The length of time oil can be used can be extended by filtering it through an oil filter paper, stronger versions of kitchen towel, or a fine sieve. Food particles left in the oil and reheated several times will cause the oil to deteriorate more quickly. Make sure the oil has completely cooled for several hours before attempting to do this.
The amount of times oil can be used before discarding will vary according to the type of oil and the food cooked within it. For example, good quality corn or groundnut oil can be used up to 8-10 times, whereas rapeseed oil should only be used 3-4 times. If strong aromatic food is fried bear in mind that this can affect the flavour of other foods cooked in the same oil.