preservation methods is all you need to get started!
Please share this article if you learned something new!
The history of the tomato is not as mundane as you would expect from a simple fruit. In fact, there’s absolutely nothing simple about the tomato or its tumultuous history at all. If all of the tomatoes ever produced could talk, they would captivate you with a harrowing story of persecution and eventual redemption. The truth is that throughout history, the “apple of love” has been revered, feared, hated and only relatively recently accepted. However, this is a story for another blog article (and rest assured, it’s coming).
Today, while tomatoes and their virtues have been widely embraced, the truth is that they are still steeped in controversy. I’m of course referring to that age old debate- Are they fruits or vegetables?
In canning, a food’s acidity is incredibly important. Knowledge of your food’s pH will guide how it is processed and canned. Fruits are typically acidic, having a pH below 4.6 while vegetables are generally low acid, with a higher pH. True to their controversial nature, tomatoes reside smack-dab in the middle. Most are acidic, but many varieties exist at a pH of 4.6 or higher. So, the debate continues- what the heck are tomatoes and how does this affect your canning?
Low Acid Tomato Varieties
Not all tomatoes are high acid, and not all tomatoes are low acid, a somewhat annoying division that has frustrated many a home canning enthusiast. Luckily, the USDA and University of Minnesota Extension have done us a favor by listing the tested tomato varieties that have a pH of 4.6 or higher. They’re listed below.
Big Early Hybrid
Burpee VF Hybrid
It’s important to note that these are only the tomato varieties that have been tested. There are likely more that should be considered low acid. Figs can also be considered borderline acidic, so the following input regarding canning tomatoes applies to them as well.
Canning tomatoes is one of the primary joys associated with home canning. There is so much that can be done with them. Whether canning them whole, crushed, peeled, in a sauce or paste it’s important to know that they require an extra step. Acidifying your tomatoes with lemon juice or citric acid is currently considered best practice, no matter what variety you’re using and no matter how you process them.
Acidification of Tomatoes
The process of acidifying tomatoes is relatively simple and the USDA has developed a well-researched method to do so for all varieties. The acidification protocols for canning whole, crushed or juiced tomatoes are shown below:
Add 2 tablespoons of bottledlemon juice or 1/2 teaspoon of citric acid per quart of tomatoes.
Add 1 tablespoon of bottled lemon juice or 1/4 teaspoon of citric acid per pint of tomatoes.
The lemon juice can be added directly to the jar before OR after filling it with the tomato product.
The lemon juice must be bottled as it has a standardized acidity, the acidity of fresh-squeezed lemon juice may vary.
Sugar can be added to offset the acidic taste that accompanies lemon juice and citric acid.
The acid can NOT be decreased after canning has occurred.
It is highly recommended that you follow these steps while canning tomatoes, no matter what variety you’re using. After acidifying your tomatoes, you can safely process them in a water bath canner and rest-assured that your final product will be safe to consume.
Acidification of Tomato Products
You should take special care when canning tomato products like sauces or pastes. Most sauces require the addition of low acid foods like onions, carrots, celery etc. for flavor. The addition of these extra low acid components may alter the acidity of your mixture enough that the above acidification methods are not sufficient. To be safe, tomato products should always be pressure canned at higher temperatures, especially when meat and mushrooms have been added to the mix. Please be aware that acidification of tomatoes is still required when pressure canning.
Processing times are also very important for safe canning of tomatoes. The following standard processing times were developed at Penn. State and taken from the PSU Extension website.
Raw-packed acidified tomatoes in pint or quart jars should be processed in a boiling-water bath canner for 85 minutes or a pressure canner for 25 minutes (10 PSI for a weighted gauge canner, 11 PSI for a dial gauge canner at an altitude of under 1000 ft).
Hot-packed crushed tomatoes in pint jars should be processed in a boiling-water bath canner for 35 minutes or a pressure canner for 15 minutes.
Hot-packed crushed tomatoes in quart jars should be processed in a boiling-water bath canner for 45 minutes or a pressure canner for 15 minutes.
Hot-packed tomato juice in pint jars should be processed in a boiling-water bath canner for 35 minutes or a pressure canner for 15 minutes.
Hot-packed tomato juice in quart jars should be processed in a boiling-water bath canner for 40 minutes or a pressure canner for 15 minutes.
