Sous Vide Flank Steak (Gluten-Free Mongolian Style)

Sous vide flank steak marinated and glazed with a gluten-free Mongolian sauce! Learn how to make this scrumptious recipe with just seven ingredients.

If you asked me for the best way to cook a flank steak, I’d look you in the eye and tell you “sue veed” with a straight face. Hands down, sous vide, my friend!

This statement came after multiple tries at moving my Gluten-Free Mongolian Beef from a slow cooker into a sous vide water bath. I am not saying that the slow cooker version is bad. I absolutely adore the unique, rich Asian flavor of that recipe, but I wanted to experiment with the flank steak’s texture.

Well, the result was an astonishingly tender steak with a velvety glaze!

What Are the Benefits of Cooking Flank Steak Sous Vide?

In general, sous vide is a fantastic way to cook steak. Whether it’s a ribeye, a sirloin, or a tenderloin, the sous vide cooking process allows you to have total control over the temperature and doneness of your steak without having to worry about overcooking it. 

When it comes to tough cuts like flank steak, skirt steak, or hanger steak, it works exceptionally well, as the sous vide process helps tenderize more fibrous cuts of beef and break down the connective tissues without losing any of the beefy flavor. This is really really hard to do with traditional cooking methods. 

How Long Does It Take to Sous Vide Flank Steak?

The cook time for sous vide flank steak ranges from 2 to 24 hours. The wide range yields very different results. 

Between 2 and 6 hours, your flank steak is already tender. It preserves the sensation that you are eating a steak when you bite into it. 

Longer than 6 hours, the flank steak is going to be tenderized further. The longer you cook it, the softer it gets. When the steak cooks for an extended period, it’s so soft that you don’t feel like you are eating a steak anymore. If that’s what you are going after, by all means, leave that steak bag in the sous vide water bath overnight. 

For me, the sweet spot for cooking flank steak sous vide is 2 to 3 hours. By then, the steak is perfectly tender and evenly cooked from edge to edge.

At What Temperature Should You Sous Vide Flank Steak?

As when you sous vide any cut of steak, the doneness is directly related to the temperature you set, which gives you full control. 

• Rare: 125°F (51.7°C)
• Medium-rare: 129°F (53.8°C) – 133°F (56°C)
• Medium: 140°F (60°C) 
• Medium-well: 145°F (63°C)
• Well-done: 150°F (65°C)

My recommended temperature for sous vide flank steak is between 129°F (53.8°C) and 133°F (56°C). Post sous vide cooking, a quick sear on both sides gives you a beautifully cooked flank steak that almost melts in your mouth. 

How Do You Sous Vide a Frozen Flank Steak?

If you’ve been following my sous vide adventures, you already know that you can absolutely sous vide frozen steak. So there’s no doubt that a frozen flank steak can be cooked to perfection in the same way. 

How do you do it? 

• If your flank steak comes with sous vide-friendly packaging, you can plunge it directly into the water bath. If not, repackage it in a Ziploc bag or sous vide vacuum sealer bag before cooking. Apply seasonings before finishing it or make a steak sauce to go with it.
• You can also season or marinate a sous vide flank steak, then seal and freeze it until you’re ready to cook. 

One thing to keep in mind is the cook time for frozen flank steak. If you plan on cooking it for a long period (say 12 to 24 hours), it doesn’t matter if the steak is fresh or frozen. You are going to get fully tenderized and super soft steak either way. But if you normally cook flank steak sous vide for 2 hours or so, you’ll want to add some time when starting with a frozen steak. 

A rule of thumb for frozen steak is to take the cook time for fresh steak and multiply it by 1.5. 

For your convenience, I’ve compiled a breakdown in the chart below.

Sous Vide Flank Steak Cook Time and Temperature Chart

Cook Temperature	Doneness	Cook Time (Fresh)	Cook Time (Frozen)
125°F (51.7°C)	Rare	2 hours (or up to 24 hours)	3 hours (or up to 24 hours)
129°F (53.8°C) – 133°F (56°C)	Medium-rare	2 hours (or up to 24 hours)	3 hours (or up to 24 hours)
140°F (60°C)	Medium	2 hours (or up to 24 hours)	3 hours (or up to 24 hours)
145°F (63°C)	Medium-well	2 hours (or up to 24 hours)	3 hours (or up to 24 hours)
150°F (65°C)	Well done	2 hours (or up to 24 hours)	3 hours (or up to 24 hours)

Essential Ingredients

Flank Steak 

The flank steak is a piece of meat located directly under the loin of a cow. It corresponds to the abdominal muscles. This cut tends to be lean and very tough. It’s inexpensive but flavorful when properly cooked. A flank steak is about one inch thick and cooked whole rather than divided into smaller individual steaks.

