You can usually tell when oil isn't usable anymore when it goes very dark and gets smoky when frying. I think it would depend on the type of oil you'd be using and what you'd be frying. I know that the canola oil we use at at the grill (for fries, chicken tenders, crispy chicken burgers) under constant use lasts safely for 1.5 weeks. I think the amount of oil the fryer holds may affect oil longevity as well, the same deep fryer uses about 25L yet I see the same oil used on smaller deep fryers under the same usage don't last as long. |