From Waste to Food: Conversion of Organic Waste Substrates into Gourmet Edible and Medicinal Mushrooms in Washington

Henry Hurt

doi:10.7273/000006370

Mushroom cultivation in the US has expanded greatly in recent decades. However, the industry remains concentrated among a few major producers, leading to logistical limits on sources of available substrates. By contrast, small-scale mushroom cultivation is better positioned to leverage locally produced organic materials due to lower transportation costs and economies of scale. The choice of substrates plays a vital role in mushroom cultivation, impacting both yields and quality. Washington state, a major agricultural region in the US, is renowned for its diverse wide edible mushrooms and has a strong presence of organizations dedicated to mushroom research and cultivation. For these reasons, small-scale specialty mushroom cultivation in Washington state can greatly benefit from research tailored to address local markets and native mushroom species. Currently, most research focuses on commercially dominant species such as shiitake and portobello, leaving many local species under-researched. Therefore, this study aims to identify optional species and substrate combinations sourced mainly from local waste streams that promote small-scale mushroom cultivation. To assess the effects of substrate materials on harvest yields and mycelium growth rates, edible mushrooms were cultivated using agricultural and food waste materials obtained from Pullman, WA, and its surrounding areas. A total of five mushroom species were examined, including widely cultivated species such as Auricularia auricula (Wood Ear), Pleurotus ostreatus (Oyster Mushroom), and Lentinula edodes (Shiitake), as well as Washington native species Coprinus comatus, (Inky Cap) and Hericium americanum (Bear’s Tooth), which are less commonly cultivated. Substrate mixtures were formulated consisting of wheat straw, sawdust from Pseudotsuga menziesii (Douglas Fir), spent brewer’s grain, coffee grounds, and gypsum, carefully adjusting nutrient contents to optimize for fungal growth. As an industry-standard control, we used commercial oak pellets mixed with wheat bran. Additionally, P. menziesii and Pinus ponderosa sawdust were treated with alkaline solutions of hydrated lime to remove resins, resulting in significantly improved mycelium growth rates compared to untreated sawdust. The experimental results revealed a significant variation in mycelial growth rates depending on the choice of substrate, with substrates containing both spent brewer’s grain and coffee grounds demonstrating growth rates comparable to the control. Finally, a survey among mushroom growers in Washington state was conducted to ascertain the most commonly grown species, prevailing prices, and cultivation techniques. Commercial growers with publicly available information were contacted and asked to fill out a brief survey regarding mushroom-growing techniques and local market trends. The data gained from this survey was then compared to information on the national and international mushroom market to identify best business practices for selling mushrooms and estimate potential revenue generated by different species. The conclusions from this analysis were utilized to assess the potential of the substrates and techniques employed in the research to enable economically competitive small-scale mushroom cultivation.

From Waste to Food: Conversion of Organic Waste Substrates into Gourmet Edible and Medicinal Mushrooms in Washington

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