Oyster mushroom cultivation using spent coffee grounds and hardwood sawdust

Final report for FNE17-874

Project Type: Farmer
Funds awarded in 2017: $14,994.00
Projected End Date: 05/15/2019
Grant Recipient: Firefly Farm
Region: Northeast
State: New York
Project Leader:
Renee Jacobson
Firefly Farm
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Project Information


Our project question was "Can spent coffee grounds be used to successfully grow oyster mushrooms for commercial sale and what ratio of coffee grounds to oak sawdust produce the optimal yield?"

With delays due to initial contamination with Trichoderma, we were able to start the trial in the fall of 2017.  Trichoderma was nearly eliminated with changes in the process of sterilization, drainage of the sterilized medium, better personal sanitation, improved positive pressure airflow and use of plastic steroclavable bags. Additionally, a repeatable process for mixing media with a tumbling composter, ease of filling bags, and steroclaving medium was developed resulting in medium entering the inoculation area sufficiently sterile to provide a clean base for mushroom inoculation. In addition, the upending of the steroclaved bags to drain freely on top of a rack proved important in providing a better moisture content for a successful spawn run. Having the bags drain for a minimum of 30 minutes after steroclaving removed excess moisture introduced during the steroclaving process.  Excess moisture increases the likelihood of anaerobic activity at the bottom of the bag leading to reduced yield due to competition with foreign microbes.

Using a mixture of 25% to 50% of coffee grounds provided a reliable production of mushrooms and a reliable second fruiting.  The 50% coffee ground mix produced the greatest yields and the most reliable second flush of mushrooms, and usually a third flush.  The 50/50 mix of coffee grounds and sawdust with 2 TBS of baking soda per 15 liter bucket provided the greatest number of usable bags of inoculated medium as well as the longest lasting bags for mushroom fruiting.  For easier conversion, use 30 grams of baking soda for each 15 liter bucket of coffee grounds containing filters and each 15 liter bucket of oak sawdust.  For a complete batch, use 2-15 liter buckets of coffee grounds with filters and 2-15 liter buckets of oak sawdust per batch and 120 grams of baking soda (8 TBS).  Mix thoroughly and remove all filters before bagging raw medium for processing.  Yields will vary greatly per bag but average around 1 pound of fresh mushrooms per 6 pound bag of medium.

There was farmer-to-farmer outreach with an on-farm tour, through Cornell Cooperative Extension, and a webinar which became a Youtube video available at: http://www.youtube.com/watch?v=ui5eK7Qb5So&t=32s

Project Objectives:

The goal is to find an optimal mixture of spent coffee grounds to hardwood sawdust that yields the greatest amount by weight of oyster mushrooms to make this crop profitable. Additionally, using amendments to these mixtures to improve yield and quality was studied. The initial intent was to have cultivators created by obtaining 15 liter plastic buckets from local grocery stores, drilling holes for air exchange, sterilizing and filling them with inoculated medium, and ultimately observing their yield. After inoculation, it is necessary to conduct at least weekly observations during the spawn run to detect if contamination from Trichoderma is occurring. Trichoderma is a genus of fungi that competes with the mushrooms for resources thus reducing yield. Contaminated cultivators needed to be culled to prevent spreading of contamination. The amount of culled buckets was logged and taken into account when determining profitability. Insect control is critical to reduce the spread of contamination. Sticky traps made from Tanglefoot insect barrier was used along with window and door screens to help reduce insects.

It was proposed that trials would be conducted by varying the ratio of spent coffee grounds to hardwood sawdust as well as trials using the optimal coffee ground to oak sawdust ratio determined above with additions of gypsum or sodium bicarbonate.

Using plastic buckets proved to be too cumbersome and were especially difficult for harvesting second or third flushes of mushrooms due to shrinkage of the medium inside the bucket.  Filling the buckets with sterilized medium added a step where contamination frequently occurred causing loss of that trial.  Therefore, the use of buckets was not conducive to obtaining data for this experiment.  Switching to plastic steroclave bags was necessary to conduct the experiments.  This switch proved to be beneficial in reducing contamination and providing more consistent results.

