Wine & Sugar, Why Brix is not an accurate predictor of potential alcohol %?

By American Wine Appassionata February 20, 2017

Wine & Sugar, Why Brix is not an accurate predictor of potential alcohol %?

Winemakers rely on juice chemistry analysis of certain fundamental compositions of must that goes beyond TA, pH and Brix. Before I address the impressive role that sugar content plays in wine making. I will define some terms used daily by winemakers but unfamiliar to the average wine drinker.

Definitions:

Wine; Wine is an alcoholic beverage made from fermented grapes.

Must; Must is freshly pressed fruit juice (usually grape juice) that contains the skins, seeds, and stems of the fruit. The solid portion of the must is called pomace; it typically makes up 7–23% of the total weight of the must. Making must is the first step in wine-making.

Fermentation; Fermentation is a chemical process that occurs when yeast is added to fruit juice (grapes), mostly in a controlled environment (alcohol and carbon dioxide are produced). Wines can be fermented in a variety of containers (e.g. Oak barrels or stainless steel tanks).

Brix; The quantitative measurement of sugar in a grape. The discussions you will hear usually revolve around the level of Brix at the time the fruit is harvested, which directly relates to the ultimate percentage of alcohol in the bottle.

Titratable Acidity (TA)*: Measures total available hydrogen ions in solution. This measurement includes both the free hydrogen ions and the undissociated hydrogen ions from acids that can be neutralized by sodium hydroxide. TA is the most widely used measurement of acidity in wine. Although generally considered a simple parameter, titratable acidity is actually a reflection of complex interactions between the hydrogen ions, organic acids, organic acid-salts, and cations in solution. Often there is no direct correlation between TA and pH. Two musts with similar titratable acidity may have very different pH values (ETS Labs, 2016).


pH*: Measure of free hydrogen ions in solution (which corresponds to the chemical definition of acidity) and is used as a gauge of wine acidity. Wine color stability, potassium bitartrate stability (cold stability), calcium stability, and molecular SO2 level are directly related to wine pH. pH is also critical in relationship to microbial stability, interactions of phenolic compounds, and color expression (ETS Labs, 2016).

Malic Acid*: Accumulates early in berry development and declines during ripening due to dilution and respiration, Vinicultural practices and grape cluster environments may directly affect respiration rates of malic acid. Malic acid levels affect pH and titratable acidity. Malic acid is converted to lactic acid during malolactic fermentation, causing the loss of an acid group. The effect of this acid reduction on pH depends upon the initial amount of malic acid and buffer capacity of the wine. Malolactic fermentation in wines containing low levels of malic acid and high buffer capacity will have little impact on wine pH. Malolactic conversion in wines with high acid and low buffer capacity can result in substantial pH increase (ETS Labs, 2016).

(*) Burns, Marjorie, and Gordon Burns, comps. "Beyond Brix." Winemaker's Quarterly 3.1 (2016): 8-9. Web. 19 Feb. 2017.

       

Sugar (Brix) & Alcohol % in Wine 

Brix is used as an estimate of sugar concentration and often as a predictor of potential alcohol. Brix is not a true measure of ferment-able sugar. Two juices with identical Brix may have very different final alcohol concentrations due to varying amounts of ferment-able sugar.
Brix is a measure of soluble solids in juice and must. The soluble solids in juice are primarily sugars. Organic acids, however, have significant impact on brix with unripe grapes. Sugar concentration increase rapidly in grapes as they mature. This increase is usually due to sugar movement from the leaves to the fruit. During the final stages of berry development, berry dehydration may also contribute significantly to the final sugar concentration.
It’s important to note that in ripe fruit, glucose + fructose numbers often appear higher than the corresponding Brix results. This is because Brix is measured as a percentage by weight, meaning Brix values are greatly influenced by the density of juice. Glucose + Fructose is measured as weight by volume and is independent of juice density. A must with 23.3 Brix will not have 23,3% by volume ferment-able sugar. 

Residual Sugar

Residual sugar In wine usually refers to the sum of: Glucose + Fructose, which is an indication of the amount of ferment-able sugars remaining post fermentation, which is also an indication of dryness.

Acid and Wine

The acid composition of must is a complex balance of free hydrogen ions, acids, salts and cations. Concentrations of these various components and their interaction influence many wine-making parameters. The principal objective of acid management is to achieve and maintain a pH level favorable to optimum wine balance and stability.

How to Predict Potential Alcohol Levels in Wine? (*)

Old School Vs. New School

The "Old School" method is to multiply Brix X 0.6 = Alcohol % by vol. One degree of Brix is defined as 1 gram of sucrose in 100 grams of aqueous solution. However, grape juice does not naturally contain sucrose, but rather glucose, fructose and a variety of organic acid and other dissolved solids. So, when used for grape juice , Brix is actually just an approximation of dissolved sugar, not an accurate representation of the ferment-able sugars and using Brix for estimating potential alcohol adds an additional layer of uncertainty to alcohol prediction. Differences between Brix and actual ferment-able sugar content are even more pronounced in high Brix fruit and in fruits affected by fungal growth.

 The "New School" A more modern calculation that has proven more accurate uses glucose + Fructose analysis, which provides a more accurate measurement of the level of ferment-able sugar compared to using Brix. Note that ripe fruit, glucose + fructose numbers often appear higher than the corresponding Brix results because Brix is measured as a percentage by weight, meaning Brix values are greatly influenced by the density of the juice, while glucose + fructose is measured as weight by volume and independent of juice density.  An official conversion rate formula used in Europe is: Potential Alcohol (% by vol.) = glucose + fructose (g/l) / 16.83 

The Bottom Line

Although sugar plays an important role in wine characteristics, tannin is another component that fundamentally impacts balance and wine age-ability. Most wine enthusiasts believe that Brix is the dominant indicator of grape harvest and believe it is one of the indicators of alcohol percentage in wine. This is far from factual. Tannin, seed maturity and flavor are among other important indicators of grape harvest.
Winemakers are challenged each season, when to pick?
It is a fine balance to pick the fruit at optimum tannin maturity and fruit ripeness. If the Brix are at favorable number but the tannin has not reach maturity or full flavor have not been reached, then what?
Do you sacrifice flavors, lack of tannin maturity to pick the fruits at a desired brix numbers? What happens if you would let the fruit hang longer, will the flavor develop, tannin mature and would catch up at reasonable brix?
Grape harvest is not scheduled but rather determined by so many factors that start early in the growing season such as rain, humidity, tempurature, wind, fog, etc.

Wine Nutrition Facts

Serving:                          5 fl. Oz (148 g)
Calories:                                          123

Daily Value (**)
          Total Fat: 0 g                           0%
           Saturated fat:                         0 g
           Polyunsaturated fat:             0 g
           Monounsaturated fat:          0 g

Cholesterol: 0 mg                                                            0%
Sodium:                                            7 mg                        0%
Potassium:                                  147 mg                       4%
Total Carbohydrate:                         4 g                          1%
Dietary fiber:                                     0 g                          0%
Sugar:                                             1.2 g

Protein: 1 g                                                                      0%
           Vitamin A:                                                              0%
           Vitamin B-6:                                                           0%
           Vitamin B-12:                                                         0%
           Vitamin C:                                                               0%
           Vitamin D:                                                               0%
           Calcium:                                                                 1%
           Magnesium:                                                           4%
           Iron:                                                                         2%

(**) Percent Daily Values are based on a 2,000 calorie diet.
Your daily values may be higher or lower depending on your calorie needs.

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