Oenology: Determination of the dry extract

Oenology: Determination of the dry extract


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Determination of the dry extract

The dry extract is a parameter that gives an idea of ​​the "body" of a wine. On the basis of this parameter a wine can be defined:

  • lean: anomalous and insufficient structure (wines obtained from incorrect processing);
  • weak: modest structure (young wines to drink);
  • full-bodied: good structure (wines obtained in harmony with the type of grapes and their degree of ripeness);
  • robust: well structured and balanced;
  • heavy: excessive structure (wines with incorrect processing or still in need of aging).

From an analytical point of view, two types of dry extract are distinguished:

  • total dry extract, consisting of all the non-volatile substances of the wine (fixed acids, salts, polyphenols, glycerin, pectins, sugars etc.), that is, from those substances that remain after removing all volatile substances from the wine (water, alcohol and acetic acid ...) by heating to 100 ° C;
  • net dry extract, consisting of the complex of non-volatile substances of wine (fixed acids, salts, polyphenols, glycerin, pectins, etc.) net of reducing sugars, which are considered as potential alcohol.

Red wines, due to the presence of coloring substances and tannins, usually have an extract superior to that of white wines.

Expression of the parameter
The value of the dry extract is expressed in g / L. The law in establishing limit values ​​for dry extract refers only to the net dry extract, setting minimum values ​​that correspond to 14 g / L for white wines and 18 g / L for red wines.

Indirect proceeding
Let the density of the wine, determined at 20 ° C, Dv. Instead, be that of the alcoholic distillate, always
determined at 20 °, Dd. The density of the wine deprived of alcohol is given by the formula (of Tabarié):

D e = 1 + Dv - Dd

From the value of De, by using the Reichard tables, the value of the total extract can be calculated. To calculate the dry extract after deducting the sugars, subtract from the value of the total dry extract that of the sugars expressed in g / l, decreased by 1 if it is greater than 1 g / l.

Direct proceeding
A porcelain capsule is used, the weight of which is known and constant after appropriate calibration, and 50 ml of the wine under examination are introduced, which is slowly evaporated over low heat until a syrupy residue is obtained. After that, the capsule is introduced into the stove for about 3 hours, and it is cooled in a dryer: at this point it is weighed with an analytical balance. The weight thus obtained is multiplied by 20, giving the dry extract in g relative to one liter.
It should be emphasized that many factors (size of the capsule, volume of the wine, evaporation system, duration of heating, etc.) influence the result of the determination of the dry extract directly on the wine, therefore it is necessary to operate in standardized conditions. Given the laboriousness for its application, the direct method is not used in practice and it is preferred to resort to the more comfortable and precise indirect method.

Red, rosé and white wine (photo http://www.assaggiatori.com)

Bibliography
Davanzo P., “Appunti di enologia”, Sixth Edition (available online in pdf)

Sitography
www.emattei-urbino.it
www.smauro.it
www.chimica-cannizzaro.it
www.isii.it
www.federica.unina.it
www.matteocattadori.it
www.enotre.com
www.vinicoltura.it
www.gallini.org
www.enocentro.it
www.itspoleto.gov.it


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