A second change to this project was to abandon finding the optimum amount by weight of gypsum.  Literature had indicated that a range between 0.5 and 5% was used by others and an objective to find the optimum was planned.  However, there was excessive humidity during the growing seasons of 2017 and 2018 preventing the coffee grounds from being air dried quickly enough to prevent mold from significantly infecting the coffee grounds making them unusable.  Thus a dry weight of the coffee grounds was not able to be determined leading to an inability to determine by weight the amount of gypsum to be used.  Without proper drying equipment, this part of the experiment had to be abandoned.


The research objective is to determine if coffee grounds can be successfully mixed with oak sawdust to produce enough mushrooms to create a profitable agricultural enterprise as well as determine the optimal amount of coffee grounds to oak sawdust needed for optimal yields.  Spent coffee grounds are typically added to the garbage at coffee shops which results in the coffee grounds ending up in landfills.  These coffee grounds produce methane upon decomposition leading to increased methane levels in landfills which tend to escape into the atmosphere.  Instead, coffee grounds can be intercepted at the coffee shop and used to produce mushrooms, providing a food source, a source for compost (the spent mycelium), and improving the environment by reducing methane emissions form landfills.  Additionally, it was found that the taste of mushrooms grown in coffee is superior to those grown only in sawdust.

Preliminary data by Firefly Farm from 2016 shows the potential to profitably grow oyster mushrooms on a mixture of spent coffee grounds and oak sawdust yielding up to 5 pounds of mushrooms per 15 liter cultivator. Online research, including those recommended by SARE, provided no information on using a combination of spent coffee grounds and sawdust mixtures. Other growers, Tradd Cotter [2] and Steve Gabriel [3], mentioned the use of these items together but had not yet gathered research data into their use. Both have indicated that the use of coffee grounds leads to low production yield due to excess nitrogen and acidity. Field and Forrest staff [4] have likewise stated that growing only on spent coffee grounds provides inconsistent and low yields thus not a path to a viable source of farm income. Finding an optimal mixture for production yield and quality would help assist small growers to address an emerging and rapidly growing market, increase farm product diversity, provide real-world information for high mushroom production yield, and grow a crop that tastes better than using sawdust alone. It also removes a nutrient-rich material from the waste stream. Yet there are challenges: 1) contamination by Trichoderma, a genus of fungi that competes with the mushroom fungi for resources thus reducing yield; 2) moisture content being too high creating a potential for anaerobic bacteria; 3) pH being low thus promoting undesirable fungi and bacteria.

Indoor cultivation of oyster mushrooms requires mixing spawn with growth medium and placing it into a container for the spawn run, and ultimately fruiting. With these experiments, varying amounts of spent coffee grounds and oak sawdust were mixed together as outlined in the methods and measurements section to determine optimal mixture for highest yield. Once this was determined, experiments were conducted using this optimal mixture with gypsum to stabilize the mixture or chemically buffering the mixture with baking soda to see if yield could be further improved.

Gypsum is not a liming agent and does not have an affect on the pH. It does have the potential to positively affect the mixture by adding minerals and improving water holding capacity. [5] The use of baking soda determined if raising the pH of the mixture increases yields. Baking soda (sodium bicarbonate), a buffering agent, increases the pH of the mixture helping to neutralize the acidity of the spent coffee grounds. Finding a mixture that consistently improves yields is needed to make the use of spent coffee grounds reliable and profitable.

1. “Chemical, Functional, and Structural Properties of Spent Coffee Grounds and Coffee Silverskin,” Food and Bioprocess Technology, December 2014, Volume 7, Issue 12, pp 3493–3503
2. Tradd Cotter, Mushroom Mountain, private communications
3. Steve Gabriel, Wellspring Forest Farm & School, private communications
4. Field and Forest Products, Kozuzek Road, Peshtigo, WI 54157, suppliers of mushroom spawn and
cultivation supplies, private communications
5. Fisher, M. (2011), "Amending soils with gypsum," Crops & Soils Magazine, November-December 2011.


