Test Method for Smoke Point of Vegetable Oils

Test Method for Smoke Point of Vegetable Oils

Vegetable oils are natural oils extracted from plant seeds, fruits, or germs. They are mainly composed of esters formed by the reaction of higher fatty acids and glycerol. Most of these oils are liquid at room temperature and are one of the important nutrients in the human diet, providing essential fatty acids and fat-soluble vitamins (such as vitamin E and K).

Vegetable oils are not only used for food consumption but also widely applied in industrial fields including food processing, biodiesel, soap, and cosmetics. According to processing methods, they can be divided into pressed oils and solvent-extracted oils; by refining degree, they are classified into Grade 1 to Grade 4. The higher the grade, the higher the refining level, though some nutrients may be lost in the process.

Experimental Purpose

The purpose of testing the smoke point of vegetable oils is to evaluate the thermal stability and edible safety of oils during heating, determine their suitable cooking methods, and provide scientific evidence for production, processing, and quality control.

1.Ensure cooking safetyWhen oil temperature exceeds its smoke point, the oil decomposes to produce harmful fumes such as acrolein, which irritate the eyes and respiratory tract. Long-term inhalation may endanger health. By measuring the smoke point, users can be guided to select cooking oils suitable for different high-temperature operations such as frying, stir-frying, and deep-frying to avoid excessive oil fume generation.

2.Evaluate oil qualityThe smoke point is closely related to the refining degree and freshness of the oil. Oils with high refining degree and low content of impurities (such as free fatty acids, moisture, and phospholipids) usually have higher smoke points. Therefore, the smoke point can serve as an important indicator for measuring oil purity and processing level.

3.Support optimization of production processesIn the oil refining process, processes such as deacidification and deodorization directly affect the smoke point value. Through smoke point testing, enterprises can monitor process effects and adjust parameters in a timely manner to improve product quality.

Experimental Samples and Instruments

Experimental sample: Vegetable oil

Experimental instrument: ST123 Oil Smoke Point Tester, compliant with GB/T 20795

Experimental Steps

1. Sample Cup Cleaning and Sample Loading

Wipe the inner wall of the copper sample cup with an anhydrous ethanol cotton ball. After the ethanol has completely evaporated, pour the vegetable oil sample to be tested into the sample cup so that the liquid level is precisely at the graduated line of the cup, preventing overflow or insufficient volume from affecting the test result.

Place the loaded sample cup on the heating furnace of the instrument, and adjust the position of the spotlight so that the light beam passes through the center of the sample cup to ensure a clear observation field.

2. Sensor Installation and Instrument Calibration

Hang the PT100 temperature sensor vertically at the center of the sample cup, with the sensor probe approximately 6 mm above the bottom of the cup, and the small hole of the probe fully immersed in the oil sample to ensure accurate temperature measurement.

Connect the instrument power cable, turn on the power switch and the spotlight switch, preheat the instrument for 5 minutes, and proceed with subsequent operations after the instrument stabilizes.

3. Heating and Smoke Observation

Based on the estimated smoke point range of the olive oil sample (≥205℃), set the preset temperature to 200℃ using the instrument’s increase, decrease, and function keys. When the instrument temperature reaches 42℃ below the set value, it will automatically enter temperature control mode and heat up steadily at a rate of 5–6℃ per minute.

Closely observe the smoking condition of the oil sample during heating. When a small amount of continuous pale blue smoke appears from the sample, press the temperature lock button quickly. The instrument will immediately lock the current temperature value, which is the smoke point of the oil.

To ensure accuracy, perform two independent tests on the same sample and take the average value as the final smoke point result.

Experimental Results

The smoke point temperatures from two independent tests were 206℃ and 207℃ respectively, with an average of 206.5℃, rounded to 207℃.The smoke point of this brand of refined olive oil is 206–207℃, which meets the requirement of “smoke point ≥205℃” on its product label. This indicates that the oil has a high refining degree and good thermal stability, making it suitable for medium and high-temperature cooking methods such as frying and stir-frying.