Quick Answer
Canned goods are generally safe to leave in a hot car for short periods of time, but it’s best to avoid leaving them for extended periods when possible. The main risk is that the cans may swell or burst from the pressure created by the heating and cooling cycle. Spoilage is unlikely with unopened canned goods, but taste and texture can be affected. If bulging, leaking, rusting, or exploding cans are noticed, the products should be discarded.
How Hot Do Cars Get In The Summer?
Studies have shown that on an 80 degree F day, the internal temperature of a parked car can reach up to 119-123 degrees F in just 20 minutes. In 60 minutes, the interior temperature can climb to 133-157 degrees F. These temperatures are hot enough to kill pets left in vehicles and pose significant risk to children. For canned goods, these extreme temperatures can impact the integrity of the cans, causing swelling, leaks, bursts, and an accelerated deterioration of quality.
How Does Heat Affect Canned Goods?
Canned goods are sterile products packed in hermetically sealed containers, designed to prevent microorganisms from entering and proliferating. The integrity of the can is important for maintaining sterility and safety. Heating cans causes an increase in internal pressure from expansion of the contents. This places stress on the can seams and lining.
Over time, high heat can degrade the can lining leading to corrosion, rust, and leakage. As internal pressure continues rising, it can reach a point that ruptures the can. Swollen or bulging cans are the first warning sign that dangerous internal pressure is building.
While swelling and bursting are the most pressing risks, heat can also degrade food quality and nutritional content even if the can remains intact. High temperatures accelerate chemical reactions and can lead to changes in taste, color, and texture. Nutrients like vitamins C and B can be lost. Enzymes and other proteins are denatured with improper heating. Spoilage bacteria are killed but the heating process diminishes freshness.
How Long Can Canned Goods Safely Stay in a Hot Car?
There is no defined safe time period for leaving canned goods in a hot vehicle. On a cool day around 75 F, unopened canned foods can be left in a car for several hours with minimal quality loss. However, on a 90+ degree day, swollen cans have been reported within 1-2 hours.
To prevent potential risks, canned goods should be removed from hot vehicles as soon as possible. If needed for a picnic or trip, transfer canned items to a cooler while traveling. Avoid leaving cans in direct sun whenever possible. Do not store cans in the trunk for more than a short trip. High value or irreplaceable canned goods are safest kept in temperature controlled environments rather than vehicles.
Signs of Spoilage in Swollen, Leaking, Rusted, or Bulging Cans
If canned goods have been exposed to hot temperatures for prolonged periods, inspect thoroughly before use. Warning signs include:
– Swollen cans – Internal pressure has caused can walls to expand. Do not open, contents may burst out. Discard swollen cans.
– Leaking cans – Seam failures or pinholes allow contents to leak out. Dried fluid on the can is a telltale sign. Discard leaking cans.
– Rusted cans – Check any rusted areas for pinholes where contents may have leaked. Rust weakens the can and increases risk of seam failures. Discard rusted cans.
– Bulging or distorted cans – A bulging lid is a sign of unsafe internal pressure. Contents may spray out violently when opened. Discard bulging cans.
– Hissing, spurting, or spewing cans – These are signs of bacteria converting contents to gas. Gushing liquid or foam when opening indicates spoilage. Discard any cans exhibiting these traits.
Safety first! Do not taste contents of suspect cans. When in doubt, throw it out. Botulinum toxin causes life threatening illness and can be produced by bacteria in compromised canned goods.
Are Dents or Broken Seals a Problem?
Dents in cans are not an automatic sign of spoilage, but the risks depend on the size and severity of the dent. Slight surface dents are not a major concern for safety or quality. However, deep dents could compromise the integrity of seal, increasing likelihood of contamination during temperature fluctuations. Cans with large or sharp dents near seams should be discarded.
Broken seals or pop tops do allow air exchange and contamination. Unopened canned goods rely on their hermetic seal. Once that seal is broken, bacteria and oxygen can enter the can and accelerate food spoilage. Discard any cans with broken seals. Even if the food looks and smells normal, it is no longer sterile and microbes could start growing given the right conditions.
Will Canned Goods Explode from the Heat?
It is possible but rare for canned goods to violently explode, especially when left for extended periods in extreme heat. As internal pressure continues rising, the metal walls can reach a bursting point. Highly pressurized contents will then rapidly blast out the can.
These “can bombs” are more likely with carbonated beverages but can happen with food products containing proteins, starch, or sugars. Canned goods stored by Survivalists in bunkers for decades have reportedly exploded from the pressure build up over long periods of time.
