Marinating Flank Steak
I'm marinating flank steak for fajitas ( I wanted skirt steaks but they were out!) and I am using a soy sauce, vinegar, water marinade. I heard that flank steaks can get mushy if marinating for too long in anything vinegar based. Do you think it would be okay to marinate overnight, or I should I do it tomorrow morning? Or even later? Dinner is at 6:00.
Thanks in advance.
Acidic marinades can actually make your meat tough. It's the enzymatic marinades that tend to make the meat mushy if left too long in the mix (pineapple juice, papaya juice, etc.) I never marinate meat for longer than two hours in an acid based mixture. Even less time in an enzymatic mix. I believe that the way you cut the flank steak when serving, after it's cooked of course, is as important to how "tender" it feels in the mouth as any method of marinating you might apply. Remember to cut across the grain of the meat in very thin slices.
So that recipe must be from the Osaka Texicans.
I have not had a problem with acidic marinades making meat mushy or tough. To quote McGee, "The acid in marinades does weaken muscle tissue and increase its ability to retain moisture. But marinades penetrate slowly, and can give the surface an overly sour flavor." He goes on to explain that you can reduce the marinading time by cutting the meat into thinner pieces or using a cooking syringe to inject the marinade into the thicker pieces. He never mentions mushiness. I've only experienced mushiness with enzymes and brining, usually not with acidic marinades.
I'm not sure that I'd even worry about under-marinating a thin piece like a flank. Over-marinating could be a problem, so keep it to about 2 hours, like Toao says. I've never done ir for longer than that - certainly never over-night.
I much prefer skirt to flank for Fajitas - but you have to make do with what you have. Remember to cut the slices on the bias so that the meat is very, very thin and short grained when placed into the burrito - other wise people are not going to be able to cut it with their teeth as they take a bite - they'll be pulling out chunks of meat - an unpleasant site, indeed.
For a good fajitas marinade, use lots of garlic, lime, and cumin, mixed with light flavorless vinegar (I use rice vinegar). If you must use soy, use a small amount (tablespoon) for the salt and umami, not for the base flavor. You can thin out the marinade with a small amount of water, but don't use too much or you'll lose the acidity and then you will have a brine, which could lead to your mushiness problem, especially if soaked overnight. I reserve the marinade to add to the vegetables and sliced meat after cooking.
The fibers would be just as short either way depending on your slicing thickness. You get more cross-section when you cut on the bias and the still thin but larger (on the flat) piece can be torn apart easier with your teeth when being pulled out of a burrito wrap. Of course, if you use skirt, you can cut straight up and down, since it's such a thin piece of meat. It probably doesn't matter a whole heck of a lot. I'm just used to slicing flank on the bias to make a better presentation for the plate.