Acids in wine

The acids in the wine play an important role in both winemaking and the finished product of wine. They have a direct influence on the color of the wine as well as on the sensory evaluation by the counterplay to sugar and alcohol. They play a crucial role in the energy metabolism of yeasts during alcoholic fermentation. Investigations to the acids in the wine briefly touching areas as diverse as the sensor technology, biochemistry and microbiology of fermentation, wine-growing technical practices, methods of treatment the removed wine and the stabilization and preservation of the wine. In particular, the high performance liquid chromatography provided important insights into the pH - values ​​of the individual acids, as well as acids that are present only in minute traces.

Certain acids are already present in the berry. The concentration of the total acid in the grape berries rises with the start of the soft growth in the berries to a maximum. After reaching the maximum, the synthesis of fructose as well as a decrease in the concentration of the acids begins. The pH of a wine, depending on variety and growing region from 2.9 to 4.0. The pH is a measure of the acidity or alkalinity of an aqueous solution. Lower pH values ​​in the wine caused by stronger acids and / or higher concentrations of acids present. The three most important acids in the mature berry are the tartaric acid, malic acid and citric acid, all of which belong to the non-volatile acids. During the alcoholic fermentation and during subsequent expansion of the wine in containers such as wooden barrels or stainless steel container is subject to other acids. Among the most prominent representatives include acetic acid, butyric acid, lactic acid and succinic acid.

In the sensor, the acidity gives the wine freshness and structure and promotes a balance of the most important flavor components of wine. However, this does not apply to all acids. The well-known as vinegar note, vinegar stitch or volatile acidity of wine error is caused by a too high proportion of acetic acid. During the normal alcoholic fermentation approximately 0.2-0.4 g / L volatile acid is formed. The value can be in contact with air to increase to 0.6 g / l. These concentrations represent the normal range and should not be exceeded for reasons of taste. In addition to the acetic acid include formic acid and to a lesser extent, propionic acid and hexanoic acid to the perpetrators of this error.

Depending on the country of production of ascorbic acid, sorbic acid and sulphurous acid may be added as part of the local wine laws for the stabilization of the wine.

Gustatory perception

Currently it is assumed that at least five basic qualities of gustatory perception:

Since the beginning of the 20th century is known that the different taste qualities are perceived by all the sensitive areas of the tongue. The differences between the tab portions relative to the sensitivity to individual grades are small in humans. Nevertheless, in many textbooks is still a division of the tongue be found in " taste zones ".

Determination of total acidity as well as national peculiarities

If in wine analysis of acid is mentioned, one speaks of the total titratable acid. However, the determined by titration value does not match the computed as the sum of the individual acids total acid. Nor correlates the total titratable acid with the pH of the wine. In determining the total acid by chromatography, however, the concentration of all acids is measured regardless of the extent of buffering. Both the calculated with the chromatograph total acidity and pH are thus a clearly inferior measure of the acid perception than the total titratable acid. Tartaric acid and citric acid to reduce the pH at the same concentration significantly higher than malic acid, lactic acid or succinic acid.

The calculation of the total titratable acid is not performed in all countries by the same method! While in Germany the total acidity expressed as tartaric acid, you are in France, the acid in g / l sulfuric acid. The conversion factor between the two values ​​is 1.53. If a wine according to German method has an acid of 6 g / l, is given by the French method for the same wine, a value of 3.9 g / l ( = 6 g / l divided by 1.53 ). A mere statement of the acid without information about the reference acid is therefore unhelpful.

Volatile and non - volatile acids

In contrast to the non-volatile acids, the volatile to evaporate in the wine at a distillation or evaporate over time. The volatile acids contained in the wine are mostly acetic acid ( 0.15 to 0.6 in a healthy wine g / l ) and its chemical compounds, and formic acid, succinic acid, butyric acid and propionic acid. The readily observable volatile carbonic acid is not expected in the wine to the group of volatile acids.

The three most important non-volatile acids are tartaric acid, malic acid and citric acid, which account for about two-thirds. Present in minor amounts are lactic acid, galacturonic acid, gluconic acid, glucuronic acid, glycolic acid, oxalic acid, and mucic acid, as well as a variety of other acids that are present only in traces in the wine.

The maximum values ​​of the volatile acid are dependent on the type of wine and the quality level and may not be exceeded at any time of winemaking.

