1 Look:
Look at the transparency, pure vegetable oil is transparent, and the transparency will decrease due to the mixing of alkali grease, wax and impurities in the production process; Look at the color, pure oil is colorless, in the production process, because the pigment in the oil is dissolved in the oil, the oil will be colored; Look at the sediment, its main component is impurities.
colour contrast
2 smell
Each oil has its own unique smell. You can drop a drop or two of oil on your palm, rub your hands together, and smell it carefully when you are hot. Oil with odor indicates that there is a problem with the quality, and it is likely to be waste oil with odor; If there is a smell of mineral oil, you can't buy it.
3 Chang
Take a drop of oil with chopsticks and taste it carefully. The oil with sour taste is unqualified, the oil with bitter taste has been rancid, and the oil with peculiar smell may be "waste oil".
4 listen
Take one or two drops of oil from the bottom of the oil layer, coat it on flammable paper, light it and listen to its sound. The products with normal combustion and no noise are qualified products; If the combustion is abnormal and makes a "squeaky" sound, the water content exceeds the standard and it is an unqualified product; When burning, it makes a "crackling" explosion, indicating that the water content of the oil is seriously exceeding the standard, and it may be an adulterated product, so it is absolutely impossible to buy it.
5 questions
Ask the merchant about the purchase channel, ask for the purchase invoice or check the sampling test report of the local food hygiene supervision department if necessary.
In addition, based on the relationship between metal ion concentration and conductivity, the amount of metal ions in oil can be judged by detecting the conductivity of oil. Many experiments show that the conductivity of hogwash oil is 5 to 7 times that of first-class edible oil, so hogwash oil can be accurately identified.