Sumptuous Servings of Food and Chemistry
November 26, 2002
By CLAUDIA DREIFUS
When Robert L. Wolke comes to your house, you want to give
him something nice to eat.
Dr. Wolke, 74, is a retired University of Pittsburgh
chemistry professor and researcher who discovered the
longest half-life radioisotope known, cadmium 113. He also
is a leading writer about the corners where chemistry and
In addition to producing academic textbooks, he has
published several popular works on science in everyday
life, including "What Einstein Told His Cook: Kitchen
Science Explained," published in May. He also writes a
twice-monthly syndicated newspaper column, "Food 101."
But on this particular afternoon, he has already had his
lunch. So the talk is about his work.
"I love what I do," Mr. Wolke said. "I'm teaching people
about two things I'm passionate about, food and science. To
me, science is nothing more than what's going on around us
as we carry out our daily activities. Food and cooking are
gold mines of everyday science."
Q. How did you develop this odd beat, the chemistry of
A. I grew up in Brooklyn during the Depression, and food
wasn't important in our house, except that there'd be
enough of it.
I knew nothing about fine cuisine until I went to graduate
school in nuclear chemistry at Cornell. They had a school
of home economics there, and it had a cafeteria which was
cheap and wonderful. Going to that cafeteria opened up the
world of food to me. I experienced things I had never seen
before: eggplant, Camembert cheese.
So then, as a young professor, I moved around the country a
bit and did a lot of cooking. In my first marriage, my wife
hated food and cooking. Food meant only one thing to her:
Another thing: I liked to write, and I'd moonlight from the
academic world by submitting humor articles to newspapers
and they'd get published. Eleven years ago, I met my
current wife, Marlene Parrish, a food professional, and my
writing started turning toward food because of our shared
About five years ago, I pitched a story to Nancy McKeon,
who was then food editor of The Washington Post. She
replied: "I can't use the story but I like your style.
Let's see if we can work together."
Q. How did you manage to meld your writing career with that
of being a respected academic? In the subculture of the
academy, "popular" writing is not necessarily respected.
A. It was thought of as "frivolous." Arghhh! Every year
when I'd have to submit my list of publications, after I'd
put down my research publications, I'd write "other" rather
stating, "humor piece in the Sunday supplement." And you
know, I was really proud of some of my non-chemistry
publications! This column, which deals with chemistry and
cooking, is finally a way of putting these two parts of my
Q. What are some of the things you've uncovered as a food
writer? For instance, we understand you devised an
experiment to determine the most efficient means of
extracting juice from a lemon?
A. It's supposedly common knowledge that if you want to get
the most juice out of a lemon, you roll it on the table
before squeezing. Another school has it that you put the
lemon in the microwave oven for 30 seconds and then
Well, I got myself a case of limes and set up four test
groups. One, I rolled the fruits on the table, another I
microwaved, a third I did nothing to, and a fourth, I
microwaved and rolled on the counter. Then I cut the limes
in half, squeezed them out and counted the number of
milliliters of juice per gram of fruit. Rolling
accomplished nothing, as did microwaving. But if you rolled
and then microwaved, you got somewhere between 20, 30
percent more juice.
Q. In another experiment, you discovered that it might be
easier to cook an egg on a dark blue Taurus than on a Texas
sidewalk. Why learn this?
A. In the summers, when people get tired of saying, "Is it
hot enough for you," they often say, "It's so hot that you
could fry an egg on the sidewalk." I decided to find out if
this was really possible.
My daughter lives in Austin, where it gets pretty hot, and
one year during a visit, I brought along a noncontact
thermometer to read the temperatures of various surfaces.
So when it got to be about 100 degrees out, I measured the
temperatures of sidewalks and black asphalt paving. I never
found anything close to what is required to congeal an egg
- about 158 degrees.
