1 (3 and 1/2-pound) center-cut boneless pork loin, patted dry
In a medium heavy-bottomed saucepan over medium heat, simmer wine until it is reduced by half, 20 to 30 minutes; adjust heat to low and continue to cook down to 2 tablespoons. Cool completely.
In a food processor combine salt, thyme leaves, lemon zest and wine reduction. Pulse 2 or 3 times. Add sugar and pulse again until mixture has the consistency of damp sand. If your mixture is moister, spread it evenly on a sheet pan and leave it out on the counter for several hours or overnight.
Place pork in a baking pan. Spread about 1/2 cup of the salt rub all over the pork (reserve remaining rub for another use; it will keep for a month in the fridge). Cover tightly with plastic wrap and refrigerate for at least 3 hours or overnight.
Light the grill for high-heat indirect cooking, piling charcoal on one side of the grill and leaving other side unlighted. (For gas grills, turn on the heat on one side of the grill only.) Spread a piece of foil or place a disposable metal roasting pan underneath grill on the unlighted side to catch any drips. Place pork on the grill over the foil. Cover grill and cook, turning every half hour until meat reaches 140 degrees, from 1 hour to 90 minutes. Transfer to a cutting board and let rest 10 minutes before carving.
An earlier version of this recipe included a drying phase, where the wine-salt rub was placed in the oven. Due to the fact that many home ovens are not perfectly calibrated, this step led to undesirable results for some readers. The recipe has been retested and amended. As it currently reflects, the wine-salt rub should be at or near the right moisture level after it has been put through the food processor. If the rub is still too moist, spread it evenly on a sheet pan and leave it out on the counter for several hours or overnight.