We extract biological nutrients (the goodness) from the fruiting bodies of the mushrooms so that they're bioavailable (meaning they're readily available for our bodies to absorb and utilise).    Just like plants, mushrooms are made up of thousands of cells. The cell walls of fungi are made up of a substance called chitin which is super tough (for reference, crab shells are made from chitin). Humans don't tend to have the enzyme needed to break down chitin so essentially the goodness within the mushroom cells remain locked inside the cell, and passes through our digestive system and out again, much like dietary fibre does.     For this reason, we extract the goodness from the mushroom cells and dry it into a powder. Solvents such as heat and alcohol work to break down the chitin and extract the biological nutrients.