Port wine formation

The spectra were recorded in the positive-ion mode in the range of m/z 120-1 500. Some chromatograms illustrating the effect of aldehydes on the interaction of mv3gl and B2-3 -gallate are shown in Fig. 2.120. The chromatograms demonstrate that different aldehydes influence differently the formation of anthocyanin-flavanol pigments. The results of HPLC-MS measurements are compiled in Table 2.94. Because free aldehydes display an unpleasant aroma in Port wine these reactions may improve the quality of wines and contribute to the colour formation [266],... 

Silva Ferreira, A. C., Rodrigues, P., Hogg, T., and Guedes de Pinho, P. (2003a). Influence of some technological parameters on the formation of dimethyl sulfide, 2-mercaptoethanol, methionol, and dimethyl sulfone in Port wines. ]. Agric. Food Chem. 51, 727-732. 

Anthocyanin-pyruvic acid adducts are known to be more abundant in Port wines than in red table wines, as seen from previous analysis in our laboratories (data not shown) and as referred by other authors (77). This feature may be related to the higher levels of pyruvic acid expected in fortified wines as a result of a shortened fermentation. In fact, when wine spirit is added in order to stop fermentation, the pyruvic acid concentration is expected to be higher than when the fermentation is allowed to go to dryness. Effectively, the pyruvic acid excreted by the yeast at the beginning of the fermentation is further used in the yeast metabolism (35). Therefore, could favor the formation of anthocyanin-pyruvic acid adducts. 

Hence the aim of this work was to (/) evaluate the impact of Sotolon on the perceived age of Port wine (ii) determine which parameters (e.g. temperature, dissolved oxygen, pH and free SO2 content) have the greatest effect on Sotolon concentration, (Hi) and to establish mathematical models describing the rate of formation of Sotolon during storage, taking into account the critical parameters selected. 

The presence of 2-ketobutyric acid in Port wine was investigated (P). Although the quantities found could reach 2 mg/L, these were always lower than 0.5 mg/L for wines older than 10 years. No correlation between the levels of keto-acid neither with age nor with the amount of furanone could be found. Conversely a very liigh correlation was observed with acetaldehyde (r=0.8906). Thus, 2-ketobutyric acid may contribute to Sotolon formation, but taking into accoimt the linear trend observed with time for the Sotolon levels, it seems unlikely that this keto-acid constitutes the only source of Sotolon in Port wine. 

Kinetics Studies After determining tlie parameter witli the highest effect upon Sotolon concentration in port wines, attempts were made to establish a matliematical model, which reflects tlie impact of oxygen level, temperature as well as the time of storage, on the rate of formation of Sotolon. 

The Sotolon formation was studied as a function of temperature, pH, SO2 and oxygen concentration. Temperature and to a lesser extent, dissolved oxygen were tlie most important parameters influencing the rate of Sotolon formation. A first order model was applied and the Arrhenius equation described well the temperature dependence of the reaction rate constant. Therefore, oxygen levels during aging have a major impact on age perception" in Colheita and Vintage Port wine. 

Carbon Dioxide 2C + 02 = = >CO Carbon monoxide When shaken with water, the Carbon Dioxide, CO, dissolves forming a solution of the very weak and unstable solution of Carbonic Acid, H COj, which changes the blue colour of litmus to a port-wine red colour C02-hHp= = >H2C03 Carbon Carbonic Dioxide Acid If another jar of containing Carbon Dioxide, CO2, from the combustion of carbon is shaken with lime water, this becomes milky from the formation of a... 

Certain heterocyclic compounds are also important aromatic substances in wines, such as pyrazines in Cabernet Sauvignon and Sauvignon Blanc wines (see Section 8.2.11.1.7) and both enantiomers of 3-hydroxy-4,5-dimethyl-5if-furan-2-one (sotolon), which occur in white wines, sherries and are a key component of the typical aroma of aged Port wines. The precise chemical reactions leading to the formation of bouquet substances are not yet widely known. There are two types of reactions that produce bouquet constituents oxidation, which is characterised by the presence of aldehydes and acetals (e.g. in Madeira-type wines) and reduction (such as in quality table wines after a period of bottle maturation the flavour of low-quahty wines does not improve under the same conditions, but instead maturation often leads to a loss of freshness). During wine aging, glycosides of terpenic alcohols and... 

Another application for gum arabic is in the production of vins de liqueurs, rancio wines, aperitifs, vermouth, port, Pineau des Charentes, etc. As these products are frequently stored in contact with air and their aging process includes deliberate oxidation, the formation and precipitation of colloidal coloring matter is the main cause of turbidity. Gum arabic, at doses of 20-25 g/hl, prevents flocculation of the coloring matter. This treatment is not recommended for wines of this type intended for long bottle aging. 

If the wine is heated in the presence of air, there is a maderization effect, with the formation of aldehydes, acetals and other aromatic compounds, giving a rancio character. These are standard practices for certain wines, mainly vins de liqueur (sweet fortified wines), including Madeira, Port and French vins doux naturels. Heating in these instances may be very intense, e.g. 60 days at 60°C. 

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