A commercial device and method for cooking food product in cooking oil includes a fry vat containing an amount of cooking oil used to cook discrete batches of uncooked food in discrete batches of a weight relative to the amount of cooking oil in the range of from about 0.0375 to about 0.1, with the total amount of food being cooked at any one time relative to the amount of oil in the fry vat being about 0.1 or less. Cooking the food results in an uptake of oil by the food in an amount of from about 5.5% to about 13% by weight of the uncooked food, and an oil turnover ratio of from about 0.0026 to about 0.007 per discrete batch. Replacement oil is periodically added, and a sufficient number of batches are cooked over 60 hours of operation to achieve at least one vat oil turnover. Automated intermittent filtration is employed in the device and method that can include monitoring the elapsed time since the last filtration of the cooking oil, monitoring the amount of food by number of batches or by weight of food product cooked in the oil since the last filtration, and filtering the oil when a predetermined threshold value is reached based on the elapsed time since the last filtration and the amount of food cooked. An automated device and method for maintaining a level of oil in a fry vat having a volume includes sensing the level of oil in the vat. When the sensed level of oil in the vat is less than or equal to a first predetermined level, replacement oil is automatically added to the fry vat, typically when at ambient temperature at a low average flow rate in the range of about 0.008 to about 0.08 gallons per minute per gallon of the oil present in the vat at the first predetermined level. The low average flow rate of added oil avoids a temperature drop of more than 15.degree. F., 10.degree. F. or 5.degree. F. in the bulk oil present in the fry vat as result of adding the oil as desired.