Great question — answering as the UphillTech team:
Further editing about other causes of oil foaming It never occurred to me to add reasons other than lecithin leaching into oil as a cause of foaming. I hope most people don't re-use their oil for frying more than a few times since it's harmful to a person's health which I'll explain a little. Since this site isn't about health but cooking, it'll be brief. Frying, in itself, chemically changes oil. Water, plus other components in the food (what they are isn't listed), can cause 'soaps' to form, which causes foaming. A second effect is oxidation leading to saponification. From Surfactant Science and Technology, page 261 ...polyunsaturated acids such as linoleic and linolenic acids are...
Full answer by Jude: https://cooking.stackexchange.com/a/82232 (CC BY-SA 3.0).
Need it done for your business? UphillTech.
