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Canning

Canning is a method of food preservation in which food is placed in airtight containers, such as jars or metal cans, and heated to a temperature that destroys microorganisms and inactivates enzymes, creating a vacuum seal that allows storage at room temperature for extended periods.^[1]^[2] This process maintains the food's quality and safety by preventing spoilage, with high-acid canned foods like fruits and tomatoes retaining best quality for 12 to 18 months, while low-acid foods such as vegetables and meats can last 2 to 5 years under proper conditions.^[3] The technique originated in the late 18th century when French inventor Nicolas Appert developed it in response to a prize offered by Napoleon Bonaparte in 1795 to find a way to preserve food for military campaigns.^[4] After years of experimentation, Appert successfully preserved food in glass jars sealed with cork and wax in 1809, publishing his method in 1810 and earning the 12,000-franc reward.^[2] The process was later adapted for metal cans by British merchant Peter Durand in 1810, leading to widespread commercial adoption in the 19th century, particularly for supplying armies and navies.^[1] There are two primary home canning methods recommended by the United States Department of Agriculture (USDA): boiling water bath canning, suitable only for high-acid foods with a pH below 4.6, and pressure canning, required for low-acid foods to achieve temperatures of 240–250°F necessary to eliminate dangerous bacteria like Clostridium botulinum.^[5]^[6] Pressure canning, recognized as essential for low-acid foods since 1917, uses steam pressure to reach these higher temperatures, ensuring safety.^[7] Canning revolutionized global food supply chains by enabling year-round availability of perishable goods without refrigeration, playing a critical role in wartime efforts—such as World War II home canning drives in the U.S.—and supporting modern commercial food production.^[8] Today, it remains a popular home preservation technique, guided by USDA standards to minimize risks like botulism, with commercially canned products undergoing rigorous quality controls for even longer shelf stability.^[9]

History

Origins in France

The origins of canning trace back to early 19th-century France, where the need to provision Napoleon's army during the Napoleonic Wars spurred innovation in food preservation. In 1809, French inventor and confectioner Nicolas Appert developed a process to preserve food by sealing it in glass jars and heating them in boiling water, effectively creating the foundation of modern canning.^[10]^[4] This method allowed perishable items like vegetables, fruits, meats, and even dairy to remain edible for extended periods without refrigeration, addressing the military's logistical challenges of supplying troops on long campaigns.^[11] Appert's breakthrough came after over a decade of experimentation, building on his background as a chef and distiller, and was motivated by a 1795 prize offered by the French government of 12,000 francs for an effective preservation technique.^[12] In recognition of his invention, Appert received the 12,000-franc award from the French government in 1810, following demonstrations of successfully preserved foods submitted to a panel of experts.^[4] That same year, he published L'Art de conserver les substances animales et végétales (The Art of Preserving Animal and Vegetable Substances), detailing his empirical process for replicating the technique.^[13] By 1812, Appert established the world's first commercial canning factory, known as La Maison Appert, in Massy near Paris, where he produced preserved goods on a larger scale for both military and civilian markets.^[10]^[14] Appert initially relied on wide-mouthed glass jars sealed with cork stoppers dipped in pitch or wax, which were then immersed in boiling water for varying durations depending on the food type.^[15] While this heat treatment—later termed appertization—proved effective, the fragile glass containers posed significant limitations, often breaking during heating or transport, which increased costs and risks in production.^[11]^[16] In 1810, British merchant Peter Durand patented the use of tinplate cans for food preservation, inspired by French innovations including ideas from inventor Philippe de Girard, though the core heat-processing technique remained a French contribution.^[17] Appert's process was inherently empirical, relying on observation rather than scientific understanding, as the underlying principles of microbial inactivation were not elucidated until Louis Pasteur's germ theory work decades later in the 1860s.^[13]

Spread to the United Kingdom and Europe

Following the development of canning techniques in France by Nicolas Appert in the early 19th century, the technology quickly spread to the United Kingdom, where British engineer Bryan Donkin established the world's first commercial canning factory using tin cans in Bermondsey, London, in 1813.^[18] Using tin cans based on Peter Durand's 1810 patent, Donkin's operation focused on producing preserved meats, soups, and vegetables, initially supplying the British army and navy with durable, portable rations.^[19] By 1818, the Royal Navy alone consumed up to 24,000 large cans annually, equivalent to nearly 40,000 pounds of preserved food, demonstrating the method's reliability for military logistics.^[19] The adoption extended rapidly across Europe, with factories emerging to support naval forces and international trade. In Germany, where tinplate had originated centuries earlier, the first tin cans for food preservation were produced by hand in 1830, marking the start of commercial canning tailored for export markets.^[20] Similarly, the Netherlands saw early integration of canning for its navy and merchant fleets, building on pre-1810 experiments with tinned provisions to facilitate colonial trade routes.^[21] These developments emphasized exporting canned goods, such as meats and fish, to sustain European exploration and commerce in the 1820s and beyond.^[22] Early innovations in Europe enhanced canning's viability, particularly through refinements in tinplate production. Artisans and engineers improved the coating process for iron sheets, making cans more corrosion-resistant and scalable for industrial use, while the 1846 invention of a mechanized tinplate-cutting machine reduced production time and costs.^[23] By the 1830s, the focus shifted from primarily military applications to civilian markets, with factories like Donkin's beginning to sell canned products directly to consumers, including soups and meats for household use.^[18] Economically, canning played a pivotal role during the Industrial Revolution by addressing the food needs of rapidly growing urban populations in Europe. As mechanization increased and cities expanded, demand for non-perishable foods rose sharply, enabling reliable supply chains that supported workers and reduced seasonal shortages without relying on fresh produce.^[15] This transition helped transform canning from a wartime necessity into a cornerstone of everyday nutrition and trade by the mid-19th century.^[15]