Now, my daughter's car, which was dark blue, seemed a
better bet. I reasoned that in principle, when you break an
egg on a metal surface, that surface won't cool down as
much. The heat will be replenished by heat conduction
through the metal. And indeed, a reader later told me about
seeing a movie where Germans in the Afrika Corps fried eggs
on the fender of their tank. If it gets hot enough and it's
on a surface that's a good enough conductor of heat, I
decided it can be done.
Q. You've investigated whether human belching contributes
to global warming. Does it?
A. It actually might. After reading about how many billions
of gallons of carbonated beverages are consumed in this
country every year, I asked myself what happens to all of
that carbon dioxide. CO2 is a greenhouse gas. Some of the
carbon dioxide goes directly into the atmosphere from the
opened containers, and the rest must be either breathed or
belched out by the drinkers.
I found out the pressure it takes to fill all these bottles
and cans, and calculated how much carbon dioxide would be
equivalent to that pressure. It turned out to be about
Q. Don't your calculations assume that the gas is all brand
new CO2 that has been specifically manufactured for the
A. I made rough corrections for that. If the gas was made
by heating limestone, which much carbon dioxide is, then
it's brand new in the atmosphere. But in alcoholic
beverages like beer, the CO2 comes from the fermentation of
grains, which took the carbon dioxide originally from the
atmosphere by photosynthesis, so it doesn't count as brand
new. And some of the CO2 in soda pop is obtained from the
air, so it gets pretty complicated. All in all, carbonated
beverages don't seem to be much of a threat to the planet.
Q. Since we are on the subject of beverages, can you
explain why tea made in the microwave almost always tastes
A. You need very hot water to get the maximum flavor and
color out of tea. That's why the British go as far as to
preheat teapots. Heating a cup of water in a microwave oven
is not a uniform process. Some parts of it may be boiling
and others are not. When it looks as if it is boiling, it
is just not hot enough to take the flavor out of the
Q. What can science teach us about the chilling of martini
A. A good bartender will always chill the martini glass
because it should be as cold as possible. And what they
will do is put ice water in a glass and let it sit for a
few minutes while they are mixing the martini, then dump
the ice water out and pour the martini in.
I say that's not as good a method as it could be. Ice water
can never be colder than 32 degrees or else it wouldn't be
water, it would be solid ice. So I say, don't chill it with
ice water, chill it with cracked ice because ice straight
out of the freezer can be something like 10 below zero.
Much colder. Unfortunately, though, bartenders' ice usually
isn't anywhere near that cold because it's been sitting out
for some time.
Q. Should cooking schools give their student chefs a basic
A. To some extent. But it needn't and shouldn't be a
separate course, such as we get in high school or college,
with all that math and balancing of equations stuff. It
should be here-and-there, now-and-then bits of chemistry or
physics, applied to specific food and cooking situations on
a "need-to-know" basis.
Q. What is it about the chemistry of turkey that makes it
such a potential public health hazard?
A. It's not so much the chemistry as the physics, and it's
not so much the turkey as the stuffing.
A turkey is shaped physically like a big round ball, and
when you're roasting it the heat has to come in from the
outside. That makes the inner parts of the turkey the last
to become hot enough to kill dangerous bacteria; the
U.S.D.A. recommends at least 165 degrees.
But by the time the inner thighs get to that temperature,
the breast is overcooked. And if the bird is stuffed, the
stuffing may never get that hot, and at lower temperatures
stuffing is a wonderful growth medium for bacteria.
So what can you do to avoid poisoning your family or
winding up with a dried-out, overcooked turkey? You can
bake the stuffing in a separate casserole dish instead of
burying it inside the bird.
But the best suggestion I've heard is to place the stuffing
in the roasting pan beneath the turkey. It can then cook
thoroughly, and the drippings will flavor it. I haven't
tried this yet, and I wonder if you might not wind up with
greasy, mushy stuffing. Also, it kills the possibility of
making pan gravy. But I guess you can't win 'em all. Not
until they breed flat turkeys.
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