Copper in wines

Iron and copper in wines may form complexes with other components to produce deposits or clouds in white wines. Iron clouds generally occur at a pH range from 2.9 to 3.6 and are often controlled by adding citric acid to the wines (2). Copper clouds appear in wines when high levels of copper and sulfur dioxide exist and are a combination of sediments, protein-tannin, copper-protein, and copper-sulfur complexes (169). Further, the browning rate of white wines increases in the presence of copper and iron (143). The results of this study indicate that iron increased the browning rate more than copper. 

In the analysis of teas, the AO AC [7k] recommends matching the matrices of standard solutions to those of samples by the incorporation in standard solutions of Na, K, Mg, Ca and Al, at levels found in sample digests, in addition to digestion acids. The procedure of Ecrement [36] for direct FAAS determination of copper in wines also involves matrix matching as outlined in note 5 to Section IV.B.l. 

Zeeman and Butler (Zl) determined copper in wines. Following acid digestion and dry-ashing the samples were taken up in nitric acid and aspirated. None of the elements found in the ash, when tested individually, had any effect on copper absorption, but when synthetic ash solutions were investigated, containing a combination of the ash constituents, absorption depression occurred. This effect had to be compensated for in the calibrating solutions. 

Baldo MA, Bragato C, and Daniele S (1997) Determination of lead and copper in wine by anodic stripping voltammetry with mercury microelectrodes assessment of the influence of sample pretreatment procedures. Analyst 122 1—5. 

Fig. 8.19. Histograms of trace elements in wine for manganese (a) and copper (b) (according to Danzer et al. [2001])...

The appreciation of color and the use of colorants dates back to antiquity. The art of making colored candy is shown in paintings in Egyptian tombs as far back as 1500 bc. Pliny the Elder described the use of artificial colorants in wine in 1500 bc. Spices and condiments were colored at least 500 years ago. The use of colorants in cosmetics is better documented than colorants in foods. Archaeologists have pointed out that Egyptian women used green copper ores as eye shadow as early as 5000 bc. Henna was used to redden hair and feet, carmine to redden lips, faces were colored yellow with saffron and kohl, an arsenic compound, was used to darken eyebrows. More recently, in Britain, in the twelfth century, sugar was colored red with kermes and madder and purple with Tyrian purple. 

Danilewicz, J. C. (2003). Review of reaction mechanisms of oxygen and proposed intermediate reduction products in wine Central role of iron and copper. Am. J. Enol. Vitic. 54, 73-85. 

The mechanism of copper casse and the factors influencing its development in wines have been investigated by Joslyn and Lukton (18, 27), Kean and Marsh (15, 16,17), and Peterson et al. (28). 

Copper. In the presence of sulfur dioxide, copper-protein cloudiness may develop in white wines. Only small amounts of copper (about 0.3 to 0.5 mg/liter) cause cloudiness. Widespread use of stainless steel in modern wineries has reduced copper pickup, but many wineries routinely test their wines for copper. Atomic absorption spectrophotometry is the method of choice (51) although reducing sugars and ethanol interfere, and correction tables must be used (107). To reduce this interference, chelating and extracting with ketone is recommended (108). Lacking this equipment colorimetric procedures can be used, especially with di-ethyldithiocarbamate (3, 4, 6, 9,10, 22,109). Neutron activation analysis has been used for determining copper in musts (110). 

Iron. Excess iron in wines causes cloudiness, interferes with the color, and can impair flavor. The mechanism of ferric phosphate precipitation has been intensively studied, and numerous colorimetric methods have been developed. For routine purposes the color developed with thiocyanate is adequate (6,9), but many enologists prefer the orthophenanthro-line procedures (3, 4, 6, 22). Meredith et al. (Ill) obtained essentially the same results for iron using 2,4,6-tripyridyl-s-triazine (TPTZ) to develop the color. Atomic absorption spectrophotometry can be used but, as with copper, corrections for reducing sugar and ethanol are necessary (51). 

Several minerals and trace elements are vital to the human organism and must be ingested with daily food in sufficient amounts. Wine can contribute not only minerals containing potassium, calcium, and magnesium but also numerous essential trace elements, such as chromium, cobalt, iron, fluorine, copper, selenium, and zinc, among others. The contents found in wine are very low ranging from mg L 1 to igL, sometimes even lower. 

While the hydrogen sulfide formed during fermentation can be easily removed with the addition of copper sulfate, the international legal limit of 0.2 mg/L residue in wines and the natural complexing and binding of copper ions in wines often prevent suitable additions from being made in practice. Of more concern is the secondary thiols and thioacetates that are produced with hydrogen sulfide (J) and the inability of copper to remove them or their oxidized disulfide forms. 

In wines, traces of iron, which are picked up, perhaps, from processing and/or storage, or copper, which are picked up from mildew sprays, such as Bordeaux mixture, affect the oxidative stability of wines by acting as the redox shuttles as they transfer between oxidation states. Winemakers discovered that adding ferricyanide to wine, in a process known as blue fining, precipitates copper and iron and thereby reduces their concentrations below 1 ppm, which is considered to be acceptable. Critical control of ferricyanide addition is necessary, as cyanide is also a contaminant that must be measured. Where vineyards have replaced cherry and apple orchards, low concentrations of arsenic have started to appear but they are present at very low concentrations in high quality wines. The arsenic appears from arsenical compounds such as lead and calcium arsenates that were used for many decades as pesticides on apples and cherry orchards. 

The pararosaniline method has found numerous applications owing to its sensitivity and selectivity. It has been used in determinations of sulphur (or SO2) in air [22,97,98], plants [99,100], wine [101], soils [102], organic compounds [25], selenium [103], and copper [6,8]. This method has also been applied for continuous determination of SO2 in wine [ 104,105]. 

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