When redwood is stained by grease, wine, or a condiment, the staining material can be washed off with water, in most cases. If brushing it with a broom and squirting it with water do not work, the staiined area can be powerwashed. It should be noted that a powerwash nozzle should be kept at least a foot away from any natural wood. If this does not work, Oxalic acid, mixed with water makes a very good deck wash. As a very last resort, Redwood can be sanded, and the edges of the sanded area feathered, so that there is little noticable effect from the stain.