Is it safe to drink a beer with a rusted cap on it?

November 12, 2025 •

5 min read

According to the USDA, consuming rust is not recommended, making the question 'is it safe to drink a beer with a rusted cap on it?' a common and important one. While the rust itself is not poisonous, its presence on a beer cap can indicate a compromised seal, opening the door to potential contamination and spoilage.

Quick Summary

This article explores the health risks and quality issues associated with a rusted beer cap. It covers the likelihood of seal compromise, potential bacterial contamination, flavor changes, and debunks common myths, like the link between rust and tetanus. Discover what to look for and when to discard a bottle with a rusted cap.

Key Points

Compromised Seal: The primary risk of a rusted cap is that the corrosion may have broken the bottle's seal, allowing oxygen and bacteria inside to spoil the beer.
Tetanus is a Myth: You cannot get tetanus from ingesting rust. Tetanus is caused by bacteria, Clostridium tetani, entering the body through a deep puncture wound, not from drinking.
Inspect the Rust: Superficial rust on the outside is less of a concern than rust on the rim or underside of the cap, which signals a likely seal failure.
Trust Your Senses: Listen for a proper 'psst' sound, inspect for unusual cloudiness or sediment, and smell for off-aromas like skunky or cardboard. A metallic taste is also a clear warning.
Small Ingestion is Not Highly Toxic: Ingesting tiny amounts of rust (iron oxide) is not poisonous and will likely cause no harm beyond potential minor stomach irritation.
When in Doubt, Throw It Out: The minimal cost of a bottle of beer is not worth the risk of drinking a potentially contaminated or spoiled beverage.

The Core Risk: A Compromised Seal

The primary danger associated with a rusted beer cap is not the rust itself, but what the rust represents: a potentially compromised seal. Beer bottles are hermetically sealed to prevent oxygen from entering and to keep the carbonation inside. A cap's rust is a sign of corrosion, which can weaken this seal over time. If moisture and oxygen were able to get under the cap to cause rust, it is possible they also entered the bottle, leading to potential contamination and spoilage of the beer inside.

Why a Rusty Cap Signals Trouble

Loss of Carbonation: The hallmark of a well-sealed beer is its carbonation. If the seal has been compromised, the CO2 will leak out, resulting in a beer that is noticeably flat upon opening.
Oxidation: Air getting into the bottle will cause the beer to oxidize. This leads to stale, unpleasant flavors often described as cardboard or sherry-like.
Bacterial Contamination: The broken seal allows unwanted bacteria or wild yeast to enter the beer. These microbes can cause off-flavors, cloudiness, and in rare cases, more serious health issues.

Examining the Rust: Surface vs. Interior

The location and severity of the rust matter greatly. For minor, superficial rust on the exterior of the cap, the risk is minimal. However, if the rust extends to the rim of the cap or is visible underneath when you open the bottle, the beer should be discarded. The USDA states that heavily rusted cans can have small holes that allow bacteria to enter, and this same logic applies to bottle caps.

The Tetanus Myth: Separating Fact from Fiction

One of the most persistent misconceptions is that ingesting rust directly causes tetanus. This is incorrect. Tetanus is a bacterial infection caused by Clostridium tetani, which is commonly found in soil and animal feces, not in rust itself. The association stems from the fact that dirty, discarded, and therefore often rusty, objects like nails are a common cause of puncture wounds, which provide the anaerobic (oxygen-free) environment that the bacteria need to thrive. Drinking a beer from a rusty cap will not give you tetanus.

Potential Health Effects and Risks

While the risk of a severe illness like botulism from a rusted cap is extremely low, there are other potential health concerns, mainly related to contamination and ingestion of rust particles.

Minor Gastrointestinal Distress: Ingesting small flakes of rust (iron oxide) may cause minor stomach irritation or discomfort, but it is generally not considered harmful in small quantities. The body can handle a certain amount of iron, but excessive amounts could lead to digestive issues.
Iron Overload: Long-term, repeated exposure to iron from rust, especially for individuals with certain genetic conditions like hemochromatosis, could contribute to an iron overload. However, this is not a concern for a single beer.
Bacterial Illness: If the seal is compromised and harmful bacteria have entered, you could risk foodborne illness. Though the alcohol content in beer can inhibit some bacteria, it is not a fail-safe sanitizer.