Click linked name(s) to expand/collapse or show everyone's info
  • Michael Lanahan
  • Steve Gabriel - Technical Advisor (Educator)
  • Roger Ort (Educator)
  • Ariel Kirk (Educator)
  • Shona Ort (Educator)


Materials and methods:

Site Preparation:

Choosing a site depends upon the resources available.  The site available at Firefly Farm of Hornby is a small four season room that can be partitioned off into three sections.  Every attempt has been made to create an environment that can be easily cleaned and disinfected, provide air movement, air turnover, humidity control but not air cooling. Caulking around windows and any areas that can provide infiltration of mold and competitor fungi have been done. In turn, caulking helps reduce moisture build up in walls and moisture movement around windows. This step can be time consuming and fraught with delays when working with an existing building and contractors.  Placing partitions inside large existing buildings is quicker and more cost effective than having to retrofit a smaller space to create a controlled environment.  The partitions were framed wood with plastic sheet as the walls.

When choosing space, consider the requirements for efficient and effective production.  The space will need to tolerate humidity near 95%, provide the ability for air exchange with large fans, have access to electricity, as well as a water supply and sewer drain.  It needs to provide enough work space to maneuver considerable amounts of materials including an easy way to removal of all mushroom material once it is no longer fruiting.  The entire area has to be periodically cleaned and sprayed with 99% isopropyl alcohol, OMRI approved sanitizer and or other OMRI disinfectants.

Using The New Site:

Each mushrooming facility will require a minimum of six areas: medium preparation, medium sterilization, inoculation, spawn run, fruiting area, and compost site.  The spawn run can be part of the inoculation area if there is not an option for a separate area with the assumption that the area can be kept very clean.  However, a separate area is ideal.

With my facility, space is limited so the spawn run is located in the same area as the spawn inoculation.  This area has positive pressure to help reduce mold and fungal contamination. It was found, that even with clean room techniques being applied, the first inoculation attempts were contaminated. The process of sanitizing/sterilization and the process of inoculating prepared medium need greater examination to evaluate potential sources of contamination.  Commonly observed contaminates are Trichoderma species and white molds similar in visual appearance to molds found on raspberries.  2017 was a very wet year which may be adding excess spore load to the air creating a greater chance for spore to hitch hike into the inoculating room.

By October of 2017, contamination issues had been successfully dealt with reducing lost inoculated medium to less than 2%.  A switch from steroclaving bulk medium and filling plastic buckets to mushroom bags was the step change to get to this low level along with several additional steps.  First was making certain there is air space in the center of the steroclave for better sterilizing as well as providing draining to the bags after steroclaving nearly eliminated contamination issues.  Second, the use of both 99% isopropyl alcohol, an OMRI-approved sanitizer, and a clean room suit reduced contaminates.  Thirds, dedicated shoes for each of the tree rooms also greatly reduced contaminants being tracked around.  It was found that there is no such thing as being to cautious when looking at sources of airborne, person-born and medium-born contaminates.  The closer attention payed to each detail reduces the likelihood of failure due to contamination.

Medium Preparation:

Based on conversations and written information as well as field use of hardwood logs, oak sawdust was chosen for baseline data with the belief that it will colonize without contamination issues once the sawdust has been sterilized in a steroclave by following manufacturers directions.  Results to date show that contamination of oak sawdust occurs quickly while colonization of oyster mushroom target spawn occurs slowly. Thus, the oyster mushroom spawn cannot out-compete the potential contamination. Medium preparation has been revisited and found to be sound.  More research both online and in contacting other mushroom growers as well as spawn sources indicate that oak alone is not an adequate medium for the spawn run.  This ran counter to what had been learned prior to attempting the use of oak sawdust alone.  This was due to getting advise with important parts omitted, e.g., "I grow on oak" instead of "I grow on oak and soybean hulls augmented with proprietary ingredients." This is perhaps due to the desire to hold on to the secrets of medium recipes.  The point of this research is to create an openly available medium recipe that is likely to produce positive results that can be passed on to other growers.

Project Trials:

Trial runs were done in July and August of 2018.  These runs showed that there was still airborne contaminates that needed to be further reduced.  Taping of all potential cracks with duct tape was done to reduce blow back from the fruiting room and new trials began using steroclavable mushroom bags.