Adoption and Innovation in the United States

Canning techniques, initially developed in Europe, were introduced to the United States in the early 19th century by immigrants familiar with the process. William Underwood, an English immigrant, established the first successful food preservation operation in Boston in 1819, initially using glass containers to pack fruits and lobster.^[24] Concurrently, Ezra Daggett and his son-in-law Thomas Kensett began canning oysters and other seafood in New York around 1819, marking the establishment of the country's earliest commercial canning efforts focused on perishable seafood and fruits.^[25] These ventures laid the groundwork for domestic adoption, adapting European methods to abundant American resources like coastal seafood and orchard produce. Key innovations accelerated the shift from glass to tin containers, enhancing durability and scalability. In 1825, Daggett and Kensett received the first U.S. patent for preserving food in tin cans, specifically for "preserving animal substances in tin," which protected their method and spurred broader commercialization.^[25] This patent facilitated the expansion of canning beyond coastal areas, enabling the preservation of diverse foods. Post-Civil War, vegetable canning surged in the Midwest, where fertile lands supported large-scale production of corn, peas, and tomatoes; by the 1870s, factories in states like Wisconsin and Illinois capitalized on this agricultural boom to process and distribute vegetables nationwide.^[26] Further advancements included Gail Borden's development of canned condensed milk in 1856, patented as a stable, shelf-life-extended dairy product that addressed spoilage issues during transport.^[27] The California Gold Rush of 1848–1855 significantly boosted fruit canning by creating urgent demand for non-perishable foods among miners facing shortages of fresh produce, prompting local entrepreneurs to establish canneries for peaches, apricots, and other fruits in regions like the Santa Clara Valley.^[28] Overall industry growth was explosive, driven by expanded rail networks that connected farms to urban markets and waves of European immigrants providing skilled labor for processing operations.^[26]

Role in World Wars and Beyond

During World War I, the canning industry in the United States experienced a dramatic surge in production to supply military rations, as canned goods like corned beef, beans, and stews became essential for sustaining troops overseas.^[15] This mobilization freed up fresh foods for domestic consumption while innovations in sealing technologies, such as improved tinplate soldering and hermetic closures, enhanced the durability and portability of rations under harsh battlefield conditions.^[18] Home canning efforts complemented commercial output, with American households preserving approximately 1.45 billion quart jars of produce by 1918 to support conservation campaigns and reduce reliance on imported supplies.^[29] World War II further elevated canning's strategic role, with the U.S. government promoting widespread adoption of pressure canning techniques developed in the 1930s, which enabled higher-temperature sterilization (up to 250°F) for low-acid foods to ensure safer, longer-lasting military provisions.^[30] These advancements, including refined retort processes for uniform heat distribution, addressed spoilage risks in mass production and were critical for shipping durable rations to global fronts.^[31] Commercial output expanded rapidly, while home canning reached its zenith in 1943 at over 4.1 billion jars, driven by Victory Garden initiatives and rationing that prioritized commercial cans for armed forces.^[32] Postwar globalization transformed the industry, as the introduction of two-piece drawn-and-ironed cans in the mid-1950s—first commercialized by the Coors Brewing Company in 1959—minimized seams, reduced metal usage by up to 20 percent, and lowered production costs for widespread export.^[19] Aluminum alternatives, debuting in beverage cans by 1963 and expanding to food packaging in the 1960s, further lightened containers and resisted corrosion, fueling a convenience foods boom through the 1970s as processed canned soups, vegetables, and ready-to-eat meals aligned with rising dual-income households and time-saving culinary trends.^[33]^[34] By the late 20th century and into the 2020s, traditional home canning declined sharply—from 44 percent of U.S. households in 1954 to 34 percent by 1964—largely due to the proliferation of household refrigerators and frozen foods, which offered fresher alternatives with less labor.^[35] Commercial canning, however, adapted through sustainable innovations, such as recyclable steel and aluminum packaging that achieves near-infinite recyclability rates (over 70 percent in the U.S.), minimizing environmental impact while integrating with hybrid preservation like retort pouches for extended shelf life alongside refrigeration-dependent supply chains.^[36] As of 2025, the global canned food market continues expanding at a 4.98 percent CAGR, emphasizing eco-friendly coatings and lightweight designs to counter plastic alternatives and support circular economies.^[37]

Principles of Preservation

Microbial Inactivation

Microbial inactivation is the foundational principle of canning, relying on thermal processing to destroy or render harmless microorganisms that could cause spoilage or foodborne illness. This process applies controlled heat through specific time-temperature combinations to reduce the microbial load in food to levels deemed safe for long-term storage at ambient temperatures. For low-acid canned foods, the standard targets a 12-log reduction (12D process) of the most heat-resistant spores, those of Clostridium botulinum, ensuring the probability of survival is extremely low—approximately one spore in 10¹².^[38]^[39] Central to designing these thermal processes are the concepts of D-value and z-value, which quantify microbial heat resistance. The D-value, or decimal reduction time, represents the duration at a specific temperature needed to decrease the population of a target microorganism by 90%, or one logarithmic cycle. For instance, the D-value for proteolytic C. botulinum spores at 121°C is approximately 0.21 minutes, meaning a 12D reduction requires about 2.5 minutes at this temperature, often extended to 3 minutes to account for safety margins.^[40]^[39] The z-value measures the temperature sensitivity of this resistance, defined as the increase in temperature required to reduce the D-value by a factor of 10; for C. botulinum spores, it is roughly 10°C, allowing processors to adjust times for varying heating conditions while maintaining lethality.^[40]^[41] Canning achieves commercial sterility rather than absolute sterility, as the former ensures no viable pathogens or spoilage organisms capable of growth under non-refrigerated storage conditions survive, while absolute sterility—complete elimination of all microbes—is unattainable without excessively damaging food quality.^[42] The food's pH plays a pivotal role in process selection: low-acid foods (pH > 4.6) support C. botulinum spore germination and thus demand high-temperature pressure processing for spore destruction, whereas acid or acidified foods (pH ≤ 4.6) inhibit such growth, permitting milder heat treatments sufficient for vegetative cells and less resistant spores.^[42]^[43] Historically, thermal processing emerged empirically in the late 18th century when Nicolas Appert developed canning methods without understanding microbiology, relying on heat and sealing to preserve food.^[44] This was later explained scientifically by Louis Pasteur in the 1860s, who demonstrated microorganisms' role in spoilage and validated heat's destructive effect.^[45] Modern practices, however, are rigorously guided by regulatory frameworks from the FDA and USDA, which mandate validated processes based on microbial kinetics to prevent botulism and ensure public health.^[46] This inactivation creates a safe internal environment, which is then maintained through effective container sealing.

