To make the marinade, mix together in a bowl all ingredients except the pork.
Place pork in a large zip-top plastic bag. Pour the marinade over the pork and close the bag trapping as little air as possible. Marinate in the fridge at least 8 hours and up to 2 days. Be sure to turn the bag every time you open the refrigerator so that all sides are in the down position for at least 2-4 hours.
Preheat oven to 160 C / Gas 3.
Place pork in a roasting tin along with the marinade. Cover with a pan lid or foil. Roast for 2 hours, then remove the cover and continue roasting for at least another 30 minutes. The roast should be cooked until the centre reaches at least 65 degrees C (slightly pink) or up to 75 degrees F (well done).
Remove from oven and loosely cover with foil for at least 10 minutes before carving.
Scrape the bottom and sides of the roasting tin with a wooden spoon to loosen up and dissolve any dark bits. Sieve the liquids into a sauce pan and bring to a slow boil to reduce slightly. Taste and adjust seasoning accordingly. Add a drop or two of extracts (orange, lemon and/or lime) to intensify the citrus flavours, but be careful not to over power the cumin (which should be the predominate flavour).
Carve the roast into thick slices and place on a platter. Add the juices from carving into the sauce and stir well. Drizzle the sauce over the pork.