°Brix is a useful measurement used to approximate sugar concentration in grapes and fermenting wine. As a percentage by weight (% w/w), one degree brix represents 1 gram of sucrose in 100 grams of water. Because sugar only accounts for 90-95% of dissolved solids in grapes, it is best described as “apparent sugars” (Waterhouse et al., 2024). In the vineyard, °Brix is valuable for estimating the amount of alcohol that will result after fermentation with a common conversion factor between 0.55 to 0.64. Interestingly, while heat events increase °Brix in berries through dehydration, they generally decrease the dry weight of sugar in each berry shifting clusters from being nutrient sinks to nutrient sources. This is one reason why measuring the grams per berry of glucose and fructose (aka berry sugar loading) is a valuable tool for evaluating vine metabolism, and why both parameters are included in our Grape/Juice panel. Similarly, °Brix is used to track the progression of fermenting must in the winery. °Brix values less than 0 are indicative of near completion, and Glucose/Fructose measurement can be used to characterize dryness (below 2 g/L). Interestingly, °Brix can also be used to predict stuck fermentations using the Boulton Model that was created in the 1980s. The rate of Brix change is representative of the active fermenting yeast population. By juxtaposing the speed of fermenation with the fermentation temperature, the Boulton Model can reasonably predict whether or not a fermentation with finish. As you can see in the graph below, the model predicted a struck fermentation until the winery increased the fermentation temperature allowing the wine to achieve 0 °Brix. Figure 1. The Boulton Model Prediction using pressure transducers for continuous °Brix in a commercial white wine fermentation. (The Future of Winemaking: Honoring the Vision of Professor Roger Boulton, 2022). While °Brix measurement is ubiquitous across grape growing and winemaking in the United States, understanding its relationship to environmental factors like temperature and other parameters like Glucose and Fructose can help producers make the best decisions for their desired outcome. To learn more about the scientific tools used in winemaking and see how they apply to wines from around the world, become a Bound advising client.
