Nature knows many sugars, and chemists have produced many more. Sugars are often generalized and referred to as carbohydrates, because of a common, naive interpretation that a formula, such as C6H12O6 used for glucose or fructose, leads one to believe that it contains 6 carbon atoms married with 6 molecules of water. More recently, phonetic erosion has birthed the fashionable term “carbs” from carbohydrates.
It is equally fashionable to blame carbohydrates in the contemporary diet on health problems. Is it necessary for us to point out that alcoholic fermentation is an easy way to eliminate carbohydrates in food by converting them into alcohol?
The common sugar has the scientific name sucrose. It is industrially produced, primarily out of either sugar cane or sugar beet. If we dissolve sucrose in water and add some wine yeast, we notice – that nothing happens. This simple experiment shows that not all sugars are fermentable. In the case of sucrose, one must add that yeast contains the enzyme invertase (more precisely, β-fructofuranosidase) which “inverts” sucrose into fermentable sugars, so that eventually, fermentation can begin.
It is not just that some sugars are not fermentable – among the fermentable sugars, not all are fermentable equally. Yeast has a rather clear preference for glucose. It is time to learn more about a few sugars.
Some Theory and Names
As stated in this sections introduction, glucose and fructose share C6H12O6 as their summary formula, which means that they are isomers. Both are structural isomers, and to complicate things further, they have several asymmetric carbon atoms. Suffice it to say there are many more sugars that possess this formula. There are 8 aldo-hexoses and 4 keto-hexoses as D-isomers, and the same number as L-isomers, and all can and do exist in half-acetal- or half-ketal-form, and … Not to forget tetroses, oentoses, heptoses, … This list is quite long… Sugars that are based on a six carbon atom unit are called hexose. Let it be stated that nature also knows other molecule lengths, the mix of carbohydrates in rye for example contains a significant contribution of pentose (meaning that they are based on five carbon atoms). This is a partial explanation of why rye cannot be baked like wheat, but requires a sourdough process.
There is far more than just hexose and pentose “units”, but we will just focus on hexose sugars; they are the only major sugars of concern in wine-making. The layman’s term “unit” can be refined into “monosaccharide”, where “mono” is the prefix indicating the numeral 1, and sugars are “saccharides,” after the latin saccharum. Other frequently used prefixes are di- for 2, tri- for 3, and poly- for “many.” This terminology is used in the list of sugars below, which contains only sugars that are of significance in wine-making.
A common property of saccharides is their high solubility in water, with the exception of polysaccharides like starch and cellulose. An example of cellulose is cotton, which means that cotton is a sugar, even when it is not cotton candy. All saccharides are heat sensitive – just think of caramel. This is important to remember when we prepare highly concentrated sugar solutions. It is also important to know that almost all sugars do not want to crystallize, which honey as an example shows convincingly. Bees would have a serious problem if they had to mine solid sugar crystals in the hive.
To finalise the above description it is important to mention that “not all sugars are created equal”, not all sugars are equally sweet, some lack any sweetness at all (starch for example). Some sugars have a “straight” sweetness, and some a “funny” sweetness. This certainly influences the taste of the finished wine.
Fruits are dominated by fructose, glucose, and sucrose, in this sequence of abundance. In most fruits, the fructose : glucose ratio is near 1, with a slight advantage on the side of fructose. Apples and pears have a fructose : glucose ratio of about 2, which is already extreme; additionally in grapes, this ratio is 1.1.
Density of Sugar Solutions
The density of sugar solutions changes significantly with increasing concentration, and this is made worse by the fact that concentrations can go very high, i.e. the range is rather wide. Interestingly, the concentration / density relationship is linear, which makes calculations simple. A common calculation method is the measurement of density, which is used to measure concentration. A concentration increase of 100 g/l increases the density by roughly 0.0368 g/ml, and this almost does not depend on the chemical nature of the sugar, at least not for sucrose, glucose, and fructose, as the most important in wine-making. The density is usually measured with a hydrometer (not to be confused with hygrometer!), which measures the density of wine batches directly. In vineyards, the rapid, but indirect measurement of a refractometer is used, because it requires only a drop of juice from a single berry. Obviously, this causes sampling errors, because one cannot assume that each berry has the same sugar concentration. Therefore, the average over measurements with several berries is taken.
Since density can easily be measured, it has been used to measure the sugar concentration of grape juice for about two centuries. These measurement units deserve to be mentioned not only because of their historical significance, but also because they are still occasionally used.