During October and November of 2018, trials with 1/3rd spent coffee and 2/3rd oak sawdust were completed.  With changes in the process of sterilization, drainage of the sterilized medium, better personal sanitation, improved positive airflow and use of plastic steroclavable bags, there has been a near elimination of Trichoderma contamination. It was unfortunate that recycled plastic buckets needed to be abandoned for commercial use.  They are still viable for hobby and home production.

During the harvest phase of each experiment group, it quickly became clear that adding 1 TBS of baking soda per 15 liter bucket of medium was too little as Trichoderma tended to form more readily in the fruiting room leading to bags needing to be removed from production.  Using 3 TBS per 15 liter bucket of medium tended to cause excess moisture to be held in the medium creating a layer of anaerobic activity in the bottom of the bag.  This reduced yields and provided a greater chance for Trichoderma contamination to occur early in the fruiting process leading to bag removal before fruiting completion.

Current Methods:

The coffee grounds are collected at a local coffee shop in 15 liter buckets. The sawdust is measured by filling 15 liter buckets with dry sawdust then added to the tumbler. Rotating of the tumbler is done to help mix the wet coffee grounds and dry sawdust. Tumbling and removal of filters is done during this mixing time.  Once all filters are removed, the baking soda is sprinkled into the mixture and the tumbler rotates for a minimum of 13 times which tends to provide adequate even mixing of the three components. Water is added as needed to create a moisture content just short of field capacity when thinking of soil moisture content.  If water can be squeezed out of the medium, too much has been added.  The medium is checked to see if it appears evenly mixed and felt to see if it is too dry.  If it appears dry, water is added.  Drain holes are located in the compost tumbler allowing excess water to drain via gravity thus reducing the risk of the medium being too wet.  If the mixture is too moist, allow the water to drain freely from the holes in the bottom of the tumbler. No moisture readings are conducted at any time.

Steroclavable, gusseted, polypropylene bags with a filter disc to allow gas exchange between culture and outside environment are used. Bags measure 7.75" x 5" x 19.5".  These bags are filled with approximately 26 cups of loose medium, closed with a rubber band (but not tightly so air can escape), and placed four at a time into a 45 quart steroclave.  It is important to close the bags to reduce the build up of moisture condensation in the medium during the steroclaving process.  In addition, it is imperative to have air space in the center of the steroclave from the top to the bottom in order thorough heating and proper sterilization to occur.  Failure to leave this air space reduces the effectiveness of the sterilization process and can lead to medium containing viable contaminates that grow very successfully under ideal mushroom spawn run conditions.

Follow the manufacturer's steroclave instructions. It does not harm the medium to undergo longer than minimum required sterilization. It does however lead to viable contaminates existing in the medium if any steroclave step is shortened in its duration.  Once the medium has been completely steroclaved, follow manufacturers directions to open and remove the sterilized medium.  Move the steroclave insert to the inoculation room. Place the bags upside down in a large plastic container fitted with a rack.  Leave the bags this way until they are cool (below 100 degrees F).  This allows for any excess moisture to leave via gravity thus providing an idea moisture level for the spawn run.

Once cool, the bags can be inoculated.  At any time that the inoculation room is to be entered, it is imperative to be as clean as possible. Wash, wear new, clean clothing and spend minimal time in the inoculation room unless a clean room suit, gloves and hair cover have been put on.  When inoculating be sure to spray gloves, wrists, lower arms, ankles and feet with isopropyl alcohol to help reduce contaminates that have been introduced by entering the inoculation room.  Use a sanitizer solution to spray the floor as well.  From time to time (at least once per month) or any time that it is thought that the room has been compromised with contamination, spray the walls, ceiling, and all objects with isopropyl alcohol followed by sanitizer to aid in reducing airborne and surface contaminates.  The spawn run will indicate the success of the clean room procedures by showing visible signs of contamination.  At any time during a spawn run if a bag appears to be contaminated, it must be immediately removed and the cleanliness of the inoculation room examined and the cleaning processes reviewed.  The human entering the room is the greatest source of contamination.  This cannot be understated.

