Refining edible oils involves very high heat, often in multiple stages:

1. Degumming & Neutralization – Heated to around  200 °C to remove gums and free fatty acids.

2. Bleaching – Heated to about 110–130 °C with bleaching clay to remove color pigments.

3. Deodorization – This is the most intense step, where oil is heated to 180–270 °C under vacuum with steam to remove odors and flavors.

At these temperatures, natural vitamins (like vitamin E), antioxidants, and enzymes are destroyed, and harmful compounds such as trans fats and free radicals can form.