????Yeast: White or grey-colored surface growth found on beer system components (faucets, keg couplers and drains) that are exposed to air.
????Mold: Brown or black-colored surface growth found on beer system components (faucets, keg couplers and drains) that are exposed to air.
????Beer stone: Grey or brown in color, (calcium oxalate) builds up and eventually flakes off if the system is not properly maintained, potentially ending up in the pint and having a negative effect on taste.
????Bacteria: Beer-spoiling bacteria will ruin a beer’s flavor and aroma. While these micro-organisms are not health risks, they will cause buttery off-flavors called diacetyl, or sour, vinegary off-flavors called acetic acid.