- For every 1 kg of mushrooms grown, around 5 kg of spent mushroom substrate (SMS) is generated (Zhang et al., 2014).
- SMS improves soil structure, boosts microbial life, and can enhance plant growth in organic farming (Phan & Sabaratnam, 2012).
- SMS can yield biogas comparable to food waste, making it a viable renewable energy source (Ahlawat et al., 2010).
- SMS shows promise as a supplementary animal feed, reducing feed costs in livestock farming (Sharma et al., 2017).
- Residual enzymes in SMS have industrial uses in detergents, textiles, and pharmaceuticals.
Mushroom cultivation is expanding, both for hobbyists and commercial operations, leading to significant mushroom production annually. However, for each kilogram of mushrooms harvested, a considerable amount of residual material, up to five kilograms, accumulates. This material, known as spent mushroom substrate (SMS), is often considered agricultural waste. Actually, SMS has significant value. It is becoming recognized as a useful resource in agriculture, energy production, waste management, and sustainable practices. Let's examine the reasons why SMS could be a very valuable byproduct that you might not be taking advantage of yet.
What Is Spent Mushroom Substrate and How Is It Made?
Spent mushroom substrate (SMS) is the organic and fibrous material remaining after mushrooms are harvested. It comprises the initial components used for mushroom cultivation, such as wheat straw, sawdust, cottonseed hulls, corn cobs, coffee grounds, or gypsum, mixed with mushroom mycelium that has largely consumed its nutrient source during mushroom production. To prepare the substrate, mushroom farmers sterilize or pasteurize these organic materials and then introduce fungal mycelium. As time passes, the mushrooms absorb nutrients from the substrate to grow. After several harvests, the substrate becomes less productive, meaning it is not efficient for further mushroom production, and it is then considered SMS. The amount of SMS produced is significant. According to Zhang et al. (2014), about 5 kg of SMS is produced for every 1 kg of mushrooms. This indicates that medium to large mushroom farms can generate substantial quantities of SMS in a single growing period. Therefore, it is important to view this byproduct not as waste but as a reusable renewable resource.
The Science Behind Mushroom Feeding
Fungi have a special function in the environment as natural decomposers. Different from green plants, mushrooms do not use photosynthesis. Instead, they secrete enzymes such as lignin peroxidase, cellulase, hemicellulase, and xylanases into their growth medium. These enzymes decompose complex plant structures like lignin, cellulose, and hemicellulose into simpler sugars and nutrients that fungi can then take in. The main phases of metabolism include
- Colonization Phase: Mycelium grows into the substrate, breaking down organic materials.
- Vegetative Stage: Nutrient uptake continues, and biomass increases.
- Reproduction: When conditions are suitable, the mycelium develops mushrooms.
Even after this process is complete, the remaining material still contains partially decomposed lignocellulosic material, microbial organisms, organic acids, and structural fibers. This remaining nutrient content and microbial activity allow for impactful mushroom waste recycling.
Mushroom Waste Recycling: Why It Matters
Organic waste, if not managed correctly, becomes an environmental problem. Disposing of SMS in landfills contributes to methane gas release, inefficient use of land, and lost opportunities to recycle valuable nutrients biologically. Mushroom waste recycling solves this problem by using waste in a sustainable way. With the global mushroom market growing quickly, and projected to surpass $86 billion by 2028, the quantity of SMS produced will continue to increase. If reused responsibly, SMS can contribute significantly to circular agricultural systems, lessen reliance on artificial fertilizers and animal feed, and decrease carbon footprints across different sectors. From a policy perspective, mushroom waste recycling supports global sustainability objectives
- Reducing greenhouse gas emissions
- Minimizing landfill usage
- Restoring soil health
- Encouraging rural bio-based economies
Therefore, considering SMS as a valuable material instead of waste represents a significant change in approach for agricultural and environmental sustainability.
Agricultural Gold: SMS as a Soil Enhancer
One of the most well-known uses for SMS is as a soil amendment and organic fertilizer. Farmers, permaculture practitioners, and home gardeners are increasingly aware of its advantages, which include
- Improved Soil Structure: The fibrous nature of SMS increases soil spaces and air flow, especially in dense or clay-rich soils.
- Enhanced Water Retention: SMS functions like a sponge, assisting plants in getting water during dry periods.
- Increased Microbial Activity: SMS contains many beneficial microbes that speed up nutrient cycling and protect plants from diseases.
- pH Adjustment: Depending on the starting material, SMS can reduce soil acidity or alkalinity, improving nutrient absorption.
