Short answer
Change fryer oil when it shows it is worn out, not on a fixed calendar: dark colour, smoking at normal frying temperature, heavy foaming, a strong odour or off flavours in the food. How long that takes depends on volume, what you fry and how often you filter. Filtering at least once a day usually extends oil life considerably.
Breaded and battered foods and fish break oil down faster and leave more debris than plain fries, and salt dropped over the vat speeds breakdown. Many kitchens keep a separate vat for fish or allergen-sensitive items.
Topping up with fresh oil between changes and keeping the fryer at its set temperature, rather than hotter, both help. Turning the fryer down during slow periods also reduces wear on the oil.
Oil test strips, or a handheld meter that reads total polar materials, give an objective reading if you want one consistent change rule across staff and shifts.
Updated · By Norpex