Sarah Brown
Growing mushrooms is a delicate process that requires a sterile environment and careful attention to detail. One common issue faced by mushroom growers is exposed grain, which can lead to contamination and impact the growth of the mushrooms. Exposed grains can dry out and become contaminated easily, and this guide will explore the causes and solutions to this problem, helping amateur and professional growers alike to cultivate healthy mushrooms.
| Characteristics | Values |
|---|---|
| Exposed grains | Dry out and get contaminated easily |
| Reason for contamination | Excessive exposure to air |
| Prevention | Mixing with substrate or bottom watering |
| Common contaminants | Trichoderma, orange bread mold, cobweb mold, bacterial blotch, etc. |
| Signs of contamination | Discoloration, slimy patches, bacterial endospores, etc. |
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What You'll Learn
- Exposed grains can dry out and be more susceptible to contamination
- Bacillus can survive sterilisation and cause dull grey slime
- Cobweb mould can be mistaken for mycelium but has a different growth pattern
- Sterile tools and environments are crucial to prevent contamination
- Common pests like sciarid flies can infest grain spawn and mycelia
Exposed grains can dry out and be more susceptible to contamination
Mushroom cultivation is a tricky task that requires a lot of care and cleanliness. The leading cause of crop failure is contamination, which can come from impurities in the air, soil, or water, or even the tools used for cultivation. One of the common issues faced during mushroom cultivation is exposed grains drying out and becoming more susceptible to contamination.
Exposed grains will dry out and not fruit well. This drying problem can be fixed by mixing the grains with a moist bulk substrate or by bottom watering. If the grains are surrounded by a moist bulk substrate, they will not dry out. However, if left exposed, the grains will dry out and be more vulnerable to contamination.
Contamination can occur in many ways, and it is important to know how to identify and prevent it. Discoloration is one of the most obvious signs of contamination. If you spot green, blue, grey, or black patches on your substrate or mycelium, it is likely contaminated. However, blue stains may be bruising, especially if the grain or substrate is pressing against glass jars or plastic bags/tubs. To determine if it is bruising or mould, gently wipe a Q-tip over the discolouration; mould will colour the swab, while bruising will not.
Slimy patches on the substrate or mycelium can also indicate bacterial contamination and excess moisture. Bacterial contamination on grains is characterised by a dull grey slime with a sour-smelling stench, and it makes the grains look excessively wet. This type of contamination is known as "wet spot" or "sour rot". To prevent this, grains can be soaked for 12 to 24 hours before sterilisation to allow the endospores to germinate and be killed during sterilisation.
To prevent contamination in general, it is crucial to maintain a sterile environment and use sterile processes. This includes sterilising tools and surfaces before use and ensuring that the substrate is properly pasteurised and sterilised before inoculating with a mushroom culture.
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Bacillus can survive sterilisation and cause dull grey slime
Bacillus Bacteria and Mushroom Contamination
Mushroom cultivation is a delicate process that requires a sterile environment and careful processes to ensure success. One of the most common contaminants is known as "wet spot" or "sour rot", caused by Bacillus bacteria. This results in a dull grey slime with a sour odour, resembling mucus, and often forms in patches along the bottom of grain jars. The bacteria produce heat-resistant endospores, which can survive the sterilization process and ruin the mushroom crop.
Bacillus Bacteria and Slime Formation
Bacillus bacteria, such as Bacillus spp. and Bacillus anthracis, are known to cause the formation of slime. This slime layer is an extracellular matrix composed of exopolysaccharides, glycoproteins, and glycolipids. It is amorphous and varies in thickness, depending on the cell type and environment. While the slime layer is typically associated with bacteria, it can also be found in some archaea.
Survival of Sterilization
The heat-resistant endospores produced by Bacillus bacteria can survive the sterilization process, particularly if grains are not properly soaked before sterilization. These endospores can remain dormant and come to life after inoculation, leading to contamination. To prevent this, grains should be soaked for 12 to 24 hours at room temperature before sterilization, allowing endospores to germinate and be eliminated during the sterilization process.
Impact of Contamination
Contamination in mushroom cultivation can have significant impacts, leading to crop failure and the ruin of fruiting blocks. Bacillus bacteria, in particular, can negatively affect the growth of mushrooms, causing a dull grey slime that impairs the development of the mycelium. This bacterial contamination can be identified by its distinct appearance and sour odour.
Prevention and Mitigation
To prevent Bacillus contamination, it is crucial to follow proper sterilization procedures, including the soaking of grains prior to sterilization. Additionally, the use of a flame-sterilized spoon or alcohol sanitizer can help remove small, contained bacterial patches. Maintaining a sterile environment, regularly cleaning tools and surfaces, and working efficiently to minimize exposure are also essential for preventing contamination.
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Cobweb mould can be mistaken for mycelium but has a different growth pattern
Cobweb mould, or cobweb disease, is a common contaminant in mushroom cultivation. It is a species of harmful fungi that can be mistaken for mycelium due to its similar appearance. However, cobweb mould has a distinct growth pattern that sets it apart from mycelium.