• White and rosé wines: Table wine, table wine, quality wines psr, Kabinett, Spätlese, Auslese, 1.08 g / l
• Beerenauslese, Eiswein 1.80 g / l
• Trockenbeerenauslese 2.10 g / l

• Table wine, table wine, quality wines psr, Kabinett, Spätlese, Auslese, 1.20 g / l
• Beerenauslese, Eiswein 1.80 g / l
• Trockenbeerenauslese 2.10 g / l

The role of acids in wine

In addition to the must weight of the total acid content is an important indicator of the winery when you can begin harvesting. The proportion of total acid is shortly before the onset of ripening of the berries on top and then increase steadily from. While the malic acid is respired, stops the production of acid in the wine is no longer green tissue of the berries. In particular, for the production of sparkling wine, the berries are aware harvested before they are fully ripe, to give the base wine a strong acid backbone. In the hot 2003 vintage, it came at the high temperatures to an intense respiration of malic acid. This often results in particular in the white wine wines flat with little aging potential.

In winemaking, the acid plays an important role in addition to the sulfur dioxide in the stabilization of the wine. In acidic medium, almost no bacteria survive longer. Important exceptions are the acetic acid bacteria and lactic acid bacteria. To a lesser extent you can after malolactic fermentation can also butyric acid bacteria responsible for the acetone smell ( Uhu - tone) be held responsible in the faulty wine.

In red wines, the acid helps in the long-term stabilization of color and is also a defining element of color. Anthocyanins absorb light in the wavelength range 270-290 nanometers ( ultraviolet radiation ) as well as in the visible range 465-560 nanometers ( blue to green). The wavelength range is influenced except by the molecular structure and by the pH value of the environment. The color spectrum ranges from blue to red, it can be found all colors except green. In the acidic environment outweighs the red color in basic are a lot of blues and purples to find. Wines with high pH ( such as in wines from Syrah) have more blue color pigments, however, are not very stable. These wines can age in color then faster and then have an ugly grayish or brownish tone.

Acid in the wine sensory

Sensory total acid plays a major role. It gives the wine structure and ideally a fresh, mostly fruity taste impression. This impression is reinforced by a slight tingling sensation on the tongue. Wines with too low acidity are usually perceived as flat and uninteresting.

In particular, in the language of wine cooler wine-growing regions such as in Germany or even in northern France, there is a wealth of descriptive words that describe the specific through the acid taste impression:

Pungent, green, alive, resh, acidity, steely, acidity, lively, edgy or angry.

Tartaric acid

Tartaric acid, also known as 2,3- dihydroxysuccinic acid or 2,3- dihydroxybutanedioic acid ( IUPAC nomenclature ), is an α - hydroxycarboxylic acid. The salts and esters of tartaric acid are called tartrates. The occurring in grapes L -( )-tartaric acid is approved in the EU as a food additive E 334. In Germany, the total acidity of wines - calculated as tartaric acid - specified. In particular, the L-( )- tartaric acid and its calcium, potassium and magnesium salts are found in abundance in the vines, grapes and leaves of the vine.

For the tartaric acid is: the more mature the grapes, the higher the proportion of tartaric acid in the total acid. Tartaric acid plays an important role in the wine. Firstly, the chemical resistance of the wine is positively influenced by a high content of acid, that is, the wine has a better aging potential. On the other hand supports a high acid content, the color of the wine. The taste influences the tartaric acid not unlike the malic acid also. Both acids are indistinguishable in taste.

During the ripening of the berries, the concentration of both the malic, and tartaric acid decreases. While the malic acid is metabolized by cellular respiration and the degradation of acid thus also temperature-dependent (and thus by year dependent), the tartaric acid is no longer produced in no more green fruit tissue of the berry. Due to the increase in berry size of the consistently high proportion of tartaric acid is increasingly diluted.

During the production of wine, tartaric acid precipitated to a large extent in the form of tartar. During fermentation, the acid crystallizes out on lees, mash residues, tannins and pigments. The former frequently observed Weinstein in the bottle, the crystallized form of tartaric acid, which is located at the cork on the bottle or basic, depending on the type of storage is almost impossible to watch. The crystals possibly affect the clarity of a beverage and can thereby reduce the drinking pleasure. White wine is decanted, among other things, to separate tartar from wine. Weinstein is tasteless and feels like sand in the mouth of. Since this harmless Depot often ( unprovoked ) resulted in complaints today through many destined for the mass market wines a so-called cream of tartar stabilization. Here, the wine is vaccinated for two weeks at 4 ° C or cooled down and with very little Tartratkristallen. At these temperatures, the tartaric acid is brought into the supersaturation to accelerate the crystallization.

