The other day I made salad dressing, refrigerated the half cup left-over, and naturally the oil gathered on top. No matter how I shake the dressing, it's so stubborn and wouldn't want to socialize and mix with the vinegar, unlike store-bought dressing. Then I remembered I have soy lecithin I bought a while back. It's supposed to aid in emulsifying everything from candy bars to sauces to hand cream, and it's also used to make breads rise higher.