Marinade or Seasonings

Like skirt steak, flank steak benefits greatly from a marinade. In this recipe, I’ve included a four-ingredient Mongolian marinade that’s gluten-free and absolutely delicious. The four ingredients are

• Coconut aminos (I used Bragg Liquid Aminos for this recipe.)
• Fresh garlic
• Fresh ginger
• Sesame oil

If you don’t have coconut aminos, you can substitute low-sodium tamari or low-sodium soy sauce (not gluten-free). Please note that neither of those substitutes offers the delightful hint of sweetness that the coconut aminos do. Therefore, if using tamari or soy sauce, I’d recommend adding some maple syrup, honey, or brown sugar to the marinade. 

I usually marinate my flank steak overnight before cooking sous vide. Some say that the long marinating time doesn’t really make that much difference to the result. I think if you are going to cook your flank steak for an extended period of time, you can let it marinate as it cooks.

Essential Equipment

• A sous vide immersion circulator. I used an Anova Precision Cooker for this sous vide flank steak recipe. 
• A large pot or a sous vide container. This 12-quart container is compatible with most sous vide machines on the market. I personally use an Anova sous vide cooking container which holds up to 16L of water with a removable lid and a rack to prevent food from floating. 
• A large Ziploc bag or vacuum sealer bag. You do not need a vacuum sealer and vacuum seal bags if you plan to sous vide flank steak for 2-3 hours. Use a large Ziploc bag to marinate your steak, then drop the bag directly into the sous vide bath using the water displacement method. However, if you plan on cooking the steak for an extended period of time (over 5 hours) or if you want to store the cooked flank steak to enjoy later, I’d recommend using a vacuum sealer with vacuum sealer bags or reusable sous vide bags.
• A cast-iron pan. For finishing sous vide flank steak, I seared it in a cast-iron skillet over medium-high heat. A heavy-duty flat-bottom pan also works. 
• A sharp knife. I love my Global Chef’s Knife for slicing the flank steak. 
• Tongs. Since flank steak is cooked whole, you’ll need kitchen tongs to transfer it in and out of the cooking bag.

How to Sous Vide Flank Steak Step by Step

Here’s the step-by-step guide to making the sous vide gluten-free Mongolian flank steak. You can choose a different marinade for your flank steak, but the general cooking guidelines are the same. 

Step 1: Marinate the flank steak. Place the flank steak and the marinade (coconut aminos, garlic, ginger, and sesame oil) in a large Ziploc bag or vacuum sealer bag (cut the steak in half to fit in the bag if necessary). Move the contents around and allow the steak to be well coated with the marinade. Arrange in a single layer, squeeze the air out with your hands, and seal. Refrigerate and marinate for at least 2 hours or overnight. (You may also skip the marinating time and directly move on to the next step.) 

Step 2: Sous vide the flank steak. When ready to cook, preheat water to 131°F (55°C) or your desired temperature using an immersion circulator. Submerge the flank steak into the sous vide water bath. Use the water displacement method to squeeze out as much air as possible if using a Ziploc bag. Set the timer for 2 hours (or longer if you prefer).

Step 3: Finish the steak. Once the timer goes off, remove the bag from the sous vide. Open the bag and transfer the steak onto a cutting board and pat it dry on both sides using paper towels. Reserve the cooking juice. Heat a cast-iron skillet over high heat until really hot, add some olive oil, and sear the steak on both sides, about one minute on each side. Transfer the nicely seared steak onto the cutting board and let it rest.

Step 4: Make the Mongolian sauce. Pour the cooking juice from the steak bag into a small saucepan. Bring to a boil (this will allow the solids to form), then strain. Discard the solids and return the cooking juice into the saucepan and simmer until the sauce is thickened. Optionally, if you’d like a thicker sauce, dissolve one teaspoon of cornstarch in one tablespoon of cold water and add it to the sauce. Stir immediately. It will thicken right away. Remove from heat. 

Step 5: Serve. Slice the flank steak against the grain and plate it. Pour the Mongolian sauce over the steak, and garnish with green onion and toasted white sesame seeds. For a complete meal, serve with a side of vegetables and/or rice. Enjoy! 

What to Serve with Sous Vide Flank Steak

You can enjoy your sous vide flank steak in tacos, fajitas, or in this steak salad with chimichurri sauce. 

For the Mongolian style particularly, a side of Asian vegetables is my go-to. This quick and easy—Sautéed Baby Bok Choy with Shiitake Mushrooms is literally the perfect pair for Mongolian flank steak. 

Or use the flank steak juice to cook these Pan-Steamed Broccolini and Portobello Mushrooms. 

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