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

Today’s winemakers, like other food and beverage producers, are working in unusual and changing times. Paradigms have shifted in the COVID-19 era, where booming online selling channels and the limited availability of raw materials is prompting winemakers to adapt their business models to the realities of fast-changing consumer demands.

In several regions, including North and South America, China, and parts of Eastern Europe, unfavorable weather patterns and natural disasters have either limited grape harvests or changed the characteristics of the grapes, placing increasing importance on the testing of grapes and other raw materials. Further, the pandemic has spurred a major shift in consumer behavior toward online buying channels as restaurants temporarily closed to prevent the spread of the virus. Given large selections online versus what is available in most standard brick-and-mortar establishments, consumers are also exerting more buying power and demanding more transparency and quality.

To remain competitive, many wineries are starting to leverage more advanced analytical testing to supplement traditional sensory evaluations and basic testing, helping to ensure product consistency and reduce losses tied to poor product and raw material quality. They also aim to use the collected data as a competitive advantage. Although testing has played an important role at large wineries for decades, many small to mid-sized wineries, often citing budgetary concerns or gaps in technical proficiency, have not yet embraced the potential that analytical testing offers. Recent advances in Fourier transform infrared (FT-IR) spectroscopy instrumentation can help address these challenges, not only by drastically reducing the complexity of testing procedures, but also by reducing the upfront investment required to purchase instrumentation, making advanced yet easy-to-use testing more attainable to wineries of any size.

FT-IR Spectroscopy for Winemakers

Figure 1. Spectrum of a wine sample generated with PerkinElmer LQA 300 FT-IR instrument.

Credit: Courtesy of PerkinElmer.

FT-IR instrumentation uses spectroscopic imaging to essentially map, or “fingerprint,” a sample by creating an infrared spectrum of the absorption or emission of components in the sample across a number of wavelengths. Spectral images, such as those shown in Figure 1, are then compared to a library of known components to both identify and quantify compounds in the sample. Modern FT-IR instruments can produce results in less than a minute and are small enough to transport in the trunk of a small sedan, allowing for agility and portability throughout the winemaking process.

The benefits of onsite FT-IR testing are numerous and include fast results, ease of use, and a low cost of operation, allowing winemakers to monitor their process by measuring critical parameters throughout vinification, thus enabling more comprehensive process control. This provides a more beneficial approach than conducting single data-point measurement, as it helps to ensure full process and input control and avoids product loss if processes fall out of specification before or after isolated test points. As such, it is recommended that testing occur throughout the winemaking process, including the analysis of grapes at intake, must under fermentation, and the finished product after fermentation.

Grape and Must Testing

Testing grapes throughout the growing process and at harvest using an FT-IR ensures product soundness, optimal grape maturity, and fair pricing. Deciding when to harvest grapes has often been more of an art, with harvesters and wineries relying on decades of experience, skill, and a “gut feel.” Supplementing this human knowledge with actionable data enables an optimal blend of experience and science. Striking the correct balance between phenolic and physiological maturity is key and, taking into account the potential impacts of unfavorable climate changes, the importance of testing grapes to determine harvest dates has become increasingly important.

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.

An Investment in Quality

Analytical equipment, such as FT-IR instrumentation, that is used to inform decision making throughout vinification is a sound investment for wineries of all sizes. Although the trends influencing the market may change in coming years, the need for data-driven decisions and a focus on quality raw materials and finished products will always be paramount. Making the decision to further invest in a more robust quality and process control program that includes testing at all stages of winemaking will not only safeguard against costly quality lapses but can also lead to improved margins and revenue.