Container Sealing and Integrity

Container sealing in canning ensures the hermetic integrity of the package, preventing recontamination after microbial inactivation has been achieved through heat processing. This physical barrier is essential for long-term preservation, as any breach can allow ingress of oxygen, moisture, or microorganisms, leading to spoilage or safety risks.^[47] The primary method for achieving this seal is double seaming, a mechanical process that forms an airtight closure by interlocking the can body flange and the end (lid) curl. In the first operation, a seaming chuck and first-operation roller curl the end curl under the body flange, creating initial hooks. The second operation employs a second-operation roller to flatten and compress the seam, interlocking the body hook and cover hook to form a double layer of metal overlap typically consisting of three thicknesses from the end and two from the body, sealed with a compound for added impermeability. This results in a hermetic seal capable of withstanding internal pressures and external stresses during storage and transport.^[48]^[47] Traditional canning containers are made from tinplate steel, a low-carbon steel sheet coated with a thin layer of tin via electrolysis to prevent corrosion from acidic or sulfur-containing foods. To further protect against chemical reactions between the metal and food contents, sanitary enamel coatings—such as epoxy or phenolic resins—are applied internally, providing a non-reactive barrier while maintaining adhesion to the tinplate. Due to health concerns and regulatory developments, many modern coatings are formulated to be bisphenol A non-intent (BPA-NI), complying with bans such as the EU's prohibition on BPA in food contact materials effective January 2025 (Regulation (EU) 2024/3190).^[19]^[15]^[49]^[50] The evolution of can construction included the shift from soldered to welded side seams in the 1960s, which improved seam strength and reduced the risk of leaks by fusing the body edges without lead-based solder, enhancing overall container integrity for food applications.^[19]^[15]^[49] Quality control of the double seam focuses on key metrics to verify hermeticity, including seam thickness, which typically ranges from 0.031 to 0.047 inches depending on can size, and cover hook wrinkle count, where 4 to 6 evenly spaced wrinkles indicate proper tightness and compression. Testing methods include teardown analysis, where the seam is manually dismantled to measure hook engagement and overlap, and vacuum checks using tools like seam micrometers or leak detectors to confirm no air ingress under negative pressure. These evaluations ensure the seam meets standards set by regulatory bodies for commercial canning operations.^[47]^[51] Common defects compromising seal integrity include false seams, where the body and cover hooks fail to interlock due to misalignment or insufficient pressure, resulting in a visible gap or incomplete overlap, and loose covers, often from improper flange formation or excessive end curl, leading to partial detachment. These issues are detected through routine visual inspections, micrometer measurements, and teardown examinations, with corrections typically involving adjustments to seamer pressure, roller settings, or alignment to restore proper hook formation and tightness.^[51]^[47]

Canning Methods

Water Bath Canning

Water bath canning is a preservation method that utilizes boiling water at atmospheric pressure to process high-acid foods, ensuring safety through a combination of acidity and heat that inactivates spoilage organisms. This technique is suitable exclusively for foods with a pH of 4.6 or lower, such as fruits (e.g., apples, peaches, berries), pickled vegetables, and tomatoes (often with added acid like lemon juice or vinegar to achieve the required pH). The process achieves a temperature of 100°C (212°F), which is adequate for destroying vegetative bacteria, yeasts, and molds in acidic environments but not bacterial spores. Processing times typically range from 5 to 85 minutes, varying by food type, pack style (hot or raw), jar size, and altitude; for instance, at sea level (0-1,000 feet), pints of most fruit jams require 5-10 minutes, while raw-packed quart jars of pears may need up to 30 minutes.^[52]^[53]^[54] The step-by-step process begins with preparing the food according to a tested recipe, typically involving hot packing where the product is heated to boiling before filling to enhance vacuum formation and reduce processing time. Clean, hot jars are filled with the hot product, leaving a headspace of 1/4 to 1/2 inch between the food and the jar rim to allow for expansion and proper sealing. Jar rims are wiped clean to ensure a good seal, followed by applying treated lids and bands fingertip-tight. The filled jars are then placed on a rack in a boiling water canner filled with water to cover the jars by at least 1 inch; the water is brought to a vigorous boil, and the processing time begins once the boil is reached. Throughout processing, the boil must be maintained, and water level kept adequate by adding boiling water if needed. After the specified time, the heat is turned off, the canner lid removed, and jars allowed to sit in the water for an additional 5 minutes before being carefully lifted out using a jar lifter to cool undisturbed on a towel-covered surface for 12 to 24 hours. Seals are checked by ensuring lids do not flex when pressed; unsealed jars must be refrigerated or reprocessed.^[55]^[56] To ensure safety and efficacy, water bath canning must follow USDA-tested recipes from authoritative sources like the National Center for Home Food Preservation, which account for acidity, heat penetration, and microbial risks. For example, USDA guidelines for apple butter specify processing hot-packed pints or half-pints for 5 minutes at altitudes of 0-1,000 feet, while choice salsa requires 15 minutes for pints under the same conditions. These recipes are scientifically validated to achieve the necessary lethality for high-acid products.^[57]^[58] A key limitation of water bath canning is its ineffectiveness for low-acid foods, such as vegetables (e.g., green beans, corn), meats, or soups without sufficient acidification, as the 100°C temperature fails to destroy heat-resistant spores of pathogens like Clostridium botulinum, potentially leading to botulism risk. In acidic conditions, however, the low pH prevents spore germination and toxin production, allowing boiling water to suffice for preservation. This method is thus confined to home and small-scale use for suitable foods only. Atmospheric steam canning serves as an alternative to water bath canning for high-acid foods, approved by the USDA in 2015 based on research from the University of Wisconsin. It uses a specialized canner that generates steam at 100°C (212°F) to process jars, with times matching water bath methods but limited to 45 minutes or less to avoid boiling dry; a steady 6-8 inch steam column must be maintained for safety.^[52]^[59]^[60]^[61]