Use these standard processing times to assess recipes that you come across while planning your preserve. As a general rule, it’s suggested that you only follow recipes from the USDA and cooperative extension or from a Ball Blue Book which have been scientifically tested.
A word of Caution
Note that tomatoes must be acidified in order to prevent germination and growth of C. Botulinum spores. Growth of this bacteria in low acid food increases your risk of botulism.
While acidification theoretically mitigates this risk, it’s still possible for the Botulinum bacteria to grow in high-acid food. Improper acidification of foods may result in internal pockets of low acidity. Further, if acidified food is improperly processed, some strains of fungi can survive and produce local pockets of non-acidity, facilitating bacterial growth and formation of the toxin. Proper processing and acidification should eliminate this risk, so please follow approved USDA or Ball Blue Book recipes.
Respect Canned Tomatoes
Canning tomatoes is not something to be feared, but it should be respected. They are a unique fruit that requires extra care to can safely. Make sure that you’re educated and have all the right equipment and ingredients beforehand and you shouldn’t have any problems.
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!
“When in doubt, throw it out” is a classic home canning mantra, and it’s probably the most important one that you can learn before getting into food preservation. Its meaning is clear – unless you’re 100% sure that your food is safe to consume, don’t eat it.
Food starts to spoil immediately after harvest or slaughter through multiple mechanisms including: light exposure; autolysis; oxidation; and most importantly, bacterial putrefaction.
Many different types and strains of food-spoiling microbes exist. Some grow at low temperatures (like the refrigerator), some at mid-range temperature (the danger-zone) while some even grow at very high temperatures (thermophiles). This broad spectrum of life ensures that no matter how you store your unprocessed food, it will eventually spoil.
Limiting these sources of decomposition is the key to keeping your food fresh. Spoilage is usually accompanied by some pretty obvious sensory indicators. We’ve all had to stifle a gag after discovering that forgotten sandwich residing in the depths of our fridge. Stumbling upon “rotten” food is always an unpleasant experience and you certainly wouldn’t want to eat it. However, ingesting spoiled food won’t necessarily end up with a stint in the emergency room. In fact, most spoilage-causing bacteria are harmless when ingested. For example, Pseudomonas spp. and Brochotrix thermosphacta will introduce an unpleasant odor, taste and slime to your food but secrete no toxins and aren’t pathogenic.
Unfortunately, not all bacteria are so friendly. In fact, a few of them are actually quite dangerous. These are known as the pathogens. Pathogenic bacteria can cause severe illness and even death to individuals who consume them. These hazardous food-borne bacteria pose a risk for all home canners. So, we’ve compiled a list of four of the most dangerous to show why it’s so important to adhere to the mantra- “when in doubt, throw it out”.
Salmonella is a particularly nasty bacteria that’s commonly found in the intestines of animals and birds. As a result, it is usually transmitted when people eat foods contaminated with animal feces. All types of foods can become contaminated and eating them can lead to infection, causing salmonellosis. Symptoms of salmonellosis include: diarrhea; vomiting and fever. Most people who become infected with salmonella recover within a few weeks. However, in some cases it can result in serious illness or even death.
While the overall mortality rate of the disease is fairly low (under 1%), there are variations of the bacteria that can be more fatal. Salmonella poisoning certainly is a deadly food-borne pathogen, but proper processing of canned food will mitigate the risks significantly.
Listeria is a food-borne bacteria that is found everywhere in soil, sewage and untreated water. These sources often pass the bug onto the fish, meat, fruits, vegetables and dairy that we consume. Infection by Listeria bacteria causes a disease known as listeriosis. Individuals who become infected can start to exhibit symptoms from 3 – 70 days of eating contaminated food. Fever, Nausea, Diarrhea, cramps, vomiting, headache, constipation and muscle aches are common symptoms of the disease. However in severe cases the bacteria can cross the blood-brain barrier and spread to the nervous system. Such a spread often results in more serious neurological symptoms and can even be fatal.
Fortunately, an extremely large number of bacteria need to be present on contaminated food for infection to take hold. Nevertheless, taking proper processing precautions is vital to prevent Listeria from taking root in canned food.
E.coli lives in the gut of humans and animals, and has been shown to play an important role in protecting their host from various diseases. However, certain Shiga toxin-producing strains of E.coli (STECs) synthesize a toxin that can cause illness in humans. These bacteria are most commonly found in cows, but are occasionally present in other commonly canned foods as well. Symptoms of Shiga-toxin poisoning progresses in stages, starting mildly but progressing into severe cramps, nausea and bloody diarrhea.
