Grenadine is pomegranate syrup.
There is also commercially available pomegranate juice. I believe the name is Pom. I don't know whether it has preservatives, but depending on how they preserve the juice, you might be able to just add it to secondary. That'd be easy as hell.
FYI, I've fermented apple juice with a Hefeweizen strain. Done it twice. And the result is fantastic.
In Process: Mango Beer, Homebrewers Pale Ale
Bottled/Kegged:Spicy Light Rye, Rice-adjunct Pale Ale, Mild Bourbon Porter, Roasty Stout, Basic Light Mead, Bourbon County Stout Clone
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