# Spectroscopic Techniques Application for Wine and Wine Byproduct Authentication
## 2 Food Spectral Print Approaches
### Infrared (IR) Spectroscopy
#### 2.2.1 Mid-Infrared (MIR) Spectroscopy  
MIR spectroscopy is a subset of infrared (IR) spectroscopy that specifically analyzes molecular vibrations in the mid-infrared region (4000-400 cm\({}^{-1}\)), as shown in Figure 2. It is widely used for identifying functional groups, chemical bonding, and molecular structures in organic and inorganic compounds. MIR spectroscopy investigates the interaction of MIR photons with molecules, exciting their vibrational and rotational modes. This interaction offers molecular selectivity and sensitivity, making it suitable for analyzing complex molecules and gases [42; 43]. Some MIR spectroscopy techniques involve frequency up conversion, where MIR photons are converted to the near-infrared range. This process preserves quantum correlations and enables high-sensitivity detection using single-pixel detectors [42; 43]. MIR dual-comb spectroscopy (DCS) utilizes two frequency combs to achieve high-resolution and high-speed spectral analysis. This method is effective for molecular metrology and can be enhanced with active phase control to improve coherence and the signal-to-noise ratio [44; 45; 46]. Table 3 presents examples of wines where MIR spectroscopy has been applied, along with referenced works. MIR spectroscopy enables the rapid analysis of various wine parameters, including alcohol content, acidity, and sugar levels, providing a comprehensive chemical fingerprint \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Wine Type/Variety** & **Application of MIR Spectroscopy** & **Ref.** \\ \hline Australian Red and White Wines & Varietal classification using MIR spectroscopy combined with PCA and LDA. & [47] \\ White Wines & Routine analysis of alcoholic strength, total acidity, and other parameters using MIR. & [48] \\ Chokeberry, Blackberry, Raspberry & Authentication and classification of fruit wines using Fruit Wines & [49] \\ Red Wines & Prediction of phenolic compounds during fermentation using ATR-MIR spectroscopy. & [31] \\ Various Grape Varieties & Prediction of chemical compositions using combined visible and MIR spectroscopies. & [50] \\ Cabernet Sauvignon and & Modeling sensory properties of wines using MIR spectra. & [51] \\ Chardonnay & Determination of sugars and acids using FT-MIR spectroscopy. & [52] \\ Chinese Rice Wine & Prediction of alcohol content, sugar levels, and total acidity using FT-MIR spectroscopy. & [53] \\ Italian Straw Wine & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Mid-infrared (MIR) spectroscopy techniques apply to wine and its byproducts. Figure 2: The electromagnetic spectrum. Retrieved from [[https://www.metrohm.com/pt_pt/](https://www.metrohm.com/pt_pt/)]([https://www.metrohm.com/pt_pt/](https://www.metrohm.com/pt_pt/)) discover/blog/2024/nir-vs-ir.html and accessed on 24 February 2025.  
of the wine. This capability is crucial for monitoring changes during wine production and ensuring quality control [34; 54; 55]. Combined with chemometric techniques, this approach is practical in classifying wines based on their geographic origin and grape variety. Studies have shown that MIR can accurately predict the geographic origin of wines and differentiate between monovarietal wines, which is crucial for authenticity and quality assurance [56; 57]. The technique is also applied to authenticate fruit wines from chokeberry, blackberry, and raspberry. Researchers can classify fruit wines by plant species by establishing chemometric models from MIR spectra, demonstrating the method's versatility beyond traditional grape wines [49]. A significant advantage of MIR spectroscopy is that it is non-destructive, requiring minimal sample preparation and no chemical reagents, making it an environmentally friendly option for routine wine analysis [34; 56]. Moreover, the technique offers high precision and accuracy in determining wine parameters, outperforming other spectroscopic methods, such as NIR and Raman, in specific applications, including measuring alcohol strength and total acidity [48].