The illness is most dangerous if the Shiga-toxin gets into the bloodstream, which can cause the kidney’s to shut down. Pancreatic damage and impairment of the nervous system can further complicate the illness. E. coli poisoning will not be a problem for the home canner who follows correct processing protocols and is easily deactivated by water bath canning. However, it is always a risk if your food was improperly processed or sealed.
C. Botulinum is the most important pathogenic bacteria to consider when discussing canning safety. Mainly, because it becomes dangerous only under certain conditions. Conditions which are met by canned low-acid foods. Botulinum seals itself within a spore when it comes into contact with oxygen because it is anaerobic (oxygen-hating). Upon being moved to a moist, low-acid and oxygen-free environment, it germinates and begins to grow. Once a culture is established, the bacteria releases a deadly neurotoxin that you may know as Botox. If ingested, Botox causes botulism, a paralytic disease that can be lethal if it reaches the respiratory system.
Unfortunately for the unknowing canner, this environmental change occurs the moment that you seal your vegetables, fish or meat in a jar. Botulinum spores are very resistant to heat and the amount of time required for processing at the temperature of boiling water is greatly increased. That’s why pressure canning is highly recommended when processing low-acid foods.
To learn more about botulism, and how to control it follow this link.
When in Doubt, Throw it Out
Many food-spoiling bacteria leave obvious signs of their presence. Their unpleasant tastes, odors and appearances make it crystal clear that a bounty has spoiled. Unfortunately, the above-listed pathogens don’t leave any of these telltale signs. You simply cannot determine from its taste, odor or appearance whether or not your food is contaminated. The detection of food-borne pathogens requires rigorous scientific testing and it’s often impossible for the average home canner to know if they’re sealing up a deadly poison. Whether it be concern over your processing method, a faulty seal or just a bad feeling- when in doubt, throw it out.
Feel free to leave us a comment, story or fact from your personal canning experience. We would love to hear from you!
Today, many people view canning and preserving food at home as a hobby or means to become less reliant on their local grocery store. However, in the past preserving your food was actually a way of life. Food wasn’t as easily accessible as it is today and it often had to be preserved in preparation for the inevitably lean times ahead. So, when Nicolas Appert developed his method of canning in France during the 17th century, the world took notice. Unfortunately, there wasn’t much rhyme or reason behind early canning protocols. In fact, Appert’s reason for heating and isolating food from air was simply because he noticed that otherwise, it spoiled.
Today, we know that the main reason food spoils when in prolonged contact with air is due to the presence of microscopic organisms that require oxygen to grow. A desire to kill these food-spoiling yeasts, fungi and bacteria is the reason why canned food is processed before being stored on the shelf. In particular, some bacterial growth in improperly processed can foods can even result in illness or even death.
It’s important to note that very few bacteria are associated with disease. In fact, there are many bacteria that provide us with crucial benefits like: nitrogen-fixing bacteria in the soil and those that reside in our gut. However, others aren’t so friendly and can actually provide a real danger when food is canned at home.
While it’s true that we have little to fear (aside from spoilage) from most bacterial strains that are found in food, a small subset are pathogenic. Pathogens are agents or organisms that cause diseases in humans if given the opportunity. Salmonella, E.coli (STEC), Listeria and Camptylobacter are four well-known bacterial pathogens found in food. While these bugs have been implicated in many cases of food poisoning, they pose little threat to the home canner and can easily be destroyed with moderate heat treatment. Clostridium Botulinum,the pathogen responsible for botulism, poses the biggest risk for the home canner. In fact, C. Botulinum is so dangerous that controlling its growth is really what canning safety is all about.
From Sausage Poison to Botulism
In the 10th century, the manufacture of blood sausage was outlawed by Emperor Leo VI of Byzantium due to the increasing number of food poisoning cases that resulted from eating them. Back then, people had no concept of microorganisms. However, they observed symptoms that resembled botulism as we know it today.
Approximately 700 years later, a German poet and district medical officer by the name of Justinus Kerner published the first accurate description of these symptoms and called the unknown agent “sausage poison”. The term was later renamed “botulism” after “botulus”, a Latin term meaning sausage. It wasn’t until 80 years later that Emile Pierre van Ermengen identified C. Botulinum as the bacterium responsible for these symptoms. This was after Appert first discovered how to can food, and after many had already died from the deadly toxin that vegetative (actively replicating) botulism produces.
