I do some wood working and am thinking what you would use that you would be ok with putting in 150 degree water, I can't think of anything. Some of the chemicals that are in varnish, laquer, urethanes are not food safe. Something like linseed oil, mineral oil would come out in the water. The wooden spoons you use in your kitchen aren't treated. Whatever your stirring is still going to get boiled later. I say unfinished.