Adding SMS to topsoil can increase production for various crops, such as tomatoes, cucumbers, beans, and corn. Research by Phan & Sabaratnam (2012) confirms that the enzymes that break down lignin and nitrogen-containing substances in SMS stimulate beneficial soil life, similar to aged compost but with fungal qualities that aid in disease resistance and healthier root systems. Furthermore, composting SMS with green waste or animal manure can further increase its nutrient content, helping farmers to move towards organic farming methods with fewer external inputs.
Transforming Spent Mushroom Substrate into Bioenergy
The fibrous and sugar-rich composition of SMS makes it very suitable for conversion into bioenergy. Two primary methods can be applied
- Anaerobic Digestion: Microorganisms break down SMS in environments without oxygen to create biogas, a combination of methane and CO₂. The methane can then be utilized for heating, electricity production, or cooking.
- Fermentation: SMS is processed through hydrolysis and fermentation to produce bioethanol, a useful fuel in rural areas and places not connected to the main grid.
Ahlawat et al. (2010) showed that SMS from button and oyster mushrooms can produce biogas amounts similar to those from typical food waste. When SMS is treated beforehand with enzymes or mild chemicals, it breaks down more effectively, making it a possible energy source derived from agricultural waste.
The potential benefits are significant
- Decentralized power sources for farms
- Less dependence on fossil fuels
- Self-contained energy systems within greenhouses
- Economic use of waste at a local level
Investment in biodigester technology and fermentation facilities could transform mushroom waste recycling into a local bioenergy advancement.
SMS as Animal Feed: A Low-Cost Protein Boost
Even though SMS has been largely depleted of nutrients for fungi, it still contains a variety of fiber, protein, and minor nutrients that can supplement animal diets when used correctly. It has applications as
- Roughage in the diets of ruminants: Cows, sheep, and goats can digest fibrous materials well.
- An addition to poultry feed: When mixed with grains or concentrated feeds, it lowers overall feed expenses.
- A component in aquaculture feed: SMS serves as a prebiotic material in fish feed formulations.
According to Sharma et al. (2017), up to 30% of SMS can be incorporated into ruminant feed mixtures without causing negative health effects. Studies showed that cows and goats maintained their weight and production levels even with some SMS in their diet.
However, unprocessed SMS should not be given directly to animals because it might contain pollutants like pesticide residues, ammonia, or mycotoxins. To ensure safety
- Dry and sterilize SMS before adding it to feed.
- Conduct tests for mycotoxins to maintain quality.
- Use SMS as a partial substitute, not as the only feed source.
In areas experiencing feed shortages or financial limitations, SMS provides a sustainable, locally obtained source of animal nutrition.
Sustainable Materials: Biodegradable Packaging & Eco Construction
By considering SMS and mycelium as bio-based resources instead of waste, researchers and environmentally focused startups are creating innovative sustainable products. One promising area is mycelium composites, which are light and shapeable materials created by growing mycelium on agricultural waste, including SMS. These composites can take the place of plastic and foam in
- Protective wrapping
- Shipping boxes
- Building panels
- Furniture interiors
Companies such as Ecovative and MycoWorks have increased the production of biodegradable packaging materials using SMS as a primary ingredient, developing methods that involve carefully managed mycelium growth in molds before drying and finishing. Similarly, SMS can be used to fill wall spaces as natural insulation or compressed into bricks for building projects that produce low emissions. This results in affordable, fire-resistant, water-resistant building materials that have minimal environmental impact.
Hidden Value: Enzymes and Bioactive Compounds in SMS
Even after the mushroom growing cycle is complete, SMS still contains a wealth of valuable biochemical byproducts. Researchers have discovered remaining activity of
- Laccase: Used for removing color from dyes, bleaching paper pulp, and treating wastewater.
- Xylanase: Helps in breaking down hemicelluloses in food, textiles, and cleaning products.
- Protease: Important for pharmaceuticals, waste processing, and certain health supplements.
In addition to enzymes, SMS also contains small amounts of bioactive substances, including antioxidants, phenolics, and polysaccharides, which have potential health benefits. Extracting these biomolecules from SMS can offer
- Affordable enzyme sources for environmentally friendly industries.
- Bio-based additions for animal feed or health supplements.
- Base materials for biodegradable plastics and chemical processes.
Instead of depending on new plant or microbial sources, innovators can obtain useful substances directly from this underutilized biomass.
