Place the wine and butter in a small pot. Bring to a simmer, and simmer just until the butter is melted. Removed from the heat and stir in the garlic, herbs and cayenne.
Preheat barbecue to medium-high. Layer the sheets of foil, slightly overlapping them lengthwise. Set the salmon in a row down the centre of the foil. Drizzle fish with wine/butter mixture; season with salt and pepper. Fold the foil over the fish and seal at the top. Set the salmon on one side of the barbecue. Turn the heat underneath it to low; leave the other side set to medium-high. Close the lid and cook the fish 20 minutes, or until cooked through.