How To Tell If A Mushroom Liquid Culture Has Gone Bad


This guide will show you how to identify if there is an issue with your mushroom liquid culture.

mushroom liquid culture gone bad

Table of contents:

1. What are the different methods of identifying whether there is an issue with my mushroom liquid culture?

2. Visual signs of contamination of your mushroom liquid culture

3. Smell and odor of a contaminated mushroom liquid culture 

4. Mycelial Growth and Appearance

5. Sterility Testing of your mushroom liquid culture

6. Remedial Actions

7. Preventive Measures

8. Final Thoughts

What are the different methods of identifying whether there is an issue with my mushroom liquid culture?

If you have followed our guide on how to make a mushroom liquid culture you will want to be able to assess whether the culture is good before going to the effort and expense of inoculating substrate. In this article we are goingto address the following signs that your mushroom liquid culture has been contaminated:

1. Visual Signs of Contamination: We will explore the visual cues indicating a contaminated liquid culture, such as changes in color, cloudiness, or the appearance of molds, bacteria, or unusual growth.

2. Smell and Odor: We will discuss how a healthy liquid culture should smell versus signs of a bad odor, indicating potential contamination or spoilage.

3. Mycelial Growth and Appearance: We will describe the expected growth patterns, texture, and appearance of healthy mycelium in a liquid culture, contrasting it with irregular or abnormal growth indicative of contamination.

4. Sterility Testing: We will discuss methods for conducting sterility tests on liquid cultures to confirm or rule out contamination, such as inoculating a sterile medium to observe growth.

5. Remedial Actions: We will offer suggestions on what to do if a liquid culture is suspected of being contaminated, such as discarding the culture, sterilizing equipment, or salvaging healthy mycelium if possible.

6. Preventive Measures: We will provide tips on preventing contamination in liquid cultures, including maintaining sterile conditions, proper storage, and handling techniques.

By going through these different ways of analysing your culture you will be able to identify whether your mushroom liquid culture is fit for cultivation or the bin!

Visual signs of contamination of your mushroom liquid culture

Often the first sign that something is off with your mushroom liquid culture is something doesn’t look quite right. Visual signs of contamination in a mushroom liquid culture can include:

1. Cloudiness: A clear liquid culture should remain transparent. Cloudiness or turbidity can indicate the presence of bacteria or fungal contamination.

2. Color Changes: Healthy liquid cultures typically maintain their original color or exhibit subtle changes expected during growth. Unusual color shifts, such as darkening, changes to yellow, green, or pink hues, might signal contamination.

3. Presence of Sediment or Particles: Any unusual sediment, debris, or floating particles that weren’t initially present in the liquid culture can suggest contamination.

4. Mold Growth: Visible molds appearing as fuzzy growth, irregular patches, or spots on the surface or within the liquid culture are clear indicators of contamination.

5. Unusual Growth Patterns: Irregular or unexpected mycelial growth patterns, clumping, or abnormal structures within the liquid culture could be signs of contamination by foreign microorganisms.

6. Gas Formation or Foaming: Abnormal gas bubbles, foaming, or air pockets forming in the liquid culture might signify contamination by gas-producing bacteria or other contaminants.

Observing any of these visual cues should prompt careful examination and consideration of whether the liquid culture may have become contaminated. Further investigation may still be required before discarding your culture.

Smell and odor of a contaminated mushroom liquid culture

A normal liquid culture will have a slightly earthy/ mushroomy smell as you would expect. This odor is not overly strong. Contaminated mushroom liquid cultures might emit various unusual or off-putting odors compared to healthy cultures. These smells can include:

1. Foul or Putrid Odors: A strong, foul smell resembling rot, decay, or sewage can indicate bacterial contamination or spoilage in the liquid culture.

2. Sour or Vinegary Odors: A distinct sourness or vinegary smell might suggest contamination by certain bacteria or yeast species, indicating spoilage. Tis is the most common odor signal that I have found which indicates your culture has gone bad.

3. Moldy or Musty Smells: A moldy, musty, or earthy odor resembling dampness or mold growth could indicate fungal contamination within the liquid culture.

4. Ammonia-like Odors: An ammonia-like or pungent odor can sometimes be linked to bacterial contamination, especially in cultures that have been overgrown or contaminated with unwanted bacteria.

Recognizing these atypical odors during the examination of a mushroom liquid culture can signal potential contamination. It’s essential to trust your senses and, if unsure, conduct further tests or evaluations to confirm the presence of contaminants before using the culture for cultivation purposes.

Mycelial Growth and Appearance

Contamination in a mushroom liquid culture can manifest in mycelial growth and appearance in several ways:

1. Abnormal Growth Patterns: Contaminated cultures may display irregular, erratic, or uneven mycelial growth patterns that deviate from the typical uniform spread observed in healthy cultures.

2. Discoloration or Darkening: Unusual discoloration of the mycelium, such as darkening, browning, or changes in color inconsistent with the strain’s usual appearance, can indicate contamination.

3. Clumping or Aggregation: Clumps or aggregations of mycelium forming large clusters or irregular masses within the liquid culture may signify contamination.

4. Unusual Structures: Presence of unexpected structures or formations in the mycelium, such as nodules, lumps, or abnormal growth morphologies, could suggest contamination by foreign microorganisms.

