c("Submerge the zests of the grapefruit in olive oil and heat up to 160 degrees for five minutes.", "Put oil and remaining ingredients in a shallow glass dish and  submerge shrimp in it. Cover with plastic and refrigerate.  Marinate shrimp for  at least 3 hours so flavors can penetrate.  Remove shrimp from marinade and  place on a paper towel before grilling.", "Grill for 1 1/2 minutes on each side  over hot coals.", "Season with salt and pepper if desired.")