Pressure Canning

Pressure canning is a preservation method that utilizes high-pressure steam to process low-acid foods, achieving temperatures necessary to inactivate heat-resistant bacterial spores, such as those of Clostridium botulinum. Unlike water bath canning, which is suitable only for high-acid foods with a pH below 4.6, pressure canning is essential for low-acid items to ensure safety by reaching internal temperatures of 116–121°C (240–250°F).^[62]^[63] The mechanism involves dial-gauge or weighted-gauge pressure canners that maintain 10–15 pounds per square inch (psi) of pressure, corresponding to the required temperatures for sufficient duration. Processing times typically range from 20 to 90 minutes, adjusted according to food density, jar size, pack style (hot or raw), and altitude to account for reduced atmospheric pressure at higher elevations, which necessitates increased psi or time. For instance, at sea level, a dial-gauge canner operates at 11 psi, while weighted-gauge models use 10 psi.^[54]^[64]^[65] This method applies primarily to low-acid foods like vegetables, meats, poultry, seafood, and soups or stews containing these items. A representative example is canning green beans (snap or Italian varieties), where raw- or hot-packed pint jars are processed at 11 psi for 20 minutes in a dial-gauge canner or 10 psi for the same duration in a weighted-gauge canner at altitudes of 0–1,000 feet. Quart jars require 25 minutes under the same conditions.^[66]^[67] Process times and pressures are validated through research-based recipes developed by authoritative sources like the USDA and Ball, derived from heat penetration studies that measure how heat distributes within specific foods to ensure microbial destruction throughout the jar. These studies simulate home canning conditions to establish safe parameters, preventing underprocessing that could lead to spoilage or illness. Home canners must adhere strictly to these tested guidelines, avoiding unverified recipes.^[68]^[69]^[70] Safety in pressure canning emphasizes proper operation, including venting the canner for 10 minutes after heating to exhaust air before placing the gauge weight or closing the vent, which ensures pure steam circulation and uniform pressure buildup without cold spots. Failure to vent adequately can result in incomplete heat penetration and increased risk of botulism. Canners should also test dial gauges annually for accuracy at local extension services.^[62]^[71]^[72]

Aseptic and Other Advanced Methods

Aseptic processing represents an advanced industrial method for preserving liquid and semi-liquid foods by sterilizing the product separately from its container in a continuous flow system, ensuring commercial sterility without post-filling heat treatment. This technique involves ultra-high temperature (UHT) treatment, where the food—such as juices or milk—is rapidly heated to 135–150°C for a few seconds using direct steam injection or indirect heat exchangers, followed by rapid cooling and filling into pre-sterilized containers like cans or cartons under aseptic conditions.^[73] Unlike traditional canning, this separation minimizes thermal damage to nutrients and sensory qualities while achieving the required microbial inactivation for shelf-stable products.^[74] Retort pouch systems offer another innovative approach, utilizing flexible, multilayer laminated pouches that are filled with food and then sterilized in a retort using overpressure steam or water cascades at approximately 121°C to prevent pouch deformation. These pouches, often lighter and more space-efficient than rigid metal cans, are particularly suited for ready-to-eat meals, pet foods, and military rations, providing equivalent microbial safety with reduced energy use during processing and transportation.^[75]^[76] Emerging non-thermal alternatives like ohmic heating and high-pressure processing (HPP) are gaining traction as complements to traditional canning, offering better preservation of flavors, colors, and textures in heat-sensitive products. Ohmic heating applies an electric current directly through the food for uniform volumetric heating, reducing processing time and overcooking risks compared to conventional conduction methods.^[77] HPP subjects packaged foods to pressures of 400–600 MPa at ambient temperatures, inactivating pathogens and enzymes without significant heat, though it is less prevalent in standard canning due to equipment costs and suitability for high-moisture liquids and solids.^[77]^[78] These methods enhance product quality but require validation to meet regulatory standards for low-acid canned foods.^[79] The adoption of aseptic processing accelerated in the United States following FDA approvals in the 1980s, particularly the 1981 authorization of hydrogen peroxide combined with heat for sterilizing packaging materials, enabling widespread use in beverage production. Today, aseptic methods account for a significant share of U.S. canned and carton-based beverages, supporting extended shelf life without refrigeration and reducing packaging waste.^[80]^[74]

