I take no position on doing this, but if obtaining the
maximum possible shelf life in your cooking fats is important
to you, it is possible to add antioxidant preservatives to
the fat you have purchased. Used in conjunction with a
gas impermeable container, either opaque in color or stored
in a dark place, and cool storage temperatures (70� F
21�C or less) then shelf life can be extended to about five
years, possibly longer.
The antioxidant in question is Butylated HydroxyToluene
(BHT). It is often used in the food industry to slow the
development of off-flavors, odors and color changes
caused by oxidation, mostly in foods with significant fat
contents. BHT is on the U.S. Food and Drug
Administration�s Generally Recognized As Safe (GRAS)
list as a common preservative. The FDA limits the use of
BHT to 0.02% or 200 parts per million (ppm) of the oil or
fat content of a food product. The directions that I give
below will be for the FDA limit. BHT is available over the
counter in the retail trade, typically found in health or natural
foods stores or vitamin and nutritional supplement
suppliers. It may also be found from various suppliers on
the Internet.
To get the best results you will need the freshest oil you
can find. Purchasing from a large, busy supermarket will
usually suffice. You�ll also need containers that are gas
impermeable such as glass jars, or metal cans. There may
be plastic containers with high gas barrier properties that
will also serve, but I cannot knowledgeably say about this.
It is important that your containers be food grade, clean,
dry and dust-free. In keeping with the FDA�s GRAS
guidelines you want to add 5.3mg of BHT crystals per
fluid ounce of oil or fat. If you�re using a scale calibrated
in grains, such as a reloading powder scale, you may use
the following table.

Remove the BHT crystals from their gelatin capsules and weigh
them, if you�re going to. Once you have the appropriate
amount, add the crystals to a pint or so of the oil, shaking
vigorously. It may take several hours for the preservative to
dissolve completely. Bringing the oil up to a warm, NOT HOT,
temperature will speed the process. Once completely
dissolved, pour the antioxidant laden oil into the rest of the oil
and mix thoroughly. Once mixed, the oil can then be poured
into its storage containers leaving approximately 1/2 inch of
headspace. If you have a vacuum sealer the jars or cans may
be vacuum sealed to remove most of the oxygen laden air
from the container, otherwise just seal the lid. Store in a cool
place and if using transparent jars, be certain to put them in a
larger container such as a box to keep the contents in the
dark. Don�t forget to label and date the jars.
Before I close out this section on fats and oils, please allow
me to reemphasize that no amount of preservatives that can
be added to your stored fats will substitute for proper storage
and rotation.