What to Do If You Find a Rusty Cap


Observation	Safety Recommendation	Explanation
Rust is only on the exterior of the cap	Wipe off the rust and pour into a glass.	A clean wipe can prevent rust from falling into the beer. Pouring into a glass allows you to check for visual signs of spoilage.
Rust on the rim or underside of the cap	Discard the bottle completely.	This is the most critical sign of a compromised seal. Bacteria could have entered and the beer is likely spoiled.
Beer looks or smells normal after opening	Proceed with caution and taste.	The appearance and smell test can indicate if spoilage has occurred. An off-flavor is a good reason to dump it.
Beer is flat or has a metallic taste	Discard the beer immediately.	A flat taste means the seal was broken, leading to oxidation. A metallic taste is also a sign of contamination from the cap.

How to Assess the Beer's Condition

Before you take a sip, you should assess the beer’s condition using your senses. This helps determine if the compromised seal has led to spoilage.

Check the Sound: Listen for the satisfying "psst" upon opening. If it's silent, the beer is flat due to a lost seal.
Inspect the Appearance: Pour the beer into a glass. Look for unusual cloudiness, floating debris, or a strange color. While some craft beers are naturally hazy, an unexpected haziness is a red flag.
Perform the Smell Test: Take a good whiff. Fresh beer should have its characteristic aroma. Sour, moldy, skunky, or cardboard-like smells indicate spoilage or oxidation.
Taste Cautiously: If it passes the visual and smell tests, take a small, cautious sip. An unpleasantly stale, sour, or metallic flavor means it's time to pour it down the drain.

Proper Beer Storage to Prevent Rust

To avoid encountering a rusted cap in the first place, proper storage is key. Keep beer bottles in a cool, dark place away from moisture and humidity. Storing bottles upright can also minimize contact between the liquid and the cap, although this does not prevent exterior rust. For homebrewers or those with valuable beer collections, controlling humidity and using oxygen-absorbing caps can be a good preventative measure.

Conclusion: Better Safe Than Sorry

In short, while a small amount of external rust on a beer cap is not inherently dangerous and won't cause tetanus, it serves as a crucial warning sign that the integrity of the bottle's seal may have been compromised. A healthy adult is unlikely to suffer serious harm from a single sip of slightly tainted beer, but the potential for unpleasant flavor, and in worst-case scenarios, mild illness from bacterial contamination, makes it a risk not worth taking. The best and safest course of action is to inspect the cap closely and trust your senses. If there is any rust on the underside or rim, or if the beer looks, smells, or tastes off in any way, discard it immediately. The minimal cost of a beer is not worth the potential health and flavor risks.

Authoritative Source

For more information on food safety standards, consult the United States Department of Agriculture (USDA), which provides extensive resources on identifying safe and unsafe food packaging practices.

USDA Food Safety and Inspection Service

Frequently Asked Questions

No, rust does not cause tetanus. Tetanus is a bacterial infection caused by Clostridium tetani, found in soil and feces. The bacteria enter the body through deep wounds, not through ingesting rust.

Ingesting small flakes of rust (iron oxide) is unlikely to cause serious harm. You might experience some minor stomach irritation, but it is not considered poisonous in small amounts.

Check for signs of spoilage by pouring the beer into a glass. Look for a flat or off-taste, a metallic smell, unusual cloudiness, or a lack of carbonation (no "psst" sound upon opening).

While the alcohol in beer can inhibit some bacterial growth, it is not a reliable method to guarantee sterilization. If the seal is compromised, bacteria can enter and still cause spoilage.

The risk of botulism from a rusted beer cap is extremely low, as the conditions necessary for Clostridium botulinum to produce toxins are very specific and usually involve non-acidic, anaerobic environments. However, the general risk of contamination means a damaged container should be discarded.

If the rust is only on the outside and not on the rim or underside, you can wipe it clean before opening. To be extra cautious, pour the beer into a clean glass and check for any off-flavors or visual irregularities before drinking.

You can use expired beer for cooking if it still smells and tastes fine, as the cooking process will destroy microbes. However, if a rusty cap has caused a metallic, sour, or foul odor, it's best to discard it to avoid ruining the dish.