Unit of measurement for expressing the relative density or specific gravity of grape must, i.e. the mass (weight) in relation to volume. This mass, also known as extract, consists of the substances dissolved in the grape must. This is mainly sugar (fructose, glucose), but also acids, minerals, phenolic compounds, proteins and others (some of these substances are then found in the total extract of the wine). The specific gravity of grape must is always greater than 1.0 (water), the difference is largely due to the sugar content. The difference between "weight of a certain volume of must" and "weight of the same volume of water" is called weight ratio. The measurement is carried out by means of hydrometers (plummet), pycnometers and refractometers (refraction of light).
Units of measurement
Different units of measurement are in use in the individual countries; the most common ones are
Klosterneuburg must scale (KMW)
The method was developed by August-Wilhelm Freiherr von Babo (1827-1894) in 1861 at the Klosterneuburg Viticulture Institute on the basis of the saccharometer invented by Carl Joseph Balling (1805-1868). This unit of measurement is mainly used in Austria, Hungary, Italy and some eastern states. The KMW balance is calibrated to a temperature of 20 °C. The exact conversion from KMW to Oechsle = KMW x (4.54 plus 0.022 x KMW); roughly calculated KMW x 5. The conversion formulas of KMW degrees to alcohol content are a rough determination and only between 16 and 21 KMW relatively accurate:
- 1 KMW = 10 grams or 1% sugar in 1000 grams must
- 1 KMW equivalent to 4,98 Oe or 0,65 Bé (KMW/1,53)
- (KMW - 4) x 0,85 = % vol alcohol for white wine
- (KMW - 4) x 0,80 = % vol alcohol for red wine
Oechsle (Oe)
The method or unit of measurement developed by Christian F. Oechsle (1774-1852) in the 1820s is mainly used in Germany, Luxembourg and Switzerland. The Oechsle balance is usually calibrated to a temperature of 17.5 °C. One degree Oechsle (Oe) is defined as the increase in weight of 1000 millilitres of must by 1 gram. One litre of must with 50 Oe weighs 1050 grams.
Brix or Brix-Balling (Bx)
The method or unit of measurement developed by Adolf F. Brix (1798-1870) in 1870 is mainly used in English-speaking countries. The unit of measurement Balling, also used in English-speaking countries, is almost identical and is often expressed as "Brix-Balling".
Baumé (Bé)
The method developed by the French chemist Antoine Baumé (1728-1804) or the unit of measurement named after him is mainly used in the Mediterranean countries, including France and Australia. It is used to measure the total substances dissolved in grape must and thus the approximate amount of sugar. The Baumé degrees correspond fairly exactly to the possible alcohol content.
NM
Abbreviation for Normalizovaný Muštomer(Slovakia) or Normalizovaný Moštoměr(Czech Republic). 1 °NM in these two countries corresponds to 1 kg of sugar per 100 l of must.
Plato
Unit of measurement for the original wort content (malt sugar) in beer, named after the German chemist Fritz Plato (1858-1938). 1 °P corresponds approximately to 1 °Bx (balling).
Ratio table
The ratios of the units of measurement are not linear. They can therefore only be converted into each other using complicated formulas. For this reason, tables are usually used that often differ due to non-identical formulas. The table shows the relationship between the three most important units of measurement, as well as the sugar content and possible alcohol content. As a rule of thumb, 10 g of sugar results in 0.66% vol. alcohol content due to fermentation. This means that 16.5 to 18 g of sugar result in about 1% vol. As a rule, white wines are at the lower limit and red wines at the upper limit.
Significance Must weight
From the must weight, approximately the potential alcohol content in the wine can be derived if the sugar (theoretically) completely ferments. Only approximate because this depends on the composition of the grape must. Two grape musts with the same must weight do not necessarily have the same sugar content. A must with high levels of acidity and minerals has correspondingly less sugar than another must that contains them in smaller quantities. Sweet wines, such as Trockenbeerenauslese can reach 60 KMW or 300 Oechsle and more. Of course, only a relatively small amount of sugar is fermented in this type of wine.
The Frenchman Victor Pulliat (1827-1896) worked out a classification for the classification of grape varieties according to their time of ripeness and established the must weight as a criterion for comparison. In Germany and Austria the must weight is an important quality criterion, which classifies a wine by this alone. The must weight is also important for the allocation of the official test number (D) or state test number (Ö). In the two countries, too much importance is attached to it, because there are also other important criteria (see there for values defined by wine law)
In the warm wine-growing regions the must weight is not very significant. The time of harvesting is therefore determined by the acidity values, which are more difficult to achieve in warm climates. This is because the acidity, pH and total extract play at least as important a role. Today, the term physiological ripeness is used to describe the maturation (state of ripeness) of the grapes in a much more comprehensive way. With regard to the various analytical methods used to determine or measure the content of unfermented sugar(residual sugar) in wine, please refer to the section on sugar content.
Refractometer left: From User Kandschwar - Own work, CC BY-SA 2.0 de, Link
Grapes: Pixabay