Keep oil in good condition

As well as cooking temperature, there are several factors that affect the quality of the frying oil:

Keeping the fryer topped up with fresh frying oil helps it keep its light colour and fresh flavour. It also helps extend its fry life.

Filtering the frying oil is very important for increasing its fry life.
Manual filtering is common in New Zealand but it can be very dangerous to the operator and is not recommended.

Deposits of degraded frying oil (gum) around the fryer are difficult to remove if they are left for long periods.
Water, soap or detergent remaining after cleaning the fryer will cause the frying oil to breakdown more quickly.

Light, air and dust speed up the degradation of the frying oil. If the fryer is not going to be used for extended periods it should be cooled and covered with the fryer lid.

Filtering the frying oil improves the quality and consistency of the finished product. Topping up regularly with fresh frying oil also helps.
Different frying oils have different characteristics so the same criteria for discarding don’t necessarily apply for all frying oils. For example: some oils go dark early in their fry life, therefore, deciding to discard an oil should not be based on colour alone.
There are some quick tests available to test for degradation of the frying oil.
Fresh batter mix, crumbs, seasoning, sausages and seafood speed up the damage to the frying oil. So if practical, chips should be cooked separately from other fried foods