Managing Spent Mushroom Substrate the Right Way
Whether you are a commercial mushroom producer or a home grower, managing SMS sustainably is important for a circular system and for protecting your local environment. Important practices to consider
Composting SMS
- Mix it with green materials like kitchen scraps or grass cuttings.
- Keep moisture levels at 50–60%.
- Turn compost piles regularly to add air.
- Check the temperature (135°F–160°F) for proper decomposition.
Storage Best Practices
- Air-dry SMS to prevent decomposition without oxygen.
- Store it in containers or bags that allow air circulation, away from direct sunlight.
- Label it with the type of substrate and the material used for inoculation for future reference.
Direct Field Application
- Apply SMS during off-seasons or before planting crops.
- First, check the soil pH and nutrient levels.
- Use it together with cover cropping methods for maximum soil improvement.
By reusing SMS locally, growers can help lower transportation emissions while improving soil, feeding animals, and improving their financial situation.
The Future of SMS in Circular Economies
SMS is more than just a waste material; it is a key element for the future of circular agriculture and sustainable industries. The incorporation of SMS into broader environmental systems is already leading to
- Vertical systems in mushroom farms: Composting SMS on the farm itself to regenerate substrate.
- Intelligent farms using AI to track SMS composition and improve reuse methods.
- Government policies that encourage SMS recycling through farm support programs.
- Small-scale biorefineries that convert SMS into valuable products across various sectors.
As the global need for food, energy, and eco-friendly materials increases, SMS will be very important in reducing waste and increasing production. From cooking to building to environmental strategies, the question is no longer if spent mushroom substrate can be reused, but to what degree we decide to reuse it.
Common FAQs About Spent Mushroom Substrate
Can I reuse SMS to grow more mushrooms?
It is possible but not optimal for high yields. Nutrient levels are often too low for top quality mushroom types, but some gourmet mushrooms or wild mycelium might grow in leftover SMS.
Is SMS safe to compost at home?
Yes, definitely. When mixed with green materials (like food waste or coffee grounds) and turned regularly, SMS composts well in home gardens.
How long does SMS take to decompose?
The decomposition process takes from 2 to 6 months, depending on the temperature, how often it's turned, and moisture content.
Is all SMS the same?
No. SMS differs depending on the type of mushroom, the initial substrate, growing conditions, and any added materials. Some SMS types might be more acidic or have more microbial activity than others.
How do I know if my SMS is safe for animal feed?
If you plan to use it for animal feed on a large scale, send samples to a local laboratory to check for mycotoxins and nutrient content. For smaller amounts, examine it for mold, unusual smells, or insect problems before using it.
Zombie Mushrooms’ Approach to Responsible SMS Use
At Zombie Mushrooms, our thinking extends beyond just the mushroom itself. Our grow kits are created considering the entire life cycle, including what to do after harvesting is complete. We encourage all of our customers to compost their SMS, or use it to improve their gardens. This is another way we support zero-waste growing practices. Check out our composting guides, environmentally friendly products, and tips for soil improvement to ensure that every component of your grow kit is used effectively.
SMS Applications Table: Quick Reference
| Application | Description | Benefit |
|---|---|---|
| Soil additive | Enhances soil structure & nutrients | Boosts organic crop production |
| Animal feed | Residual proteins and fiber | Lowers feed costs |
| Bioenergy production | Methane and ethanol generation | Renewable off-grid energy |
| Packaging material | Mycelium-based composites | Biodegradable and compostable |
| Construction | Used in eco-bricks and insulation | Lightweight, thermal-efficient |
| Enzyme extraction | Source of industrial-use enzymes | Textile, detergent, or pharma use |
References
- Zhang, R., Wang, Y., & Ma, D. (2014). Utilization of spent mushroom substrate as a feedstock for bioenergy production. Renewable and Sustainable Energy Reviews, 35, 61–69. https://doi.org/10.1016/j.rser.2014.03.032
- Phan, C. W., & Sabaratnam, V. (2012). Potential uses of spent mushroom substrate and its associated lignocellulosic enzymes. Applied Microbiology and Biotechnology, 96(4), 863–873. https://doi.org/10.1007/s00253-012-4428-8
- Ahlawat, O. P., et al. (2010). Bioconversion of spent mushroom substrate to methane. Biomass and Bioenergy, 34(12), 1811–1814. https://doi.org/10.1016/j.biombioe.2010.07.012
- Sharma, S. K., Gautam, R., & Shrivastav, M. (2017). Utilization of spent mushroom substrate in animal feed. J. Animal Health and Production, 5(4), 148–152.