Inoculating involves the following steps: spraying the stainless steel table with isopropyl alcohol; moving the bagged medium from the plastic bin to a stainless steel table; spray tops of the bag with isopropyl alcohol; place the bagged spawn on the table and spray the outside of the bag with isopropyl alcohol; open the bag with sterilized scissors or a razor blade; use a sterilized stainless steel measure cup and place it in the spawn bag; open the medium by removing the rubber band; place the bag on the side and press down on the side so that space is created; tip the bag up slightly and add 1 to 1 1/2 cups of spawn to the side of the bag; place the cup immediately back into the spawn bag; seal the inoculated bag with your favorite sealing method; shake the bag to help distribute the spawn; press down on the top to compact the medium to the point where it stays standing upright looking like a large block; label and set on a rack to grow a spawn run leaving about 1 to 2 inches between bags.  This appears to be a lengthy process but only takes about 2 to 3 minutes per bag.  Spray any surfaces, the cup, hands and clothing every few bags to help reduce airborne contaminates that are landing on you or the cup as it travels from the spawn bag to the medium bag.  Be sure to wear gloves and if smelling isopropyl alcohol wear a proper mask for personal safety.  If sick, be sure to wear a mask to prevent contamination of the inoculated medium.

Leave the bags on the shelves and visually inspect once a week.  Healthy bags will show white fuzzy growth within 1 to 3 days after inoculating and take 3 to 5 weeks for the spawn run to be completed, depending upon the amount of spawn used during the inoculation phase.  Once the spawn run appears to be near completion, bags can be prepped for fruiting by creating holes in the bags for the mushrooms to emerge through.  This can be done in many ways from using a nail to punch holes about every 2 inches around the bag, by cutting off the top of the bag or by cutting X holes in the bag with a razor blade.  It was found that the initial fruiting was most aggressive when cutting the tops of the bags off but resulted in drying of the mushroom block and subsequently leading to poor second flushes.  Nail holes also produced too small of areas for large pinning clusters to emerge from.  The X pattern has given the best results in fruiting for these experiments to date.  It is clear that there is substantial variability in procedures that can be done during the pinning and fruiting stage of the mushroom production and one must choose what they are most comfortable using.

Harvesting needs to be done up to twice per day when fruiting is occurring to catch mushroom clusters at their optimal weight and quality.  Airflow and humidity must be monitored and adjusted as needed due to changes in the amount of carbon dioxide that is being given off by the mycelium as well as the ever changing outside environmental humidity affecting incoming air.  Two humidistats as well as a carbon dioxide monitor are needed and must be monitored to assist in assessing the indoor climate.  Optimal humidity is near 95%.  Optimal carbon dioxide is below 600 PPM.

Research results and discussion:

As of the end of November 2018, a repeatable process for mixing medium with a tumbling composter, ease of filling bags, and steroclaving medium was completed.  The result is medium enters the inoculation area sufficiently sterile to provide a clean base for mushroom inoculation.  In addition, the upending of the steroclaved bags to drain freely on top of a rack proved important in providing the proper moisture content for a successful spawn run.  Allowing the bags to drain for a minimum of 12 hours after steroclaving removed excess moisture introduced during the steroclaving process that creates an anaerobic environment in the bottom of the bag leading to reduced yield through competition with foreign microbes.  This also allows the medium to come to room temperature.

In the spring of 2019, larger oyster mushroom bags were used.  This reduced labor costs by 1/3 for the handling of bags.  It also provided more air space in the bag to aid in ease of mixing the inoculated bags.  Better and quicker spawn runs were achieved due to easier mixing of the grain spawn into the coffee/sawdust medium.  This was not expected and has allowed me to reduce the price per pound of mushrooms making them more appealing at the market place.


Research conclusions:

The project set out to find a recipe that can provide consistent quality mycelium runs that lead to fruiting yield that is profitable, repeatable and sustainable.  The initial research intent was to find an optimal level of coffee to oak mix along with an optimal level of baking soda supplementation.  This was to be followed with augmenting with gypsum at a weight percentage rate to dry medium.  Due to two very moist summers, it was not possible to dry coffee grounds without them becoming covered in trichoderma and other contaminates.  I was not able to find any research that might give me information on the weight of dry spent coffee grounds and found it challenging to try to dry them in an indoor oven. It is an area for future study.