For canned goods sitting in a hot car for a few hours, swelling and seepage are more likely than an explosion. But compromised integrity increases the chances of a pressurized blast when opening. Cans that have been subjected to high heat are best discarded to prevent injury.
Are Home Canned Goods Also at Risk?
Home canning in Mason jars has different temperature considerations than commercial canned goods. The glass jars are less impacted by heating but the contents still suffer quality loss.
As with commercial cans, color, texture, nutrients, and flavor can degrade with heat exposure. Temporary storage in a hot car for a few hours is unlikely to cause major damage. However, the safety threshold is lower since home canned goods lack the sterilization processing used by commercial canners.
Bacteria are killed by the heat processing but spores can survive. Germinated spores and toxins will produce gasses that pressurize jars. For home canned goods, it’s advised to discard any jars with bulging lids, leaks, slimy contents, or unnatural odors. Play it safe rather than risk botulism poisoning.
Tips to Prevent Problems from Heat
– Store cans in a cool, dry place rather than garages and sheds
– Use a cooler with ice packs when transporting canned goods
– Keep canned products out of direct sunlight whenever possible
– Avoid leaving cans in a hot car for more than 1-2 hours
– Transfer cans to a refrigerator upon arriving home
– Consume canned goods within 1-2 years for best quality
– Check canned goods carefully prior to use after heat exposure
– Discard any cans showing signs of swelling, bulges, rust, or leakage
– Report illnesses to CDC if botulinum poisoning is suspected
Canexternal heat damage canned goods Nutritionally?
Yes, heat can degrade the nutritional quality of canned goods over time. Exposure to high temperatures accelerates the breakdown of heat-sensitive nutrients in canned foods.
Vitamin C – Ascorbic acid is very prone to oxidation. Prolonged heating causes vitamin C levels to substantially decline.
Vitamin A – Also degraded by heat exposure. Low moisture foods like canned grains lose vitamin A activity more rapidly than canned fruits and vegetables.
Thiamin – This B vitamin is sensitive to thermal processing. Canned goods tend to have lowered thiamin content compared to fresh.
Phenolic Compounds – Polyphenols and flavonoids like lycopene in tomatoes show significant loss after heating. These function as antioxidants.
Other heat-liable nutrients include riboflavin, pantothenic acid, pyroxidine, niacin, and vitamins E and K. Minerals fare better but high temperatures can breakdown folate.
Enzyme activity and protein availability decrease. Maillard browning causes changes to amino acid composition. Sugars caramelize and oxidize. Oils undergo oxidation and rancidification.
So while commercial canning preserves food, nutrient losses still occur over time, accelerated by heat. For maximum nutrition, canned goods are best consumed soon after purchase and storage should be in a cool, dark place.
Do can appearances indicate spoiled contents?
The appearance of swollen, leaking, rusted, or dented cans can indicate spoiled contents, but looks alone do not guarantee good products. Never rely solely on appearance when inspecting canned goods. Some signs of potential spoilage based on can appearance include:
– Swollen can – Internal pressure has expanded walls, high risk of bacterial contamination if seam fails.
– Leaking can – Dried fluids around seams or pinholes can indicate seam failure and microbial growth.
– Rusted can – Check underneath rust spots for pinholes, rust weakens metal. Air exchange occurs if pinholes breach inner protective lining.
– Dented can – Slight dents are OK but deep sharp dents along seams jeopardize integrity of seal.
– Corroded or faded labels – Indicates cans have been stored for long periods or exposed to moisture/sunlight. Higher likelihood of degradation.
– Bulging or loose lids – Pressurization from food spoilage microbes produces gas, causing lids to bulge or loosen.
Appearances can mislead. A can may look normal but still contain toxins. Always verify safety before tasting. When canned goods have been subjected to temperature extremes or long storage, best to discard any questionable cans.
Conclusion
While canned goods are made to be shelf-stable, exposure to extreme temperatures should be minimized when possible. Short term storage in hot cars is not ideal but unlikely to cause major issues if cans are undamaged. However, leaving cans for longer periods in hot conditions could lead to swelling, leaks, deterioration, or increase risk of bacteria growth in any compromised containers. Keep storage times minimal, inspect carefully, and discard any cans showing signs of damage like bulges, rust, or leaking seals. When in doubt, throw it out to avoid the serious health hazards posed by contaminated canned goods. Follow proper storage, handling, and inspection guidelines and canned goods can remain safe and nutritious pantry staples.
