If you’re a wine connoisseur or even if you’ve been to a wine tasting event at your local vineyard or liquor store, you’re most likely aware of the five S’s” of tasting wine—See, Swirl, Sniff, Sip, and Savor. In this article we will discuss the first “S” of wine tasting, which is “See” – meaning observing the color and intensity of the wine.
If you are tasting the wine, you’ll be looking at it to help determine the grape variety, the concentration, or even the age of the wine. If you are producing the wine for consumers, however, you are trying to help ensure the quality and consistency of your product. UV-Visible spectroscopy can be utilized to help ensure your company is meeting those requirements.
The Federal Alcohol Administration Act (FAA Act) of the Alcohol and Tobacco Tax and Trade Bureau provides for the regulation of those engaged in the alcohol beverage industry, and for the protection of consumers. In addition to ensuring the integrity of the industry, the FAA Act ensures that labeling and advertising of alcohol beverages provide adequate information to the consumer concerning the identity and quality of the product. The U.S. Food and Drug Administration (FDA) is responsible for “determining which ingredients are prohibited from being used in food and/or beverage products….
“Many alcohol beverage products contain coloring agents. Coloring agents are added to impact color which is not natural to the product. There are two categories of coloring agents that are used – FDA Certified Colors and Non-certified Colors. Certified colors are synthetic dyes approved by the FDA for use in beverage products. The non-certified colors are natural coloring agents approved for use in alcohol beverages. See a list of these agents and other limited ingredients.”
The color comes from pigments in the skins of the grapes and can tell you a lot about the wine. For example, it can indicate the age of the wine as white wines get darker as they age and red wines typically get lighter. As a result, color tests are an important quality measurement for wine makers.
Analysis via UV-Vis Spectrophotometer
A wine analysis experiment was conducted using UV-Visible spectroscopy — a well-established analytical technique used in the food and beverage industry for testing in the quality control stages. UV-Visible spectroscopy measures the absorption or reflectance of light in the ultraviolet and /or visible region of the spectrum.
In the most basic terms, spectrophotometers enable photometric comparisons of relative light intensities across the ultraviolet and visible spectrums. Directing a controlled, constant intensity light source (halogen, deuterium, or xenon) across the spectrum or at a specific wavelength through a sample easily can confirm known or calculate unknown characteristics of the sample. The incident light (I0) can be redirected backward as reflection, suffer an energy loss as absorption, and pass through transparent or translucent samples as transmission. (Read more about UV-Vis spectrophotometers.)
A UV-Vis spectrophotometer was utilized to measure the UV-Visible spectrum of wine samples. The collected spectrum was used for further data processing through a wine analysis software which has color tests for white, red and rosé wines. The software has conventional methods based on single wavelength measurements and color analysis methods based on full spectrum measurements. It also allows for the use of different size cells. This can be important for analysis of most red or rose wines, as they can be so dark that they require a dilution or measuring in shorter pathlength cells whereas white wines can be use in a normal 10 mm cell.
White wines are often classified by a conventional color test depending on its absorbance at 420 nm. A wine with the absorbance between .05 and .07 is considered pale white wine whereas an absorbance of .1 to .15 is considered a golden white wine. The browning of white wine can also be checked by measuring its absorbance at 440 nm and at 520 nm. Here are some examples for white wine:
Red wine has more complex single and multi-wavelength measurements. The designation of the sample’s color is according to the sample’s absorbance at a combination of 420 nm, 520nm or 620nm. In a production setting winemakers would typically be comparing batches or different aged wines.
In addition, phenolic content in various wines can be analyzed using UV-Vis instruments combined with the appropriate wine analysis software. Phenolics — which come from the grape and sometimes the oak barrels — contribute to color, taste, astringency, and bitterness of the wine.
You can get more details and see the results, including an analysis of a conventional color test on a red wine using a 2 mm cell, the color differences of wine samples compared to a deionized water sample, and the parameters and instruments used for the experiment by watching the webinar: UV-Vis Spectroscopy Techniques in Food and Beverage Analysis. During the webinar, the phenolic content in various wines was also measured through UV-Vis measurement and matched published values.
The next time you see your customers seeing, swirling, sniffing, sipping, and savoring your wine, remember that UV-Vis spectroscopy can help ensure they are seeing the color you intended.
Additional Resources
- Webinar: UV-Vis Spectroscopy Techniques in Food and Beverage Analysis.
- Find more information on food & beverage analysis
- UV-Vis instruments
- Join the Materials Research Community