Success was found in creating a recipe by volume that is doable on the farm as well as being forgiving enough to handle the needs of farm variability and resource variability.  The results of this are available in a webinar through Cornell Small Farms at http://blogs.cornell.edu/mushrooms/ or at http://www.youtube.com/watch?v=ui5eK7Qb5So&t=32s .  The recipe is outlined in the webinar as well as here.  Use 2-15 liter buckets of spent coffee grounds.  Add 2-15 liter buckets of fresh oak sawdust.  Tumble and remove all paper filters and other non-compostable materials.  Add 120 grams of baking soda per 4 buckets and tumble until uniformly mixed.  Adjust moisture content such that the mixture is uniformly moist without there being any water that can be squeezed out the the mixture.  Steroclave according to manufacturers directions.  Transfer to a positive pressure inoculation room. Invert bags on racks to drain and cool.  Inoculate, seal and shake and/or tumble to mix the mycelium uniformly.  Allow for a spawn run of 3 to 4 weeks.  Transfer to a fruiting room with humidity and air flow control.  Harvest and enjoy.

Participation Summary
1 Farmers participating in research

Education & Outreach Activities and Participation Summary

2 On-farm demonstrations
1 Tours
1 Webinars / talks / presentations
1 Workshop field days

Participation Summary:

31 Farmers participated
4 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

Steve Gabriel was provided with a tour and demonstration of the experiments as well as a question and answer session.

Steve Gabriel organized an online mushroom webinar on May 1st, 2019 for the Cornell Small Farms Program on Specialty Mushrooms.  I was the guest speaker at the webinar with a 75 minute talk on using spent coffee grounds and oak sawdust augmented with baking soda to provide a viable oyster mushroom business.  There were 25 participants.  The webinar was recorded and is available for viewing at http://blogs.cornell.edu/mushrooms/ and at the Small Farms Program YouTube channel.

Roger Ort of Schuyler County CCE facilitated an on-farm tour and educational event showcasing growing oyster mushrooms on spent coffee grounds and oak sawdust.  12 participants signed up but due to illness and perhaps difficulty locating the farm on GPS, 6 participants attended.  Additionally 3 CCE agricultural specialists participated.  Photocopied materials from the previous webinar were provided to the participants.  Feedback from the agriculture specialists was that there is a great interest in having more on-farm tours and hands-on events for oyster mushroom cultivation.  Future programs with the three CCE agencies will likely be developed in the fall of 2019.

At this point (6/9/19), there are 189 views of the webinar posted through Cornell with 6 likes and no dislikes.  It appears that many people are finding it educational.

Learning Outcomes

4 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

The attention to detail that is needed to successfully grow mushrooms indoors is higher than thought.  The requirement to have 4 separate parts to an indoor mushroom growing facility first appears daunting.  The ability to execute the detail is easier than thought once the need to segregate the process into 4 distinct stages separated by barriers, air flow and humidity requirements is absorbed and accepted. All indoor mushroom facilities follow a similar pattern, but are carried out in very unique ways depending upon the facilities available.  This differs from the outdoor production where air flow and humidity are not part of the daily process.  Neither is the need for a clean positive pressure inoculation area.  Many of the participants at the on-farm tour had experienced outdoor or forest mushroom production, but not indoor production.

The ability to control contamination by Trichoderma species using something as simple and every day as baking soda appeared surprising to experienced growers as well as new growers.  Baking soda is sodium bicarbonate. When I explain how bicarbonate affects the soil and it's interactions with water, it became easier for growers and agricultural specialists to understand the complex nature of interactions occurring in the mushroom growing bags.  The baking soda has proved to be a significant disrupter in the growth of certain fungi, molds and mildews that enjoy wet coffee grounds.  The surprise is that too much or too little baking soda creates challenges surprised growers and agricultural specialists.  It is surprising how hydrophylic the baking soda medium becomes and how easy it is to then create an anaerobic mushrooms block.

Agricultural specialists were impressed that a small area can be so readily segregated into the component rooms, provided sterilization, air movement, air flow and humidity. In creating this on-farm demonstration, the agricultural specialists representing three counties were surprised at the high level of interest there is in learning about small scale mushroom production as well as the use of coffee grounds in the production of oyster mushrooms.