The tartaric acid can be contrary to the malic acid determined quite simply with a quick test after Rebelein. The tartaric acid in the wine is transferred with an ammonium derivative, the ammonium monovanadate in an orange - yellow color complex. The intensity of the color is measured at a wavelength of 540 nm by means of photometry visually. For a conversion table of tartaric acid content is read.

Malic acid

Malic acid (2 -malic acid ) is a dicarboxylic acid that occurs as a right-handed D- malic acid, and as a left-handed L- malic acid. The L-form is an intermediate in the citric acid cycle. In nature, L-malic acid is present in unripe apples, quinces, grapes, barberries, bird berries and gooseberries. In particular, in the wine description, the flavor of green, unripe apple is falsely attributed to a high content of malic acid. Malic acid, however, can not be distinguished in taste of the tartaric acid and is rather an indicator that the maturity of the fruit has not been reached.

Together with the tartaric acid is malic acid, the most important of the generated within the grape organic acids. It is formed in the chlorophyll-containing tissues of the berry by metabolism of sugar and acts as an energy vector in the vine. At the onset of ripening of the berries, the proportion of the chlorophyll-containing tissue decreases ( the berries change color from green to yellow, white, red or blue-black) and it comes to a stop the production of acid. Just after the stop of the production, the concentration of malic acid is present in the grapes at a very high, 20 g / l The amount of acid is in part dependent on the vine. Have varieties such as Barbera, Carignan, Colombard, Riesling and Silvaner inherently a high percentage of malic acid. When you tire of the berries it comes to acid degradation by Zellveratmung. The rate of degradation is strongly temperature dependent and may be higher than the rate of physiological maturation, especially at high night-time temperatures. This resulted in the very warm 2003 vintage in Germany to very low-acid musts. Acid musts arms flat yield wines and are microbially not stable enough. In warmer growing areas, this phenomenon has long been known and Aufsäuerung of the must with tartaric acid or citric acid belongs to the current practice. In Germany citric acid is not allowed to acidification.

At full maturity usually still a high proportion of malic acid in the cool climate viticulture remains in the berries. To the high acid oppose a flavor component was aimed at the highest possible must weight in grapes in Germany up to the beginning of the 21st century. A high must weight is usually a guarantee for a high alcohol content in the wine and gives room for creating a residual sweetness, which can disguise a too sharp acidity.

The remaining maturity at the amount of malic acid can depending on the year, growing area and microclimate at 1-9 g / l and is therefore an important cause by year of related or position- related differences in quality.

With the process of malolactic fermentation (see the article malolactic fermentation), the content of malic acid can be influenced. During malolactic fermentation (also often called BSA) is the aggressive malic acid metabolized by lactic acid bacteria in the less strong lactic acid. In healthy grapes can be found on the berries only small quantities of lactic acid bacteria. The earlier sporadically and spontaneously occurring malolactic fermentation is carried out today especially in red wines targeted. Here, the fermented wine is vaccinated still in a wooden barrel with lactic acid bacteria.

Lactic acid

Lactic acid (Latin acidum lacticum ) is a chemical compound which is an important intermediate in metabolism. Lactic acid is a product, for example, in reducing sugars by the anaerobic glycolysis. Lactic acid is added to many foods in the form of calcium lactate or calcium lactate gluconate salts for calcium fortification. As a food additive it bears the designation E 270 Lactic acid is (brewery, bakery, as the acidulant in confectionery, isolated in lemonade ) used in the beverage industry. Yogurt and sauerkraut, foods that are caused by the action of lactic acid bacteria.

The monocarboxylic acid occurs naturally not present in the berries. It was only by the action of bacteria of the genera Oenococcus, Pediococcus and Lactobacillus mild lactic acid is produced. The lactic acid bacteria convert into lactic acid during malolactic fermentation of sugar and malic acid. As a byproduct also carbonic acid. Add the wine terminology of malolactic fermentation Malolactic fermentation is called. The name of fermentation is misleading and is only the production of carbonic acid due. The mechanisms of malolactic fermentation only be understood since the 1960s and have since been used specifically in winemaking. The malolactic fermentation gives the wine a bit more complexity and more aggressive converts the malic acid into the softer lactic acid. However, whites lose fruitiness, so that the passage of the acid degradation is not always welcome. The wines of Chenin Blanc or Riesling usually lose quality. In a non-controlled implementation of the lactic fermentation it can also come to the turbidity of the wine.

When going through malolactic fermentation and the biogenic amines histamine ( → histamine intolerance ), tyramine, putrescine and phenylethylamine arise. The biogenic amines are reputed to cause headaches. Addition of sulfur dioxide in the wine can be stabilized and spread of the lactic acid bacteria are avoided. This allows the malolactic be prevented. Lactic acid bacteria can survive deep in the walls of a wooden barrel. An expansion in the barrel is therefore problematic when the wine through malolactic fermentation should not go through.

