# Quality Identification of Sauce-Flavor Liquor Based on the Tyndall Phenomenon
## 2 Principle  
The effect of colloid on a light field is summed up as the attenuation action of sol particles on the light. From the perspective of energy transmission, the process of light transmission in a colloidal solution can be summarized as the process of light absorption and scattering, which causes it to decay continuously. When light enters a substance, different phenomena, such as absorption, scattering, refraction, and reflection, will occur according to the size of the particles and the wavelength of the light [19,20]. The interaction of liquor colloids with light mainly causes scattering, which is reflected in the corresponding relationship between the particle size of the colloid and the waveband of the light.  
Figure 1 shows a diagram describing the principle of sauce-flavor liquor identification based on the Tyndall phenomenon. This identification system includes a light source, a liquor cup, and a light intensity detector receiving device. When the light passes through the liquor volume, it will generate the Tyndall phenomenon which can clearly be seen by the human eye in the direction of the vertical light. The light is scattered in the liquor, resulting in the Tyndall phenomenon, and then the light will be received by the light intensity detector. Liquor colloids have a distribution of large and small particles. The light entering scatters the particles in the liquor, and the scattered light continues to be scattered by other particles. The same particle is scattered by many rays of light at the same time. Therefore, this particle can be regarded as an illuminator, macroscopically, which forms a bright pathway in the liquor that is the Tyndall phenomenon [19].  
In the scattering system of liquor, because the colloidal particles move irregularly in the solution, the small particles in the solution constantly collide with sol particles that are much larger than themselves. Due to the irregularity of the collision, the sol particles that receive the impact force of the sol cannot cancel each other out, and the difference of the resultant force will result in different velocities of the colloid particles. In addition, for particles of the same size, particles with a smaller size have a larger scattering angle, and particles with a larger size have a smaller scattering angle [20]. Combining these two factors, in terms of macroscopic performance for the same incident light, if the colloidal liquor particles are small, the scattered light has a weak flood angle and its brightness is high; if the particles are large, the scattered light has a large flood angle and low center brightness. Good quality liquor has good particle size uniformity. When good quality liquor is irradiated, the light scattering tends to be produced by small particles. The light scattering angle of the particles is large, the center brightness is high, the flooding is small, and the Tyndall phenomenon shown is obvious. Poor quality liquor has poor particle size uniformity, and the light tends to be scattered by large particles. The light scattering angle of the particles is small, the center brightness is low, the flooding area is large, and the Tyndall path is dark.  
Figure 1: Principle diagram of sauce-flavor liquor identification based on the Tyndall phenomenon.