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FAQ: Diacetyl and Coffee

Understand the science behind this naturally occurring compound.

What is diacetyl?

Diacetyl is an organic compound that is created naturally during certain cooking and fermentation processes. It has a distinct buttery flavor and aroma. Diacetyl naturally occurs in the production of butter (in fact, giving butter its flavor), cheese, milk, yogurt, whiskey, wine, beer, vinegar, roasted coffee, processed tomato products, and citrus juices. 

Until recently, artificial diacetyl was added to some processed foods to impart a buttery flavor, and is still applied to flavored e-cigarettes vapes. More study is needed to understand the potential implications of using artificial diacetyl in these contexts. 

For the science geeks out there, diacetyl goes by the chemical formula CH3CO. It is also known as the alpha-diketone 2,3-butanedione, or by its Chemical Abstracts Service (CAS) number, 431-03-08.

Is diacetyl in coffee?

Diacetyl occurs naturally in unflavored coffee as a byproduct of the process of roasting coffee beans. Commercial roasting and grinding of beans can release diacetyl into the air along with other volatile compounds in the workplace.

What are the concerns for coffee drinkers?

There are no diacetyl-related risks in drinking coffee (or in eating cheese, sipping wine or drinking orange juice). The U.S. Food and Drug Administration (FDA) says diacetyl in foods and beverages is safe to consume.

Media reports have raised unfounded concerns about diacetyl exposure levels from the process of roasting and grinding coffee in commercial settings, although not at home. Coffee preparation, from grinding the beans to extracting the brew, is safe for consumers (in fact, regular consumption is scientifically linked to many potential wellness benefits).

Are coffee workers safe?

During commercial-scale coffee roasting and grinding, some diacetyl can be emitted into the surrounding air. To ensure worker safety, there are well-established safety protocols and procedures that should be followed to monitor exposure and reduce risk.

Scientific evidence does not support a link between  natural diacetyl exposure in coffee production and obstructive lung disease, including an extremely rare lung disease, bronchiolitis obliterans (also known as “popcorn lung” because it was initially discovered in popcorn factory workers exposed to high concentrations of the liquid, artificial chemical).

Independent research published in 2015 confirms that airborne concentrations of naturally occurring diacetyl in coffee processing “are far below the concentrations that are expected to cause even minimal responses in the human respiratory tract.” 

(Please see the list of resources below to learn more.)  

What is the industry standard for diacetyl exposure?

Currently, the U.S. government has issued no regulatory standard, such as an Occupational Exposure Limit (OEL), for levels of diacetyl. The numbers proposed by various governmental and scientific organizations vary widely: 

  • National Institute for Occupational Safety & Health (NIOSH): 5 parts per billion (ppb) over an 8-hour workday, or 25 ppb during a short-term, 15-minute exposure.
  • American Conference of Government Industrial Hygienists (ACGIH): 0.01 parts per million (ppm), which is 10 ppb, over an 8-hour workday, or 0.02 ppm, which is 20 ppb, during a 15-minute exposure. 
  • Toxicology Excellence for Risk Assessment (TERA): 0.2 ppm, which is 200 ppb, over an 8-hour workday.

Remember, every coffee roasting facility is different. The conditions affecting diacetyl exposure vary widely, from ventilation to equipment to production process. Diacetyl levels can also vary in different areas of any given facility.

We encourage all organizations to learn more, follow suggested best practices (see the resources listed below), and take informed action to do what is right for you. 

Providing a safe workplace for everyone is our top priority, and the NCA will continue to monitor any new information on this issue.

How can coffee roasters effectively control diacetyl levels?

Commercial coffee roasting machines are generally “closed systems” that are built to channel the natural byproducts of roasting through closed pipes to exhaust stacks. Even the “cooling carts,” where coffee beans cool after roasting (as the name implies), are designed to minimize potential exposure. A system of fans and holes in the bottom of these trays draw the air down through the beans, and then out via exhaust pipes to the outside.

For more information, please see the following resources. 

Resources & Tools for Your Business

Respiratory Health and Safety in the Flavor Manufacturing Workplace, Flavors & Extracts Manufacturing Association (FEMA)

Best Practices: Engineering Controls, Work Practices, and Exposure Monitoring for Occupational Exposures to Diacetyl and 2,3-Pentanedione, U.S. Centers for Disease Control (CDC)

Diacetyl and Food Flavorings, NIOSH Science Blog

Research: Naturally occurring diacetyl and 2,3-pentanedione concentrations associated with roasting and grinding unflavored coffee beans in a commercial setting, Toxicology Reports, 2 (2015), pp. 1171-1181


The NCA Statement on Diacetyl 


This is an ongoing conversation that will be updated should more information become available. 

For advice specific to your coffee roasting facility, please consult with a qualified specialist such as a qualified Industrial Hygienist. Other comments or questions? Contact us.