Coffee contains carbon monoxide

almost had a heart attack this week when I opened a bag of coffee beans in the same room as a carbon monoxide (CO) detector. Within seconds the detector started screaming and flashing. It was pegged at over 1000 ppm (parts per million), over 20 times the OSHA maximum allowable limit of 50 ppm for continuous exposure in air.

Carbon monoxide detection This detector started alarming almost immediately when placed at the opening of a freshly opened bag of coffee beans and was pegged at >1000 ppm CO (shown by the ‘HHHH’). A can of ground coffee was even higher, remaining above 1000 ppm for several minutes. Luckily the detector wasn’t ruined.

Ground coffee was even worse. A freshly opened plastic container of ground coffee also pegged the meter. After I moved the detector into the next room to prevent the sensor from being damaged by the high levels of CO, the meter gradually decayed to zero over a period of five minutes, suggesting that the level was higher in ground coffee than in the beans. The atmosphere above a half full jar of iced coffee that had been in my refrigerator for about a week also showed about 430 ppm of carbon monoxide. This is also in the hazardous range.

Carbon monoxide is not to be confused with carbon dioxide (CO₂), which is much less dangerous.

CO rapidly dissipates from an open container. After one hour outside, the level at the top of the bag containing beans had dropped to 120 ppm. After being left overnight, CO was below the minimum of 1 ppm. Sadly, the coffee aroma was also greatly diminished (though I didn’t get very close.)

The good news was that there was no detectable hydrogen sulfide or explosive vapors any sample. There were only 29 ppm of carbon monoxide in a freshly opened box of 48 tea bags. And the readings were zero for milk.

Diet soda caused the low oxygen alarm to go off, as did breathing on the sensor, but no CO was detected in either sample.

A bag of coffee beans that had been opened six months ago showed no reading, as did a plastic container of coffee that was about two years old (I rarely drink coffee these days, having mostly switched to tea). But tea is no picnic either. If you put lemon in tea and drink it hot, it could gradually dissolve the enamel on your teeth. And both coffee and tea will stain your teeth if ingested hot.

Deadly Colombian Arabica Beans? This product is known to the State of California to contain chemicals that may cause jitteriness, wakefulness, and increased ability to perform boring tasks, and oh yes, I almost forgot, it’s packed with carbon monoxide

Are you taking your life in your hands by drinking coffee?

Unfortunately, if you slapped a household carbon monoxide detector up against a cup of coffee or even a container of coffee grounds, it would show ‘0.’ This is because commodity CO alarms are designed to make certain never to give a false alarm. This is done by strongly damping the time response and by suppressing any readings below 100 ppm. The detector I used was NIST-calibrated and was designed for industrial R&D and professional field use. In retrospect, I should have bought the extra pump and the stainless steel probe. This would have made measuring the exposure to those deadly Colombian Arabica beans a little safer.

It’s easy to make jokes, but the risk of inhaling coffee aroma is quite real. And to be honest, I’ve always had my doubts about those baristas at Starbucks. They always look a little dizzy to me.

Those drinking water test strips are also questionable, at least for lead. Most people never notice, but the minimum detectable limit for lead on those strips is 20 ppb, while the trigger level for lead in drinking water is 15 ppb. The industry knows about this problem and they’re working on more sensitive lead detectors.

Household bathroom scales are even worse. Most of them are programmed to show the same weight if you weigh yourself again within five minutes or so. The purpose is to make you think they’re accurate when they’re really not. On an analytical instrument, if you weigh something twice you rarely get exactly the same reading. There is always noise.

The human body produces carbon monoxide

The body produces small amounts of many toxic gases, including nitric oxide, hydrogen sulfide, and carbon monoxide. These molecules are neurotransmitters, sometimes called gasotransmitters, and they’re important for brain function. Endogenous CO is produced by heme oxygenase, which catalyzes the breakdown of heme to CO, reduced (ferrous) iron (Fe²⁺), and biliverdin.

This is not a new discovery. Roasted coffee beans emit so much carbon monoxide that the US CDC says coffee is a potential respiratory hazard for workers in the coffee industry. Sealed cans of ground coffee can bulge over time as CO and aromatic gases are released. Coffee also releases α-diketones including diacetyl and 2,3-pentanedione ^[1], the molecules that cause the infamous “popcorn lung” from inhaling microwaved popcorn fumes. The function of CO in the body is not known for certain. One theory is that CO could be involved in heat stress response. ^[2,3]

How do plants produce carbon monoxide?

CO is a signaling molecule in plants.^[4] Plants are believed to produce CO the same way humans do: by heme oxygenases.^[5] There are alternative theories. One study ^[6] hypothesized that flavonoids such as quercetin and 2,3-dehydrosilybin could release CO upon exposure to light. Another theory is that CO release is caused by reactive oxygen species produced by UV exposure. Plants can also absorb CO from air and detoxify it with cytochrome p450.

Many other plants besides coffee and tea, including Pinus halepensis (Jerusalem pine) trees, produce CO.^[4] It is thought that this protects the plant against stress.

Carbon monoxide releasing drugs

CORMs, or carbon monoxide releasing molecules, are drugs designed to release small amounts of therapeutic CO. They were thought to reverse diet-induced obesity in mice.^[7] An example is CORM-401, which was said to reduce inflammation. There are also claims that CORM-401 induces nitric oxide (NO) release and that it raises body temperature by activating thermogenesis and also lowers white adipose tissue mass. It also supposedly elevates serum corticosterone levels.

However, these claims are controversial. An influential paper ^[8] was sharply critical of CORM-2, -3, -A1, and -401 and suggested that their effects were not due to CO but to the molecules the CO was complexed with.

One interesting question: does the CO from coffee ingestion benefit humans by supplementing the CO produced by the body, or does it work against the caffeine effect?

sep 03 2026, 5:05 pm