On Food and Cooking

comes from the mass of muscle fibers, which
cooking makes denser, dryer, and tougher.
And their elongated arrangement accounts for
the “grain” of meat. Cut parallel to the
bundles and you see them from the side, lined
up like the logs of a cabin wall; cut across the
bundles and you see just their ends. It’s easier
to push fiber bundles apart from each other
than to break the bundles themselves, so it’s
easier to chew along the direction of the fibers
than across them. We usually carve meat
across the grain, so that we can chew with the
grain.
Muscle fibers are small in diameter when
the animal is young and its muscles little
used. As it grows and exercises, its muscles
get stronger by enlarging — not by increasing
the number of fibers, but by increasing the
number of contractile protein fibrils within
the individual fibers. That is, the number of
muscle cells stays the same, but they get
thicker. The more protein fibrils there are