This was an email that spread through Microsoft like wild fire when I was
an intern in Summer 2000.
I ate in cafe 9 today, and I had an orange, and I though it was kind of
wierd that the orange melted the knife I was using to cut into it. I dunno
what those plastic utensiles are made out of, but you may want to look into
different ones maybe.
Thank you for your comments regarding the cutlery used by the Dining
Centers. These utensils are injection molded polystyrene with colorant
(polystyrene is translucent white is raw pellet form, the colors are pigment
pellets adding to the raw styrene).
Polystyrene is derived from the oil processing industry and is subject to
similar chemical processes as oils, grease and other petro-chemical
Orange peel contains a number of aromatic organic solvents, 90% of which is
One significant industrial use for d-limonene is parts degreasing . As such,
the d-limonene in the peel will begin to attack the petrochemical
hydrocarbons in the polystyrene. Another petro-chemically derived plastic,
polyethylene, will not react in the same manner due to it's high surface
tension, however due to it's soft nature, is not preferred for this
In the manufacturing process of the polystyrene cutlery, minute particles of
the molded product can develop on surface, generally from abrasion in
shipping and handling. These can be picked up and carried by the oils within
the orange peel and give the impression that the utensil is
Please be assured that all the polystyrene and the colorant are FDA approved
for food use.
Should you have any further questions or if I may be of further service,
please do not hesitate to contact me.
Does this mean that I can just eat the black stuff that rubs off and not
worry about it?
I really would not recommend eating it (but it is FDA approved). Let me
replicate your activity and just see the results for myself. Are you using
the knife to cut perfect quarters and eating it out of the peel?
no, i just cut the peel off. its not a big deal... honestly i'll probably
never eat another orange again... i don't really like them. : )
I wouldn't stop eating oranges because of this. Let me take a look.
I was able to replicate your actions in the peeling of an orange using a
polystyrene knife as found in the Dining Centers.
Unable to affect the oils in the orange (d-limonene specific)
Unable to affect the chemical properties of Polystyrene (C6H5CH=CH2)
Orange at room temperature of 72 degrees Fahrenheit
(2) Knives obtained at random from Cafe 123, one used for test, one retained
as control sample
Using a wide slicing pattern to provide maximum exposure to the oils on the
surface of the knife blade
Slicing the outer peel only deep enough to remove the zest, most of the rind
The d-limonene altered the surface of the blade in a manner consistent with
thermal degradation above 212 degrees Fahrenheit for limited duration
(affected surface with little penetration). Where surface was affected by
d-limonene, remained somewhat sticky for several minutes until d-limonene
A residue remained on the inner surface of the removed peel, dark gray to
black in color. Little coloration appeared on the remaining rind of the
If it is desired to utilize polystyrene utensils to remove the peel from
citrus fruits (especially oranges) and discoloration occurs on the edible
portion of the remaining rind, peel the discoloration from the segmented
portion of the orange prior to eating.
While little known hazards exist from the ingestion of styrene (see
<<<http://www.styrene.com>>>), it is not recommended to
I hope this answers your concerns. If I may be of further service, please
Okay folks, this is worth its weight in gold...
I just hope we don't sound like this when we talk about our product! :)