Equipment and Processes

Commercial Canning Operations

Commercial canning operations encompass a continuous, automated production line that processes vast quantities of food products while adhering to stringent safety standards. The workflow typically starts with the thorough washing and sorting of raw ingredients to eliminate contaminants and ensure uniformity, often using high-volume conveyor systems and water sprays. This is followed by filling the pre-formed metal cans or glass jars with the prepared food—employing either volumetric fillers for liquids and semi-solids or gravimetric fillers for weighed solids—to achieve consistent portion sizes and minimize waste. After filling, the cans undergo exhausting, where steam is introduced to displace air from the headspace, preventing oxidation and facilitating a proper vacuum seal during subsequent steps; this is critical for low-acid foods to avoid incomplete sterilization. Seaming then hermetically seals the lids using multi-head rotary machines that form a double seam, with high-speed models capable of processing up to 2,000 cans per minute through precision rollers and automation controls.^[81]^[82] The sealed containers are next subjected to retorting in large pressure vessels, where they are heated to temperatures typically between 121°C and 135°C under overpressure conditions—often 2-3 atmospheres—to counteract internal steam pressure and prevent container bulging or deformation, especially for flexible packaging like pouches. This thermal processing inactivates microbial spores, with the exact time-temperature profile determined by thermal death time (TDT) calculations tailored to each product's pH, viscosity, and microbial load. Cooling follows immediately via water sprays or immersion baths to halt cooking and reduce the risk of post-process contamination, after which cans are dried, labeled with product details and batch codes using automated printers, and inspected for integrity.^[83]^[84] Automation permeates the entire line, enhancing throughput and consistency; for instance, inline quality control includes ultrasonic leak detectors that scan seams non-destructively at line speeds, identifying defects by analyzing sound wave reflections from potential voids. These systems integrate with programmable logic controllers (PLCs) to divert faulty cans automatically. Regulations govern these operations rigorously: under FDA's 21 CFR Part 113 for thermally processed low-acid canned foods, processors must file scheduled processes with the agency and implement controls akin to HACCP principles, first incorporated in the 1970s through FDA regulations such as 21 CFR Part 113 for low-acid canned foods—which require hazard analysis, critical control points like retort temperature monitoring, and validation via TDT studies.^[85]^[86]^[87] At scale, facilities like Campbell Soup Company's Maxton, North Carolina plant exemplify industrial capacity, producing approximately 6 million cans of soup per day through integrated lines that handle everything from ingredient blending to palletizing. Such operations underscore the industry's emphasis on efficiency, with annual outputs in the billions of units globally, supported by modular equipment that allows quick changeovers between products.^[88]

Home Canning Practices

Home canning allows individuals to preserve fruits, vegetables, and other foods safely using accessible equipment and tested procedures. This practice requires adherence to established guidelines to ensure effective sealing and microbial control, typically applying water bath canning for high-acid foods or pressure canning for low-acid ones.^[89] Essential tools for home canning include Mason jars, which are heat-tempered glass containers available in various sizes, and two-piece lids featuring a flat metal lid with a rubber gasket for sealing and a screw band for securing. Pressure canners, such as Presto models that comply with USDA standards for dial-gauge or weighted-gauge operation, are critical for processing low-acid foods to achieve temperatures above boiling. pH testers, like digital meters or test strips, can assist in verifying acidity for custom recipes, though they are not a substitute for adding prescribed amounts of acid.^[62]^[90]^[91] Best practices focus on precise preparation to maximize shelf life and quality. For borderline foods like tomatoes, acidification involves adding 1 tablespoon of lemon juice or ¼ teaspoon of citric acid per pint to lower pH below 4.6 without relying on testing. Proper headspace—usually ½ inch between the food and lid—allows for expansion during heating and prevents siphoning, where hot liquid seeps out and disrupts the vacuum seal. Processed jars should cool undisturbed for 12–24 hours before checking seals, then be stored in a cool, dark, dry location at 50–70°F, where they retain optimal quality for up to one year.^[92]^[93] Common errors among amateur canners include over-tightening screw bands, which hinders air escape and can cause lids to buckle, and failing to adjust processing times or pressures for altitudes above 1,000 feet, both contributing to seal failures. A national survey revealed that 32% of home canners experienced at least some jars failing to seal after processing.^[94]^[95]^[96] Reliable resources for home canners include the guidelines from the National Center for Home Food Preservation, which offer research-based recipes and procedures updated through 2025 to reflect current safety standards.

Nutritional Considerations

Impact on Food Nutrients

Canning, as a thermal processing method, primarily affects heat-sensitive nutrients such as vitamin C, which can experience significant losses due to the high temperatures involved. In vegetables, vitamin C retention is generally around 50% compared to fresh counterparts, though it varies by type and processing conditions. These reductions occur because vitamin C is water-soluble and degrades rapidly under heat, though overall losses are often comparable to or less than those from prolonged storage of fresh produce.^[97] In contrast, B vitamins like thiamin, riboflavin, and niacin show greater stability during canning, with retention rates typically 80-90%.^[97] Minerals such as iron and potassium are largely unaffected by canning, with retention near 100% for iron and 90% for potassium, as they are heat-stable and not prone to leaching under standard processing conditions.^[97] Protein undergoes some denaturation from heat, but this does not substantially impair its nutritional value or digestibility. Fiber content in canned fruits is well-preserved, sometimes even higher due to the concentration effect from water evaporation during processing. Certain canning processes can enhance nutrient bioavailability, particularly for fat-soluble compounds. For instance, the lycopene in tomatoes becomes more bioavailable after canning, with studies showing absorption rates up to 2.5 times higher in processed tomato products compared to fresh tomatoes, due to heat-induced breakdown of cell walls and isomerization.^[98] This benefit extends to reduced-water products like tomato paste, where nutrient concentration increases without proportional losses. Nutrient preservation varies by food type and processing conditions.

