You can easily seal a wooden cutting board with mineral, vegetable or walnut oil to help repel moisture while keeping the wood from drying out. Sealing a cutting board also helps prevent it from absorbing food odours and helps protect it from staining. You should always seal a cutting board before you use it, then at least once each week to keep it conditioned. A good wooden cutting board that's cared for will last for generations.
Pour a small amount of mineral oil onto the surface of your wooden cutting board and rub it in with a soft cloth. Rub in the direction of the grain and coat the entire face of the cutting board, along with the edges.
Place a soft cloth on a flat surface and flip the board over onto the cloth, oiled side down. Pour mineral oil onto the back of the cutting board to seal this side as well. It doesn't matter if you plan to cut on the back or not, both sides of the cutting board should be sealed to protect against moisture.
Season the cutting board with as much oil as it will take. When the oil begins to remain on the surface rather than be absorbed by the wood, the cutting board is sealed. Wipe off any excess oil. Let the board dry before using it.
Seal your board each time you wash it. Clean your wooden cutting board with warm soap and water on both sides. Dry the board with a cloth as much as possible, and then let it air dry in a dish drainer or over the sink. Seal the cutting board only after it is completely dry. If you use and clean your board daily, you can safely use a thin coating of walnut or vegetable oil on both sides to keep it from drying out.
Mineral oil is not as bacteria prone as some vegetable oils, making it a good choice to use to seal your cutting board. It doesn't matter if you plan to cut on the back or not, both sides of the cutting board should be sealed to protect against moisture. Butcher block cutting boards do not hold onto bacteria as long as plastic cutting boards.
Make sure the oil you select is approved for use with food preparation.