It goes from solid at room temperature into your mouth. Your body heat melts it to a liquid that you swish around for 20 minutes. It will turn to liquid.

I don't know that it is the empty stomach that is so important, as much as that you are doing oil pulling at opportune times when more bacteria has accumulated in the mouth. Certainly, first thing in the morning is the absolute best time to oil pull. There is a maximum amount of bacteria in the mouth; if you eat breakfast and then oil pull afterwards, you have already swallowed most of the bacteria that had accumulated overnight. So in my opinion, you oil pull before or many hours after meals to remove the maximum amount of harmful bacteria/toxins.

According to Dr. Bruce Fife's book, "Oil Pulling Therapy" it's best to OP before meals because that's when your mouth contains the most bacteria and toxins. Eating causes us to swallow a lot of bacteria. Also, if you have a sensitive gag reflex than OP on an empty stomach is the way to go. If you're going to gag and throw up it's best that your stomach is empty. Hope this helps. :)