Although acceptable in some products and specialities, bitter flavors are a major issue in food-product development, e.g., in proteins of emergent sources. Many mushroom species have been known historically for their bitterness, which is perceived later than the other flavors, and whose perception lingers in the mouth. To date, the substances responsible for this taste could not be identified, possibly due to the extremely variable molecular structures of bitter compounds in nature. The growing sector of mycelium-derived foods is constantly including novel species into their development pipelines, and the need for ways to control off-flavors, particularly the bitter aftertastes, is becoming evident. Identifying the chemical groups responsible for these perceptions is the first step towards finding solutions. Reviewing the perception of bitterness, masking methodologies, and in particular, the occurrence of bitterness in mushrooms, we find that fungal bitterness is chemically diverse, mainly attributable to peptides, phenolics, terpenoids, and alkaloids, with direct receptor-level evidence so far restricted to a few metabolites such as oligoporins and infractopicrin, while most reported compounds remain inferred. Fungal bitterness is likely multicausal, so masking strategies will need to be developed on a species- or group-specific basis rather than universally.
