Well, we process several thousand pounds of beeswax a year into candles so maybe I can help.
My understanding is that the sputtering can be EITHER due to water or to other impurities.
We use a two-step process. First, make your cappings into what I call a 'country cake'. Use a Kelley melter or something similar. This get all the big stuff out, and does not involve water.
Take that country cake and melt it in water. For many years I used a $30 Wal-Mart Turkey Roaster. Electric, but without visable coils so just about totally safe. I put in 20 lbs or so of wax, five pounds or so of water. Boil the heck out of it for 10 minutes. Let cool a few minutes (10-15) and then run through a tight nylon curtain material into a five gallon bucket.
Wash out the Turkey Roaster, and pour the contents of the five-gallon bucket back into it. At this point, either turn off the water and let the cake form overnight or take off the wax to make candles.
If you let the clean cake form overnight, the next time you heat it do so without water. Strain through a BOUNTY paper towl (yes, it makes a difference) into a warm coffee carafe kept on a coffee maker burner. Pour into the molds from the coffee carafe.
If you don't let the 2nd cake form, carefully dip the wax from the top of the water and, again, pour through the BOUNTY paper towel into the coffee carafe. This is the process when most beginners put in water. To avoid doing so, let the 2nd cake form and then reheat without water.
Do not pour above 160 degrees or below 140. Use a candy thermometer.
Lloyd Spear, Owner of Ross Rounds, Inc. Manufacturers of round section comb equipment and Sundance Pollen Traps.