Sap can caused a problem on decks and in houses where wood beams are used for support. When it is wet, it is sticky and can rub off on clothing or attract dust and dirt. When it dries, it hardens and becomes difficult to remove, creating unsightly spots or bumps in the wood surface. You can try removing sap with several different cleaning techniques, but there is a chance it will come back.
First, use a cleaner to get rid of the sap that you can see. Generally a solvent or some type of oil-based cleaner works best. If you have turpentine, try using a small amount, especially if the sap is still wet. A small amount of liquid oil soap may also be effective. If the sap has hardened, you may need to use more than just a cloth. A paint scraper or similar device should work against tough spots.
When you are finished removing what sap you can, lightly sand the area. This will remove any sap stains you may have missed and will scrape away dried sap deposits that cannot be removed any other means. Restain or reseal the sanded patch if possible so that it matches the rest of the wood; sealing will also keep the sap from escaping again.
Sap can be a continuous problem, especially in pressure-treated beams. These are beams that have been placed in a chemical solution so that preservatives have been forced throughout their cells. This keeps the wood from drying out and cracking or warping once it is installed, but there is a price. The pressure treatment is designed to remove water, so sap can still be present in the wood. The treatment itself can create small pockets of vacuum-like conditions in the wood that draws the sap outward into the open air.
This means that, while you can clean off outer sap, the sap could continue to slowly bubble up from pockets deep within the wood. There is no solution to this problem, other than to keep cleaning off the sap as soon as it reaches the surface. If the beam can be removed, consider replacing it if the sap continues to be a problem.