Project Outcomes

2 Farmers changed or adopted a practice
3 New working collaborations
Project outcomes:

Growing oyster mushrooms on coffee grounds has been an exercise in humility and frustration.  The chance that it would work and for how long was more akin to gambling.  When it worked, it worked well.  When it didn't it, it definitely did not work - total failure with the lesson being the need for more cleaning.  Without this grant, I would have given up trying to grow oyster mushrooms at all.  Because the mushrooms produced on a mixture of coffee and hardwood sawdust taste significantly better than those on other medium (sawdust, soybean hulls, straw or other agricultural products), many people in the community provided me consistent encouragement to continue trying.  The community support is driven by their breakfast and dinner plate enjoyment and willingness to pay a $4 premium for oyster mushrooms over the grocery store price for the superior flavor profile of oyster mushrooms grown on coffee. The grant from SARE combined with the community support provided me the motivation needed to try and try again until a formula and process was found that not only provided a reasonable yield of oyster mushrooms, but was also repeatable, work flow doable, profitable and successful time over time with minimal setbacks due to spot contamination.

Improvements were made in all stages of mushroom production.  Simple step changes made huge differences. Details as simple as making sure there is an open air space in the center of the steroclave to provide better sterilization of the bags of prepared medium along with turning them upside down over a cooling rack to gravity drain excess moisture after the completion of the steroclave process were just a few of the small but necessary steps to ensure success.  Perhaps the greatest surprise was the high failure rate of inoculated blocks that contained the 3 TBS baking soda mix.  The ability for water retention in the bags was unexpected and the release of that water during the spawn run created a layer of moisture at the bottom of the bag that created conditions for competing bacterial and fungal growth.  The need to cull these bags before fruiting created significant difficulties in the fruiting process.  They also tended to create a mess in the fruiting room leading to both less harvestable mushrooms and more labor as well as more cross contamination to existing bags.  The use of 1 TBS baking soda created a stable bag but reduced the ability for the mycelium to grow rapidly enough to give a reliable and quick yield.  The 2 TBS level seems to help the coffee grounds break down at a more rapid rate than the 1 TBS level yet not hold the moisture that is in the 3 TBS level.  Since farming profitably is about finding the sweet spot for labor inputs, material inputs, yield and quality, this grant helped to deliver that.  Thus it did surprise me that the 50% spent coffee grounds to 50% oak sawdust with 2 TBS baking soda per 15 liter bucket was the sweet spot.

There is a great deal of appreciation for tasty high quality oyster mushrooms in the Southern Tier of New York State.  Oyster mushrooms grown this way command a 40% premium over ones offered through traditional markets.  They are not able to be grown and priced for the wholesale market by a small grower, but likely can be scaled up for larger producers who have the space and equipment to handle large volumes of raw materials for processing.  At his point, I am humbled and gratified by the feedback received from individual sales and farm market sales.  People seek out the mushrooms grown on coffee.  There has been feedback stating that these mushrooms equal the flavor profile of ones found in German and Polish woods.  One customer has stated that the mushrooms are the best he has ever had in the US and as good as ones found in the Polish woods. Many customers refuse to purchase oyster mushrooms elsewhere and wait until mine are available.  With the changes in production flow, the sweet spot recipe and the positive customer feedback, growing oyster mushrooms had become consistently satisfying.  There are minimal set backs at this point and they are much more easily overcome.

Growing oyster mushrooms is rewarding.  It is now also profitable.  With the use of raw materials that otherwise would go into a landfill it is environmentally friendly.  With the resulting mushroom compost, it is garden friendly.  I look forward to continued oyster mushroom growing as well as working with the local CCE agents in my 3 county area.  There are many improvements that still need to be researched in the use of coffee grounds and growing mushrooms.  Hopefully this research is a stepping point for me and others to continue to gain knowledge in the area of coffee ground reuse.

Assessment of Project Approach and Areas of Further Study:

The key to success for this project was perseverance and community support. Without the community support and commitment made to SARE to complete this research, the overwhelming challenge of working with spent coffee grounds would have been too much to continue their use in oyster mushroom production.  Simply put, coffee grounds are a nutritious food for anything that drifts in on the wind be it aerobic or anaerobic.  Because they are difficult to dry and need to be air dried, the two wet summers that were encountered made it impossible to do the second part of  the experiment with gypsum.  I hope to be able to do that on my own when the weather permits.

