John Miller
Mushrooms are versatile fungi that can be used in a variety of dishes, from savory to sweet. However, mushrooms are susceptible to various forms of deterioration and contamination. One notable sign of spoilage is when mushrooms turn powdery, indicating the presence of mold or slime. This can be caused by excess moisture, resulting in sticky and slimy mushrooms, or the growth of mold spores, which can appear as powdery patches on the mushroom's surface. Proper storage methods, such as using paper towels and brown paper bags, can help extend the shelf life of mushrooms and prevent them from turning powdery or moldy.
| Characteristics | Values |
|---|---|
| Type of Mushroom | Puffballs |
| Scientific Name | Lycoperdon |
| Shape | Spherical, ball-shaped or pear-shaped |
| Texture | Powdery |
| Odor | Unpleasant |
| Contamination | Trichoderma, orange bread mold, bacterial |
| Discoloration | Yellow or brown spots or streaks |
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What You'll Learn
Puffballs: Mushrooms that house powdery spores
Puffballs are a group of mushrooms (Gasteromycetes) that do not expose their gills and forcibly expel their spores into the wind. Instead, they rely on external forces, such as raindrops or small animals, to release and disperse the spores. As the name suggests, puffballs are typically spherical, ball-shaped, or pear-shaped mushrooms that house a mass of powdery spores inside.
The spores of puffballs mature within a pliable, spherical sac (the peridium) that is entirely enclosed except for a hole at the top through which the spores are emitted. This process is fairly passive, as the energy needed to eject the spores is supplied by an external force. When the spores are released, they form a cloud that resembles a puff of smoke, giving puffballs their name.
Puffballs belong to the division Basidiomycota and encompass several genera, including Calvatia, Calbovista, and Lycoperdon. The distinguishing feature of puffballs is that they do not have an open cap with spore-bearing gills. Instead, spores are produced internally in a spheroidal fruit body called a gasterothecium (gasteroid 'stomach-like' basidiocarp).
While most puffballs are not poisonous, some may resemble young agarics or deadly Amanitas. Young puffballs in the edible stage have undifferentiated white flesh, while immature Amanita mushrooms have visible gills. Puffballs have been used by Native American tribes for various purposes, including as a styptic to stop wounds from bleeding, and as a food source.
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Mushrooms going bad: slimy, shrivelled, discoloured, or mouldy
Mushrooms are versatile vegetables that can be used in a variety of dishes. However, they are highly perishable and can go bad quickly if not stored properly. Here are some signs to look out for to determine if your mushrooms are past their prime:
Slime
A slimy coating on mushrooms is one of the most common signs that they have gone bad. This slime is an indication of excess moisture, which can occur if the mushrooms are left in the refrigerator for too long or are not stored properly. The slime also affects the texture of the mushrooms, making them sticky and wet. This slime is often accompanied by a loss of taste and an increased presence of bacteria on the surface.
Shrivelled
Mushrooms have a high water content, which makes them smooth and plump when fresh. However, as they start to go bad, they lose moisture and begin to wrinkle and shrivel. If your mushrooms have a few wrinkles but are not yet slimy, smelly, or discoloured, they are still safe to eat but should be consumed immediately. However, if they are significantly shrivelled and dry, it's best to discard them.
Discolouration
Mushrooms that have turned brown or developed dark spots are likely going bad. Discolouration often occurs when mushrooms are exposed to air for too long and begin to oxidize. While minor spots may not indicate spoilage, a mushroom completely covered in spots or a noticeable change in colour is likely past its prime.
Mould
The presence of fuzzy mould on the surface of mushrooms is a sure sign that they have gone bad. Mould can occur when mushrooms are stored in a humid environment or when excess moisture is trapped, as in the case of plastic containers. Mouldy mushrooms should not be consumed as they may contain harmful bacteria.
It's important to inspect your mushrooms regularly and discard any that exhibit these signs of spoilage. Proper storage, such as wrapping mushrooms in a paper towel and placing them in a brown paper bag, can help extend their shelf life. Additionally, fresh mushrooms should be consumed within 7-10 days of purchase to ensure optimal quality and flavour.
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Common contaminants: trichoderma, orange bread mould
Mushrooms are susceptible to various contaminants, including trichoderma and orange bread mould. Trichoderma is a genus of green mould that preys on other fungal mycelium and is distinguished by its vibrant blue-green colour during sporulation. It is one of the most challenging types of contamination to contain. Trichoderma can grow at any stage of the cultivation process, feeding on the desired species under cultivation. If left untreated, it can wipe out an entire crop. To prevent a trichoderma infestation, growers should increase air circulation and ventilation, maintain a clean and sanitised growing environment, and regularly monitor their operation for signs of contamination. If trichoderma is detected, the contaminated substrate must be removed and disposed of immediately to prevent the spread to other areas. Tools should be washed with a bleach solution or alcohol to kill any remaining spores.