Mycelium is the part of the mushroom that grows and colonises the substrate. Healthy mycelium can appear web-like, rope-like, or fluffy, and is always bright white. It grows and fully colonises the substrate in a few weeks.
On the other hand, cobweb mould is usually light grey in colour, with a wispy, cotton ball-like texture. It is made up of very fine strands and has a mildew-like smell. Cobweb mould protrudes above the surface of the mycelium, forming a cloud-like structure. It grows extremely fast, covering an entire jar or monotub in 24 to 48 hours. It thrives in environments with still air, very little oxygen, and high humidity, often occurring in the last days of incubation.
To prevent cobweb mould, it is important to improve fresh air exchange (FAE) or airflow around the grow kit. Additionally, maintaining a sterile environment and using sterile techniques are crucial in preventing contamination in mushroom cultivation. This includes properly sterilising tools, surfaces, and substrates before inoculation.
In conclusion, while cobweb mould and mycelium may share similar appearances, they can be distinguished by their growth patterns, colour, texture, and speed of growth. By understanding these differences and implementing proper cultivation practices, mushroom growers can minimise the risk of contamination and promote healthy mushroom growth.
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Sterile tools and environments are crucial to prevent contamination
Growing mushrooms require a sterile environment and processes to achieve success. The hard work of transferring cultures, inoculating grain jars, and making fruiting blocks can be ruined by a single mold spore. Therefore, it is crucial to maintain a clean environment during the cultivation process and prevent contamination.
Contamination, or 'contam' in grower slang, refers to anything in the substrate or mycelium that negatively impacts mushroom growth, including bacteria, molds, and animal pests. Common contaminants include trichoderma, orange bread mold, and "wet spot" or "sour rot," characterized by a dull gray slime with a sour-smelling odor. To prevent contamination, it is essential to sterilize equipment, use sterilized substrates, and maintain a clean and controlled environment.
One common reason for contamination is incomplete sterilization or improper pasteurization of the bulk substrate before inoculating with a mushroom culture. The substrates and grains naturally contain competing organisms and dormant spores that need to be reduced or eliminated. Supplemented sawdust fruiting blocks and mushroom grain spawn should be sterilized before inoculation. This can be done using a stovetop pressure canner capable of reaching high pressure and temperature for an extended period.
Additionally, it is important to sterilize tools and surfaces before working with mushrooms. This includes flaming sterilizing scalpels or blades between culture transfers and wiping down all surfaces and tools with rubbing alcohol. Contamination can also come from the cultivator, so it is important to consider showering and washing your hair before any lab work. Gloves can also be worn to prevent contamination.
Furthermore, the mushrooms themselves can be a source of contamination. Exposed grains, for example, can dry out and contaminate easily. To prevent this, grains can be soaked for 12 to 24 hours at room temperature before sterilization, allowing endospores to germinate and be eliminated. If contamination occurs, it can be physically removed using an alcohol-sanitized or flame-sterilized spoon.
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Common pests like sciarid flies can infest grain spawn and mycelia
Mushrooms are vulnerable to contamination, which can come from impurities in the air, soil, or water, and can also be caused by pests. Common pests like sciarid flies can infest grain spawn and mycelia, and they are one of the most common and damaging insects encountered when growing mushrooms indoors. Also known as fungus gnats, these flies can destroy a fungus crop, leaving mushrooms brown and leathery and inedible. Sciarid fly larvae are voracious eaters that devour mycelium and compost. After about 15 days of feeding, they enter a pupal stage by spinning a web around themselves.
The adult flies are most evident around light sources and have a black body, long antennae, and gray wings. Infestations of sciarid flies can be prevented by promoting drainage and reducing standing water in compost wharves. Rooms should be sealed and properly screened to exclude breeding flies, and lights and traps near doorways may be of value.
Other common pests that can infest grain spawn and mycelia include phorid flies, which are very small (0.125 inches long) with a humpback appearance and small antennae. They are stockier than sciarid flies and are very active, running and hopping erratically. Phorid flies feed on mycelia, depressing crop yields. Both sciarid and phorid adult flies carry disease organisms into the crop.
To prevent pest infestations, it is important to maintain a sterile environment when cultivating mushrooms. This includes sterilizing tools and surfaces, using sterile grain jars and fruiting blocks, and minimizing the exposure of these sterile materials to the surrounding environment.
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Frequently asked questions
Grain spawn, also known as mushroom spawn, is an essential ingredient in mushroom cultivation. It is a substrate composed of sterilized grains, such as rye, wheat, barley, or millet, that have been inoculated with mushroom mycelium.
Grains are full of starch and sugars, which provide an ideal food source for mushroom mycelium. However, they also create an ideal growing environment for mold and bacteria, which can outcompete the mushroom mycelium. Therefore, grains must be sterilized to kill off any mold spores or bacteria before inoculation.
To sterilize grains, start by rinsing them 4-5 times in cold water to remove any contaminants. Then, soak the grains in water for 12-24 hours to allow them to absorb water and cause any remaining contaminants to sprout. Finally, bring the grains to a boil and let them simmer for 10-15 minutes. Drain the grains and spread them out to dry for 1-2 hours before using them for inoculation.
