Sous Vide Flank Steak: Temperature and Time

Sous vide flank steak cooks at 131°F (55°C) for medium-rare. A steak 0.75 in (1.9 cm) thick needs at least 50 min in the bath, is at its best between 50 min and 1 hr 50 min, and should come out by 4 hr.

That short cook gives a steak with normal chew. For a more tender flank steak, the calculator has a separate long cook at the same temperature: 12 to 24 hr, with a maximum of 48 hr. Every time on this page comes from the calculator.

What flank steak is

Flank steak is a flat, boneless steak from the flank primal, which sits below the loin. The beef industry's cut guide lists flank steak as lean, with 6 g of fat in a 3 oz cooked serving, and calls it a thin, coarse cut.

Jason Logsdon's flank steak guide at Amazing Food Made Easy describes a very long grain that runs the length of the cut.

If the package says London broil, read the label for the cut. The London broil guide covers top round, which needs a much longer cook than flank.

Flank steak temperature and doneness

The default is 131°F (55°C), medium-rare. Choose 140°F (60°C) for a medium steak that is pink throughout, firmer and still juicy. Rare, at 125°F (51.7°C), is bright red and very soft, and it has a shorter time limit that the safety section covers.

At 150°F (65.6°C) flank is faintly pink, firm and drying out, with a grainy texture. At 160°F (71.1°C) it has no pink and is firm and dry. Douglas Baldwin's guide to sous vide cooking gives the cause: above 140 to 150°F (60 to 66°C) muscle fibers shrink along their length and lose a substantial amount of water.

The sixth row, medium-rare long cook, uses the same 131°F (55°C) bath for much longer and has its own section below. The Time column gives each short setting's shortest and longest minimum across the thickness range, marked "by thickness", and gives the long cook's own 12 hr to 48 hr window. The steak temperature chart compares the other five levels across cuts.

How long to sous vide flank steak, by thickness

Measure the steak at its thickest point. The calculator covers flank steak from 0.5 to 1.5 in (1.3 to 3.8 cm).

At 131°F (55°C) the minimum is the heat-through time, which is the time for the center to come within 1°F (0.5°C) of the bath. A 0.5 in steak needs 30 min, a 1 in (2.5 cm) steak needs 1 hr 15 min and a 1.5 in steak needs 2 hr 15 min. The maximum for all of them is 4 hr.

Time rises faster than thickness, and a flank steak folded to fit the bag is twice as thick. Cut a long steak in half and lay the pieces side by side.

Nicole Poirier's basic flank steak recipe for Anova uses a single time, 90 minutes at 131°F (55°C). That is past the calculator's minimum for a steak up to 1 in thick, and short of the 1 hr 45 min a 1.25 in steak needs. How long to sous vide steak explains why thickness sets the time.

At 140°F (60°C) a 0.75 in steak also needs 50 min. A 1 in steak needs 1 hr 30 min, which is its pasteurization time, so do not shorten it.

The long cook: 12 to 48 hours

The long cook is a separate tenderizing setting. The minimum is 12 hr at every thickness, the best window is 12 to 24 hr and the maximum is 48 hr.

The two options give different textures:

• Short cook, set by thickness. A steak with normal chew.
• Long cook. More tender and softer than the short cook, and starting to shred at the long end.

Baldwin's guide explains what the extra time does. The enzyme collagenase stays active below 140°F (60°C) and can significantly tenderize meat that is held for more than 6 hours.

The calculator's range follows two sources. Logsdon allows up to 2 days and prefers 12 hours. Stefan's Gourmet Blog ran a flank steak temperature experiment and described 48 hours at 131°F (55°C) as juicy and very tender, with a slightly loose but steak-like texture. The same test found 24 hours at 140°F (60°C) noticeably less juicy.

Marinades

Logsdon's method is to marinate the steak first and take it out of the marinade before sealing the bag. Two cautions apply.

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. Baldwin notes that most marinades are acidic and contain vinegar, wine, fruit juice, buttermilk or yogurt.

Baldwin also says alcohol that is not cooked off before marinating can turn to vapor in the bag and make the meat cook unevenly.

How to sous vide flank steak

1. Heat the bath. Set it to 131°F (55°C), or to the temperature you chose above.
2. Season. Salt and pepper on both sides.
3. Bag flat in a single layer. Use a vacuum sealer, or a zipper-lock bag sealed with the water displacement method.
4. Cook. Use the time for the thickness, or 12 to 24 hr for the long cook. Keep the bags in a single layer, fully under the water, and not overlapping. Crowded or overlapping bags heat more slowly, and the times shown will be too short for them.
5. Dry and sear. Pat the steak dry and sear it in a very hot skillet or on a hot grill. The Poirier recipe uses a cast iron pan brushed with 1 tablespoon of avocado oil.
6. Slice thinly across the grain.

A thin steak has little depth between the surface and the center, so a long sear cooks the inside past the bath temperature. Logsdon lets the steak cool for 5 to 10 minutes before searing.

Slicing across the grain

The fibers of a flank steak run along its length. Cutting across the grain means the knife crosses those fibers at a right angle, so each slice holds short pieces of fiber.

The beef industry's guide says slicing against the grain matters even more for thin, coarse cuts such as flank. Logsdon says to cut it thinly across the grain so that it is not chewy.

Cooking flank steak from frozen

Frozen steaks go straight into the bath and stay longer. At 131°F (55°C) a frozen 0.75 in steak needs at least 1 hr 15 min and a frozen 1 in steak needs 2 hr, both with a maximum of 4 hr. The long cook is 12 hr from frozen as well.

Freeze the steak flat in a single layer so the thickness is the same as when thawed. The frozen steak guide covers freezing steaks flat, timing them and searing them.

Safety

The USDA safe minimum internal temperature for steak is 145°F (62.8°C) followed by a 3 minute rest, as listed on FoodSafety.gov. The rare, medium-rare and medium settings are below that.

On the short 131°F (55°C) setting, flank steak is heated through at the minimum time but not pasteurized. That is normal for a whole, intact cut of beef cooked to this doneness. To pasteurize a 0.75 in steak at this temperature, cook it for at least 2 hr 45 min. A 1 in steak needs 3 hr.

Use that longer time, or a higher temperature, when cooking for pregnant women, children under 5, adults 65 and older, or anyone with a weakened immune system. If the label says mechanically tenderized or blade tenderized, or the meat has been injected, use the longer time as well.

The long cook is pasteurized at its 12 hr minimum, and only because it is held for that full time, so do not shorten it. Its 48 hr maximum is a texture limit.

Mechanically tenderized, blade tenderized or injected beef needs the pasteurization time, which is not possible at 125°F (51.7°C). Choose 131°F (55°C) or higher for it.

From frozen, rare is recommended only up to 1 in. At 1.25 in the center of a frozen steak needs 2 hr 45 min to warm through, which is longer than the 2 hr 30 min limit for food cooked at 130°F (54.4°C) and below. Choose a temperature of 131°F (55°C) or higher, thaw the steak first, or use a thinner piece.

The sous vide safety guide explains why the limits change at 131°F (55°C).

Common problems

The steak is chewy. The short cook leaves flank with normal chew, and slices cut along the grain keep the fibers long. Slice thinly across the grain, or use the long cook.

The steak is soft and shreds. It was at the long end of the long cook. Stay inside the 12 to 24 hr window.