Inoculated grain bags serve as a sterile, nutrient-rich substrate for the fungal organism to establish itself. After a sterile liquid culture or spore solution is introduced, the grains must be stored in an ideal environment for the vegetative body of the fungus, the mycelium, to colonize the substrate. This period of storage, known as incubation, is a foundational step that determines the success of the entire growing cycle. Successful colonization requires a strictly controlled microclimate, managing temperature, air quality, and cleanliness to favor mycelial growth over competing organisms.
Required Conditions for Mycelial Colonization
The most influential factor during colonization is temperature, which must be specific and stable to encourage rapid mycelial growth. For most cultivated species, the optimal temperature range falls between 70°F and 80°F (21°C to 27°C). Maintaining consistency within this range promotes the enzymatic activity that allows the mycelium to digest the grain nutrients efficiently.
Temperature fluctuations are detrimental because they stress the fungal culture, slowing its metabolic rate and weakening its defense mechanisms against invaders. Temperatures above 86°F (30°C) are hazardous, as they allow thermophilic bacteria and other contaminants to thrive and quickly overwhelm the mycelium. The mycelium’s own metabolic process generates heat, which can raise the internal temperature of the grain bag by 1–3°C above the ambient air temperature.
The grain bag requires continuous gas exchange to support the mycelium’s aerobic respiration, consuming oxygen and releasing carbon dioxide. Specialized mushroom bags have a filter patch to facilitate this exchange while barring airborne contaminants. The filter patch must remain unobstructed to prevent carbon dioxide buildup that can stall growth. Light is not required for colonization, and most species prefer low-light or dark conditions, primarily to avoid the heat generated by direct sunlight.
Maintaining an Aseptic Storage Environment
The storage location must be meticulously clean to prevent competing mold and bacteria spores from entering the bag. Surfaces in the colonization area should be routinely disinfected using a 70% isopropyl alcohol solution, which is highly effective at sanitizing surfaces without harmful residues. Avoiding high-traffic areas, such as kitchens or entryways, significantly reduces the introduction of dust, pet dander, and airborne contaminant spores.
One aggressive threat is Trichoderma mold, often called green mold, which can quickly colonize the substrate. Trichoderma spores are ubiquitous in soil and air, making rigorous environmental cleanliness necessary. Separating the incubation space from houseplants or pets is a practical step, as both can introduce mold spores, insects, and bacteria. Maintaining the optimal temperature acts as a primary defense, allowing the mycelium to grow fast enough to outcompete any introduced contaminants.
Practical Locations for Incubation
A dark closet or a dedicated, temperature-controlled shelving unit often provides the most stable environment for colonization within a home setting. Closets naturally offer darkness and can be easily insulated, helping to buffer against external temperature swings. Placing the bags on wire shelving or racks instead of directly on the floor is essential, as this ensures filter patches are not blocked and allows for passive air circulation.
Many cultivators create a small microclimate by placing their bags inside a plastic incubation tote or container. This effectively manages temperature stability, especially when paired with a seedling heat mat. Instead of placing the grain bag directly on the heat source, the mat should indirectly warm the air or a water reservoir beneath the bags, preventing localized overheating that can kill the mycelium. A simple thermometer placed next to the bags is necessary to monitor the actual temperature within the microclimate, confirming it remains within the desired range.
Monitoring and Management During Storage
Regular observation of the grain bags is necessary to ensure the health of the mycelial network. Healthy mycelium appears as a thick, bright white substance, presenting in two primary forms: rhizomorphic (strong, rope-like strands) or tomentose (fluffy, cotton-like appearance). While rhizomorphic growth is often desired as a sign of vigor, both types are healthy and will colonize the substrate effectively.
Once the mycelium has colonized approximately 20% to 50% of the grain, “break and shake” is employed to accelerate the process. This involves gently massaging the bag to break apart the colonized grain clumps and then shaking the bag to evenly distribute the colonized pieces throughout the remaining uncolonized grain. This action creates numerous new inoculation points, significantly shortening the time until the entire bag is fully colonized.
During this management phase, watch for signs of contamination, which manifest as patches of unusual color or texture. Green, black, or pink coloration indicates mold, while slimy patches or a foul, sour odor suggests a bacterial infection. If contamination is discovered, the bag must be immediately isolated from the rest of the cultivation area and safely disposed of to prevent the airborne spread of spores that could infect other healthy bags.