it means you use boiling water to heat up the alcohol. the oven heated up the bud, the water heats up the alcohol and you leave it in there for 20 minutes at 170. the need for the water bath is because it isnt safe to cook alcohol over an open flame or electric stove as the flame or coil will get really really hot, and when cooking a highly flammable substance that isnt a good thing

and also "Pre-baking should stink up the house."