What They Found: Yeast and mold
How to Clean It Properly: First remove any knives stored in the block. Turn the knife block upside down and shake lightly or use a can of compressed air to remove crumbs and other loose debris. Hand wash the knife block in hot soapy water, using a small brush (like a baby bottle nipple brush) to scrub out the knife slots. Rinse thoroughly with clean water.
To sanitize, prepare a mixture of 1 gallon lukewarm tap water with 1 tablespoon of 5.25% household bleach. Either immerse the complete block in the water/bleach mixture or fill the knife slots. Allow the bleach/water mixture to sit in contact with the slots for one minute. Rinse the block and knife slots thoroughly with clean tap water and place the block upside down on a clean surface to dry.
To avoid mold and bacterial buildup, wash knives thoroughly after each use and let them dry completely before placing them in the knife block.
Wash and sanitize the knife block monthly if used frequently.