Saltpeter (potassium nitrate) helps preserve the color and flavor of cured meat, and also inhibits the growth of Clostridium botulinum, the bacteria that causes botulism. Another product that serves the same purpose is Insta Cure #1, a combination of salt and sodium nitrate.
Cut any excess fat from the tongue. Combine the salt, sugar, spices, and garlic, and rub the mixture well into the meat. Put the mean into a non-reactive container.
Dissolve the saltpeter in the warm water. Pour the water over the tongue, cover the tongue with a plate that fits inside the container, and weight it down with a large, well-washed stone or water-filled jug. Cover the container, and refrigerate it for 10 to 14 days, turning the tongue every two to three days.
When you're ready to cook the tongue, put it into a large pot, cover it with cold water, bring the water to a boil, and drain the tongue. Repeat this process three times, using fresh water each time. Then cover the tongue with cold water again, and bring the water to a boil. Reduce the heat, and simmer the tongue for about two hours, or until it is tender.
Remove the tongue from the cooking water. Let it cool just a little, and then peel off the skin. Slice the tongue immediately if you want to serve it warm. If you'll be serving it cold, let the tongue cool completely before you slice it.
Linda Ziedrich is a freelance writer and editor and the author of The Joy of Jams, Jellies, and Sweet Preserves and The Joy of Pickling. She lives with her family near Scio, Oregon, where she grows most of the fruits and vegetables she pickles, preserves, and otherwise prepares.