Flank steak was so tough!

I use flank stead frequently for my BBQ salad recipe. The important thing is to slice it very thinly with your knife positioned against the grain as much as you can. The knife is held at a slanted position . It will result in a very tasty and not too tough cut of steak. I don't use much marinade and I cook it on the rare side. It will continue to cook a bit after it is cut.

Look for a needle tenderizer either from amazon.
http://www.amazon.com/Deni-MT45-Meat-Tenderizer-Blade/dp/B002R0FRHC/ref=sr_1_2?ie=UTF8&qid=1375225611&sr=8-2&keywords=needle+meat+tenderizer
Or Academy Sports (in their outdoor cooking section where I got mine).

It make tougher *cheaper* cuts of meat tender and speeds up marinating and cooking time. Just don't over do it...unless you're making southern fried 'chicken fried' steak and gravy. Then just pound it flat and needle that sucker to death.

I'm from europe and the flank steak is pretty new to us, but I've had it a few times and I love the taste and texture. It has always been served as a steak and not a thinly carved roast but it has been far from rough. In fact what I love so much about this cut is the grainy texture. I want my steaks medium rare and do you think that's why I don't experience flank steaks to be tough?
FYI, This is a common steak in France and it's never marinated, only seasoned with salt and pepper

Acid marinades don't actually tenderize meat; they don't penetrate more than a few millimeters. All you will accomplish with a long soak in an acid marinade is to make the outside of the meat mushy. (They are good for flavor, since the flavor WILL stick to the surface, but they don't tenderize. Meat won't benefit from an acid marinade after 3-4 hours.)

Flank steak comes out tender and juicy when marinated in a vinegar-based marinade. I also marinade for 24 hours, minimum.

Thanks everyone! I used this recipe from epicurious: http://m.epicurious.com/recipes/food/views/Grilled-Flank-Steak-with-Rosemary-731

I definitely cut it against the grain though I'm thinking I didn't slice it thin enough. Next time I think I'll try skirt steak instead.

Judging by your question, I am brought to three possible reasons.

1) you over cooked it. It has to be Medium rare. that's a warm red center. Pull the steak off the grill at approximately 125 F. The internal temperature will continue to rise for a while even after you take it off the grill.

2) You're grill was not hot enough. As mentioned above, the heat has to be seriously high, and the grilling time very short. Remember to rest your meat after cooking.

3) You are not slicing it correctly across the grain. Please don't be offended if Im wrong here, I don't mean to insult your inteligence. The only reason I bring this up is because I've met more than one person who didnt' know what "across the grain" actually was. They told me they had sliced across the grain, but upon inspection, I actually had to explain that they were doing it wrong.

there are many other less expensive cuts you can try that are less though than flank. I like flat iron and try tip.

Okay, Pierino, here it is: I use briquettes.

I gave up lump charcoal after sparks burned numerous holes in our redwood deck and through more than one good shirt. I've since found briquettes to be far less expensive, more consistent and controllable, and they have a longer burn time (which comes in quite handy for smoking). They're also more versatile -- all it takes is a handful of wood chips of the species of your choice to match whatever you're cooking. I keep hickory, apple, red oak and kiawe on hand.

I know you're going to think less of me but, hey, at least it's not propane?

I love flank and agree with Chef Ono above. You can try again with skirt with better results. Curious about your marinade.

I agree with shauna on this one. It is one tough piece of meat unless you treat it with care. This is my korean style recipe for it http://www.food52.com/recipes/13423_mysteries_of_korea_town_kalbi_style_flank_steak

Putting those bias slashes on does help at least a little bit.

And ChefOno, buddy, what the hell are you doing even owning briquettes?

The keys to that cut are to cook it for a very short time, over very high heat, medium rare max. It should have chew but it shouldn't be tough.

Alton Brown has a crazy technique for flank steak which involves setting the steak directly on the coals for the quickest possible sear. The first time I tried it, it wasn't until I was chewing on and subsequently spitting out crunchy black bits that it dawned on me -- I should have used lump charcoal. I'd grabbed the briquettes without thinking.

Flank steak is tough. It will never eat like a regular steak unless you're in Japan and it's Kobe Beef. I am not a fan of this cut of meat but, those who are slice it very thin and have strong jaws. I have known these people to marinate it for 2-3 days in the fridge.