Comparison to Fresh and Other Preserved Foods

Canned foods often provide nutritional profiles comparable to fresh produce, with retention of key vitamins and minerals influenced by the heat processing involved. While fresh fruits and vegetables harvested at peak ripeness offer optimal levels of heat-sensitive nutrients like vitamin C, canning can preserve or enhance others, such as lycopene in tomatoes, where bioavailability increases up to 2.5 times due to thermal breakdown of cell walls.^[98] Similarly, beta-carotene levels in canned carrots and other vegetables may be higher than in fresh counterparts because of concentration effects and improved extractability during processing. However, water-soluble vitamins like vitamin C and some B vitamins experience greater losses in canned items, with average retention rates of about 50% for vitamin C compared to near 100% in fresh produce immediately after harvest.^[97] Minerals such as potassium and magnesium remain largely stable, retaining over 90% of their original content, while dietary fiber content can increase in canned vegetables due to softening and breakdown of plant structures. A notable drawback of canned foods is the frequent addition of sodium for preservation and flavor, which can elevate levels to 200-400 mg per serving—far higher than the negligible amounts in fresh produce—potentially contributing to hypertension risks if not moderated.^[99] Low-sodium or no-salt-added options mitigate this, retaining nutritional benefits without excess.^[99] Studies indicate that regular consumption of nutrient-dense canned foods correlates with higher overall intake of vegetables and associated nutrients like fiber and antioxidants, supporting dietary guidelines that endorse them as equivalent to fresh for meeting daily requirements.^[100] Compared to frozen foods, canning generally results in slightly lower retention of heat-labile nutrients due to the higher temperatures and longer exposure times, whereas freezing after brief blanching preserves vitamin C with losses ranging from 10% to 80%, averaging about 50% retention.^[101] Frozen produce also maintains higher levels of folate and other B vitamins, but canned items excel in carotenoid content and offer year-round accessibility at lower costs, with nutrient scores often matching or exceeding frozen in minerals and phenolics.^[102] Relative to dried preserved foods, canning better retains water-soluble vitamins, as drying processes can lead to significant losses in vitamin C and B vitamins through oxidation and dehydration, though dried options concentrate insoluble fiber and minerals like iron.^[102] Overall, all preservation methods—canned, frozen, and dried—deliver substantial nutritional value when selected mindfully, with no single form universally superior to fresh but each contributing effectively to balanced diets.^[102]

Safety Hazards

Biological Risks Including Botulism

Canning, while effective for food preservation, carries biological risks primarily from microbial contamination, with Clostridium botulinum posing the most severe threat due to its ability to produce botulinum neurotoxin in anaerobic environments. This spore-forming bacterium thrives in low-acid foods (pH > 4.6) during improper processing, where the canning process depletes oxygen, creating conditions for spore germination. Spores of C. botulinum can germinate under anaerobic conditions at temperatures between 3°C and 50°C, particularly in the mesophilic range of 35–40°C, leading to vegetative cell growth and toxin production. The resulting botulinum toxin is heat-labile and can be inactivated by boiling for 10 minutes, but the spores themselves are highly heat-resistant, necessitating specific thermal processes to prevent toxin formation.^[103]^[104]^[105]^[106] To mitigate this risk, the canning industry employs the 12D process, a standard thermal treatment that achieves a 12-log reduction in C. botulinum spores—from an initial hypothetical load of 10¹² spores to 10⁰ (effectively one survivor)—ensuring commercial sterility in low-acid canned foods. This process typically involves heating to 121°C (250°F) under pressure for a calculated time, accounting for the food's heat penetration characteristics. Foodborne botulism remains rare but severe, averaging approximately 20-25 confirmed cases annually in recent years (as of 2024), with many linked to home-canned low-acid foods such as green beans; for instance, in June 2024, an outbreak of 8 cases was linked to home-canned prickly pear cactus. Historical outbreaks, including those in the late 20th century involving home-canned green beans, underscore the dangers of inadequate processing, often resulting in paralysis and respiratory failure if untreated.^[107]^[108]^[109]^[110]^[111] Prevention strategies emphasize proper acidification, pressure processing, and post-processing handling to inhibit C. botulinum growth. For low-acid foods, acidification to a pH of 4.6 or below prevents spore germination, allowing safe water bath canning, while pressure canning at 10–15 psi (116–121°C) is required for non-acidified products to achieve the necessary spore destruction. High-risk home-canned items should be refrigerated if not fully processed, and any suspect food boiled for 10 minutes before consumption to degrade potential toxin. Symptoms of botulism, including double vision, muscle weakness, and difficulty swallowing or breathing, typically appear 18–36 hours after ingestion and require immediate medical attention, with cases reported to the CDC for surveillance and outbreak investigation.^[112]^[52]^[113]^[103] Beyond botulism, other microbial hazards in canning include yeasts and molds in high-acid foods, which can cause spoilage through fermentation or visible growth if seals fail or processing is insufficient, leading to off-flavors and texture degradation. In underprocessed low-acid meats or vegetables, Listeria monocytogenes may survive, posing risks of listeriosis, a serious infection particularly dangerous to pregnant individuals, newborns, and the immunocompromised. Sealing failures can exacerbate these issues by permitting post-process contamination.^[114]^[115]

Chemical and Physical Contaminants

Chemical contaminants in canned foods primarily arise from the migration of substances from can linings and metals into the food, particularly under conditions of acidity, heat, or prolonged storage. Bisphenol A (BPA), historically used in epoxy resin linings to prevent corrosion, has been a major concern due to its potential endocrine-disrupting effects; however, many major U.S. food manufacturers have phased out BPA in can linings, with over 95% of cans reported as BPA-free as of 2020.^[116] Lead, once common in can seams and solders, migrates at low levels but is strictly regulated; for example, the FDA has established an action level of 0.1 ppm for lead in certain candies accessible to young children to minimize health risks such as neurological effects.^[117] Tin dissolution occurs more readily in acidic foods like tomatoes or fruits, where the metal reacts with organic acids, potentially leading to concentrations exceeding safe thresholds and causing gastrointestinal issues if levels surpass 200 ppm.^[118] Added preservatives such as salt and sugar are commonly incorporated during canning to enhance stability and flavor, but they can elevate dietary intake of these compounds. In diets heavily reliant on canned soups, sodium from these products can contribute up to 40% of the recommended daily limit of 2,300 mg, increasing risks for hypertension and cardiovascular disease.^[119]^[120] Sugar additions serve similar preservative roles but are less directly linked to acute health concerns in this context. Physical contaminants and structural issues stem from handling or reactions during storage. Denting of metal cans can compromise integrity by creating pinholes or fractures in the seams, allowing external entry points for contaminants or oxygen.^[121] Swelling, often caused by hydrogen gas generated from the reaction between acidic food contents and the tin-iron alloy in the can, indicates potential metal dissolution and should prompt discard to avoid ingestion of elevated metal levels.^[121] Regulatory frameworks address these risks through limits on migration and mandatory testing. The European Union's 2008 ban on BPA in baby bottles marked an early precautionary step that influenced global standards for food contact materials, culminating in a comprehensive prohibition on BPA and related bisphenols in food contact materials, including can coatings, effective January 20, 2025, across the EU.^[122] In the U.S., FDA guidelines enforce low tolerances for metals, with tin migration limits typically set at 250 mg/kg in solid foods to prevent toxicity.^[123] Contaminants are detected using atomic absorption spectroscopy, a precise method for quantifying trace metals like tin and lead in food samples by measuring light absorption at specific wavelengths.^[124] These measures ensure canned foods remain safe when properly manufactured and stored.

