Sous Vide London Broil: Temperature and Time

Sous vide London broil cooks at 131°F (55°C) for 24 to 60 hours for pink, sliceable meat that is tender like a good steak. London broil is usually top round, a lean and tough cut, and the long time is what makes it tender.

The time does not depend on thickness, as long as the piece is no more than 2.25 in (5.7 cm) thick.

Which cuts are sold as London broil

London broil is not a single cut. America's Test Kitchen calls it a generic label that butchers put on large, inexpensive steaks. It says flank steak was the usual choice until its price rose, and lists the cuts now sold under the name:

• Chuck shoulder steak
• Top round steak
• Bottom round steak

Wikipedia's entry, which cites James Beard, makes the same point: the name originally meant grilled flank steak and has come to describe a method of preparation more than a cut. The method is to marinate the beef, grill or broil it, and cut it across the grain into thin slices.

The calculator's London broil setting is for top round. Read the package for the name of the cut. If it is flank steak, use the flank steak guide. If it is from the chuck, the chuck roast guide covers that part of the animal.

London broil temperature and texture

The calculator has three settings. The Time column gives the window for each.

131°F (55°C), medium-rare. This is the default. The meat is pink and sliceable, tender like a good steak, after 24 to 60 hours.

140°F (60°C), medium. The meat is light pink, sliceable and a little firmer. The time is 18 to 60 hours, so the minimum is 6 hours shorter than at 131°F (55°C).

150°F (65.6°C), tender braise. The meat is gray-brown, moist and soft, like a pot roast that still slices. The time is 12 to 36 hours.

The first two settings are steak doneness levels, medium-rare and medium. The steak temperature chart compares them with the other levels.

The 131°F (55°C) window is wide, and its two ends come from two sources. The roast beef recipe in Douglas Baldwin's guide to sous vide cooking lists top round among its cuts and cooks the roast at 131°F (55°C) for about 24 hours, which is the calculator's minimum. Jason Logsdon's London broil guide at Amazing Food Made Easy gives 18 to 60 hours, and the calculator takes its 60 hour maximum from that range.

Logsdon says the time depends on which cut is under the label: flank needs the least time, chuck more, and round the most, 36 to 48 hours or even up to 60. For top round, plan for the middle or the long end of the window.

Why a lean steak takes this long

A tender steak only has to heat through, which is why the times in how long to sous vide steak are set by thickness. London broil also has to tenderize, and that takes far longer than heating.

Iowa State University Extension explains what makes a cut tough. Muscles that bear weight or are in constant use, such as those in the legs and the front and rear of the animal, hold more collagen. Collagen is the connective tissue that binds muscle together, and more of it makes meat harder to cut and chew. Cooked slowly with moisture, collagen becomes gelatin.

Baldwin's guide says collagen begins to dissolve into gelatin above 122 to 131°F (50 to 55°C). He reports that tough cuts of beef were most tender when cooked between 131°F and 140°F (55°C and 60°C), and that 24 hours at those temperatures significantly increased tenderness. He also notes that an enzyme in the meat, collagenase, stays active below 140°F (60°C) and tenderizes the meat when it is held for more than 6 hours.

The 150°F (65.6°C) setting is faster and costs moisture. In Baldwin's guide, muscle fibers shrink lengthwise above 140 to 150°F (60 to 66°C) and lose substantial water. Top round is lean, so it has little fat to offset that loss.

The thickness limit

Thickness is not an input for London broil in the calculator, because it changes a tenderizing time very little.

The times cover pieces up to 2.25 in (5.7 cm) thick, measured through the thickest part. Thicker pieces heat too slowly and are not covered, so cut larger pieces down before cooking. The calculator assumes a typical piece is about 1.5 in (3.8 cm) thick.

Marinades

London broil is traditionally marinated, and that affects a sous vide cook in two ways.

An acidic sauce or marinade can make beef take up to twice as long to pasteurize. If the beef is in one, do not rely on the pasteurization time shown.

Logsdon marinates the meat ahead of time and takes it out of the marinade before bagging. He also leaves butter and oil out of the bag, and says salt or a spice rub can go on before the bath.

How to sous vide London broil

1. Trim. Logsdon removes large fat deposits and connective tissue.
2. Season. Salt the meat or apply a dry rub. If you marinated it, take it out of the marinade first.
3. Bag. Vacuum seal the meat, or seal it in a zipper-lock freezer bag with the water displacement method.
4. Heat the bath. Set it to 131°F (55°C), or to the temperature for the texture you chose.
5. Cook. Keep the bags in a single layer, fully under the water, and not overlapping. Leave the meat for 24 to 60 hours at 131°F (55°C). Cover the bath to limit evaporation.
6. Dry and sear. Logsdon dries the meat thoroughly and sears it for about 30 to 60 seconds per side. He lets it rest for 10 to 15 minutes before searing so the sear does not overcook the inside.
7. Slice. Cut thin slices across the grain.

Slicing across the grain

Slice thinly across the grain. Thin slices cut across the grain are also part of the traditional London broil method described above.

The grain is the direction the muscle fibers run. Iowa State University Extension says to look for that direction and slice perpendicular to it, because that leaves short fibers in each slice and makes the meat more tender to chew.

Cooking London broil from frozen

Cooking from frozen adds 2 hours 30 minutes for the center to thaw and heat.

At 131°F (55°C) the frozen time is 26 hours 30 minutes to 62 hours 30 minutes. The first cell of the table gives the size the time covers, and frozen pieces have a lower thickness limit at this setting: 1.75 in (4.4 cm), against 2.25 in (5.7 cm) for chilled meat. At 140°F (60°C) and 150°F (65.6°C) the limit stays at 2.25 in (5.7 cm).

From frozen, the time is 20 hours 30 minutes to 62 hours 30 minutes at 140°F (60°C) and 14 hours 30 minutes to 38 hours 30 minutes at 150°F (65.6°C).

Safety

All three settings are pasteurized at their minimum time.

The USDA safe minimum internal temperature for London broil is 145°F (62.8°C) followed by a 3 minute rest, as listed on FoodSafety.gov. The 131°F (55°C) and 140°F (60°C) settings are below that. They pasteurize the meat only because it is held for the full minimum time shown, so do not shorten it. The explainer on whether sous vide is safe covers how time and temperature work together.

Baldwin's guide gives the reason for the thickness limit: the center of the food should reach 130°F (54.4°C) within 6 hours to keep Clostridium perfringens from multiplying to dangerous levels.

Crowded or overlapping bags heat more slowly, and the times shown will be too short for them.

Common problems

Chewy slices. The meat needs more time, or thinner slices cut across the grain. Logsdon puts round at the long end of the time range.

Dry meat at 150°F (65.6°C). The muscle fibers have shrunk and pushed water into the bag, and a lean cut has little fat to make up for it. Use 131°F (55°C) or 140°F (60°C) for a juicier result.

An overcooked layer under the crust. Logsdon rests the meat for 10 to 15 minutes after the bath and keeps the sear to 30 to 60 seconds per side so the inside does not cook further.

A bag that floats. Baldwin's guide notes that some of the liquid in the bag turns to gas, so the bag puffs and may float. Hold it under with a rack or a weight.