I want to know what is the right temperature for deep-frying, for: Schnitzels French-fries Crockets and Onions.
I want to know the lowest temp for the right frying, because I want to keep the oil as much as I can.
325 to 375 for fries...
Most recipes shallow-fry their schnitzel, if you want to boldly chucks them in the deep-fryer instead, it presents two problems; it makes them super crisp, which is usually not what we're after, and it excludes the possibility of using butter, which, I think, is a must. I find the richness of butter unbeatable. Obviously frying it in just butter would present practical problems, as the schnitzel requires more fat than a mere splash, and butter burns easily. You could use a great dollop of clarified butter, but a mixture of that and neutral oil imparts flavour at less expense. The secret to great schnitzel is to "trap air in the crust when you cook the meat by moving and shaking the pan". It works – the coating is noticeably lighter.
For fries, a common recommendation is cook them at 284-325, let them cool a bit, and re-fry at 375-392. Be aware there are health controversies about frying starches at such high temperatures.
For onions - if you want bare onions pieces brown and crispy, I found working in rising temperature (start at 284 and let get hotter) works well... do not start in the 375 range, you will make scorched shoestrings :)