Oyster Mushroom Cultivation (Pleurotus ostreatus): Substrates, Incubation, and Fruiting

Biological Fundamentals and Substrate Selection for Pleurotus ostreatus

Integrating sustainable practices at home has gained increasing relevance, and among these, the cultivation of edible mushrooms emerges as a fascinating and rewarding activity. Oyster mushrooms (Pleurotus ostreatus), also known as ‘oyster fungi,’ represent an ideal option for those seeking to start in domestic mushroom cultivation. Their adaptability to various substrates and their relatively short life cycle make them an accessible project for hobbyists and a sustainable source of food. This process not only offers the satisfaction of harvesting fresh, nutritious ingredients but also allows for a deeper understanding of biological cycles and interaction with the natural environment.

The success in cultivating oyster mushrooms begins with understanding their biological requirements. These fungi are saprophytes, meaning they feed on dead organic matter. Therefore, the choice and preparation of the substrate are critical steps. Materials such as cereal straw (wheat, barley), used coffee grounds, sawdust from non-resinous woods, or even sugarcane bagasse, are viable options. Each substrate possesses nutritional and structural characteristics that will influence the yield and flavor of the oyster mushrooms.

Before inoculation, the substrate must undergo a pasteurization or sterilization process. Pasteurization, which involves heating the substrate to temperatures between 60-80°C for several hours, reduces the competitive microbial load without completely eliminating beneficial microbiota. This method is commonly used in domestic settings due to its simplicity and lower energy requirement compared to sterilization, which aims to eliminate all microorganisms and is generally performed at higher pressures and temperatures. The choice of method will depend on the type of substrate and the scale of cultivation.

Substrate Pasteurization and Sterilization Processes

Once the substrate is prepared and cooled, inoculation with oyster mushroom ‘spawn’ or mycelium proceeds. Spawn is the equivalent of ‘seed’ in plant cultivation: it is a culture of mushroom mycelium developed on a sterile medium, usually cereal grains. The proportion of spawn to substrate is key for successful and rapid colonization, generally ranging between 5% and 10% of the substrate’s wet weight. Adequate mixing ensures uniform distribution of the mycelium, facilitating its growth.

During the incubation phase, the mycelium colonizes the substrate. Optimal environmental conditions for this process include a constant temperature between 20-25°C and high relative humidity, above 80%. It is essential to keep the substrate in darkness or very dim light, and ensure minimal ventilation to prevent carbon dioxide accumulation, without drying out the medium. Complete colonization is evidenced by the appearance of a dense white layer of mycelium covering the entire substrate.

For those opting for coffee grounds, a readily accessible substrate in urban environments, the process is relatively straightforward. The grounds should be fresh and not stored for more than 24-48 hours to minimize the proliferation of competing molds. It is recommended to briefly pasteurize them by boiling or immersing them in hot water (70-80°C) for about 30 minutes, or even using the residual heat from the coffee maker if sufficient. After cooling, they are mixed with spawn in a perforated cultivation bag or a suitable container. Detailed information on substrate preparation can be found in publications from agricultural research institutes or specialized mycology portals.

Inoculation and Substrate Colonization by Mycelium

In the case of straw, a common method is hot water pasteurization. The straw is cut into 2-5 cm pieces and submerged in hot water (65-75°C) for 1 to 2 hours. It is then drained to achieve adequate moisture (when a handful is squeezed, only a few drops of water drip out). The pasteurized straw is mixed with spawn and compacted into perforated bags or buckets. Compaction is important to ensure good contact between the mycelium and the substrate, and to maintain internal moisture.

During the colonization phase, observing mycelial development is crucial. Healthy growth manifests as a dense white network spreading throughout the substrate. The appearance of green, black, or other colored spots indicates mold contamination, which could compromise the harvest. In such cases, it is advisable to isolate the contaminated culture to prevent spore propagation and, if the contamination is extensive, discard it. Cleaning and disinfecting tools and the work area are fundamental to prevent these issues.

Once the substrate is fully colonized by mycelium (which can take between 2 to 4 weeks, depending on the temperature and oyster mushroom species), the next step is to induce fruiting. This process simulates the natural conditions that prompt the mushroom to produce fruiting bodies. An effective method is ‘thermal shock,’ which consists of exposing the colonized block to a lower temperature (between 10-18°C) for 24-48 hours, often combined with a significant increase in humidity.

Induction of Fruiting and Environmental Management for Harvest

After the thermal shock, the block is transferred to an environment with high humidity (85-95%), good ventilation, and indirect light exposure. Light is a key factor for the formation of primordia (small mushroom buds) and the development of caps, influencing their coloration. Ventilation is equally vital, as oyster mushrooms require oxygen and carbon dioxide accumulation can inhibit their growth or lead to the development of long stems and small caps.

Primordia typically appear at the holes or cuts made in the cultivation bag. As they grow, it is essential to maintain high ambient humidity, which can be achieved by misting water finely several times a day or using a humidifier. Harvesting is done when the oyster mushroom caps reach an adequate size and their edges begin to flatten, just before they release their spores. Entire clusters are cut at the base, close to the substrate, to avoid damaging the mycelium and allow for future ‘flushes’ or harvests. Generally, a substrate block can produce 2 to 4 flushes, with diminishing yields. After each harvest, a brief rest and rehydration period for the substrate is recommended to prepare for the next batch.

Home cultivation of oyster mushrooms is an activity that combines the science of mycology with the satisfaction of small-scale food production. From substrate selection and preparation to fruiting induction and harvesting, each stage offers an opportunity for learning and experimentation. With proper attention to environmental conditions and an understanding of biological principles, any enthusiast can enjoy the freshness and nutritional value of home-grown oyster mushrooms. This approach to domestic fungiculture not only enriches the diet but also fosters a deeper connection with natural processes and sustainability.