The 2017 harvest of wine grapes in Europe and California was full of variability.

A very low yield compared to 2016 was expected in Europe ranging from 16% less in Spain to 21% less in France and Italy due to extreme weather conditions that included hailstorms, frosts, and drought. Quality, however, is expected to be good because of the hot summer weather.  In contrast, California had yields that resembled normal averages  as drought conditions subsided. In spite of the challenges occurring during this years’ growing season, winemakers must understand what is in their wine in order to guarantee their customers a high-quality finished product.

Through the entire wine production process, testing is important to monitor optimal conditions for fermentation. Besides measuring sugars and acids, such as tartaric acid, the level of glycerol can also be monitored. If required to prevent juice from browning, substances such as sulfur dioxide (SO?) can be added.

Tartaric acid is the primary acid found in grapes and contributes to the crisp, slightly tart flavor of wine. It plays a vital role in the taste, feel, and color of the wine. In addition, tartaric acid behaves as a preservative by lowering the pH to a level that improves bacterial resistance.

During fermentation, glycerol is synthesized from the glucose within yeast cells. Most of the glucose present produces ethanol, but what remains produces glycerol. The usual glycerol concentration in wine is about 5 g/L and its influence is below the level of sensory perception. However, wines with high alcohol levels have a sweet taste and viscous mouth feel that are often attributed to glycerol.

SO? is added to control the winemaking process and prevent oxidation in the finished product. Because sulfite, a form of SO?, is an allergen; levels are regulated in the European Union (from 150 to 500 mg/L) as well as in the U.S. (a maximum of 350 mg/L).

Analysis of all three parameters and more can be easily and rapidly accomplished using the discrete photometric analyzer. Multiple tests can be run simultaneously on the same sample. The tartaric acid method measures a formed complex of tartrate and vanadate. No pretreatment is required for red wine as color is removed by hypochlorite during the automated process. The glycerol method is an enzymatic assay with glycerokinase, ADP dependent hexokinase and glucose-6-phosphate-dehydrogenase. And, the free sulfite method measures a reaction between sulfur dioxide, p-rosaniline, hydrochloride, and formaldehyde. Compared to traditional methods of analysis, much smaller sample volumes are required and most tests are completed in less than 60 minutes.

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