5. Stalled or Sluggish Growth: Contaminants in a liquid culture might impede mycelial growth, causing slower or stalled growth compared to the healthy, robust expansion typically observed.

5. Lack of Expansion: Healthy mycelium exhibits rapid expansion and colonization of the liquid medium. Contamination might result in the mycelium failing to colonize or spread as expected.

Observing any of these abnormal mycelial growth characteristics can serve as indicators of potential contamination in a mushroom liquid culture.

Sterility Testing of your mushroom liquid culture


Sterility testing for mushroom liquid cultures involves assessing the absence of contaminants by inoculating a sterile medium with a sample from the liquid culture. Here’s a basic procedure:

1. Prepare Sterile Agar Plates: Sterilize agar plates and allow them to cool, ensuring they’re free from contamination before use. Alterntively you can buy these pre poured from a trusted vendor.

2. Sterile Technique: Work in a clean, controlled environment using a laminar flow hood or a still air box to prevent contamination.

3. Sample Collection: Using a sterile syringe, collect a small sample from the liquid culture. Ensure the sample is representative of the culture and collected aseptically. If you have used a magnetic stirrer when making your culture be sure to give the culture a good spin before collecting your sample.

4. Inoculation: Aseptically drop a small amount of your culture solution onto the surface of the sterile agar plate. You only need less than 1ml or about a 1 pence piece size of culture on the plate.

5. Incubation: Seal (using parafilm)and label the inoculated agar plate (i just write on the top of the plate using permanent marker). Incubate it at an appropriate temperature suitable for mycelial growth.

6. Observation: Regularly monitor the inoculated agar plate over several days to a week for any signs of microbial growth. Healthy cultures will show mycelium growing uniformaly outward from the culture deposit.

Sometimes your agar plate will show healthy mycelium growth with small patches that look irregular such as darkening. In this instance your culture may be fine when put to grain as the culture will outcompete the contaminant. Alternatively you can use the healthy mycelium to start your liquid culture again.


Remedial Action


If a mushroom liquid culture shows signs of contamination or goes bad, here are some remedial actions to consider:

1. Isolation and Discard: Immediately isolate the contaminated culture to prevent further spread. Safely dispose of the contaminated liquid culture and its contents.

2. Identify Source: Determine the source of contamination by reviewing sterilization procedures and environmental factors that might have led to the issue.

3. Sterilize Equipment: Thoroughly sterilize all equipment including containers and magnetic stirrers using a pressure cooker at 15psi to prevent recurrence of contamination.

4. Start Afresh: Obtain a fresh batch of spores or mycelium from a reputable source and restart the liquid culture using strict sterile techniques. Alternatively if you managed to grow some healthy mycelium when using agar you can isolate and use that.

5. Review Procedures: Evaluate and refine sterilization and cultivation procedures based on the identified cause of contamination to prevent future issues.

6. Consult Experts: Seek advice from experienced mycologists or forums dedicated to mycological practices if issues persist or if uncertain about handling the situation. We can strongly recommend the shroomery for this.

7. Maintain Strict Sterility: Emphasize stringent sterile techniques during all stages of liquid culture preparation, handling, and storage to prevent recontamination. Iso 70% alcohol is your friend!

Taking these remedial actions promptly can help mitigate the effects of a contaminated mushroom liquid culture and prevent further issues in subsequent cultivation attempts.


Preventative Measures


By this stage i’m sure you will have a pretty clear idea of preventative measures to avoid contamination of a mushroom liquid mushroom. To summarise:

1. Sterile Environment: Work in a clean and controlled environment using a laminar flow hood or a still air box to minimize airborne contaminants.

2. Sterilization of Equipment: Sterilize all equipment, including containers and utensils, using a pressure cooker at 15psi.

3. Personal Hygiene: Practice good personal hygiene by wearing clean clothing, gloves, masks, and hair coverings to prevent the introduction of contaminants.

4. Use Sterile Ingredients: Use sterile ingredients, such as distilled water and high-quality agar or nutrient solutions, to reduce the risk of introducing contaminants.

5. Aseptic Technique: Maintain strict aseptic techniques throughout the process, minimizing exposure of the culture to non-sterile surfaces or environments.

6. Proper Sealing and Storage: Ensure proper sealing of containers and storage in a controlled, clean area to prevent contamination during incubation or storage.

6. Regular Monitoring: Routinely monitor cultures for any signs of contamination during the preparation, incubation, and growth phases.

7. Quality Spore/Mycelium Source: Use spores or mycelium from reputable sources known for their quality and sterility.

8. Document Procedures: Maintain detailed records of procedures and observations to track the source of any contamination and refine techniques for future cultures.

By implementing these measures consistently and diligently, you can significantly reduce the risk of contamination when creating mushroom liquid cultures, ensuring higher success rates in cultivation projects.

Final Thoughts


As you can see by all the variables discussed in this blog post there are many things that can go wrong during a mycology project such as making a mushroom liquid culture. There will always be issues that present themselves. It is important to see these issues as a learning opportunity and not as a failure. One of the things mycology is sure to teach you is patience….

Happy Mushrooming!!!!

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