If you have a new butcher block countertop in your kitchen you are most likely thinking about how to finish it so it will be safe for your family. Since the wood will come in contact with food your family will consume, you can't use just any finish and need to research a bit.
One: What not to use
Research the finishes you are considering. Linseed oil use to be a favorite but it is not safe for contact with food and should not be used. Also, oil-based stains are not a good idea or paint, although the idea of painting a beautiful butcher block countertop would hide the woods, and probably not something you are considering. Also, although wood does have natural antibacterial properties simply through its capillary action that wicks away moisture from the surface, you shouldn't leave your butcher block countertop raw to further prevent bacterias from working their way on the wood and causing the bacterias from meat, poultry, and fish to propagate.
Two: Mineral Oil and Walnut Oil
Two of the cheapest and most widely used products for finishing a butcher block countertop are mineral oil and walnut oil. It is food-safe and inexpensive to use compared to some commercial-grade finishes. All you need to do is pour on a good puddle of the chosen oil, spread it around with a clean cloth or gauze fabric, and let it soak into the wood for thirty minutes, then wipe off the excess. As you wipe off the excess oil rub it aggressively to force the oil into the wood. These oils are food safe, will not go rancid, but will need to be reapplied every month or so, depending on how frequently you use your block for chopping. The mineral oil will give a fairly clear surface and only darken the wood slightly. Walnut oil will stain the wood a bit so you may want to try it on a scrap to see if you like the finish.
Three: Commercial Grade Finishes
Many companies now sell products made specifically for raw butcher block countertops. Each has its own instructions and methods for preparation and frequency of repeat coats. You can research all of these on the internet. These finishes are routinely more expensive than mineral oil and do the same job.
Four: Federal Government Standards
The FDA publishes a document outlining its rules on food-safe countertops and finishes. This can be downloaded online by going to their website. You will notice that most of the finishes they recommend they consider safe once it has totally dried. Dry is the keyword to safety guidelines. Many people criticize these guidelines as some of their rules for safety for food may not actually meet the guidelines a homeowner would want so you need to consider your choice carefully. While a finish may not cause birth defects, cancer, or food poisoning, they may still contain chemicals you wouldn't want around your food.
The federal government requires that any product that is sold safe for contact with food must publish a Material Safety Data Sheet (MSDS) and information on the solvent container on how to access this information.