Sarah Brown
Mushrooms are a versatile ingredient used in a variety of dishes, but they can quickly turn from being a chef's delight to a health hazard. It is important to be able to identify contaminated mushrooms to avoid any health risks. Blue mould on mushrooms is a sign of contamination and indicates that the mushrooms are not safe to eat. Blue mould can be identified by its distinct bright blue colour, which may be similar to indigo. The presence of blue mould may also be accompanied by other signs of spoilage such as a sticky or slimy texture, discolouration, and an unpleasant smell. It is important to note that even if the blue colour is due to dye transfer, it may still be unsafe to consume. Proper storage methods, such as wrapping mushrooms in a paper towel and placing them in a brown paper bag, can help prevent the growth of mould.
| Characteristics | Values |
|---|---|
| Texture | Mushy, sticky, slimy, shrivelled, dry |
| Colour | Green, blue, Grey, Black, Brown, Yellow |
| Smell | Unpleasant, fishy, foul |
| Other | Presence of slime, discolouration, dark spots, fuzzy mould, bruising |
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What You'll Learn
Blue stains may be bruising, not mould
Blue stains on mushrooms may be bruising and not mould. While some blue-bruising mushrooms are toxic, not all are, and some are even delicious.
Bruising is a natural process that occurs in psilocybin mushrooms. When a mushroom bruises, it means that psilocin must have degraded and broken down. The more bluish bruising on a mushroom, the more psilocin has degraded, and the less active amount there is to produce psychedelic effects upon consumption. Therefore, blue bruises are believed to lower the potency of mushrooms. However, it is unclear why blue bruises occur.
To distinguish between bruising and mould, you can perform a Q-tip test. Simply wipe a fresh Q-tip across the affected area. If the blue colour rubs onto the Q-tip, then the substrate is likely contaminated with mould. If it does not, then it is simply bruised.
It is important to note that not all blue-staining boletes are poisonous. For example, neoboletus luridiformis, suillellus luridus, and xerocomellus chrysenteron are blue-staining boletes that are edible. However, it is recommended to avoid consuming any mushrooms that have a red pore surface and blue bruises, as many of these are toxic.
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Bacteria can cause slimy patches and discolouration
Mushrooms are vulnerable to contamination by bacteria, mould (fungi), and pests. Bacteria can cause slimy patches and discolouration on mushrooms. Slime production is a tell-tale sign of bacterial contamination. Slime is often accompanied by an unpleasant smell and a change in texture, with the mushrooms becoming softer, sticky, and mushy.
Bacterial blotch, for example, is a common bacterial contamination that may be endemic on mushroom farms. It causes the formation of yellow to brown lesions on mushroom tissue. The bacteria spread by airborne soil particles and occur if mushrooms remain wet for 4 to 6 hours or more after watering. The occurrence of bacterial blotch is associated with the size of the bacterial population on the mushroom cap. Bacterial blotch can develop on the outer surface of a mushroom, on the cap or stem, or both, at any stage of mushroom growth.
Another common form of bacterial contamination in mushroom cultivation is "wet spot" or "sour rot". It is characterised by a dull grey slime with a sour-smelling odour that appears excessively wet or mucus-like. It often forms in uncolonised patches along the bottom of grain jars.
To prevent bacterial contamination, it is important to maintain a clean environment and handle mushrooms carefully. Mushrooms should be stored in a paper towel and placed in a brown paper bag to absorb excess moisture, which can cause slime and foster unwanted bacterial growth.
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Store mushrooms in paper, not plastic, to prevent mould
Mushrooms are a delicate and perishable food item, and proper storage is essential to preserve their quality and flavour. One of the most important things to remember is to store mushrooms in paper, not plastic, to prevent mould.
When stored in plastic, mushrooms spoil up to 60% faster. Plastic traps moisture, creating an ideal environment for mould and bacteria to grow. Mushrooms are approximately 90% water, and they continue to release water even after being picked. In a closed plastic bag, this water has nowhere to go, and the trapped moisture causes the mushrooms to become slimy, discoloured, and mouldy. The excess moisture also breaks down the mushroom's structure, making them limp and affecting their taste.
Paper, on the other hand, is a breathable material with tiny holes that allow air to circulate. Paper absorbs moisture, preventing the mushrooms from sitting in a damp environment. The airflow carries away the water that mushrooms naturally release, reducing the humidity inside the bag. This helps to slow down bacteria growth and keeps the mushrooms firm, fresh, and tasting as they should.
