The Mineral Composition of Wine

Mineral substances are part of the ash and their content in a given wine varies depending on the amount of rainfall in a particular area. In dry sites and in years of low precipitation their content will be lower. It is increased by the application of mineral fertilisers and by vinification methods using such methods as must adjustments and other wine treatments. In red wines a greater amount is extracted from the solid matter of the grapes during the maceration and fermentation processes. The content of mineral substances oscillates between 1.8 and 2.8 g/l. Among anions the most frequently found are sulphates and phosphates followed by anions of chlorine, boric acid and silicon.

The vine takes sulphates in trace quantities from the soil as remnants of nitrogen, potassium or magnesium fertiliser. The greatest amount of sulphates find their way into the wine, especially white wine, from the sulphuring added to the grape must. Sulphates assist with the elimination of organic toxins from the human organism, working against the setting of calcium deposits and cholestorol on arterial walls, thus slowing down the ageing of the tissue. In wines they occur in amounts of 400-1000 mg/l.

Phosphates are a part of a compound of bedrock and get in the soil in an acceptable form through the process of erosion. A smaller amount also comes from phosphoric fertilisers. According to the older methods of winemaking practiced here, it was assumed that wines with a higher content of anion PO4 are of better quality and such conclusions were probably arrived at due to the oxidative methods of wine maturation in the past. This was primarily noted on the wine's palate which was rounder and fuller. Contemporary reductive technology in winemaking picks up the volatile aromatic substances better, which lays a greater emphasis on them nowadays. Phosphates appear in the must not only as inorganic compounds, but also as about a tenth part of the phosphorus found in organic compounds (glycerophosphates, esters of phosphorus, bound compound pectin substances). A considerable amount of the phosphorus compounds are used by the yeasts during the fermentation process. After they die away, the phosphorus compounds will be extracted back into the wine provided that the dead lees forming a sediment are not removed too early. When it comes to our wine regions phosphorus-rich soils are to be found principally in the districts of Znojmo, Bzenec and in Velké Žernoseky and their surrounding areas. Phosphates are found in wines in the range of 60-1000 mg/l.

Chlorine – anions of chlorine are found in smaller amounts of 20-400 mg/l in wines and its presence is evident mainly in wines emanating from salty soils. Dangerous nutrients for the vine are sodium chloride and magnesium chloride compounds. Their concentration in the soil solution must not exceed 0.05%. Calcium chloride, on the other hand, is more or less harmless. When using fertilisers based on potassium salts, it has to be borne in mind that chlorine also leeches into the soil during its breakdown. However, since it is a very volatile element, it gets often washed away by rainfall and therefore very little of it may end up in the wine.

Boron is an extremely important element for the vine's nourishment. Its content is limited in hard, calcium-rich soils and in vineyard sites that have a modified terraced layout. Boric acid can be present in wines in quantities of 10-120 mg/l, although most of the boron content is precipitated with the compounds of tartrate crystals as deposits and is thus removed from the actual wine. However, for the grapevine itself it has a significant role to play during photosynthesis and for the supply of carbohydrates. It actively participates in the pollination as well as in the flowering and insemination processes.

Silicic acid is found in wines in quanties of 30-70 mg/l. It strengthens the surface tissue of the vine organism and gets into the wine via the skin of the berries where it is found in a biologically active, assimilable form. A sufficient amount of silicon in the vascular walls is a protection against arteriosclerosis. Wines having a higher silicon content have a sedative effect, as for example rosé wines of the French Irouléguy region which is situated close to the Spanish border in south western France. An increased level of silicon is found in soils formed as a result of the weathering process of feldspar rock and kaolin erosion during the warmer climatic conditions of the Neogene age. Wine also contains a significant number of positively charged cations, though these vary considerably in the amount contained.

Potassium plays a very significant role in the life cycle of the vine. Its importance lies mainly in ionic activity and in its great volatility. Its functions are absolutely specific and the vines ingest it mainly through their time of vigorous growth until the formation of the berries. Among all the other cations potassium has a predominant position in the wine. It is present in the wines in amounts of 160-2500 mg/l. Amounts of between 600-1000 mg/l are considered normal and commonplace, anything above that is higher. Potassium is activated by the amylase enzymes contained in the saliva as well as in the pancreatic juices. It is active in the functioning of the nerve cells and exercises the regular functioning of the cardiac muscle. It is considered to be the key element in slowing down the spread of sclerosis. In the grape must it is mainly found in the form of potassium tartrate and also as potassium sulphate. It usually exists in larger doses in red wines and also in certain dry white wines, generally made from the Pinot Blanc and Chardonnay varieties, as well as in wines from Georgian varieties such as Colicouri, Rkatsiteli, Mtsvane. Potassium gives a softening edge to the wine's palate. Wines that have a low potassium content are acidic and tart on the palate.

The vine gets its calcium in amounts commensurable with soils and subsoils rich in calcium and these predominate in our wine regions. Where there are excessive amounts of calcium in the soil vines have a tendency to develop a condition referred to as chlorosis resulting in the yellowing of the leaves and stunted growth. The calcium content in a wine is relatively constant and moves between 100 to 200 mg/l. In humans calcium is necessary for the nourishment of the bone tissue and is effective as a sedative to the nervous system. It also improves the coagulability of the blood. Wines with the greatest amounts of calcium are found from around the Pavlov hills, Strážnice, Blatnice and Mělník.

Magnesium performs its most significant function as an essential component of chlorophyl. Without sufficient magnesium the vine suffers in soils where there is a high calcium content and also in dry sandy soils. Its presence in wine is regularly between 50-200mg/l. Only a very few French wines contain levels that exceed these. In our wines the highest magnesium content is to be found mainly in the Velké Pavlovice region, especially in the red wines. Magnesium is mainly found in the brain tissue, and its presence is vital for our biological equilibrium. It improves the setting of calcium in the bones, bringing about the opening up of the arteries. Lack of magnesium contributes to the development of arteriosclerosis and an arhythmic heartbeat. It also increases the secretion of bile.

Iron is present in wine in amounts of 4-10g/l. At the higher level it is eliminated by means of fining, so that the wine does not develop a condition known as iron casse and become turbid. Certain red wines matured in barriques contain a greater amount of iron ( Burgundy , Bordeaux ). Such wines serve in the treatment of anaemia and for convalescence. In this country some wines have an above-average iron content, either coming from loess soil ( Brno , Znojmo, Litoměřice) but mostly from the basalt area of the Central Bohemian Highlands.

Source: Réva a víno v Čechách a na Moravě
© V. Kraus a kol.
© RADIX, spol. s r.o.