How quickly do saturated fats go rancid?


>> can you render a fat that have been stored dried and got rancid and make the
>> rancid taste disappear?
>
>The short answer is, maybe to some extent.
>
>There are two kinds of rancidity. Oxidative rancidity affects
>unsaturated fats and definitely cannot be reversed by heating or
>rendering. Polyunsaturated vegetable oils are highly sensitive to heat,
>light, and oxygen, and should be stored in a cool, dark place. Because
>animal fats are mostly saturated, they are much less sensitive to
>oxidation, but any unsaturated content can become oxidized.
>
>Hydrolytic rancidity involves the splitting off of free fatty acids from
>the glycerol backbone of a triglyceride fat molecule by reaction with
>water. This is what makes butter go rancid. I suppose that prolonged
>heating might partially reverse this reaction by recombining the fatty
>acid and glycerol and driving off the resulting free water, but that
>doesn't strike me as a promising solution. Well-rendered fat that is
>kept dry and sealed from humidity should be safe from this type of
>degradation indefinitely.
>
>I did find one reference to "cleaning" rancid fat...on a soap-making
>website. They advised boiling the fat with 4 times its volume of water
>to remove impurities. This could not remove all impurities, such as the
>stubs of broken fatty acids that are still part of a triglyceride
>molecule, but could remove some of the broken-off pieces and other
>oxidation products of low molecular weight. If you did that, you'd have
>to render the fat again to get rid of the water. I'm not sure I'd want
>to eat the result, but in a time of famine it might be a way to improve
>the taste of rancid fat to some degree.
>
>Bill Dooley
>
>