How To Tenderize London Broil | Chefs’ Best Secrets

London broil becomes tender through a combination of a baking soda marinade, mechanical pounding or scoring, cooking to no more than medium-rare.

You buy a thick London broil, grill it perfectly, and end up sawing through shoe leather. That tough, lanky cut — typically top round or flank steak — has almost no intramuscular fat.

The good news is that tenderizing London broil mostly comes down to four techniques you can apply in sequence. You don’t need expensive cuts or a sous-vide setup. A mallet, some baking soda, and decent timing transform this budget-friendly roast into something genuinely pleasant to eat.

Why London Broil Starts Tough

London broil comes from a hard-working muscle group. The top round sits in the cow’s hind leg, a region loaded with collagen and long, dense muscle fibers that provide propulsion. That structure makes it flavor-packed but naturally chewy.

Without some intervention, the proteins contract tightly during cooking and squeeze out moisture. The result is dry, fibrous meat that resists your knife. Understanding this biology explains why tenderizing London broil is non-negotiable rather than optional.

Bonus fact: “London broil” is actually a cooking method, not a specific cut. Butchers and grocers commonly label top round or flank steak as London broil, so the same tenderizing rules apply regardless of which exact muscle you bring home.

Why Mechanical Tenderizing Helps First

Breaking down those long muscle fibers before they hit heat gives you a head start. Home cooks and recipe developers broadly agree that a few minutes of physical work pays off more than any marinade alone.

• Meat mallet: A few good whacks with the textured side physically cracks the fibers open. This creates tiny channels for marinade to penetrate deeper. Grandbaby Cakes recommends this step before marinating.
• Bladed tenderizer: A metal tool with short, sharp blades that pierce the surface. It cuts through connective tissue without flattening the roast, which keeps the thickness even for cooking.
• Scoring or crosshatching: Using a sharp knife to make shallow, quarter-inch cuts in a crisscross pattern across the surface. This helps the marinade soak in and further breaks down fibers for maximum tenderness.
• Massage: Simply rubbing the marinade into the scored surface with your hands helps distribute the tenderizing agents evenly. Some recipes suggest doing this for a minute or two before letting it rest.

Start with one of these mechanical steps. Even just scoring the top surface improves results noticeably. Skip this part and you’re asking the marinade to do all the work.

The Baking Soda Secret

Here is the technique most casual cooks overlook. A small amount of baking soda in the marinade chemically alters the surface proteins. It raises the pH on the meat’s exterior, making it harder for muscle fibers to tighten during cooking. The side effect is that it also encourages better browning when the meat hits a hot pan.

Bon Appétit’s test kitchen uses exactly this trick in their London broil recipe. They coat the meat with a mixture that includes baking soda tenderizes the tough fibers, giving the final steak a tender texture that rivals more expensive cuts. The trick works because the alkaline environment partially denatures proteins at the surface, softening them before heat ever hits the pan.

Use roughly one teaspoon of baking soda per pound of meat. Mix it into a savory marinade with soy sauce, oil, garlic, and herbs. Four hours in the fridge is the minimum; up to 24 hours gives maximum flavor without over-tenderizing. Longer than a day and the exterior can turn mushy, so set a timer.

Notice the baking soda method occupies the sweet spot between preparation time and tenderness payoff. Mechanical steps help immediately, but the chemical change from baking soda keeps working while you do other things.

How to Cook and Rest for Tenderness

All that tenderizing work disappears if you overcook the meat. London broil is lean and rewards fast, high-heat cooking that stops at medium-rare. Beyond that, the remaining collagen tightens and moisture evaporates, returning you to chewing territory.

1. Sear in cast iron: Bon Appétit prefers stovetop cast-iron searing over grilling or broiling because the pan delivers consistent, high heat that builds a crust fast without drying out the interior. Heat the pan until smoking, add oil, then sear 4–5 minutes per side for a one-inch-thick roast.
2. Check temperature early: Pull the meat at 125–130°F for medium-rare. Carryover cooking will raise it about 5°F during resting. Use an instant-read thermometer, not guesswork.
3. Rest the meat uncovered: Let it sit on a cutting board for at least 10 minutes. Resting allows the juices to redistribute. Slice too soon and those juices end up on the board rather than in the meat.
4. Slice against the grain: Find the direction of the muscle fibers and cut perpendicular to them. This shortens each fiber in every bite, making the meat appear more tender. Cutting with the grain gives you long, chewy strips.
5. Slice thinly: Aim for quarter-inch slices or thinner. Even with tenderized meat, thin slices improve the mouthfeel and make the serving go further.

Some home cooks also reduce the leftover marinade into a pan sauce. Grandbaby Cakes suggests boiling the marinade for a few minutes to kill any bacteria, then drizzling it over the sliced meat for extra moisture and flavor.

Matching Method to Your Setup

The right tenderizing approach depends on what equipment and time you have. A grill works fine but requires careful temperature management. Broiling is faster but can overshoot doneness if you don’t watch it. Cast-iron searing on the stovetop gives the most control and the best crust.

The same combination of techniques applies across cooking methods. Score or pound the meat first. Apply a baking soda marinade for four to twenty-four hours. Cook hot and fast to medium-rare. Rest. Slice thin against the grain. Meat mallet tenderize is the quickest mechanical option if you’re short on prep time and need immediate results.

The Bottom Line

Tenderizing London broil comes down to three steps you can execute in any kitchen. Mechanically break the fibers with a mallet, score, or bladed tenderizer. Soak the meat in a baking soda marinade for at least four hours. Then cook to medium-rare in a screaming-hot pan and slice thin against the grain.

If your first attempt still turns out chewier than expected, check the marinating time and your cooking temperature. A quick-read thermometer and a sharp knife make a bigger difference than any single ingredient. Your local butcher can also advise on whether your particular roast is top round or flank, which affects optimal cooking time.