If a butcher block countertop is in need of refinishing, first clean any food residue and grease from the countertop, and then carefully scrape its surface to remove any nicks and scratches. This Old House recommends using a high-quality, sharp paint drag-scraper. Drag the drag-scraper toward you rather than using a planing motion pushing it forward to avoid splitting the wood at the ends of the butcher block.
After the butcher block countertop is thoroughly clean, sand it with a sanding block to refinish its surface. Use a coarse sandpaper, starting with about 50-grit paper. Finish with up to 100-grit paper, depending on the severity of the scratches on the countertop. DoItYourself.com recommends caution while sanding the butcher block in order to keep the surface smooth and even.
After sanding the butcher block countertop, remove all of the remaining sawdust with a cloth that has been dipped in hot, soapy water. This Old House insists that the only thing that should ever be used to treat the surface of a butcher block countertop is a good-quality mineral oil. Never use cooking oil or any other type of oil on the butcher block, and do not seal it with a urethane coating.