I used Ruby Red grapefruit juice and zest and the curd turned out beautifully. Used a double boiler and it took longer than 10 minutes to achieve the right consistency. Will definitely make again.
Amazing and low in sugar.
I was skeptical, but this was AMAZING. It would be perfect filling for shortbread sandwich cookies. I got 2/3 of a cup of juice out of just one grapefruit, but added an extra squirt or two after tasting to get it a little more tart. I also used the improvised double-boiler method, which may have resulted in a longer cooking time.