Orange bread mould, or Neurospora, is another common and fast-growing fungal contaminant. It thrives on substrates rich in carbohydrates and is often found on decaying organic matter, soil, compost, and various plant materials. Warm and humid conditions, which are often ideal for mushroom cultivation, favour the growth of orange bread mould. This mould first appears as an orange-white wisp but quickly develops into a bright orange powdery patch. If allowed to spread, these patches produce round, lumpy formations. To prevent contamination, growers should ensure that humidity levels remain within the optimal range for mushroom growth and use sterile, high-quality substrates. If orange bread mould is detected, it should be sealed in a plastic bag and disposed of immediately, taking care not to disturb the mould and release its spores.
Both trichoderma and orange bread mould can cause significant damage to mushroom crops if not identified and addressed promptly. Growers should be vigilant in maintaining sterile conditions and monitoring their crops for any signs of contamination.
In addition to trichoderma and orange bread mould, other common contaminants in mushroom cultivation include bacterial contamination, such as Bacillus spp., and cobweb mould, which thrives in high humidity and stagnant air conditions. Proper sterile techniques, regular monitoring, and early identification and treatment of contaminants are crucial for successful mushroom cultivation.
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Bacterial contamination: wet spot or sour rot
Bacterial contamination is a common issue in mushroom cultivation, and it often goes by the names "wet spot" or "sour rot". This contamination is typically caused by bacteria from the genus Bacillus, specifically Bacillus subtilis and Bacillus cereus. These bacteria are known for their resilience, as they can survive in harsh conditions due to their ability to form endospores, which allows them to endure high temperatures during sterilisation. As a result, they can remain active and cause issues even after sterilisation, when the conditions become favourable for their growth.
Wet spot contamination usually manifests as slimy, discoloured patches on the substrate used for growing mushrooms. These patches can be dull grey, brown, or beige, and they often have a wet, slimy texture. The affected areas may also exhibit excessive moisture, making them noticeably wetter than the surrounding substrate. As the bacteria proliferate, they produce a distinct sour or foul odour, which is a telltale sign of bacterial growth.
To prevent wet spot contamination, it is crucial to start with high-quality, uncontaminated substrates. This includes sourcing grains, straw, or other materials from reputable suppliers who ensure their products are clean and suitable for mushroom cultivation. Regularly inspecting these materials before use can also help prevent contamination. It is important to look for any unusual odours, discolouration, or signs of mould or bacterial growth. Any materials that appear compromised should be discarded.
Additionally, proper handling and preparation of the substrate are essential. Contamination can occur during the preparation phase if the substrate is not handled correctly or if it comes into contact with bacteria from external sources. To address this, mushroom cultivators often soak their grains for 12 to 24 hours before sterilisation. This process ensures that any bacterial endospores on the grains germinate and then die off during the subsequent sterilisation, preventing them from surviving and causing issues later.
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Fungi preying on cultivated mushrooms
Mushrooms are fungi, and like all fungi, they require specific conditions to grow. Mushrooms derive all their energy and growth materials from their growth medium through biochemical decomposition processes. They do not rely on sunlight for energy, but some fungi use light as a signal for fruiting.
The cultivation of fungi, or fungiculture, involves creating an optimized environment for mushrooms to grow, away from the competition and ravages of nature. This is typically done indoors, where light, temperature, and humidity can be controlled, and contaminants and pests can be excluded. The probability of success is much improved with this method.
Fungiculture can be traced back to caves in France, where the stable environment facilitated the growth of mushrooms. The technology was later brought to the UK in the late 1800s, and by the mid-twentieth century, it was common to have windowless, purpose-built buildings for large-scale commercial production. Today, indoor tray growing and containerized growing are the most common commercial techniques.
While some mushrooms are cultivated on straw or newspaper, others have specific requirements. For example, shiitake mushrooms are grown on hardwood logs, such as oak or American beech, in the Northeastern United States. Softwood is not suitable for shiitake cultivation due to its resin inhibiting mushroom growth.
Pleurotus mushrooms, the second most important mushrooms in production globally, accounting for 25% of total world production, are cultivated on carbonaceous matter. In the wild, they are typically found growing on wood. Other mushrooms, like morels, are most easily grown outdoors in shady sawdust/ash beds.
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Frequently asked questions
Mushrooms become powdery when they release spores. This is how they reproduce.
You can try touching them to release the spores into the air. However, avoid inhaling the spores as they can irritate your lungs.
This is likely due to contamination. Orange powder is a sign of the presence of Trichoderma, a group of green mold fungi.
Mushrooms go bad when their texture changes from firm and plump to sticky and slimy. They may also become shrivelled, discoloured, or mouldy, and may smell unpleasant.
