Ask A Scientist General Science Archive

name         Pete S.
age          20s

Question -   There is an old saying in cooking, "hot pan, cold oil,
food won't stick."  It is a true statement, but I can't come up with a
plausible explanation as to why.  Why does food tend to stick to a pan
if the pan and the oil are brought to the proper temperature together?
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Pete,

A small amount of oil added to a very hot pan almost instantly becomes very
hot oil. The oil quickly sears the outside of the food and causes water to
be released from the food. This layer of water vapor ("steam") lifts the
food atop the oil film and keeps it from touching the hot pan surface. If
the oil is not hot enough, the steam effect will not occur and the food will
fuse to the (too) cool pan surface.

Regards,
ProfHoff 409
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Pete, I am glad I am not the only one who has wondered about this! I have an
idea, but fair warning, it is total speculation. Here goes:

First, this saying originated back before DuPont's Teflon (TM), when the key to
non-sticking was a good "seasoned" pan. As anyone who owns an old cast iron
griddle or a (non-DuPont's Teflon (TM)) wok know, a seasoned pan has a nice coating of oil
more or less cooked onto the surface. Those lipids in the oil have both
hydrophobic (water-repelling) and hydrophilic (water-"loving") parts to
them. I wonder if the hydrophilic parts of the pan do not get into the act
while the pan is stored. Perhaps they attract water molecules from the
environment. Now, when you heat the pan, those water molecules are driven
off, and then you add the oil. But, perhaps if you add the oil to the cold
pan, those water molecules remain trapped with the seasoning coating on the
pan, even as the oil heats. Now if you add food, maybe (lots of maybes here)
the hydrophilic parts of the food molecules are attracted to the moisture
trapped in the layer at the bottom..... Maybe they even become covalently
bonded to them at the proteins in the food heat up and denature. That would
result in sticking. Is anyone buying this? I would be interested to know 
what you
think of this theory.

PS. I see from your address that you are in a chemistry department. One 
might be
able to test this idea by rinsing a cold, stored pan with a dehydrating
agent, such as 100% ethanol, and then adding oil to the cold pan.

Tune in tomorrow when we address the wisdom behind the age-old "starve a
cold, feed a fever", or is it "feed a cold...."?

Paul Mahoney, PhD
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