At Stone Creek Coffee, a pillar of our company is to Never Stop Learning. Let’s face it: as we grow older, it’s not always easy to change. When you’re used to doing things a particular way and you’re faced with learning, it’s not easy to accept new knowledge and to grow from it. After all, as the saying goes, “If it ain’t broke, don’t fix it.” So by that token, why not be stubborn and refuse to seek change? However, success is not born out of choosing to be stagnant or refusing to grow, but rather out of our humbly seeking to grow beyond that which we have already attained. In the past few years, humbly seeking to grow is precisely what Stone Creek Coffee has done in the face of new knowledge about workplace safety.

In 2015 and 2016, major media news sources began to pick up stories about the potential danger of a byproduct of coffee roasting called diacetyl (also known as 2,3-butanedione). Before this time, this potential danger was, by and large, unknown in the coffee industry and little information was shared about it by regulatory bodies that govern such workplace safety. By the time 2017 rolled around, and largely thanks to the media, this potential workplace danger was becoming more well known, and an issue that Stone Creek Coffee wanted to meet head on.

Rather than being behind the times, Stone Creek Coffee wanted to get ahead of them. At the time, we were unsure of what kind of can of worms we were opening, but diligently sought to learn all that we could and create a plan to move forward from it. In this article, we share our concerns about diacetyl in the workplace and disseminate what Stone Creek Coffee has done to protect its employees from its exposure, and how our commitment to Never Stop Learning has driven us as a company and called us to be better.

Diacetyl (2,3-butanedione) and 2,3-pentanedione

Over ten years ago, and long before it was on the radar of the coffee industry, the potential dangers of diacetyl exposure were shared all over the media when it became known that not only was diacetyl used in microwave popcorn to give it a buttery flavor, but dangerously so. In fact, the medical term ‘popcorn lung’ (known medically as bronchiolitis obliterans) is a direct result of the inquiry into the potential dangers of long-term exposure to the chemical at popcorn facilities. Since this initial inquiry, the scientific community, as well as our communities at large, have become more knowledgeable about diacetyl and its potential for harm.

What is diacetyl? A brief history and overview

The medical definition of diacetyl is, “a greenish yellow liquid compound (CH3CO)2 that has an odor like that of quinone, that is chiefly responsible for the odor of butter and contributes to the aroma of coffee and tobacco, and that is used as a flavoring agent in foods (as margarine)”.

Both interestingly and oddly enough, to this day if you search for the (non-medical) definition of ‘diacetyl’ on the internet, the search results by and large deal solely with the chemical additive, rather than the naturally occurring chemical compound that it is meant to mimic. In fact, OSHA’s (Occupational Safety and Health Administration) website definition simply reads, “Diacetyl (also called 2,3-butanedione) is a chemical that has been used to give butter-like and other flavors to food products, including popcorn.” There is no mention that diacetyl is a natural byproduct of fermentation, or that it is released by the process of roasting coffee. When this is mentioned, it is by news media sources acting as consumer watchdogs.

How and why is diacetyl potentially dangerous?

As was gleaned from the research into using diacetyl as a flavor additive from over a decade ago, diacetyl is unequivocally recognized as a potentially hazardous chemical when ingested. Diacetyl exposure is of particular concern for the respiratory health of those who are regularly exposed to it over long periods of time (i.e. factory workers who regularly come in contact with it). In fact, according to OSHA, severe respiratory tract injury has been observed in animals after “an acute inhalation exposure to butter flavorings. Severe respiratory tract injury, similar to that observed with butter flavoring vapors exposure, was also observed following acute inhalation exposures of rats to diacetyl or 2,3-pentanedione and repeated inhalation exposures of mice to diacetyl and rats and mice to 2,3-pentanedione.”

Further, NIOSH (National Institute for Occupational Safety and Health) has concluded that investigations of employees who suffer with obliterative bronchiolitis (aka ‘popcorn lung’) from diacetyl exposure in the workplace substantiate the claim that there is a causal relationship “between diacetyl exposure and the development of this disease”, and, moreover, “that an exposure is the likely cause of specific health effects.” Bronchiolitis obliterans is “a severe narrowing or complete obstruction of the small airways”. Additionally, NIOSH has expressed concern about 2,3-pentanedione, a chemical similar to diacetyl based on its structural similarities to it, and animal studies showing that it, too, “caused damage in the airways of animals, similar to that caused by diacetyl.”

How do you protect yourself and others from diacetyl exposure?

