Can I still eat black fungus that has been soaked in water overnight?

Generally speaking, it is not recommended to consume wood ear mushrooms (black fungus) that have been soaked in water overnight.

If wood ear mushrooms are improperly stored during the soaking process, for example left at room temperature for too long, bacteria may multiply or harmful substances could be produced, such as toxins from Pseudomonas cocovenenans. These toxins are difficult to completely eliminate even with high-temperature cooking and could pose a threat to health. Particularly in warmer conditions, bacteria multiply more quickly, increasing the risk associated with consuming soaked wood ear mushrooms overnight, so extra caution is necessary.

If the mushrooms are immediately refrigerated in a sealed container after soaking to prevent contamination, they may still be consumed within a short period. Cold temperatures effectively inhibit bacterial growth and prolong the safe consumption period of the mushrooms. Even so, the soaking time should not exceed 24 hours to prevent a decline in texture and quality, as well as to avoid potential symptoms like diarrhea and abdominal pain after consumption.

Before consumption, carefully check the mushrooms for any abnormal color or odor, and discard them immediately if any irregularities are detected—do not take chances.