5. When displayed at the grocery store,
why is some meat bright red and other
meat very dark in color?
Optimum surface color of fresh meat (i.e., cherry-red
for beef; dark cherry-red for lamb; grayish-pink for
pork; and pale pink for veal) is highly unstable and
short-lived. When meat is fresh and protected from
contact with air (such as in vacuum packages), it
has the purple-red color that comes from myoglobin,
one of the two key pigments responsible for the
color of meat. When exposed to air, myoglobin forms
the pigment, oxymyoglobin, which gives meat a
pleasingly cherry-red color. The use of a plastic wrap
that allows oxygen to pass through it helps ensure
that the cut meats will retain this bright red color.
However, exposure to store lighting as well as the
continued contact of myoglobin and oxymyoglobin
with oxygen leads to the formation of metmyoglobin,
a pigment that turns meat brownish-red. This color
change alone does not mean the product is spoiled
(see explanation in question 2).
6. Why is pre-packaged ground beef
red on the outside and sometimes
grayish-brown on the inside?
These color differences do not indicate that the meat
is spoiled or old. As discussed earlier, fresh cut meat
is purplish in color. Oxygen from the air reacts with
meat pigments to form a bright red color which is
usually seen on the surface of ground beef purchased
in the supermarket. The interior of the meat may be
grayish-brown due to the lack of oxygen penetrating
below the surface.
7. A beef roast has darkened in the
refrigerator, is it safe?
Yes, it is safe. The darkening is due to oxidation, the
chemical changes in myoglobin due to the oxygen
content. This is a normal change during refrigerator
storage.
8. Can cooked ground beef still be pink
inside?
Yes, ground beef can be pink inside after it is safely
cooked. The pink color can be due to a reaction
between the oven heat and myoglobin, which causes
a red or pink color. It can also occur when vegetables
containing nitrites are cooked along with the meat.
Because doneness and safety cannot be judged by
color, it is very important to use a food thermometer
when cooking ground beef. To be sure all harmful
bacteria are destroyed, cook raw ground beef to an
internal temperature of 160°F as measured with a
food thermometer
9. What causes iridescent colors on
meats?
Meat contains iron, fat, and other compounds.
When light hits a slice of meat, it splits into colors
like a rainbow. There are various pigments in meat
compounds that can give it an iridescent or greenish
cast when exposed to heat and processing. Wrapping
the meat in airtight packages and storing it away
from light will help prevent this situation. Iridescence
does not represent decreased quality or safety of the
meat.
10. What causes grayish or green color
on cured meats?
Exposure to light and oxygen causes oxidation to
take place, which causes the breaking down of
color pigments formed during the curing process.
Chemicals in the cure and oxygen, as well as energy
from ultraviolet and visible light, contribute to both
the chemical breakdown and microbial spoilage of the
product. Cure, such as nitrite, chemically changes the
color of muscle. Curing solutions are colored in order
to distinguish them from other ingredients (such as
sugar or salt) used in fresh and cured meat products.
For example, cured raw pork is gray, but cured
cooked pork (e.g., ham) is light pink.
THE COLOR OF POULTRY
11. What is the usual color of raw
poultry?
Raw poultry can vary from a bluish-white to yellow.
All of these colors are normal and are a direct result
of breed, exercise, age, and/or diet. Younger poultry
has less fat under the skin, which can cause the
bluish cast, and the yellow skin could be a result of
marigolds in the feed.
12. What causes the differences in
color of raw ground poultry?
Ground poultry varies in color according to the part
being ground. Darker pink means more dark meat
was used and a lighter pink means more white meat
was included (or skin was included). Ground poultry
can contain only muscle meat and skin with attached
fat in proportion to the whole bird.
13. What causes dark bones in cooked
poultry?
Darkening of bones and meat around the bones
occurs primarily in young (6-8 weeks) broilerfryer
chickens. Since the bones have not calcified
or hardened completely, pigment from the bone
marrow seeps through the bones and into the
surrounding area. Freezing can also contribute to
this darkening. This is an aesthetic issue and not a
safety one. The meat is safe to eat when all parts
have reached a safe minimum internal temperature
of 165°F as measured with a food thermometer.