Luckily for us, we live in the twenty-first century, which is rife with rules and regulations that are meant to keep workers safe–and rightfully so. Both OSHA and NIOSH are government organizations that help oversee occupational safety in the United States of America and whose job is to protect workers from undue, hazardous exposures. OSHA is an agency of the United States Department of Labor, whose responsibility is to ensure safety at work and a healthful work environment for employees in the United States of America. NIOSH is a government agency responsible for conducting research and making recommendations for prevention of work-related illness and injury, whose parent agency is the CDC (Center for Disease Control).  Although OSHA does not yet have a legal, regulated requirement for diacetyl exposure limits in place, they share NIOSH’s safety recommendations for ‘acceptable’ exposure levels, which should act as a guide for companies who encounter diacetyl exposure in the workplace. These exposure limits are no more than 5 ppb (parts per billion) in a 8-10 hour time frame, or no more than 25 ppb in a 15 minute time frame, on average, for diacetyl, and no more than 9 ppb in an 8-10 hour time frame for 2,3-pentanedione.

NIOSH itself is an invaluable resource for evaluating the amount of diacetyl exposure in a given workspace. NIOSH works with companies to conduct research and assess the occupational safety of a given workspace where there is exposure or exposure to potentially dangerous chemicals. Not only do they access the overall exposure rates of a workspace over a period of multiple days, providing both initial checks and follow-up checks free of charge, but they also check the health of the employees that work in it, ensuring that workers are in good enough health to continue to work somewhere that they face exposure.

The coffee industry, as well as other industries, can use the safety recommendations of NIOSH as guidelines when creating a plan for achieving workplace safety. If a company is not complying with the guidelines, they must reassess their situation and resolve to find a solution that puts them under the exposure limits. It is essential for worker safety that these exposure limits are not exceeded.

Fortunately for many food manufacturing employers, there are immediate, relatively affordable measures they can take to protect their employees from diacetyl and 2,3-pentanedione exposure. One said measure is to have workers wear a NIOSH-approved “full-face air-purifying respirator with organic vapor cartridges and particulate filters”. This filters the air that workers breathe in and out if they work in an area that exposes them to diacetyl and 2,3-pentanedione. Additionally, employees who are exposed to these chemicals should change their clothes immediately after work to remove any residual chemicals left on their clothing from their body.

On top of changing clothes, keeping proper hygiene is also essential to the health of workers. Workers should regularly wash their hands throughout the day, especially when switching between tasks, and at the end of a shift to avoid transference of chemicals. Another, more invested, way to achieve workplace safety is to set up and regularly test the performance of an HVAC (heating, ventilation, and air conditioning) system in a given space. A properly managed HVAC system helps ventilate the air surrounding workers who are exposed to diacetyl and 2,3-pentanedione, and is able to achieve air quality optimization that puts it below the specified NIOSH exposure limits. When handling the liquid form of diacetyl, it is also recommended to wear chemical safety goggles and chemical resistant gloves.

Stone Creek Coffee: A case study in workplace safety


To further investigate ways to mitigate diacetyl exposure, this article uses Stone Creek Coffee and the updates the company has made as an example of how to properly protect workers from it. Stone Creek Coffee is located in Milwaukee, WI and was founded in 1993 by Eric Resch. Back in 1993, diacetyl was not yet a concern for the coffee industry. In fact, it wasn’t until over a decade later that problems with diacetyl became evident in the production of microwave popcorn, and over two decades later that the coffee industry caught on. However, a core principle of the company is to Never Stop Learning, and as soon as Stone Creek became aware of the potential dangers of diacetyl exposure, we were determined to learn more and take action in the face of new knowledge.

2016 & 2017

As soon as Stone Creek became aware of the potential danger, we began offering NIOSH-approved respirators to all production employees on an opt-in basis in 2016. Then, in February of 2017, Stone Creek enlisted the help of NIOSH to test the air quality and the health of their production workers. NIOSH tested the roasting facilities of Stone Creek Coffee for one week, collecting data that would glean insights into how much exposure employees were facing during this time. They collected samples from a broad array of areas throughout the facility, ranging from the Cupping Lab where coffee samples are roasted, to the production area where coffee is roasted and ground for production. When employees were tested to gauge their overall health, several tests were performed on them, including a spirometry test, which measures lung function and capacity.

Several months after the initial tests, Stone Creek was sent a general set of data that excluded names of employees, while individual employees were sent and received the results from their personal testing. Of the 15 areas where samples were gathered, 12 had higher than recommended exposure rates to diacetyl (recommendation is no more than 5 ppb), and 10 had higher than recommended exposure rates to 2,3-pentanedione (recommendation is no more than 9 ppb). Faced with these results, Stone Creek decided to pursue HVAC as our primary means of protecting workers from the potential dangers.


In the summer of 2018, Stone Creek worked with an engineer from the Sigma Group and technicians from Pure Mechanical on HVAC installation in order to further mitigate the potential threat of diacetyl exposure. By installing the appropriate ventilation and dampers in the facility, in conjunction with the afterburner which was already present in the facility, we were able to achieve more optimal air quality. Before definitively drawing this conclusion, we enlisted the help of NIOSH once again to come and re-test the air.