The Life of C. Botulinum
So, let’s talk about this toxin, and why it’s so prevalent in any discussion involving safety while canning. C. Botulinum produces a deadly neurotoxin that acts by severing the “docking ports” of synaptic vessels. It’s so dangerous that even 1 millionth of a gram can kill a person, making it the most lethal poison in the world. Even scarier is that C. Botulinum is everywhere, residing in the soil as well as most foods.
So, if the bacteria causing botulism is found everywhere, wouldn’t everyone on earth be paralyzed? Fortunately, this isn’t the case because the pathogen is anaerobic- meaning that it hates oxygen. Consequentially, when the bacterium comes into contact with the atmosphere, it builds a wall around itself and lives as an inactive spore. Botulinum spores are unable to release botulism toxin but are extremely durable. Able to exist for thousands of years until their environment is suitable for germination. Botulism toxin is only released when the spore’s environmental conditions become supportive of this germination and growth. Specifically, these conditions are:
1) Less than 2% oxygen
2) Temperature between 40 – 120 degrees Farenheit (Danger zone)
3) Moist and low acid food (most meats and vegetables)
Each one of these conditions is fulfilled in a jar of canned low-acid food, making for a dangerous breeding ground. A knowledge of effective processing protocols and an understanding of microbiology principles is critical for successfully controlling botulism. For this reason, it’s extremely important that you only follow recipes that have been approved by a processing authority (like the USDA).
Controlling C. Botulinum
There are two ways to control C. Botulinum during the canning process.
1) Preventing the spores from germinating and growing.
2) Killing the spores.
Germination and growth of botulinum bacteria is not possible within the confines of a spore wall. Luckily, bacterial growth can be inhibited by two controllable factors: acidity and water activity.
Spores of the Botulinum bacteria germinate when they find themselves in conditions that are favorable for growth. Only then do they produce their deadly toxin. Spores are present in most foods, both high acid and low. Why then are high-acid foods safely processed at 100 degrees Celsius for 10 minutes while low-acid foods are not? Simply, because C. Botulinum is unable to leave its spore and grow in an acidic environment. Some foods are naturally acidic (fruits, an juices) while others can be acidified (cucumbers by acetic acid) or fermented (sauerkraut). The high protonic force of these foods mitigate the need to kill the spores through pressure canning.
Please be aware that it’s still possible for the Botulinum bacteria to grow in high-acid food. Multiple cases where low-acid foods were improperly acidified resulted in internal regions of botulism. Further, if high-acid food is improperly processed, many strains of fungi can live and produce local pockets of non-acidity, facilitating bacterial growth and formation of the toxin. Unless you’re a food scientist, you probably aren’t qualified to rely on acidification to prevent the growth of botulism, so follow an approved recipe!
Have you ever wondered how bacteria eats? They have no mouths, teeth or traditional digestive tracts. Instead, they absorb nutrients that are dissolved in water. Without water, bacteria cannot eat and therefore won’t grow! The amount of water that is available to a microbe is measured by the food’s water activity, or Aw. Lowering this metric is the primary factor behind the preservative power that you get from using a dehydrator.
Lowering the Aw of canned food is more difficult, and not overly practical. Added solutes (salt or sugar) grab a portion of the water in your food, limiting its availability to the microbes. A concentration of about 10% salt will effectively prevent germination of Botulism spores in your canned food. However, such a high concentration of salt isn’t very appealing when it comes time to eat your creation.
Instead of messing around with acidity and water activity, the best way for the home canner to control the growth of C. Botulinum in low-acid foods is through pressure canning. Pressure canning allows you to achieve temperatures high enough to kill the spores in a smaller amount of time. Again, following recipes that have been approved by a processing authority is the best way to ensure a safe product!
Inactivating Botulism Toxin
While the botulinum spores are heat resistant, the vegetative bacteria and toxin that it produces are not. In fact, the toxin is nothing more than a protein which is easily denatured at the temperature of boiling water. Boiling your canned food for 10 minutes prior to eating is considered good practice. Doing so will ensure that your food is toxin-free when you want to enjoy some home-canned cuisine with your family.
Please leave us a comment with your thoughts!
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