Physical property and its relationship with chemistry.

The transformation of sugar

The fermentation process by which wine is produced has sugar as its main element, which feeds the yeasts and microorganisms essential for the process

Our tongue detects four primary flavors: sweet, sour, bitter and salty. In a wine a harmony of flavors is sought, especially in dry wines, but also in sweet wines we must find the right balance between a rich sweetness and a refreshing acidity.

(Concha y Toro, 2018)

The characteristic aroma and flavor of wine is due to a variety of volatile compounds, including higher alcohols, aldehydes, fatty acids, esters, sulfur compounds and some phenolic compounds.

Determination of property physical:

Where does sugar come from?

The sugar in wine comes directly from the grape. In each berry there are natural sugars such as fructose and glucose. The longer the grape hangs on the vine, the more sugar is concentrated inside. If we wait for a long time, harvesting the grapes in autumn, we obtain wines with very high concentrations of sugar called “late harvest”.

There are several types of yeast, some more resistant than others in an alcoholic environment. While they are feeding, transforming sugar into alcohol, they faint or die on the way. That is why there is always a little residual sugar left. That is why it can be said that yeasts give their lives for wine.

The determination of sugar is an indicator of the point where the alcoholic fermentation of the must is. Therefore, the more sugar there is in the mixture, the higher the percentage of alcohol in the final product, since the yeasts are transformed into alcohol when they feed on sugar. It can also be classified as dry, semi-dry or sweet, according to its degree of alcohol, which should represent between 8.6% and 14% by volume.

(Concha y Toro, 2018)

The vast majority of wines are considered dry. Or, put another way, they have a residual sugar concentration of less than four grams per liter.

(Cromtek, 2018)

The presence of residual sugars in wines gives rise to a classification between dry wines and sweet wines. As a general rule, the presence of a sugar concentration of less than 1.5 g / liter makes the palate not detect the sweet taste, above 0.2% of the volume the senses begin to detect the sweet taste of the wine. Most people detect a sweetness if it reaches a concentration of 1%.

(Vinetur, 2021)

Still wines

• Semi-dry wines: between 12 and 18 grams of residual sugar per liter of wine

• Semi-sweet wines: between 18 and 45 grams of residual sugar per liter of wine

• Sweet wines: above 45 grams

Sparkling wines

• Brut Nature: between zero and three grams per liter

• Extra Brut: up to six grams per liter

• Brut: up to 15 grams per liter

• Extra dry: between 12 and 20 grams per liter

• Dry: between 17 and 35 grams per liter

• Semi-dry: between 33 and 50 grams per liter

• Sweet: more than 50 grams per liter

(Carlos Serres, 2020)

The equation for the calculation is based on the transformation of sugar into alcohol, discounting the alcohol in the recycled ferment, since the fermentation process used

EF = [((Vm – Vf) x ºGLv) – (Vf x ºGLf )] / Vm x %ART x 0,6475 x density

Where:

• Vm - wort volume

• Vf - yeast volume

• GLv - alcoholic strength of wine

• GLf - alcohol content of yeast

• ART - total reducing sugars in the must

(Celso Caldas,pág. 2)

In the case of sweet wines, there are different processes or approaches for their production. 

1. The first and most obvious is to harvest sweet grapes, even raisins or botrytized (when a noble fungus covers the berry and traps its sugars, aromas and acids). 

2. The second trick is to cut the fermentation or "kill" the yeast by adding a strong alcohol. This method is used in fortified wines such as Jerez, Porto or Madeira.

3. The third method is to lower the temperature during fermentation. Yeasts do not like cold. This is known by lovers of homemade bread and brioche-type desserts.

(Concha y Toro, 2018)

During maturation, some sugars undergo a structural change and end up giving dark pigments to the wine, this is the case of the melanoidin detected in fortified wines such as sherry, madeiras, etc.

The concentration of sugar in grapes or must is usually measured in the United States in Brix degrees, while in Europe it is measured in Baumé degrees.

The concentration of sugars is critical for the development of yeasts during fermentation, the main yeast in wine (Saccharomyces cerevisiae) feeds mainly on glucose and fructose.

(Vinetur, 2021)