Canning During Economic Downturns

During the Great Depression of the 1930s, consumption of canned fruit in the United States increased by nearly 50 percent compared to levels in the preceding 13 years, as it provided an affordable source of nutrition amid widespread economic hardship.^[125] Canned meats, fish like sardines, and beans became popular cheap protein options, offering long-lasting sustenance when fresh foods were scarce or expensive.^[126] Government initiatives under the New Deal further bolstered canning's role; the Works Progress Administration (WPA) employed women in canning projects, while community canning centers, supported by programs like the Federal Emergency Relief Administration, enabled low-income families to preserve homegrown produce at reduced cost.^[127] In the 2008 financial crisis, consumers shifted toward store-brand canned goods to stretch budgets, with private-label food and beverage sales adding about $8 billion between 2008 and 2010, outpacing national branded growth.^[128] Overall retail food spending increased slightly during the recession, reflecting a move to at-home preparation of preserved items over dining out.^[129] The COVID-19 pandemic from 2020 to 2022 amplified canning's economic resilience, with U.S. sales of non-perishable canned products surging due to stockpiling and supply chain disruptions. Soup sales, for instance, rose 25 percent year-over-year in mid-2020, while broader demand for canned vegetables and proteins prompted manufacturers to ramp up production amid initial shortages of empty cans.^[130] The process's long shelf life of 2 to 5 years for most commercially canned goods minimized waste during bulk purchases and economic uncertainty, allowing families to secure affordable food supplies for extended periods.^[131]

Contributions to Global Food Security

Canning plays a pivotal role in humanitarian aid efforts, particularly through organizations like the World Food Programme (WFP), which incorporates canned foods into distributions to combat hunger in vulnerable regions. For instance, in Africa, WFP has provided canned fish as part of school feeding programs in countries such as Lesotho, where these products offer essential protein and nutrients with extended shelf life suitable for hot climates lacking reliable refrigeration.^[132] Overall, WFP handled 3.3 million metric tons of food in 2024, including canned items that enhance accessibility and reduce spoilage during transport and storage in challenging environments.^[133] In global trade, canning facilitates the export of perishable goods over long distances, contributing to food security by balancing supply and demand across borders. Thailand leads as the world's top exporter of canned tuna, holding approximately 35% of the global market share for canned and processed tuna in recent years, with exports reaching 549,000 tons valued at USD 2.3 billion in 2024.^[134] The broader global canned food trade reached a market value of around USD 122.72 billion in 2024, underscoring its economic significance in stabilizing food availability worldwide.^[135] From a sustainability perspective, canning significantly mitigates food waste compared to fresh produce, which sees household discard rates of about 25% for fruits and 24% for vegetables due to spoilage. By preserving foods at peak ripeness and extending shelf life beyond two years without refrigeration, canning captures imperfect produce that might otherwise be discarded, thereby reducing overall waste in the supply chain.^[136]^[137] Recent innovations, such as the 2025 development of recyclable mono-material metallized retort pouches by industry leaders including BOBST, Brückner, and Mitsui Chemicals, further enhance environmental benefits by improving packaging recyclability while maintaining barrier properties for long-term storage.^[138] Despite these advantages, canning faces challenges related to energy intensity, particularly in the retorting process, which consumes approximately 156 kWh per ton of product for thermal sterilization. This energy demand arises from high-temperature processing to ensure safety, though it is offset in global trade by enabling non-refrigerated transport of imports, which reduces overall emissions compared to cold-chain logistics for fresh goods that account for up to 25% of food system energy use.^[139]^[140]