To store mushrooms properly, place them in a brown paper bag, either with or without a paper towel lining. Avoid using plastic wrap or containers, as these will trap moisture and speed up spoilage. If you don't have a brown paper bag, you can also wrap the mushrooms in a paper towel and place them in a bowl in the refrigerator. Remember to avoid washing mushrooms before storing them, as this will make them go bad faster. With proper storage, mushrooms can last longer—up to 7 days in a paper bag—and you can reduce food waste while enjoying fresh, tasty mushrooms.
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Signs of spoilage: slime, discolouration, stink, or mould
Blue mould on mushrooms is not always a sign of spoilage. Some mushrooms, such as magic mushrooms, instantly develop a blue coloration when they are cut or bruised. This is due to the presence of psychotropic compounds such as psilocybin and psilocin. However, if you notice any other signs of spoilage along with the blue discolouration, it is best to discard the mushrooms.
Signs of spoilage in mushrooms include slime, discolouration, stink, or mould. Slime is often an indication of bacterial contamination and is characterised by slimy or sticky patches on the mushrooms. It can also be a result of excess moisture, which can cause the mushrooms to become slimy and promote bacterial growth. Discolouration, such as green, blue, grey, or black patches, can indicate the presence of mould or other fungal species. A foul odour is another sign of spoilage, as mushrooms typically have a mild earthy scent. Mould growth, characterised by fuzzy or dark spots, indicates that the mushrooms are no longer safe to consume.
To prevent spoilage, it is important to store mushrooms properly. They should be kept dry, as moisture can promote mould and bacterial growth. Fresh mushrooms are typically stored in a paper towel and placed in a brown paper bag in the refrigerator. This allows excess moisture to be absorbed and air to circulate, maintaining freshness. Proper storage can help extend the shelf life of mushrooms, which is usually around 7 to 10 days.
In summary, while blue discolouration alone may not indicate spoilage in certain mushrooms, it is important to be cautious and look for other signs of spoilage. Slime, discolouration, stink, and mould are all indications that mushrooms have gone bad and should be discarded. Proper storage practices can help extend the shelf life of mushrooms and prevent spoilage.
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Contamination: blue mould may indicate unsafe consumption
Mushrooms are a delicious and healthy addition to any meal, but it is important to be vigilant when checking for signs of spoilage or contamination. Blue mould on mushrooms may indicate unsafe consumption, and it is crucial to identify the early signs to act accordingly.
Discolouration is one of the most obvious signs of contamination. If you spot blue patches on your mushrooms, it is likely that they are contaminated with mould. However, it is important to distinguish between mould and bruising. Small blue stains may be a result of bruising, especially where the mushroom is pressed against a surface. In this case, the blue spots are not an indication of unsafe consumption.
Nevertheless, if the blue colour is accompanied by other signs of spoilage, it is best to discard the mushrooms. Mushrooms that have gone bad may exhibit a change in texture, becoming sticky, slimy, or shrivelled. They may also emit an unpleasant odour, indicating bacterial growth.
To prevent mould and ensure the longevity of your mushrooms, proper storage is essential. Fresh mushrooms should be stored in a paper towel and placed in a brown paper bag in the refrigerator. Avoid using plastic wrap or containers that can trap moisture and promote the growth of mould.
While some blue mushrooms, like the blewitt, are known to be edible, it is always better to err on the side of caution. If you have any doubts about the safety of your mushrooms, it is best to discard them and avoid the risk of foodborne illness.
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Frequently asked questions
Mushrooms are more likely to become moldy if they are exposed to moisture, so check for slime, stickiness, or a change in texture. Discoloration is one of the most obvious signs of contamination, so look out for blue, grey, or black patches. If you're unsure, it's best to throw them away.
Eating blue-molded mushrooms could cause food poisoning or botulism. Bad mushrooms may contain bacteria that can make you very sick.
To prevent the growth of mold, mildew, and bacteria, keep your mushrooms as dry as possible. Store mushrooms on a shelf in your refrigerator, making sure the temperature is under 40 °F (4 °C). Avoid leaving mushrooms at room temperature, and keep them away from foods with strong aromas, as mushrooms absorb odors.
