Mycelium is the vegetative body of a fungus, a network of thread-like cells called hyphae, representing the growth stage before mushrooms appear. Understanding the appearance of healthy mycelium is the first step toward successful cultivation. Contamination is a frequent challenge, and the ability to rapidly identify it is necessary to save the culture or prevent the spread of foreign organisms.
The ideal appearance of mycelium depends slightly on the substrate, but it generally presents as a uniform, bright white or off-white color. On grain spawn, the growth is often described as rhizomorphic, meaning it forms thick, ropey strands that aggressively colonize the substrate. When colonizing a bulk substrate, the growth may instead appear tomentose, which is a softer, fluffier, and less dense pattern.
Healthy mycelium typically emits a mild, earthy scent, often likened to fresh mushrooms or damp forest soil. Any discoloration, patchiness, or deviation from the expected growth pattern should raise suspicion. The density of the hyphal network should be consistent, binding the substrate together into a solid mass.
Key Visual and Sensory Indicators of Contamination
Any deviation from the pure white or off-white color of healthy mycelium is the most immediate sign of contamination. Molds are among the most common intruders, typically manifesting as distinct colored patches that spread quickly. The mold Trichoderma, often called green mold, first appears as white patches similar to mycelium but quickly turns a vibrant, emerald green as it begins to sporulate.
Penicillium mold, another frequent contaminant, usually presents as a blue-green fuzzy or powdery growth. Unlike the aggressive spread of Trichoderma, Penicillium may be slower to take over, but it still poses a significant threat. Black, yellow, or pink spots are also indicators of contamination, often caused by various other molds or yeasts.
Bacterial contamination, commonly known as “wet spot” or “sour rot,” is diagnosed less by color and more by texture and odor. This contamination often causes the colonized substrate to become slimy, wet, and mushy, frequently appearing as gray or brown patches. The smell is a definitive diagnostic tool, as bacterial contamination emits a foul, sour, or acrid odor.
Yeasts can also contaminate cultures, often resulting in a milky or slimy coating on the substrate. The associated odor is typically sweet or alcoholic, indicating fermentation is occurring within the culture. When assessing a suspect culture, a simple cotton swab test can differentiate true contamination from natural mycelial bruising, which sometimes appears blue; contamination will transfer color to the swab, while bruising will not.
Common Sources and Prevention of Contaminants
Contamination results from non-sterile procedures or an unoptimized growing environment, allowing foreign spores or bacteria to outcompete the fungus. Airborne spores are a major source, entering the culture during inoculation or transfer if the work area is not properly sanitized. Tools such as scalpels, inoculation loops, and syringes, if not sterilized with heat or alcohol, can directly introduce contaminants into the substrate.
Improperly prepared substrates are another common pathway for contamination, as they may harbor heat-resistant bacterial endospores or mold spores. If the substrate is only pasteurized, which kills most contaminants but spares some beneficial organisms, it is more susceptible than a fully sterilized substrate. Furthermore, fluctuations in temperature or excess moisture create ideal breeding grounds for many molds and bacteria.
Preventing contamination relies on maintaining strict aseptic technique throughout the cultivation process. Sterilization, often performed using a pressure cooker, should be thorough to eliminate all microbial life from the substrate before inoculation. Working within a Still Air Box (SAB) or using a High-Efficiency Particulate Air (HEPA) filter flow hood significantly reduces the number of airborne particles that can land on the exposed culture.
Growers must ensure all transfer tools and container surfaces are wiped down with a 70% isopropyl alcohol solution before and after use. Careful management of the grow environment, including ensuring adequate air exchange and avoiding excessive humidity levels, discourages the proliferation of many common contaminants.
Safe Disposal and Cleanup Procedures
Upon identifying contamination, immediate isolation of the affected culture is necessary to prevent the spread of spores or bacteria to other healthy cultures. A contaminated jar or bag should be sealed securely, often by placing it inside a secondary plastic bag, before being moved from the growing area. This immediate containment minimizes the release of spores into the air of the cultivation space.
Contaminated substrates should never be simply thrown into household trash without precautions, as the spores can escape and colonize new areas. A common disposal method is deep burial in the ground, far away from the cultivation area, allowing natural decomposition to occur. Alternatively, the sealed culture can be heat-treated, such as by running it through another sterilization cycle, to kill the spores before disposal.
Following the removal of the contaminated culture, the growing area and all equipment must undergo a thorough cleaning protocol. All surfaces that may have come into contact with the spores should be wiped down with a disinfectant, such as a diluted bleach solution or 70% isopropyl alcohol. Mandatory air exchange is also necessary to clear any lingering airborne spores from the environment.
Ignoring cleanup risks a cycle of re-contamination, as mold spores are microscopic and easily settle on surfaces. Careful sanitation of the immediate area and all reusable equipment is necessary to reset the environment and protect future cultures.