Used oil, due to its high water content and residual impurities, can lead to rancidity and the production of harmful substances. Furthermore, repeated high-temperature treatment of used oil can cause it to deteriorate, which can be toxic to the human liver and reproductive organs, and may even be carcinogenic. So, how can you identify used oil? You can identify it by looking, smelling, and listening.
1. Look: When picking up food with chopsticks, they will be coated in oil. If the oil is in a liquid state, it is normal. Conversely, if the oil solidifies within a few seconds, it indicates that the oil is of poor quality. Also, check its transparency: pure vegetable oil is transparent, whereas used oil is dark in color and contains sediments and impurities.
2. Smell: The normal aroma of oil is only released after being heated for some time. If a hot pot or dish emits a strong, non-oily fragrance as soon as it is served, you should be wary.
3. Listen: Take one or two drops of oil from the bottom layer and apply it to a flammable piece of paper. If it burns abnormally and sizzles or pops, it indicates that the oil has a severely excessive water content and is of poor quality.