Coffee roaster diacetyl exposure refers to workplace inhalation of airborne diacetyl, 2,3-pentanedione, and related alpha diketones released during coffee roasting, grinding, flavoring, packaging, or other coffee production work.
Diacetyl is a naturally occurring chemical that can form in small amounts during coffee roasting, but it may also be present in larger concentrations when flavoring manufacturers add buttery or other flavors to food products.
The concern is not drinking coffee.
The concern is repeated workplace exposure to airborne diacetyl or other compounds that workers may inhale on a daily basis in a coffee production facility, especially in roasting rooms, grinding areas, packaging lines, storage bins, or other areas where roasted coffee and ground coffee release vapors into the air.
Coffee roaster diacetyl exposure has been linked to flavorings related lung disease, including popcorn lung and bronchiolitis obliterans.
These conditions can cause serious lung damage, reduced lung function, and, in severe cases, the need for oxygen support or a lung transplant.
Diacetyl and 2,3-Pentanedione in Coffee Processing
Diacetyl and 2,3-pentanedione are volatile chemical compounds that can be produced naturally during coffee roasting.
Diacetyl occurs naturally in many foods, including coffee beans, butter, dairy products, wine, and other food products.
In coffee processing, these substances can be released from roasted coffee beans during roasting, grinding coffee, flavoring, packaging, and storage.
2,3-pentanedione is chemically similar to diacetyl and has been studied as a related workplace inhalation hazard.
These compounds are sometimes discussed together because both have been linked to respiratory health risks in occupational settings.
Coffee workers may encounter diacetyl and 2,3-pentanedione from:
- Roasting coffee beans;
- Grinding roasted coffee;
- Packaging whole bean or ground coffee;
- Opening or working near storage bins;
- Handling flavored coffee products;
- Mixing liquid or powdered flavoring chemicals;
- Cleaning roasters, grinders, hoppers, or packaging machines;
- Working near concentrated emissions in enclosed production areas.
The coffee roasting industry has received increased attention because diacetyl and 2,3-pentanedione can be produced naturally during roasting, even in unflavored coffee.
Added flavors may create additional exposure concerns in facilities that manufacture flavored coffee.
How Roasting, Grinding, Flavoring, and Packaging Can Release Airborne Chemicals
Roasting coffee beans changes the beans chemically and physically.
During roasting, heat can form volatile organic compounds, including diacetyl, 2,3-pentanedione, carbon monoxide, carbon dioxide, and other airborne substances.
After coffee beans are roasted, they can continue to release gases and vapors.
Grinding coffee can release compounds trapped inside the roasted coffee, and packaging can concentrate those emissions near workers’ breathing zones.
Flavoring operations may create higher risk when employees handle liquid flavoring chemicals, pour flavoring into drums, or work near flavoring equipment without adequate controls.
Airborne chemical exposure may occur when workers:
- Open roasters after a batch is complete;
- Work near cooling trays or bins;
- Grind roasted coffee in enclosed grinding areas;
- Package ground or whole bean coffee;
- Work near bagging machines;
- Add or mix flavoring chemicals;
- Enter rooms where vapors collect;
- Clean production equipment after roasting or flavoring.
These chemicals may be present in low concentrations in some workplaces, but high levels can occur depending on production volume, ventilation, equipment design, product type, and the location of workers in relation to emission sources.
Why NIOSH Investigated Coffee Roasting Facilities
NIOSH investigated coffee roasting and packaging facilities after detecting airborne diacetyl and 2,3-pentanedione exposures among workers, including in facilities that did not produce flavored coffee.
Coffee became a focus because diacetyl can form naturally inside coffee beans during roasting through the Maillard reaction, which occurs when sugars and amino acids react at temperatures above 200°C.
Diacetyl production may increase with darker roasts, but roasted coffee beans meant for consumption are not considered a risk to consumers.
The concern is occupational inhalation: workers may repeatedly breathe concentrated emissions during roasting, grinding, packaging, flavoring, or storage-bin work.
NIOSH evaluations found exposure patterns that led to recommendations for ventilation improvements, air monitoring, medical surveillance, and respiratory protection.
Unflavored Coffee Can Still Produce Diacetyl
Many people associate diacetyl exposure with added flavorings, but unflavored coffee can also release diacetyl and 2,3-pentanedione during normal production activities.
Research cited by NIOSH has found that these compounds are naturally produced during the coffee roasting process and released into the air during roasting, grinding, packaging, and storage operations.
Grinding roasted coffee beans can further increase airborne emissions by creating additional surface area for gases and volatile compounds to escape.
NIOSH investigations and exposure studies have identified measurable levels of diacetyl and 2,3-pentanedione in facilities that handled unflavored coffee, demonstrating that flavoring additives are not the only potential source of worker exposure.
For that reason, occupational health concerns in coffee facilities often focus on inhalation exposure during production rather than whether a coffee product contains added flavors.
