As a child, grenadine seemed like the height of sophistication, mainly because I had no idea what it was. All I knew was that it was in Shirley Temples, it had an appealing, sensual burgundy hue, and it could be found near the little bottles of club soda and margarita mix. If I had known it was just pomegranate-flavored syrup, I still would have been quite impressed, because I was a child and had only read about pomegranates in Greek mythology.
You can make your own grenadine by combining pomegranate juice with an equal amount of sugar, but why stop at pomegranate, especially when you consider how expensive pomegranate juice is? Nearly any fruit juice can be made into a grenadine-like syrup. I say “nearly” because the citrus juices can be tricky. I don’t think OJ syrup would be very good, though lemonade syrup would absolutely slap.
Berry juices like cherry, cranberry, and strawberry are all natural candidates for grenadine substitutes, but I bet you could find applications for peach, Concord grape, and apple. Also, don’t ignore the “cocktail” family of fruit drinks — I think a Hawaiian Punch syrup would be quite nice, actually, particularly in a summery old fashioned. Sweetness is the goal when making syrups, and this would be a good way to use up any “too sweet” juice drinks you may have purchased in error.
To make any of these fruity syrups, all you have to do is combine a cup of juice with a cup of sugar in a sauce pan and heat it up until the sugar dissolves. If your juice is tart (like unsweetened cranberry) or you want a thicker syrup, you can double the sugar. Let everything cool, then pour it into a bottle and pop it in the fridge, where it will keep for at least a month. Add your syrup to Singapore Slings, mimosas, plain soda water, or anything that needs a bit of fruity sweetness.