Which of the following best explains the process when oil starts to smoke in a pan?

• A. The oil undergoes polymerization
• B. The oil's fatty acids shift from cis to trans configuration
• C. The oil loses all unsaturated fats
• D. The oil instantly becomes safe for frying

Answer: (B)

When oil is heated toward its smoking point, the energy can cause the cis double bonds in unsaturated fatty acids to rearrange into trans configurations. This cis-to-trans isomerization changes the shape and stability of the fatty acids, contributing to the breakdown products that cause smoke and off flavors. This is the most consistent chemical change linked to oil starting to smoke. While heat can also promote other reactions like polymerization, and it’s not true that all unsaturated fats are removed or that heating makes the oil instantly safe, the cis-to-trans shift best explains the smoking appearance and the chemical transformation occurring at high frying temperatures.