Our project question was: can spent coffee ground be used to successfully grow oyster mushrooms for commercial sale and at what rate 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. So, during October and November, trials with 1/3 coffee and 2/3 sawdust have been done. 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 sp. contamination. A sound process for mixing medium with a tumbling composter, ease of filling bags, and steroclaving medium has been completed. The result is that 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. Not allowing the bags to drain for a minimum of 30 minutes after steroclaving allowed for excess moisture introduced during the steroclaving process to provide an anaerobic environment in the bottom of the bag leading to reduced yield through competition with foreign microbes.
Harvest data will be collected in the next phase.
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 will be studied. Cultivators will be 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. Weekly observations during the spawn run will
note if contamination from Trichoderma is occurring. Trichoderma is a genus of fungi that competes with
the mushrooms for resources thus reducing yield. Contaminated cultivators will be culled to prevent
spreading of contamination. The amount of culled buckets will be 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 will be used along with window and door screens to help reduce insects.
Trials will be conducted using varying rates 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
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. 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. The research conducted aims to determine if coffee grounds can be successfully mixed with oak sawdust to produce enough mushrooms to create an agricultural enterprise as well as determine the optimal amount of coffee grounds to oak sawdust needed for optimal yields.
Preliminary data by Firefly Farm from 2016 shows the potential to profitably grow oyster mushrooms on a
50/50 mixture of spent coffee grounds to oak sawdust by yielding up to 5 pounds of mushrooms per 15 liter
cultivator. Online research, including those recommended by SARE, have provided no information on using
a combination of spent coffee grounds and sawdust mixtures. Other growers, Tradd Cotter  and Steve
Gabriel , have mentioned the use of these items together but have not yet gathered research data into
their use. Both have indicated that the use of coffee rounds being too high in nitrogen and acidity leads to
low production yield. Field and Forrest staff  have likewise stated that growing only on spent coffee
grounds provides inconsistent and low yields thus not being a viable source of farm income. Finding an
optimal mixture for production yield and quality will help assist small growers in stabilizing mushroom
production, help grow market potential and increase farm product diversity. It also removes a nutrient-rich
material from the waste stream. The main obstacles in growing oyster mushrooms on coffee grounds are: 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 growing medium and placing it into a
container for the spawn run, and ultimately fruiting, to occur. With these experiments, varying amounts of
spent coffee grounds and oak sawdust will be mixed together as outlined in the methods and measurements
section to determine optimal mixture for highest yield. Once this is determined, experiments will be
conducted using this optimal mixture with gypsum to stabilize the mixture or chemically buffering the
mixture with baking soda to see if they further improve yield.
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.  The use of baking soda
will determine 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.
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. 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 then having to retrofit a smaller space to create a controlled environment. When choosing space, consider the imputs that are needed to create a space that can tolerate humidity near 98%, provide the ability for air exchange with large fans, have access to electricity and provide enough workspace to maneuver considerable amounts of materials as well as a water supply and sewer drain.
Using The New Site:
Each mushrooming facility will require a minimum of four areas, medium preparation, medium sterilization, inoculation, spawn run and fruiting area. The spawn run can be part of the inoculation area, with the assumption that the area can be kept very clean, if there is not an option for a fifth area. Ideally, it will be a separate area thus 5 areas are ideal.
With my facility, space is limited so 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 has been found, that even with clean room techniques being applied, that the first inoculation attempts have proven to be contaminated. The process of sanitizing/sterilization and the process of inoculating prepared medium need greater examination to evaluate potential for contamination. Observed contaminates at this point are Trichoderma species and white molds similar in visual appearance to molds found on raspberries. This is 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, contamination issues have been successfully dealt with reducing lost inoculated medium to less than 2%. A switch from steroclaving bulk medium and filling plastic buckets has been changed to utilizing mushroom bags, 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 has nearly eliminated the contamination issues. In addition, the use of both 99% isopropyl alcohol, an OMRI approved sanitizer, and a clean room suit have reduced contaminates. It has been found that there is no such thing as being to cautious when looking at sources of airborne, person born and medium born contaminates.
Based on conversations and written information as well as field use of hardwood logs, oak sawdust was chosen for baseline data thinking that it will colonize without contamination issues once the sawdust has been sterilized in a steroclave 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 spawn run. This ran counter to what had been learned prior to attempting the use of oak sawdust alone. This was due to both short hand speech for example: “I grow on Oak” instead of “I grow on Oak and soybean hulls”; and the close nature of holding on to medium recipes. The point of this research is to create medium recipes that are more likely to produce positive results that can be passed on to other growers.
Removal of all growing material has been done. The entire area has been cleaned and sprayed with 99% isopropyl alcohol. It will be sprayed a second time after 48 hours to help reduce and possibly eliminate fungal gnats. Fungal gnats spread disease and non target spores rapidly. New trial runs were done in July and August. The initial runs show that there is still airborne contaminates that need to be further reduced. Taping of all potential cracks with duct tape has been done and new trials are being done with only special mushroom bags.
During October and November, trials with 1/3 coffee and 2/3 sawdust have been done. 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 sp. contamination.
Trials are now being conducted using spent coffee grounds and oak sawdust at the rate of 1/3 coffee to 2/3 sawdust. Coffee grounds are placed in the tumbler first with wetted sawdust added on top. The coffee grounds have been collected at a local coffee shop in 15 liter buckets. The sawdust is measured by filling two 15 liter buckets with dry sawdust then wetting the sawdust before adding it to the tumbler. The amount of water is approximate as the sawdust needs to be wetted, not covered in water. Manual rotation of 13 revolutions is generally adequate to evenly mix the coffee and sawdust together. 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 free water to drain via gravity thus reducing the risk of the medium being too wet. No moisture readings are conducted at any time.
Autoclavable, 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 and placed 4 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 for 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 manufacturers 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 shorted in it’s 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 dawned 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 sup 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 lengthly 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 dependent 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 formate 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 with to use during the fruiting process.
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.
As of the end of November, a sound process for mixing medium with a tumbling composter, ease of filling bags, and steroclaving medium has been completed. The result is that 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. Not allowing the bags to drain for a minimum of 30 minutes after steroclaving allowed for excess moisture introduced during the steroclaving process to provide an anaerobic environment in the bottom of the bag leading to reduced yield through competition with foreign microbes.