On Food and Cooking

activity of oxygen-consuming enzymes in the
muscle tissue, and the activity of enzymes
that can resupply brown myoglobin with an
electron, which turns it purple again. Acidity,
temperature, and salt concentration also
matter; if any is high enough to destabilize the
attached protein, myoglobin is more likely to
lose an electron and turn brown. Generally,
fresh red meat with active enzyme systems
will be red on the surface, where oxygen is
abundant, and purple inside, where the little
oxygen that diffuses through is consumed by
enzymes. When we cut into raw meat or into a
rare steak, the initially purple interior quickly
“blooms,” or reddens, thanks to its direct
exposure to the air. Similarly, vacuum-packed
meat appears purple due to the absence of
oxygen, and reddens only when removed from
the package.
The pink color of salt-cured meats comes
from yet another alteration of the myoglobin
molecule (p. 148).