Wang Xingguo, a standing council member of the Dalian Nutrition Society and director of the Nutrition Department at Dalian Central Hospital, answered that the flocculent solidification of peanut oil at low temperatures is a normal physical phenomenon and does not necessarily indicate a problem with the oil's quality. Just as water turns to ice at 0°C and ice melts back into water above 0°C, vegetable oils will also solidify when the storage temperature drops below a certain point, a temperature known as the oil's freezing point.
The freezing point of edible oil is mainly determined by the ratio of saturated to unsaturated fats in the oil. Peanut oil contains about 20% saturated fatty acids, with the ratio of saturated, monounsaturated, and polyunsaturated fatty acids being approximately 3:4:3, giving it a freezing point of around 0°C. Furthermore, an oil's freezing point is not a specific temperature but a range. It may begin to show a small amount of flocculent solids at a certain temperature, but it won't necessarily solidify completely. The solidification of peanut oil is also a gradual process; when the temperature drops near the critical point of 10°C, the peanut oil will produce some flocculent solids and become cloudy. The presence of these flocculent substances is a normal physical phenomenon. They will melt at a higher temperature and have no effect on the taste or nutritional value, so everyone can consume it with confidence. If you are genuinely concerned about peanut oil becoming cloudy or even solidifying, it is recommended to store it indoors at a temperature above 15°C after purchasing it during the winter to prevent solidification.
Because lard and palm oil are cheaper, there is indeed a possibility that some producers might adulterate peanut oil with them. However, this is also easy to distinguish. Lard and palm oil are almost entirely saturated fats, and their freezing points are higher, both above 25°C. This means these two oils will solidify at room temperature. If the peanut oil you purchased produces flocculent solids even in a warm indoor environment, it is highly likely that it has been adulterated with palm oil or lard.