Some German speaking countries (Germany, Luxemburg, Switzerland) use the Oechsle scale, abbreviated ° Oechsle or ° Oe. This scale was developed by Christian Ferdinand Oechsle (1774 – 1852), a citizen of the Grand Duchy of Baden (now part of southwest Germany), it is based on density, and relies on an areometer – a device used to measure the specific gravity of liquids or the density of solids. Oechsle published this invention 1836 with the title Über den Gebrauch der Most- und Weinwaage (“On the use of must and wine balances”). The Oechsle scale uses the excess weight in grams that one litre of juice (must) has. Let us assume that a hypothetical litre must weighs 1,084 g, so that the excess weight is 84 g. Therefore, this must has 84° Oe. Obviously, the density of said must be 1.084 g/ml, so that the density scale in modern units connects nicely with the antiquated (but still used) Oechsle scale. As one would expect with a sacred German tradition, this country that otherwise is strict in its use of SI (metric) units, does not just sanction the continued use of the Oechsle scale, but even enshrines it in some laws, like the legal relationship between natural alcohol content of wine and Oechsle degrees, published by the Federal Department of Justice in 1995.
With no apparent connection to Oechsle, Carl Joseph Napoleon Balling (1805 – 1868), an Austrian chemist from Bohemia (part of the Austria-Hungarian Empire at that time), developed in 1843 the saccharimeter, an areometer (hydrometer) adapted to the measurement of sugar concentrations. It revolutionized the brewing process by providing an efficient way to measure fermentable sugars, rather than solely relying on the colour caused by malt. For the brewing industry, this was modified in 1900 by the German scientist Fritz Plato (1858 – 1938). This derived scale is often referred to as ° Plato, and seems to still be in use in the brewing industry, but has apparently never found any application in wine-making. The term saccharimeter was used for the longest time for density measurement, but has taken a new meaning over time and has more recently been used for sugar measurement based on refractive index; the current use of the term is for measurement by polarization, with the essential advantage of providing a method that is independent of alcohol content. These three different methods must not be confused, and it is regrettable that a scientific term once established has been “recycled” this way.
Balling’s invention took a life of its own when August Wilhelm Freiherr von Babo (1827 – 1894), the first director of the 1860 founded Niedere Stiftsweinbauschule in Klosterneuburg, Austria, by now upgraded to Höhere Bundeslehranstalt und Bundesamt für Wein- und Obstbau Klosterneuburg with the officially assigned Latin Alma mater Babonensis, developed the Klosterneuburger Mostwaage (KMW) based on Balling’s saccharimeter. The official English translation of Federal Institute for Viticulture and Pomology is not nearly as colourful. The KMW scale seems to be in continued use in the countries of the former Austria-Hungarian empire, including the now successor countries of the former Yugoslavia. For example, the Czech Republic and Slovakia continue the use of KMW with the new name normalizovaný moštoměr (NM).
1° KMW = 4.86° Oechsle
Historical precedence takes the density scale defined by the French chemist Antoine Baumé (1728–1804), which he developed for the measurement of the concentration of sulfuric acid in industrial use in those days. In other words, there is no link to wine or any fermentation process, and because the scale is based on sulfuric acid, is in the opinion of these authors, rather inconvenient to use, especially because the scales rational Baumé, Dutch Baumé, American Baumé for liquids heavier than water, and American Baumé for liquids lighter than water, are all different. However, it has been the standard scale in France, Portugal, and Spain for the measurement of sugar content of juice (must), which was given in °Bé. However, France abandoned this unit in 1961 and replaced it by sugar concentration in g/l.
In Italy, Canada, USA, Australia, and New Zealand, the °Brix scale, developed by Adolf Ferdinand Wenceslaus Brix (1798–1870), is preferred. It seems that after the Oechsle scale and KMW, which both preceded the Brix scale, German-speaking countries had no need to adapt another unit of measurement developed by a German, as such this scale has in fact never received more than casual attention in the German-speaking world (with the exception of the candy industry). However, English speaking countries embraced the Brix scale, perhaps the name is easier to pronounce than “Oechsle” or “Klosterneuburger Mostwaage”.
Unlike the Baumé scale, the Brix scale has inherent practical value, because 1 °Brix is defined as the density of the solution of 1 g sucrose in 100 g sucrose solution in water. This links the Brix scale and the Oechsle scale with the following approximation:
1 °Brix ≈ 4 °Oe
List of Sugars
Glucose, in whatever form, is the most significant sugar base for wine production. Yeast prefers glucose the most among all sugars, and one should make it a habit to give the fermentation a kick-start by providing a sufficient amount of glucose, either as such, or by using invert sugar syrup (see below). The preference of glucose is true for many micro-organisms, unfortunately also for those that are not desirable.
