From "101 Recipes" food blog online. She simmers the grapefruit juice here so it reduces and concentrates. "The flavor of the curd is better, the color deeper. That said, if you don't have time to do this step, just start with 1/2 cup grapefruit juice, strained. Your curd with still be perfectly good. As far as sweeteners go, I use granulated sugar, or honey, or a blend of the two. I stay clear of brown sugar or maple syrup here just because it muddies the color. What else? Method: I cream, then combine ingredients in a stainless steel mixing bowl here, you can use the bowl from your stand mixer if you like. Then, move that bowl over a saucepan of boiling water (as a makeshift double boiler), to keep the heat gentle. Go from there. It's easy, and keeps bowl-cleaning to a minimum."