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4 Reasons Oyster Mushrooms Turn Brown (& How To Fix It)

I grow oyster mushrooms and recently noticed some of them changing from their usual color to brown. As this can be seen as a bad thing, it doesn’t always mean your mushrooms are bad. So, I came up with this guide to walk you through why your mushrooms may be turning brown and how to fix it.

Oyster mushrooms turn brown due to factors like aging, direct sunlight, moisture imbalances, and fungal or bacterial infections. To prevent browning, harvest mushrooms early, protect them from direct sunlight, maintain proper humidity levels, and keep your growing area clean to avoid infections.

Let’s dive deeper into the causes and how to prevent them from turning brown.

Oyster Mushrooms Turn Brown (4 Reasons)

Oyster mushrooms with brown caps

1. Natural Maturation

Oyster mushrooms naturally change color as they age. The older the mushroom, the more likely it is to turn brown. In particular, the gills and edges of the cap will darken, giving the mushroom a brownish color.

While this is a natural process, it’s essential to harvest your mushrooms at the right time to prevent excessive browning. The reason why most oyster mushrooms have a pale color is because they are harvested at a young age.

2. Too Little or Too Much Moisture

The correct moisture level is critical for the healthy growth of oyster mushrooms.

If the growing environment is too wet, it can lead to bacterial or fungal infections that cause browning. If you notice your mushrooms turning brown and becoming slimy, try reducing the humidity in your growing area.

On the other hand, if the environment is too dry, the mushrooms can become dehydrated, which can also lead to browning.

The ideal moisture level for mushrooms is above 80%.

3. Direct Sunlight

Oyster mushrooms can turn brown from direct sunlight or too much UV radiation due to the degradation of melanin pigment in their fruiting bodies. Melanin is a natural pigment that gives mushrooms their characteristic color and also protects them from UV radiation.

According to “Mushroom Biology and Mushroom Products” by Shu-Ting Chang and Philip G. Miles, “UV irradiation can cause degradation of melanin, which can lead to browning of mushrooms”.

The authors further explain that mushrooms exposed to direct sunlight can also undergo a similar process, where “the pigments in the fruiting bodies are broken down by the light, leading to browning”.

Therefore, it is recommended to grow oyster mushrooms in shaded areas or indoors to avoid direct sunlight or excessive UV radiation exposure, which can lead to browning and reduced quality of the harvested mushrooms.

4. Contamination

In some cases, browning oyster mushrooms can indicate contamination. If you notice off-smells, other mold growth, or your mushrooms don’t look quite right, it’s best to discard them and start with a fresh batch.

Oyster mushrooms can be susceptible to various fungal infections, which can cause browning or discoloration. Common fungal infections include Trichoderma mold, which can cause green patches on the mushrooms, and other molds that cause browning.

6 Ways To Prevent Oyster Mushrooms From Turning Brown

oyster mushrooms on a table

1. Proper Harvest Time

As mentioned earlier, age can be a significant factor in oyster mushrooms turning brown. To avoid this issue, harvest your mushrooms when they are still young and their caps are not fully opened.

Ideally, you should pick them when their edges are slightly curled under, indicating that they are at the perfect stage for harvesting.

2. Manage Sunlight Exposure

Protect your mushrooms from direct sunlight by placing your grow bags or containers in a location that receives indirect sunlight.

Alternatively, you can use a shade cloth to shield them from harsh sun rays. This will prevent excessive melanin production and keep your mushrooms from drying out and turning brown.

If your mushrooms are receiving too much direct sunlight, try moving your growing area to a spot with indirect or filtered light.

3. Control Moisture Levels

Ensure that your growing environment maintains the proper moisture levels. Oyster mushrooms thrive in humidity levels between 80-95%. Invest in a hygrometer to monitor humidity and mist your mushrooms regularly to maintain the right moisture levels.

Be careful not to over-mist or under-mist, as both excessive and insufficient moisture can lead to browning. It’s also known that oyster mushrooms turn yellow from not enough moisture.

To keep your mushroom environment at the perfect moisture, it is important to monitor the humidity and moisture levels in your growing area regularly. You can use a hygrometer to measure the humidity levels and a moisture meter to determine the moisture content of your substrate.

Adjust the humidity and moisture levels by adding or removing water. This will help ensure that your mushrooms grow healthily and avoid browning or other moisture-related problems.

4. Optimize Air Circulation

Good air circulation is essential for preventing the buildup of contaminants and maintaining healthy oyster mushrooms. Make sure your growing area has adequate ventilation, and consider using a fan on a low setting if necessary. Proper air circulation helps prevent fungal infections and other issues that can cause browning.

5. Maintain Cleanliness

Keeping your growing area clean is critical to preventing fungal infections and other contaminants that can cause browning.

Wash your hands before handling your mushrooms, sterilize your tools, and regularly clean your growing space. This will minimize the risk of infections and ensure that your mushrooms remain healthy and free from browning. I even shower before entering the room.

6. Monitor for Infections

Keep an eye on your mushrooms for any signs of fungal infections or other issues. If you spot any green, black, or brown mold, remove the affected mushrooms immediately and clean the growing area thoroughly.

By catching infections early, you can prevent them from spreading and causing further damage to your mushrooms.

What To Do If Oyster Mushrooms Turn Brown

If the mushrooms have a funny odor or a slimy texture, it’s best to toss them.

If the mushrooms are only brown in some areas, you can trim the brown areas off and cook them to ensure you don’t risk food poising.

Also remember growing mushrooms can be a trial-and-error process, and sometimes you might face unexpected issues like browning. Use the preventions listed above and try again!

Can You Still Eat Brown Oyster Mushrooms?

Oyster Mushrooms on a grill

So, the million-dollar question: can you eat those brown oyster mushrooms? The answer depends on the cause of the browning.

  1. Age or sunlight: If the browning is due to the natural aging process or exposure to sunlight, then it is generally safe to eat the mushrooms. Just make sure to cook them thoroughly, as older mushrooms may be a bit tougher.
  2. Excessive or lack of moisture: If the browning is caused by improper moisture levels, the mushrooms are likely still safe to eat. However, if the mushrooms appear slimy, moldy, or have an off smell, it’s best to discard them.
  3. Fungal or bacterial infections: If the browning is caused by fungal or bacterial infections, it’s best to stay on the side of caution and avoid eating the affected mushrooms.
  4. Unidentified causes: If you cannot determine the exact cause of the browning, use your best judgment. If the mushrooms look healthy overall and have no off smells or other signs of spoilage, they may be safe to eat. However, if you have any doubts or concerns, it’s always better to stay on the safe side and discard them.


“Growing Mushrooms the Easy Way: Home Mushroom Cultivation with Grow Kits” by Romain Gagnon