What Is the Smoke Point?

This is the temperature at which the sample is heated when the grease is heated without ventilation. Smoke point is an important indicator of refined cooking oil. It refers to the lowest temperature at which the thermal decomposition products of the sample can be continuously volatile when the fat is heated.

Smoke point refers to the maximum height of a smokeless flame when kerosene and jet fuel for lamps burn under specified test conditions. Beyond this height, black smoke will be generated. Smoke point is an important indicator of kerosene products. The high value of the smokeless flame indicates that the aromatic content is low and the cleanliness of the combustion is good. The smoke point is expressed in mm, and the general value is 22-28mm. It is a specification index for controlling the carbon deposition performance of jet coal. For edible fats, the smoke point is the temperature at which the oil is heated to a certain degree, and the oil begins to smoke. Generally, this temperature is generally above 215 degrees Celsius.

Smoke point is an important indicator of refined cooking oil. It refers to the lowest temperature at which the thermal decomposition products of the sample can be continuously volatile when the fat is heated. The generation of smoke point is mainly caused by the presence of some relatively low-boiling substances in fats and oils, such as free fatty acids, glycerides, unsaponifiables, etc. During heating, free fatty acids are more volatile than triglycerides. In general, fats and oils composed of short carbon chains or fatty acids with a high degree of unsaturation have a much lower smoke point than fats and oils composed of saturated acids with high carbon chains. The smoke points of unrefined oils and oils that have been hydrolyzed and oxidized due to use are much lower than those of high-grade refined oils. ^[1]

Oil and fat is a mixture of neutral oil and fat as the main component and contains non-glyceride components. The non-glyceride component is very complicated and the content is very low. Some are only trace amounts. Except for scientific research, it is generally not determined one by one. , And roughly use the content range as the quality standard for fats and oils. Generally, only those components that have a large impact on the quality and quality of the oil are determined, and the content and the resulting color, odor, and flavor of the fat are used as standards for assessing the quality of the fat.

For commercial oils and fats, especially edible oils and fats, internationally, quality standards such as taste, color, transparency, moisture and volatiles, impurities, acid value, peroxide value, and unsaponifiable matter are generally used for assessment and control. Most of these standards are related to the smoke point of grease. When the oils and fats of the same variety and the same batch of oil have higher moisture, acid value, and peroxide value, their smoke points must be lower. Therefore, the smoke point reflects the quality and quality of grease to a certain extent, and it can be directly operated by a grease smoke point tester. However, the smoke point is only one of the sensory values reflecting the fatty acid composition of fats and oils and non-glyceride components during heating. ^[2]

The most primitive method for monitoring the smoke point of fats and oils is to determine it visually. Affected by the rate of temperature rise, thermometer readings, and individual eye sensitivity, human factors cause large errors in smoke point measurement.

In modern times, a professional grease smoke measuring instrument is mainly used for measurement, which can overcome the disadvantages of traditional measurement methods. ^[1]

1 The relationship between the level of grease smoke point and quality

The reason for the lower smoke point of oils and fats is mainly the incomplete hydration of soybean oil, which contains a small amount of phospholipids. The oil color becomes darker and traces out during heating test at 280 . Under oxidative decomposition, it becomes black and bitter. And a large amount of smoke is precipitated, which causes a low smoke point and a large smoke.

The smoke point of the same variety of oil has an inverse relationship with the color. The color with a high smoke point is low and the color with a low smoke point is deep. The smoke point is inversely proportional to the acid value. High smoke point and low acid value indicate excellent oil quality. Therefore, for the same type of fats and oils, the quality of the fats and oils can be judged according to the height of the smoke point.

2 Linear relationship between smoke point and free fatty acids

There was a negative correlation between free fatty acid content and smoke point. The free fatty acid content can be calculated by measuring the acid value by titration. ^[2]

(1) The smoke point of soybean oil directly affects the quality of fats and oils, the higher the smoke point, the better the quality;

(2) Use the regression equation to quickly estimate the smoke point size by accurately measuring the content of free fatty acids in refined soybean oil. It can reduce many errors caused by visual observation with ordinary cigarette lighter, and improve the detection speed.

(3) To improve the smoke point of refined soybean oil, we must strictly control every step of the production process, such as alkali refining, decolorization and deodorization, to achieve the purpose of increasing the smoke point. ^[1]

The fresh high-smoke point grease has temporarily good thermal stability, which does not mean that its oxidation stability is good. The oxidation stability of the fat is poor. The oxidative decomposition will cause its thermal stability to deteriorate and the smoke point to decrease. Some refined oil products with higher smoke points have a flavor that is not better than those of the same type of oil with slightly lower smoke points, and their shelf life is much lower than those with lower smoke points. Some manufacturers of the same batch of soybean secondary oil have good transparency at low temperature without precipitates, while high cooking oil has reduced transparency, turbidity, and precipitation of crystallites at low temperature. This is caused by isomerization or polymerization during processing. The result is an increase in the melting point of some of the fats. These high melting point fats have a low digestion and absorption rate, are easy to accumulate around the internal organs, or are deposited in the blood along with cholesterol on the vessel wall, leading to atherosclerosis and cardiovascular disease. Therefore, the smoke point needs to be reasonably controlled during the production process, instead of blindly pursuing a high smoke point.

The inspection and quarantine system must not only complete a large number of import and export inspection tasks, but also do a good job of controlling the production process of the manufacturing enterprise, and also requires accurate and rapid detection of oil products. The height of the smoke point directly affects the quality of the product. Therefore, increasing the smoke point of oil and fat is a key and difficult point for manufacturers to solve. ^[2]