The best solution for knowing if the oil has reached the appropriate temperature for frying is to use a special thermometer.

The optimal temperature for frying most foods is 180°C, although in individual cases it may be higher or lower.

If you don’t have a thermometer, place a small piece of bread in the oil and observe it frying. If it turns golden brown on the outside within a reasonable period of time (1-2 minutes) it means the oil is at the right temperature.