After the 2018 HVAC installation, in February 2019 NIOSH returned to Stone Creek Coffee. They tested the facilities once more to definitively conclude whether or not the HVAC installation was successful in its goal to protect employees from diacetyl exposure. NIOSH collected 57 area air samples in 19 locations throughout Stone Creek’s facility. Sampling locations were the same as they were in January 2017 (n=15) with the addition of four locations (behind small grinders, below large grinder, behind roasted bean destoner/hopper, and packaging area to right of grinders).

2017 vs 2019 results

In 2017, the average diacetyl concentration across all samples was 16.8 parts per billion (ppb) and the average 2,3-pentanedione concentration across all samples was 12.4 ppb. When the facilities were re-tested in 2019, the average diacetyl concentration across all samples was 4.0 ppb and the average 2,3-pentanedione concentration across all samples was 3.6 ppb.

NIOSH recommend no more than 5 ppb over a 40 hour work week over a 40 year work career on diacetyl and not more than 9 ppb over a 40 hour work week over a 40 year work career on 2,3-pentanedione. When the air was re-tested at Stone Creek in 2019, both the average diacetyl and 2,3-pentanedione concentrations were below these recommended exposure limits. With these results in hand, Stone Creek can confidently say that our work on our HVAC system proved successful in improving their air quality and workplace safety. The additional availability of respirators further protects employees from exposure as well.

What next?

Abigail Adams once said, “Learning is not attained by chance, it must be sought for with ardor and diligence.” Learning, after all, is not something that we just happen upon, but something that we humbly seek with a passion to grow beyond the knowledge we have already attained. It isn’t easy, and in many ways, is one of the most challenging things that we encounter in our day to day lives; and yet, with growing pains comes growth.

Over the past couple of years, we’ve done a lot of learning and growing at Stone Creek Coffee, and while that learning wasn’t always easy, and sometimes even painful, from it, we grew and are better for it. We are grateful for our learning, and look forward to a future filled with even more learning yet to come. We are continually arriving at and departing from our learning, and although that doesn’t always make the ground steady for footing, we wouldn’t have it any other way. We continue to trek ahead on our pursuit to Never Stop Learning, and invite you to do the same.

At Stone Creek Coffee, social responsibility is a foundational element of our identity. We believe that a commitment to the environment must coexist with other elements of social responsibility for a holistic approach to doing our best for the world and others.

Stone Creek Coffee will regularly audit and identify areas of environmental strength and weakness within the overall operations of the organization.  We will attempt to reduce any negative impacts to air, surface water, ground water, public health, community quality of life, and employee health while producing coffee that is sweet, clean, and juicy. Stone Creek Coffee will strive for continual improvement in pollution prevention while meeting or exceeding all regulations.

Jessica Sheridan, Director of Coffee 
As a mission-driven company, at Stone Creek Coffee, we believe in serving and enhancing the local communities we live and work in.

We believe that the socially responsible practices we apply daily in our internal operations can proliferate with the involvement of our stakeholders, customers, and our communities. In each community where our employees work and live, we — as Stone Creek Coffee and individual members of the community — actively create opportunities to play a positive role through various initiatives. These initiatives include support of important charitable organizations through monetary and/or material donations, promoting volunteerism, and more.

In line with our mission to be socially responsible, we also commit to the following: 

Serving Local Customers
  • We commit to serve at least 75% local and independent clients or customers. 
  • Local Hiring - As a company that is committed to its local community, at Stone Creek Coffee, we are also committed to local hiring.
  • Local Suppliers - We are committed to using local suppliers when possible.

Jessica Sheridan, Director of Coffee 

At Stone Creek Coffee, social responsibility is a foundational aspect of our identity. As such, we expect our partners and suppliers to conduct themselves and their business in an ethical, legal, and socially responsible manner including, but not limited to, their commitment to the environment, their employees, and the community. 

Legal Requirements

We expect that all suppliers know and follow the laws that apply to them and their business, as well as to treat the law as the minimum standard. 

Ethical Requirements - Integrity

At Stone Creek Coffee, we believe in conducting business with integrity and as a force for good. We expect our suppliers to operate fairly and ethically. Bribes, kickbacks, inappropriate gifts or hospitality, or other improper incentives in connection with Stone Creek Coffee are not tolerated. Suppliers are expected to avoid any conflict of interest relating to financial interests or other arrangements with our employees that may be considered inappropriate, and are to work with their own suppliers to promote business conduct consistent with the principles in this Code.

Labor Requirements 

Child Labor and Slavery - We do not tolerate child labor or slavery in our supply chain. Consistent with the United Nations Global compact principles, suppliers should avoid any sort of child labor in the business operations. 

