## 1 Introduction  
It is a fact that plasmonic sensors are currently the ones that provide the highest sensitivity [1], particularly in the field of food [2, 3]. In the beverage industry, it is extremely difficult to continuously measure the real concentration of mixed substances in real-time without extracting a sample. In the fermentation of alcoholic beverages, it is essential to know the exact concentration of ethanol, glucose, fructose, sucrose, etc. in real time because this quantity determines the percentage volume of alcohol. This concentration is traditionally measured in the same way as commented above, i.e., a quantity of liquid is extracted and analyzed outside the barrel, tank, or container, therefore, the determination of the concentration is not continuous, and the fermentation process control is not possible to automate [4]. The concentration of glucose/ethanol depends not only on the moment of taking the measurement but also on the place where the sample is taken from because the mixtures are usually inhomogeneous. To carry out an analysis with an electronic tongue, as with other analytical techniques it is habitual to extract a sample from the system which can then be studied, moreover, these nongues use reactions that have to be replaced [5]. During the manufacturing process, it is necessary to know the quantity of sucrose in the mixture (both types of syrups) to control the dissolution. This control is carried out by extracting a sample and analyzing it. This is a problem because we do not know either the quantity of sucrose or the heterogeneity of the mixture in the tanks in real-time and this causes a delay in the manufacturing process. Moreover, if the sucrose distribution is not uniform (as can occur) the concentration will depend on what part of the tank the sample is extracted from, and results cannot adjust to the actual composition. Moreover, the process is time-consuming and in various steps, and the control of the concentration of sucrose has to be verified many times in many places. In 2009, [PERSON] et al. [6] measured the sucrose concentration in lemon-type soft drinks with dispersive Raman spectroscopy. To carry out the measurement, a quantity of liquid had to be extracted from the container and be analyzed outside, therefore, the measuring, although very precise and accurate, was not continuous, and these measurements depended on the sample and the place where the sample was taken from. [PERSON] et al. [7] used Raman spectroscopy to determine the concentration of fructose, glucose, and sucrose in soft drinks. This method involves extracting a portion of liquid and then measuring it. The concentration of the sample could vary depending on the place where it was extracted from and thus, the measurements were not continuous. [PERSON] et al. [8] fabricated two stable fiber optic sucrose sensors, one with EGO-Au NPs (encapsulated graphene oxide and gold nanoparticles) and the other with AuNPs tested for wavelength (450-850 nm) with a resolution of 8.7 \(\times\) 10\({}^{-5}\) RIU (EGO). The sensor measures sucrose concentration by the change in the peak absorbance due to the deposition of EGO-Au NPs in the core of an optical fiber. [PERSON] et al. [9] measured the concentration of sucrose in liquids with a coplanar waveguide loaded with a split ring resonator-based microwave sensor for aqueous sucrose solutions. The results are quite good, but the range of concentration was only 0-1 gmL\({}^{-1}\). As in the former cases, a sample has to be taken from the tank and measured, so, the measurements are not continuous. [PERSON] et al. [10] enhanced the sensitivity of a sucrose biosensor with ultra-microelectrode. In this case, a sample has to be prepared outside the product and it takes more than 20 min. [PERSON] et al. [11] developed an optical fiber sensor to determine the concentration of sucrose and ethanol in process streams and effluents of the sugarcane bio-ethanol industry. The physical principle is the Fresnel reflection.