Sous vide flat iron steak: Step-by-step

Flat iron steak for sous vide
Flat iron steak for sous vide

Sous vide flat iron steak is an excellent cooking method that perfectly prepares steak. It does take a while to cook the steak in a water bath; however, the results are incredible.

First and foremost, if you are not well familiar with flat iron steak, click on this link to learn more. It’s a beef steak carved from the chuck primal. Although the top muscle blade is a tough piece of meat because it’s a well-exercised muscle, researchers at the University of Florida and the University of Nebraska came up with a brilliant solution to trim the connective tissue resulting in a tender piece of steak.

Flat iron steak has an intense beef flavor because of the marbling and well-exercised muscle. It’s the second most tender steak cut after filet mignon.

Since flat iron steak is a newer cut, it’s not available in most supermarkets. You can buy it online or at your local butcher shop. Depending on your location, flat iron steak is also known as oyster blade steak, butler’s steak, top chuck steak, shoulder top blade steak, top blade steak, or top blade filet.

How to sous vide flat iron steak

How to sous vide flat iron steak
How to sous vide flat iron steak

Flat iron steak is a versatile piece of meat. You can cook a flat iron steak using any cooking method you like. Hower sous vide cooking flat iron steak is extremely easy. It doesn’t take much effort to cook it to a precise temperature.

Regarding sous vide cooking, you must sear flat iron steak when you finish cooking it in a water bath. Grill flat iron steak on a charcoal or gas grill to caramelize the steak’s exterior and add a smokey flavor to the meat. Alternatively, you can finish it off in a cast iron skillet, as you’ll see later in the step-by-step guide.

It’s essential to prepare the steak a night before cooking it. Season flat iron steak with a generous amount of kosher salt. It’s known as a dry brine. Salt will extract moisture from the steak and form a salty brine. The same brine will soak back into the steak, enhance the beefy flavor, and make it more tender.

You can add additional flavors to the meat by using the marinade for flat iron steak. After cooking flat iron steak, you can use it for steak fajitas, salads, stir fry, or with your favorite side dishes. Here’s an excellent steak fajitas recipe in case you want to try it with your sous vide flat iron steak.


  • Flat iron steak.
  • Light olive oil.
  • Kosher salt and freshly ground black pepper.
  • Fresh thyme.
  • Fresh rosemary
  • A knob of butter.

Cooking directions for the sous vide method:

Step 1: Season flat iron steak

Season flat iron steak with kosher to enhance flavor and tenderize the meat.

Step 2: Preheat sous vide

Preheat sous vide to 129° Fahrenheit/54°Celsius. You must set the water bath temperature to 5-10 degrees Fahrenheit lower than the desired doneness of your steak. In this case, I’m slow cooking my steak to medium-rare doneness (135° Fahrenheit/57°C).

Step 3: Add aromatics and vacuum seal the steak

Place seasoned flat iron steak into the vacuum seal bag. Add fresh thyme and rosemary into the vacuum seal bag and seal it with a vacuum sealer. If you do not have a vacuum sealer, use zip-lock bags instead. Place the steak with aromatics into the ziplock bag and slowly lower it into a pot of lukewarm water. Ensure the zip-lock bag is slightly above the water line. Water pressure will force the air out of the bag. Carefully close the bag.

Step 4: Sous vide steak

Drop a well-sealed flat iron steak into the water bath. If the bag is not sealed properly, it floats to the surface. A well-sealed steak should sink. Cook flat iron steak in a water bath for 2 hours. At the end of the article, there’s a timetable for different levels of doneness.

Step 5: Remove the steak from the water bath

Remove the steak from the water bath. Open it and place it on paper towels. Pat the steak dry to remove excess moisture. It’ll help to achieve a nice and evenly crisp exterior when searing.

Step 6: Sear the steak over medium-high heat

Preheat the cast iron skillet on a stovetop over medium-high heat until smoking. Alternatively, use any other heavy pan capable of withstanding high heat. Add light olive oil or oil with a high smoke point (vegetable oil, canola oil). Gently lay the steak away from you using tongs. Sear the flat iron steak for 45 seconds on each side. Add a knob of butter and baste the steak for an additional minute. Season the steak with freshly ground black pepper while the steak is cooking.

Step 7: Rest the flat iron steak

Rest sous vide flat iron steak for 5-10 minutes after searing. Steak juice is pushed toward the center when the steak hits the hot pan surface. It needs time to rest so that steak juice can redistribute evenly throughout the steak’s interior. It’ll result in a tender and juicy steak.

Step 8: Slice

Slice the steak against the grain. It’ll reduce the length of the muscle fiber, making flat iron steak much easier to chew.

How to take sous vide flat iron steak’s internal temperature?

Sous vide flat iron steak internal temperature
Sous vide flat iron steak internal temperature

To take sous vide flat iron steak internal temperature, you must wait until the flat iron steak is cooked. Take the steak out of the vacuum-sealed bag and insert a meat thermometer into the thickest part of the meat. Wait until the temperature stabilizes. Depending on the thermometer, it shouldn’t take more than 15 seconds.

Since flat iron steak is cooked in temperature controlled environment, the internal temperature of the flat iron steak is the same as the water temperature. The steak comes to temperature gradually and does not exceed water temperature. Here’re internal steak temperatures for cooking steak:

  • Rare steak: 125° Fahrenheit/52°C.
  • Medium rare steak: 135° Fahrenheit/57°C.
  • Medium steak: 145° Fahrenheit/62°C.
  • Medium-well steak: 150° Fahrenheit/65°C.
  • Well done, steak: 160° Fahrenheit/71°C.

How long does it take to sous vide flat iron steak?

Cooking temperatures and times
Cooking temperatures and times

Here’s how long it takes to sous vide flat iron steaks:

Rare steak120°F/49°C to 128°F/53°C45 minutes to 2 hours
Medium-rare129°F/54°C to 134°F/57°C 45 minutes to 4 hours
Medium135°F/57°C to 144°F/62°C45 minutes to 3 1/2 hours
Medium-well145°F/63°C to 155°F/68°C45 minutes to 3 1/2 hours
Well-done56°F/69°C1 to 3 hours
Cooking temperatures and times

How to store and reheat leftover sous vide flat iron steak?

You can store leftover sous vide flat iron steak in an airtight container or ziplock bag or wrap it in aluminum foil or parchment paper. Alternatively, you can vacuum seal leftover steak. When storing leftover steak, remove as much air as possible to prevent the steak from spoiling. Oxidation causes meat to go bad faster than it should. An improperly stored steak can get a freezer burn when stored in a freezer. Cooked steak can last in a fridge for up to 4 days, depending on the storage method. According to the USDA, a cooked flat iron steak stored in a freezer can last for two to three months.

There is more than one way to reheat leftover steak. However, the most convenient one is to reheat leftover flat iron steak in the oven. Preheat the oven to 275° Fahrenheit/135°C. Place the steak on a wire rack on a rimmed baking sheet lined with parchment paper. Place the steak into the oven on a middle rack. Reheat for 15-25 minutes, depending on the leftover steak size.


What is the best cooking method for flat iron steak?

The best cooking method for flat iron steak is grilling and cooking on a stovetop. Both grilling and cooking in a pan provide enough heat for the flat iron steak to sear properly. At the same time, you have more control over the heat source. You should cook flat iron steak on high heat and finish it on medium heat. Fast and hot cooking methods, such as grilling and cooking in a pan, are best for the flavor and texture of the meat.

Can I sous vide frozen flat iron steak?

Yes, you can sous vide frozen flat iron steak; however, leave it in a water bath for 30-40 minutes more, depending on the steak size.

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