Identification of Concerns - Suppliers are required to provide means for their employees to report concerns or potentially unlawful activities in the workplace. Any report should be treated in a confidential manner. Suppliers will investigate such reports and take corrective action if needed.

Wages and Working Conditions

Working Hours, Wages and Benefits - Working hours for suppliers’ employees will not exceed the maximum set by the applicable national law. Compensation paid to employees will comply with applicable national wage laws and ensure an adequate standard of living. Suppliers are expected to provide their employees with fair and competitive compensation and benefits. Compensation and benefits should aim at providing an adequate standard of living for employees and their families. Suppliers’ employees will be paid in a timely manner. It is recommended that suppliers offer their employees ample training and educational opportunities.

Diversity and Inclusion - Fair and equal treatment of all employees is expected to be a fundamental principle of all of our supplier’s corporate policies. Typical discriminatory treatment takes into consideration – consciously or unconsciously – irrelevant characteristics of an employee such as race, national origin, gender, age, physical characteristics, social origin, disability, religion, family status, pregnancy, sexual orientation, gender identity, gender expression or any unlawful criterion under applicable law. Suppliers will ensure that their employees are not harassed in any way. Stone Creek Coffee encourages its suppliers to provide an inclusive and supportive working environment while exercising diversity when it comes to their employees as well as in their decisions to select subcontractors.

Health, Safety, Quality, and Security

Health and Safety - In order to provide dignity and respect, we expect all of our suppliers to protect workers’ rights and provide safe and healthy working conditions. We encourage our supplier partners to foster an environment that is inclusive, and free of harassment and discrimination. 

Emergency Preparedness, Risk Information, and Training - Suppliers will make available safety information on identified workplace risks and suppliers’ employees will be correspondingly trained to ensure they are adequately protected. Suppliers will identify and assess likely and potential emergency situations in the workplace and minimize their impact by implementing emergency plans and response procedures.

Quality and Security - Suppliers are expected to have good security practices across their supply chains. Suppliers will maintain processes and standards that are designed to assure the integrity of each shipment to Stone Creek Coffee from its origin through to its destination and all points in between. Suppliers are expected to implement the necessary and appropriate measures in their area of responsibility to ensure that Stone Creek Coffee products, their workable components or raw materials as well as the corresponding know-how do not end up in the hands of counterfeiters or third parties and do not leave the legal supply chain.

Environmental Awareness 

Waste and Emissions - Suppliers will have systems in place to ensure the safe handling, movement, storage, recycling, reuse and management of waste, air emissions and wastewater discharges. Any of these activities that have the potential to adversely impact human or environmental health will be appropriately managed, measured, controlled and handled prior to release of any substance into the environment. Suppliers will have systems in place to prevent or mitigate accidental spills and releases into the environment.

Resource Conservation and Climate Protection - Suppliers are expected to use natural resources (e.g. water, sources of energy, raw materials) n an economical way. Negative impacts on the environment and climate will be minimized or eliminated at their source or by practices such as the modification of production, maintenance and facility processes, material substitution, conservation, recycling and material reutilization. Suppliers will engage in the development and use of climate-friendly products and processes to reduce power consumption and greenhouse gas emissions.

Preference to Purchase from Local Suppliers and Suppliers with Ownership from Underrepresented Populations - At Stone Creek Coffee, we are committed to our community and the environment. As such, we have a preference to purchase from local suppliers when possible, as well as to purchase from suppliers who support other local suppliers. We also give preferences to suppliers with ownership from underrepresented populations.

Supplier Audits and Record Keeping - In order to make responsible, well-informed business decisions and disclose truthful and timely information to our stakeholders, we expect our supplier partners to maintain accurate and honest records.  In line with this, we expect our supplier partners to do the following: maintain books and records that reflect all transactions in an accurate, honest, and timely way; employ appropriate quality audit and compliance processes for matters such as product and food safety, worker health and safety, and labor and employment; to enable traceability, disclose the location of facilities and known origins of materials upon request/audit.

When screening potential suppliers, we screen for the following:
  1. Compliance with all local laws and regulations, including those related to social and environmental performance
  2. Good governance, including policies related to ethics and corruption, as well as diversity and inclusion
  3. Positive practices beyond what is required by regulations (e.g. environmentally-friendly manufacturing process, excellent labor practices, performance to the Core Commitments, etc.)
  4. Third-party certifications related to positive social and/or environmental performance (B Corp certification, Bird Friendly, etc.)
  5. Local suppliers should be given preference (within 250 miles of Factory)
  6. Suppliers owned by underrepresented populations should be given preference

Jessica Sheridan, Director of Coffee 

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Marich Confectionery
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Milwaukee Candle Company
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