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Apr 18, 2024 · Common sources of foodborne botulism are homemade foods that have been improperly canned, preserved, or fermented. Though uncommon, store-bought ...Key Points · Overview · Most Common Types
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Preventing Foodborne Illness: Clostridium botulinum
Apr 28, 2025 · While the botulinum spores can survive in boiling water, the toxin is heat-labile, meaning that it can be destroyed at high temperatures.
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Mechanisms of food processing and storage-related stress tolerance ...
botulinum strains are mesophilic and their optimal growth temperature is commonly reported as 35–40 °C [2]. The minimum and maximum growth-limiting temperatures ...Mechanisms Of Food... · Abstract · 1. Introduction
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[PDF] Fish and Fishery Products Hazards and Controls Guidance - FDA
In reduced oxygen packaged products in which the spores of non-proteolytic C. botulinum are inhibited or destroyed (e.g., smoked fish, pasteurized crabmeat, and ...<|separator|>
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C. botulinum - Ecolab
A commercial canning process that delivers a standard “botulinum cook” or “12D process” offers a substantial margin of safety by inactivating 12 logs of ...
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Clostridium Botulinum: The Hidden Danger in Canned Foods
Jan 9, 2024 · The standard is typically a 12-D reduction, meaning the process should reduce the spore population by 12 log cycles, or 99.9999999999% (twelve ...
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Foodborne Botulism Outbreaks in the United States, 2001–2017
Jul 15, 2021 · The median number of confirmed cases per year was 19 (range: 2 to 39 cases). In 2013, a case definition for additional probable foodborne ...
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[PDF] Three Outbreaks of Foodborne Botulism Caused by Unsafe Home ...
Home-canned vegetables (green beans, green bean and carrot blend, and asparagus) served at family meals were confirmed as the source of each outbreak. In each ...Missing: 1970s | Show results with:1970s
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Apr 25, 2024 · You cannot see, smell, or taste the toxin that causes botulism. But taking even a small taste of food containing the toxin can be deadly.Safe Canning Methods · Use The Right Equipment For... · More Ways To Prevent...
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The Importance of Food pH in Commercial Canning Operations
Fortunately, the spores of Clostridium botulinum will not grow if the pH of a food is 4.6 or less. For low-acid foods with a pH value greater than 4.6, these ...Canning High-Acid Foods · Acidified Foods And... · Intermediate Foods
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Understanding the Microbiology Behind Canned Food Safety
Jan 5, 2024 · Yeasts and molds are generally less heat-resistant than bacterial spores but more resistant than vegetative bacteria. They primarily cause ...
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Microbial Contamination, an Increasing Threat to the Consumption ...
Listeria causes listeriosis, an uncommon disease but dangerous. Nonetheless, listeriosis accounts for about 30% death rate in comparison with other food-borne ...Missing: canning | Show results with:canning
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Market Actions on BPA - Breast Cancer Prevention Partners (BCPP)
Upon learning about the Buyer Beware report, Campbell's announced they would eliminate BPA in North American cans by mid- 2017. We are pleased that Campbell's ...
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Guidance for Industry: Action Levels for Poisonous or Deleterious ...
Sep 20, 2018 · This booklet lists action levels established by the Food and Drug Administration (FDA) for poisonous or deleterious substances in human food and animal feed.DDT, DDE, TDE · Heptachlor & Heptachlor... · Lead · Lindane
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200 ppm or more of tin in foods and beverages can be expected to produce acute toxic effects, including abdominal cramps, nausea, and/or diarrhea.
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Mar 5, 2024 · The Daily Value for sodium is less than 2,300 milligrams (mg) per day. Use % Daily Value (%DV) as a tool. The %DV is the percentage of the Daily ...
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May 12, 2020 · On average, canned soup has 700 mg of sodium, or 30% of the RDI, per 1-cup (245-gram) serving ( 9Trusted Source ). 3. Ham.<|separator|>
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Aug 27, 2014 · Another cause of swelling is a chemical reaction of the product with the metal in the can. This usually results in the production of hydrogen ...
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Once baby bottles that were microwaved were found to release BPA into infants' milk, the European Union and Turkey banned the chemical from baby bottles in 2008 ...
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Aug 7, 2025 · The maximum permissible levels of tin in food are typically 250 mg/kg for solid foods and 150 mg/kg for beverages 15 . ... Synthesis and anti- ...<|control11|><|separator|>
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Oct 31, 2025 · From 1929, the start of the Great Depression, to 1941, when the United States entered World War II, people ate nearly 50 percent more canned ...Missing: sales | Show results with:sales
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Oct 8, 2024 · During the Great Depression, Americans also looked to canned goods such as sardines that were inexpensive and afforded longer storage. Beans ...
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Bethel Cannery
The cannery program was instituted as one component of the WPA public works concept and was designed to serve a dual purpose – to conserve food and to train ...
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How the Great Recession Changed US Shopping Habits
Research shows that during the Great Recession, US consumers increased their spending on retail food purchases overall, while switching away from mid-tier ...
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New supply-chain crisis during pandemic: not enough cans for food
Jul 24, 2020 · Manufacturers and distributors are running out of empty cans to pack nonperishable foods that Americans are buying in bulk.
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Boom in Canned Food Means a Boom in Cans, Too
May 7, 2020 · The surge in demand for processed foods like canned soups and vegetables during the pandemic has rippled through the food industry's supply chain.
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As a general rule, unopened home canned foods have a shelf life of one year and should be used before two years. Commercially canned foods should retain their ...
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Feb 19, 2023 · The commodities delivered include vegetable oil, canned fish, fortified maize meal, super cereal plus and split peas. WFP continues to provide ...
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WFP provided life-saving and life-changing assistance to 1.8 million people, distributing over USD 50 million and more than 7,000 metric tons of food. ... Canned ...
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Jun 19, 2025 · In 2024, WFP handled 3.3 million mt of food, providing safe, life-saving food assistance to more than 120 million people.
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[PDF] 6/2024 BULLETIN: • Global: 18th INFOFISH World Tuna Trade ...
Jun 18, 2024 · Thailand, the top supplier had an estimated share of 35% in global exports of canned and processed tuna during the review period. Exports ...
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Aug 8, 2025 · Canned and prepared/preserved fish products had an export volume of 771 thousand tons (+22.0%) in 2024, or an equivalent value of USD 3.2 ...
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Jun 17, 2025 · In 2024, the estimated import value of processed fruits and vegetables is $8.0 billion. The US imports products like canned fruits, frozen ...
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Canned Food Market Size, Trends, Growth Analysis 2034
Aug 11, 2025 · The global canned food market size stood at USD 122.72 billion in 2024 and is forecasted to expand from USD 127.63 billion in 2025 to ...
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Canned Food Myths - Busted!
Luckily, choosing canned foods can help to significantly reduce food waste at all levels of the lifecycle from farm to table. Cores, peels, and other produce ...
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Waste less food. · Canned food retains quality and taste for more than two years, eliminating confusion and waste associated with “best by” or “use by” dates.
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Life cycle assessment and energy comparison of aseptic ohmic ...
Jun 22, 2021 · The energy saving of the ohmic heating line compared to the appertization line is 102 kWh/t of the product (or 65% energy saving). The energy ...
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[PDF] Food transportation issues and reducing carbon footprint
Transportation is a major contributor to global warming, with long food shipping distances and diesel use accounting for 25% of the US food system's energy. ...