FT-IR Spectroscopy for Winemakers: A Look at the Potential Benefits

Figure 2. Conceptual model of acid, pH, and sugar content in grapes during the harvest season.

Credit: Courtesy of PerkinElmer.

Three of the most common factors in the determination of optimal grape ripeness for harvest are sugar content, pH, and acidity. As grapes mature on the vine, sugar content and pH increase, while acidity decreases, as shown in Figure 2. Sugar content is measured to ensure that there is enough sugar in the grape to be converted into alcohol during vinification. Sugar content can be determined by a measurement of fermentable sugars glucose and fructose, or by calculating the total soluble solids (°Brix). Monitoring the pH and acidity of grapes and must provides insights into the potential microbial stability of the ingredients throughout fermentation and allows for the planning of acidity corrections.

Must Under Fermentation Testing

Once grape must enters the fermentation process, yeasts take center stage. Although winemakers may have less control of the process during this stage, testing during fermentation is crucial. Yeasts play a major role in winemaking, as they consume sugars and nitrogen in grape must and juice, subsequently producing ethanol and carbon dioxide.

Like the parameters analyzed at harvest, pH, sugar, and acidity levels should also be tested in must undergoing fermentation to monitor the progress of the yeast. Monitoring sugars during fermentation will provide insights on how much longer the must needs to ferment to achieve the ideal sweetness and alcohol content. Finished wines with an intended sweeter taste will have some residual sugar after initial fermentation, while dry white wines will have few or no sugars remaining after fermentation. Conversely, as sugar content declines, ethanol content will increase.

Closely monitoring pH during fermentation is important, as it correlates with the level of sour taste in wine: The lower the pH, the sourer a wine tastes. Further, pH can affect the appearance and stability of wine, with higher pH wines more susceptible to oxidation. Measuring specific acids, such as malic acid, an organic acid that produces a tart taste in wine, can also aid in monitoring progress toward the desired taste profile of the finished product. During vinification, malolactic fermentation (MLF) converts malic acid to lactic acid, producing a creamy, buttery texture in the wine. Too much acid reduction during MLF can result in a higher pH, leading to the aforementioned chance of oxidation and subsequent spoilage. Using onsite FT-IR testing allows winemakers to monitor pH, total acidity, and individual acids in one analysis, without slowing down the process.

Outside of the winemaking process, this taste profile information can help winemakers who are using online selling channels improve the customer experience. Providing detailed and accurate product descriptions both informs and entices potential buyers and can create a competitive advantage with customers who want more information about the products they buy online.

Testing at Blending and Bottling

Testing at the blending and bottling stage, often one of the most common analysis points, provides valuable insights to ensure the finished product meets quality control guidelines and standards. At bottling, it is important to measure the amount of residual sugar left in the wine, as too much sugar could lead to further, unwanted fermentation. The acidity and pH should be stable, with no malic acid present, as it may lead to spoilage during ageing. Testing at bottling also allows winemakers to ensure that their product offers a consistent taste profile and experience for customers.

Measuring ethanol content is vitally important at bottling to ensure accurate labeling and adherence to government agency regulations, such as those developed by the Alcohol and Tobacco Tax and Trade Bureau (TTB). Outside of regulatory requirements, securing more detailed, data-driven information about a finished product can also help winemakers create a competitive advantage with consumers, such as millennials, who are demanding more information about the products they consume. According to a 2021 State of the U.S. Wine Industry Report, millennial buyers are the largest growing segment of the wine industry, and they demand transparency as it relates to labeling and processes. As such, offering detailed, science-based information in marketing efforts and outreach can help winemakers provide the information many customers consider when comparing products.