color remains. The reason this happens is that
food-coloring molecules absorb some wavelengths of light and let others pass through,
resulting in the color we see (Fig. 4). But why
wouldn’t sugar or salt absorb portions of the
visible light and let the rest of it go through,
like food-coloring molecules do? Absorption
of light is caused by bringing an electron in a
molecule, atom, or ion to a higher energy level.
Sugar molecules or the ions in salt require a
large amount of energy to do that, so they do
not absorb visible light but only light of shorter
wavelength—typically ultraviolet light.
Instead, food-coloring molecules typically
contain long swaths of alternating single and
double bonds (Figs. 1– 3) that allow electrons
in these molecules to be excited at relatively
low energy. The energy required for an electron
to jump from that excited state to the ground
state corresponds to the energy of visible light,
which is why food-coloring molecules can
absorb light from the visible spectrum.
What does the
It is tempting to think that natural products
are healthier than artificial ones. But that is
not always the case. Cochineal extract is not
the only natural dye that can pose a health
risk. Serious allergic reactions have also been
reported with annatto and saffron—yellow
food colorings derived from natural products.
So what will the food of the future look
like? Some advocacy groups, such as the
Center for Science in the Public Interest, seek
to ban all food coloring, because of limited
evidence showing that food coloring encour-
ages children to eat junk food. Others envision
a different future. One company has already
manufactured an edible spray paint, called
Food Finish, which can be applied to any food.
It comes in red, blue, gold, and silver colors.
Eating involves more than just taste. It is a
full sensory experience. Both food scientists
and chefs will tell you that the smell, sound,
feel, and, yes, the sight of your food are just as
important as taste to fully appreciate what you
eat. That Slurpee would not taste the same if it
did not dye your tongue an electric blue. You
really can’t help watching what you eat.
McKone, H. T. The Unadulterated History of Food
Dyes. ChemMatters, Dec 1999, pp 6–7.
Overview of Food Ingredients, Additives, and
Colors. U.S. Food and Drug Administration,
Nov 2004; revised April 2010: http://www.
[accessed July 2015].
Fiegl, A. Scientists Make Red Food Dye from
Potatoes, Not Bugs. National Geographic, Sept
19, 2013: http://news.nationalgeographic.com/
[accessed July 2015].
Borrell, B. Where Does Blue Food Dye Come From?
Scientific American, Jan 30, 2009: http://www.
scientificamerican.com/article/where-does-blue-food-dye/ [accessed July 2015].
Brian Rohrig is a science writer who lives in
Columbus, Ohio. His most recent ChemMatters
article, “Smartphones, Smart Chemistry,” appeared
in the April/May 2015 issue. D A N
light (with its
from red to
Absorbed light is green (complementary color to red)
Absorbed light is orange (complementary color to blue)
(a) Blue dye
(b) Red dye
The caramel coloring of most
commercially manufactured colas is
derived naturally from caramelized
sugar. Suppose for a moment that you
are the chemist who works for a bottling plant. You are in charge of formulating the color for the latest batch of
carbonated beverages. Unfortunately,
the shipment of natural caramel coloring that you were expecting did
not arrive, so you have to make the
caramel coloring artificially. Can it be
◗ Red, blue, and yellow
◗ Clear plastic cups
◗ Sample of commercial cola
1. Prepare 3 cups of colored water
using the food coloring.
2. Pour a sample of the
cola in a separate cup.
This sample will remain
untouched, and will serve
as the control you are
trying to replicate.
3. Using eyedroppers, add colored
water from the 3 cups to the single
empty cup in an attempt to replicate the color of the cola.
Were you successful? What strategies
did you use? Why do you think artificial
coloring is typically not used in carbonated beverages?
Figure 4. A food dye will appear a particular color because it absorbs light whose color is complementary
to the food dye’s color, as illustrated here in the case of (a) a blue dye, and (b) a red dye.
Can the Caramel
Color of Soda Be