The easiest way to explain to someone how to slice flank steak is to slice against the grain. However, not everyone knows what "grain" means in regards to muscle composition.
Thankfully, the grain structure of flank steak is very easy to identify (pictured below), which makes slicing against the grain very easy.
Before I demonstrate how to slice flank steak, it's beneficial to understand what grain is with respect to meat. That way you can slice other meats effectively.
A more optimal word for "meat" is muscle. Meat muscle is made of muscle fibers that are then bundled together by connective tissues. These muscle fibers (myofibrils) are comprised of filaments that are arranged in a repetitive pattern alongside other myofibrils.
The direction in which these long strands of muscle fibers form is the grain direction.
This idea is in a similar vein to the wood or lumber industry; The grain describes the growth pattern of the tree.
Regardless of the meat you're working with - whether it's flank steak or a ribeye, the grain direction of meat is easier to identify when the meat is raw.
Meaning, before you cook the meat, make note of the way in which the muscle fibers run.
To illustrate, here's a picture of an uncooked flank steak:
The grain direction is readily apparent. We can clearly see the muscle fiber strands running horizontally across the meat (as indicated by the dotted white line).
The flank steak from this article was used for my steak on a stick recipe (check it out here), so I cut the meat against the grain, marinated it, and then grilled it on a skewer.
However, if I left the steak in-tact and then sliced, I'd make note of the grain orientation before grilling it.
To start, you'll need:
1. Start by looking at the flank steak raw and identifying the grain structure of the flank steak.
Here's another picture for reference:
2. Whether you're slicing the meat raw or when it's cooked, simply slice into the meat perpendicularly or against the grain.
Pictured, the grain runs vertically as indicated by the white arrow lines. Meaning, you'd slice the meat horizontally or perpendicular to the grain (as indicated by the dotted black line).
Here's a picture of my Dad slicing this flank steak against the grain:
That's all there is to it - identify the grain and slice perpendicular to it.
Technically, you could further minimize fiber length by slicing on a bias (knife angled at 45 degrees), which also improves presentation. However, this is less important than simply slicing against the grain.
The reason for slicing flank steak against the grain has everything to do with the eating experience.
Put simply: The goal when slicing meat is to shorten muscle fiber lengths as much as possible in order to make chewing easier.
Cutting flank steak with the grain leaves the muscle fiber strands in tact. Cutting against the grain effectively shortens the fiber lengths.
The next time you have a piece of flank steak, slice the meat both against the grain and with the grain.
What you'll find is:
America's Test Kitchen did a quantitative analysis of this concept using a CT3 Texture Analyzer. The CT3 texture analyzer simulated bite force by cutting 5mm into a piece of flank steak.
Force Needed to Bite
|with the grain||1729g|
|against the grain||383g|
From their example, it took 4.5x as much force to cut 5mm into the flank steak when cut with the grain.
Technically, through trigonometry and knowing that you need to slice perpendicular to the grain, you can minimize these fiber lengths; You'd make the length of the fibers the same as the width of the slice.
Granted, this is hardly practical as not many folks make use of a protractor in their kitchen when cutting meat.
This is common mistake that people make when looking at meat grain. Sear and/or grill marks have nothing to do with the grain structure of meat.
Sear marks are the result of the maillard reaction of amino acids and reducing sugars and are completely independent of grain structure.
Meaning, sear marks can form in whatever direction the meat is placed on the grill grates or cooking surface; You could technically get grill marks to form in any direction you want.
This is also the reason it's easier to identify meat grain before cooking. The maillard reaction causes the meat to brown and the surface to change color, making it hard to physically see the grain.