The initial question of using baking soda in spent coffee grounds along with the question of percentage of coffee to oak sawdust was answered.  The mixture that provided the most consistent yields and least issues with contamination turned out to be the middle ground of a 50/50 mix of spent coffee to oak sawdust by volume before filters were removed and an addition of 30 grams (or 2 TBS) of baking soda per 15 liter bucket of raw material.

Revisions to the methodology were the removal of coffee filters, the addition of baking soda after the filters were successfully removed and the need to have the medium just short of field moisture capacity before steroclaving and just at field capacity after steroclaving but before inoculation.  The simplicity of using gravity to drain out excess moisture during the cooling process improved the likelihood of having the proper moisture capacity.

It can be said that the mixture is not a perfect 50% spent coffee ground to 50% oak sawdust ratio once the coffee filters are removed which is true but this is an on-farm study.  It starts with buckets filled with coffee grounds at the local coffee shop who place both the grounds and filters in the bucket.  It is not practical to ask them to remove the filters or for me to and then remeasure the remaining grounds before continuing with the mixing process. Filter removal is much easier after mixing.  Therefore, for easy of work flow, the spent coffee grounds start with filters already taking up volume before mixing.  If a more precise formula is needed for other growers use, they are welcome to enjoy the additional work involved in separation, drying, weighing and measuring to tweak this recipe.

I am promoting the 50/50 mix and 30 grams (2 TBS) of baking soda per 15 liter bucket of raw material since it works well for me.  For on-farm use, there needs to be little requirement in weighing out medium due to moisture changes.  Volume is easier to use.  The only measurement that needs to be done accurately is that of the baking soda.  It is likely that this can also be done in the field except that baking soda tends to hydrate. Therefore it is easiest to create small premeasured packets in an indoor environment and keep them handy for mixing.  My tumbler handles 60 liters of material easily which allows for uniform mixing potential.  In turn, using 2 large steroclaves processes a single batch of material.  After steroclaving and cooling, one bag of grain spawn is what is needed to inoculate the batch.  All this leads to a good work flow.

Additional work is needed to improve yields with coffee/sawdust medium.  An understanding of just what the baking soda does within the mixture is needed in order to take the use of spent coffee grounds to the next level of production.  This will help determine what other amendments may help boost yields and shorten the length of time needed for the mycelium run.  Mycelium runs using coffee grounds are longer than that for straw or cellulose based substrates.

Can other mushrooms than the standard oyster mushroom grow on a coffee ground mix?  Is the current recipe adequate for good growth of  oyster mushrooms such as king oyster or chestnut oyster or is it limited to Grey Dove and Italian Brown oyster mushrooms?

The question of why does baking soda work so well is one that deserves answering.  What is going on chemically with baking soda in the substrate? This can only occur through lab testing and collaborative work with mycologists and soil specialists.  Perhaps an analysis of what is happening during the various stages of mycelium growth and fruiting will yield answers.

Are there improvements that can be made in the work flow process that will increase profit through reduced labor or energy inputs.  How can a building be better protected from the high humidity?

There are many varieties of oyster mushrooms available for cultivation.  Conducting trials to determine which ones are best suited to the coffee/sawdust mix needs to be done to narrow the field of what is profitable and what is best left to other growing mediums.

Small mushroom growers for profit and large hobby mushroom growers can benefit from my research and the above potential research.  This is not limited to a specific area of the country as it is indoors and requires the manipulation of the environment. Additional, these growers can benefit from the development of a work flow template.  In searching out how to set up a successful mushroom growing facility, there was little available for the small grower as almost everything is set for large operations.  With those that do have information, it is only available if purchasing their equipment which may be over powered for a small operation or simply not fit a small operation.  A simple work flow template is needed that can be readily accessed by small growers along with options and the explanation for these options is needed.  SARE can continue to fill this need through funding research and development of the above mentioned items.

Mushrooms are an area of great interest at present.  Cornell Cooperative Extension (CCE) is experiencing increased requests for assistance with small growing operations.  Working with SARE and Cooperative Extension Services is an area that is worth perusing. Firefly Farm looks forward to advances in the above mentioned areas.

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Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.