I first heard of Lomo al Trapo about four years ago when I read an issue of Bon Appétit Magazine where Steven Raichlen described this South American method of cooking beef tenderloin. Lomo al trapo literally translates to “beef tenderloin in a towel.” It’s made by wrapping a beef tenderloin in a thick crust of salt inside a towel, tying it up, and throwing it directly on a fire until it’s cooked.
It sounds crazy, but it’s one of the easiest, most foolproof, delicious, and wickedly cool methods of cooking beef I’ve ever seen. Do this for a dinner party and your guests will at first think you’re crazy, but once that juicy slice of beef is on their plate and in their mouths they’ll think you’re a genius. Okay, maybe a mad genius. All it takes is beef, salt, a few seasonings, a towel, twine, and fire.
This post is more a description of a technique than it is a recipe. Just follow the basic steps outlined here and use your imagination.
Start by soaking a clean, kitchen towel in water. Do not use a towel that you value; you’re not getting this back. I purchase packs of six terry cloth bar towels that measure 16″ square at Target for about $4.00.
Ring out the towel and lay it out on a flat surface. Then spread a thick layer of kosher salt.
Add some fresh or dried herbs if you would like and then begin rolling the tenderloin up in the towel. When you get to the point where the towel will begin to roll under the salt, pull the towel back and continue to roll. You want the beef to be in full contact with the salt. Fold the ends of the towel in like a burrito and then complete the roll. Be sure to compress the roll as you go. You want this tight.
Once the tenderloin is completely rolled. Take some cotton twine that you have also soaked in water and tie the towel to the roast. I start with a tie that runs lengthwise and holds the ends together. Next, I tie the roast about every two inches.
Place the beef tenderloin package directly into the coal bed. I like to move it around a bit to get it nestled into the coals. I like to use lump charcoal for this as I believe it is cleaner. You can use charcoal briquets if you would like. Let this sit in the coals for about 10 minutes, flip and give it another 8 minutes or so.
Pull the roast out of the fire when an instant read thermometer reads 95°F to 100°F. The heat from the hot salt will continue to cook the roast. I pulled this one right before it hit 100°F and just a few minutes later it was approaching 104° After about 8 minutes the roast will be 125-130°F .
Once the roast comes to the desired temperature, crack open the hardened cloth and salt shell. Use a pastry brush to brush off any excess salt. I recommend saving some of the excess salt to use to season any accompanying sides you may be serving. The salt will have a nice smoky flavor. Discard the remaining shell.
Move the roast to platter and carve to about 1 1/2 to 2 inch slices. The end pieces will be slightly more done. Open a nice dry Malbec and enjoy!
Here is what I did:
Lomo al Trapo: Salt-Crusted Beef Tenderloin Grilled in Cloth
1 1/2 to 2 pound center cut piece of beef tenderloin, trimmed of all fat and silver skin
Kosher salt (Approximately 2 cups)
Fresh or dried herbs like oregano and thyme
1 piece of clean cotton cloth, approximately 16 inches square, soaked in cold water and wrung out
Prepare a charcoal grill lighting a large chimney of lump charcoal. You should have a good layer of lump charcoal covering the bottom of your grill.
Spread the cotton cloth on a work surface. Spread the salt out on top of the cloth to form a layer 1/4 inch thick that extends to within 1 inch of the edge of the cloth. Place the fresh herbs or sprinkle the dried herbs evenly over the salt.
Place the beef tenderloin on top of the salt and herbs. Roll the cloth and salt around the tenderloin trying to maintain a compact roll. As the cloth begins to roll up on itself, pull the cloth back a few inches to ensure that the tenderloin completely encased in salt. Fold the ends in like you would rolling a burrito and finish the roll. When the roll is complete, first tie the roast lengthwise and then about every two inches.
Rake the charcoal out into an even layer at the bottom of the grill. Lay the wrapped tenderloin right on the coals. Moving it around a little as you place it to ensure that it is complete contact with the charcoal. The cloth will more than likely catch on fire so do not become alarmed. Grill for 9 to 10 minutes. Using long handled tongs, gently turn the tenderloin package over and grill for 8 minutes or until an instant read thermometer reads 95° to 100°F.
Remove the roast from the coals and let rest. The hot salt will continue to cook the roast. Leave the thermometer in the roast until it reaches the desired doneness: 125 – 130°F for rare; to medium-rare, 140° – 145°F. This will take as little as 10 minutes.
Tap the tenderloin hard with the back of a large, heavy chef’s knife. The burnt shell should crack and easily come off. Brush any excess salt off the tenderloin with a pastry brush. Transfer the tenderloin to a clean platter, cut it into 1 1/2 to 2 inch thick pieces and serve immediately.