I made some falafels well over a week ago, frying balls of mixture in veg oil (one and a half standard bottles) in a saucepan. Normally after the oil has cooled down, I filter it through an old sieve into a glass jug to remove as much of the impurities and little black bits, then funnel it back into the bottle. I normally reuse oil a couple or 3 times before consigning it to the bin and buying some fresh oil. The oil I made these falafels with was only used once or twice I think but I forgot to get it back to the bottle, so it's been sitting in the saucepan for days. If I filter it now is it ok or does leaving it in air do something funny to oil, and if so, throw it?