Glucose has a sweetness factor of 0.75, relative to sucrose.
More information about glucose can be found in Section Chemicals.
Please follow link to find information about other Sugars.
Simple Sugar Syrup
For preparation of 1 l Simple Syrup is required 600 g of water and 640 g of sugar.
Several pharmacopeia of European countries contain the recipe of sirupus simplex, Latin for “simple syrup”, which is just that: sugar dissolved in water. It is prepared by bringing water to boil, stirring in sugar while continuing to heat, bringing it to boil again, letting it cool slightly, skimming off the small amount of whitish crust that forms (these are residual proteins from the manufacturing process), and letting cool completely. If the goal of the syrup’s production is compliance with the Swiss or German pharmacopeia, we take care that the finished syrup contains 640 g sugar per litre of finished syrup.
CAUTION: This is not the same as using 640 g sugar and 360 g water due to the significant change in density! The density of this syrup is approximately 1.242 g/ml, this is why proportion shown above must be followed.
One can also make a more Concentrated Syrup with a density of 1.373 g/ml. This syrup has the interesting property that 1 litre contains exactly 1 kg sugar, providing an easy measure. This syrup has the disadvantage of being rather viscous, so mixing it into the wine batch is more difficult than with standard simple syrup. To prepare this syrup, 373 ml water are required per kg of sugar. This syrup is often used in the preparation of liqueur, but for liqueur, inverted syrup of the same concentration is usually preferred.
While heating sugar syrup, one must avoid overheating, indicated by the yellowing of the syrup, because this adds an undesirable caramel touch to the syrup.
Owing to its high sugar content, it has a long shelf life, without becoming mouldy. As a general rule, the higher the sugar content, the longer the shelf life.
Obviously, it can difficult to impossible to pour solid sugar into a wine barrel and dissolve it. As a result this syrup is a convenient way to add sugar.
* NOTE: Books by pharmaceutical societies, usually endorsed by their respective countries, which describe the production of those pharmaceuticals that are not ready-made medications by the pharmaceutical industries.
Invert Sugar Syrup
The inversion of sucrose takes place over a few minutes when the temperature of the mixture reaches 100 °C or above. The inversion is accomplished by preparing sugar syrup almost the same way as explained above, but making the addition of about 3 g citric acid or tartaric acid to the 1 kg of sugar; the amount of acid is not critical and can be higher or lower, because it just acts as a catalyst. Care must be taken that the mixture is not overheated, because glucose and fructose caramelize easier than sucrose.
NOTE: Invert sugar is always preferable in fermentation, because it already contains the glucose that yeast requires.
Alcohol in this context is used to describe a chemical characteristic, and is not to be confused with the common usage of the term. Certain sugar alcohols are found in nature, and for this reason deserve a passing mention.
Xylitol is a sugar alcohol that is related with the pentose sugar xylose, and is industrially produced mostly out of corn cobs after their kernels have been taken out, thus making use of an otherwise useless product (this yields xylose, which is then reduced to xylitol). Xylitol’s sweetness is similar to that of sucrose, and very little is resorbed by humans, making it attractive in certain food applications (low calorie appeal, anti-caries candies), despite its high price. It is noteworthy that for many animals, xylitol present in food can be fatal for animals such as dogs, goats, and rabbits. There seems to be no known toxic effect for humans, other than possible diarrhoea when excessive amounts are consumed. Xylitol is naturally found in vegetables (cauliflower) and fruits (prunes, strawberries).
Sorbitol is a sugar alcohol that is related with glucose and fructose, and is industrially produced on a large scale mainly out of glucose. It can be found naturally in rather high concentrations in rowan berries, it can also be found in pears, prunes, plums, apples, apricot, and peaches. Industrially, it has varied applications, from being used as a sugar substitute for diabetics, to moisture-retaining in toothpaste. Sorbitol contains 6 carbon atoms.
Mannitol is another sugar alcohol with relevance in nature. It is named after the manna ash, a plant which can be found frequently around the Mediterranean, mainly in its Eastern part. The dried syrup of the manna ash contains 13% mannitol. Mannitol is an isomer of sorbitol, and as a result is also contains 6 carbon atoms.
Most sugar alcohols are digestible by micro-organisms, and yeasts are no exception, although they have a clear preference for glucose.