"MMu" > wrote in message
...
>> No, this is not true. Rancidity is the result of the oil reacting
>> (slowly) with oxygen in the air. A trace of old rancid oil will not
>> hasten the deterioration of new oil - but it will affect the flavor.
>
> This is not true, in fact.
>
> The products of fat oxidation are (among others) Epoxides and Peroxides.
> (besides chain fragments, aldehyds etc).
> Peroxides work as starters of radical chain reactions.
> Epoxides can react (with oxygen) to Peroxides.
>
> Thus: having old oxidized oil in your new unoxidized oil will speed up the
> oxidation process
> (mostly by reducing the antioxidant capacity in the new oil).
>

You are way beyond my knowledge of organic chemistry so I'll accept what you
say. But the question remains. Regardless of what goes on theoretically,
does a trace of old oil actually make a practical difference in how long you
can keep oil in the kitchen? For example will your oil go rancid in 2 weeks
instead of 2 months? Or will it go rancid in 59 days instead of 60 days?


--
Peter Aitken

Remove the crap from my email address before using.