The grenadine is kind of optional. If you want a reddish hue, and a bit more of a "fruit punch" feel to the drink, use some. Please don't use a cheap grenadine...it will leave the drink tasting artificial after you've just used all those natural ingredients. This drink was inspired from the rum punch I had at the Rawlins Plantation in St. Kitts in the West Indies. We rented a car to drive around (literally--on the coastal road all the way around the island). We arrived too late for brunch at the Rawlins Plantation. But the staff was ever so professional. They told use they would see what they could do. Well, I headed over to the bar and asked what was good (with rum punch on my mind). The bartender said, "rum punch of course". I said, "set me up". Set me up she did. This rum punch had a depth, tanginess, tartness, and complexity that you rarely find these days. I had watched her make it and noticed she used Angostura Bitters. Bitters in a punch? YES! It balances the sugar from the passionfruit nectar along with the lime. So when I got home, I went into the Party Lab and didn't come out until I had replicated what I had down on that fair island. Here is the result. It's very close to the one I had down on St. Kitts. This is definitely one of my favorites. I stir this drink briefly so as not to get too much ice melting. This is a full-bodied drink at first, but it doesn't stand up well to dilution from the ice. Use big ice cubes if you have them (instead of bar ice). This drink may be a bit tart for some since I don't fully counter the lime juice with sweetener. If this is the case, throw a dash of cane syrup in. This is especially important if you make it in big batches. Taste and correct the sweetness with cane syrup if necessary. Rawlins Plantation Rum Punch takes very well to being made in batches. It will keep for several days in the refrigerator.