Citric acid

The colorless, sour -tasting citric acid is found in citrus fruits, mushrooms and milk. Wine is contained in a proportion of 0.1 to 0.4 g / l. However, the acid is produced in only trace amounts within the berries, but is a by- product of the alcoholic fermentation. At a malolactic fermentation, the citric acid (also known as citric acid ), reduced by the lactic acid bacteria. It has a stabilizing effect against iron and copper opacities (→ wine faults ) in the wine. Under EU law, the use of the acid is allowed in regard to the expansion of the wine (in English notation for wine stabilization purposes ).

Smaller increases the total acid of up to 0.5 g / l can also be made with citric acid. These small amounts added, the acid can not be perceived sensory and helps low-acid wines to more structure and freshness. The addition of citric acid takes place only after the alcoholic fermentation only in microbiologically stable wine, since the yeast during the fermentation of citric acid in acetic acid, the undesired diacetyl ( Butterton ) metabolized. The addition of citric acid for acidification is not allowed in Germany, only for metal stabilization. The limit is about 1 g / l

Other acids

Acetic acid

Acetic acid is a carboxylic acid and one of the volatile acids. At higher concentration of the vinegar trick belongs to the wine errors that can not be hidden in a converted wine. As spoiled by Regulation apply white wines with more than 1.08 g / l and red wines because of the powerful tannins with more than 1.2 g / l A real vinegar stitch is prominent in these wines in the nose only from 1.5 g / l of volatile acidity. Sensitive tasters can make from a concentration of 0.5 g / l of a vinegar sting already. An exception is the noble sweet wines in which the concentrated flavors are able to conceal a light vinegar note. In this case the legal limit is 1.8 g / l Acetic acid may already be present in the must, for example, when the grapes are injured by hail or birds come and present on the grape skin bacteria with the sugar of the grapes in combination. In extreme cases, a light vinegar note is already heard in the vineyard.

Vinegar (Latin Acetum ) is a highly acidic tasting spice and preservative by fermentation of alcoholic liquids (including wine, cider, beer, or rice wine) is produced by acetic acid bacteria ( mother of vinegar ).

Ascorbic acid

As a natural ingredient that acid plays little role in the berries. Your salary falls below 20 mg / l of ten times less than in citrus fruits. The stabilizing effect of the acid as an antioxidant was hardly used in Germany. Only when researchers discovered the Bavarian State Institute for Viticulture and Horticulture in Veitshoechheim that ascorbic acid may cause known since the early 1990s, wine faults UTA stop ( atypical aging ) or at least delay, woke up the interest. Since the year 2006, the addition of ascorbic acid is allowed to grapes, mash and cider. Previously allowed up to 250 mg / l are added to the wine shortly before bottling.

Wines with the error UTA have little or no typical varietal bouquet and have been superimposed after a short maturation period and considerably aged.

Butyric

The smell of butyric acid can be perceived by humans and some animals in small traces. Man rated the smell negative. It is known the smell of rancid fat in Camembert or Parmesan cheese. Butyric acid may in particular result from an incorrectly performed malolactic fermentation.

Sorbic acid

Sorbic acid is allowed up to an amount of 200 mg / l as a preservative in wine. Frequently, the acid in the form of potassium sorbate (maximum 275 mg / l) is processed. Most sorbic acid is used in sweet wines, because it suppresses both the proliferation of fungi, bacteria and yeast. However, this does not apply to lactic acid bacteria that proliferate in the presence of sorbic acid. If after the addition of acid malolactic fermentation begins unintentionally, the circumscribed with the word Geranienton wine faults can occur. Even the smallest traces of the substance 2 -ethoxy- hexa -3 ,5-diene are sensorially determined. As perception threshold are 0,001 mg / l! It is often argued, sorbic acid will already be decades no longer used in Germany. Rainer Amann from the National Institute of Viticulture Freiburg published in 2007 a ​​study of 85 German wines and found in four sweet wines nor the preservative.

Succinic acid

Succinic acid is primarily a by-product of alcoholic fermentation, is to be found, however, even in very small quantities in the berries of the vine. It is approved in the EU as a food additive under the E number 363 and is used as such for example as a flavor enhancer. Especially in the carbonic maceration creates the acid. While the succinic acid tastes slightly bitter and salty, brings the esterification Monomethylsuccinat a mild fruity component in the wine.

The following table shows an overview of the detectable in the wine organic acids is given.