If you have an older butcher block that has seen better days, it may be time to refinish it. Refinishing a butcher block will increase its attractiveness, and the seasoning process will prevent new stains and the absorption of bacteria. Filling in the wood pores so they repel food particles and liquids results in a butcher block that is safer and pleasing to the eye.
If your butcher block is screwed on top of floor cabinets, open cabinet doors below and remove any drawers to get a look at how it is attached. You may see about four to six screws holding it in place. Unscrew these from underneath with a screwdriver.
Decide whether you want to keep the current side of the butcher block on top or flip it over. Some neglected butcher blocks may have warped and will look better if flipped over, with the old wood screw holes filled in with wood putty. Others may be fine keeping the existing top surface as-is.
Sand the top, beginning with 80-grit paper and proceeding to finer grades. Use smooth, even-pressure sanding to avoid butcher-block "valleys" or a wavy surface. Sand the four edges as well. Brush off the particles.
Apply a light coat of mineral oil, or butcher block oil to what will become the underside of the butcher block. Food-grade mineral oil is available in most drugstores, in the laxative section, as mineral oil USP grade. Allow the oil to soak in for about 15 to 30 minutes. This will protect the underside of the butcher block from moisture absorption in a humid kitchen.
Replace the butcher block on top of your cabinets, using new screws to fasten them to the supports.
Coat the top and sides of the butcher block with oil, including the three sides not abutting the wall. Pay special attention to the edge nearest water sources, such as your sink. Apply about 1 oz. (2 tbsp.) per each square foot with a clean rag, rubbing the oil around evenly.
Repeat the oil coating nightly for a total of three applications, letting the butcher block absorb the oil overnight. Keep bowls, appliances and other objects off the butcher block during this period.
Complete up to six applications of mineral oil in the first week. However, you may find the oil beginning to pool and puddle after three applications. Judge for yourself how much oil your butcher block can absorb. Repeat the oil application after two weeks, and every three to four weeks thereafter. Gauge the need for additional oil by how thoroughly a test drop of water beads on top of the butcher block without soaking in.