Great question! If you've placed a bet on this debate, you can safely
start dropping broad hints for your friend to pay up. :) Dr. John
Deane, in the November 1998 issue of Olive Oil News, had this to say
in response to a reader question very similar to yours:
"People have been reusing oil for centuries without any acute
poisonings that I know of, but there is a concern over the long term
effects. Oil which has been heated extensively oxidizes and picks up
particles of food which can putrefy. Oxidized oil isn't considered as
healthy. There was much made of some studies several years back
concerning the "burnt" oils and proteins in barbecue being
carcinogenic...Restaurants have contracts with tallow companies which
pick up the oil at regular intervals and refine it for reuse or for
other industrial purposes." (
The woman behind the Ellen's Kitchen website agrees, rather
colorfully. "You are dealing with two issues when you reuse fats and
oils, flavor and health," Ellen writes at <
http://www.ellenskitchen.com/forum/messages/33.html >. "Once heated to
frying temperatures, oil begin to change from oil to, basically,
varnish." To put it in Homer Simpsonese, "Mmmmm, VARnish..."
While some maintain that there are no significant dangers to reusing
cooking oil, the answer more specific to your question is that no one
in either camp would recommend your friend's storage methods. :) While
fresh vegetable oils can safely be stored for a year at cool
temperatures, experts don't recommend reusing used oil beyond several
months of first use. In its Patio Corner section, for example, the
Garden Center website recommends reusing frying oil within 30 days,
and only using it twice, or until the flavor become objectionable
( http://gardencenter.southernstates.com/patio/turkeycooker.shtml ).
Professor Michael R. Markham, on his Fried Turkey page, is more
generous, giving used vegetable oil a six-month shelf life when stored
in a cool, dark location (
Chef Geir's Culinary Resources site lists these "signs of deteriorated
< http://www.culinary-yours.com/frying_oil.html >:
- Oil darkens with use because the oil and food molecules burn when
subjected to high/prolonged heat.
- When smoke appears on the oils' surface before the temperature
reaches 190 degrees C (375 degrees F), your oil will no longer
- If the oil has a rancid or "off" smell or if it smells like the
foods you've cooked in it, it should be discarded.
If your friend insists on reusing his french-fry oil in future,
convince him to begin afresh with safflower, sunflower, soybean,
peanut or canola oils, which break down less quickly than olive and
other vegetable oils.
Or ask him to consider other uses for the old oil - I was pleased to
see that my alma mater is working on using waste oil from the campus
dining hall to power maintenance vehicles.
Some reading material to keep you entertained:
Ask Chef Mom: Can I reuse the oil after deep frying a turkey?
< http://chefmom.myria.com/askchefmom/turkeyfryoil.htm >
Go Ask Alice!: Is reusing cooking oil safe?
< http://www.goaskalice.columbia.edu/2277.html >
I used the following search combinations in finding your answer:
reusing cooking oil
reusing vegetable oil
used cooking oil
saving cooking oil
storing used vegetable oil
All the best!