Fermentation Parameters of Wine

Propan-1-ol is directly originated by the loss of the 2-ketobutyric acid carboxyl group and subsequent reduction of propionic aldehyde formed. 

It is interesting to note that in fermented products the same alcohols always form, even if different sources of nitrogen, but not singular aminoacids, are available. Ketoacids can also be directly reduced to hydroxyacids such as lactic, 2-hydroxy-3-methyl butyric, 2-hydroxy-3-methyl pentanoic, 2-hydroxy-4-methyl pentanoic, 2-hydroxy-3-phenyl propionic and 2-hydroxy glutaric acids. The corresponding ethyl esters can dramatically influence the wine aroma. 

Production of oxalacetate by C02 addition to pyruvic acid, operated by pyruvate carboxylase (biotin coenzyme), allows the cycle to continue. 

Short- and middle-chain fatty acids are formed in the lipids metabolism. Relevant levels of acetic acid are usually present in wine (several hundred mg/L) due to the fact that this compound can be formed by different metabolic pathways. On the contrary, the levels of short and middle-chain fatty acids are relatively low, with a maximum of a few mg/L in red wines and tens mg/L in white wines. 

It was observed that yeast production of middle-chain fatty acid esters, and acetates of alcohols formed by reduction of the correspondent 

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Analysis of Fermentation Parameters of Wine 1.3.1. Alcoholic Fermentation... 

This volume is divided into eight chapters, by subject. Due to its multidisciplinary nature, analytical techniques are not described, apart from brief introductions to Chapters 7 and 8, to which readers are referred for more specific analytical chemistry books. Again, due to the enormous number of subjects discussed, only a brief summary of methods, including materials and instruments used, is given, and readers are referred to single publications. The main parameters of wine fermentation are treated in the first chapter, but discussion of volatile esters and higher alcohols were deemed to be more suitably located in Chapter 5 on aromatic compounds. 

The evalnation of phenolic snbstances in wine is a historical topic, and colorimetric methods were developed at hrst for qnality control of wine. Nowadays, it is still performed, and a parameter named optical density is still measnred as an index of color, while other indices have been developed for a rapid evalnation of phenolic componnd content. Moreover, the form of some phenolic compnnds (mono- or diglncoside) is nsed to distingnish between wines obtained by the fermentation of the jnice of Vitis vinifera or Vitis rupestris. 

Principal Parameters of Grape Ripening and Wine Fermentation... 

It is evident that only with extensive application by both the viticulture and wine industries will the practical utility of G-G be tested. A far greater body of G-G data on a range of different varieties, all grown under different conditions is needed. To aid this the assay procedure should be automated to provide the mass of information to test the practical use of the G-G parameter. Post-harvest applications must also be explored with monitoring of G-G of musts through vinification, and of wines undergoing secondary fermentation, and then maturation. 

The SO2 combination balance varies considerably between different musts (metabolism of the acetic bacteria) and wines (fermentation parameters). Furthermore, the total content of these com-binant compounds in wine may result from both sources, as shown in Table 8.11. 

Adding lysozyme does not affect fermentation kinetics. The wines have the same analytical parameters and are unchanged on tasting, provided they are adequately protected from oxidation, but only 30 mg/1 of total SO2 are required, for example, instead of 50. 

Together with biochemical reactions catalyzed by enzymes of yeasts and bacteria, chemical reactions also occur between molecules already present in the must, those gradually extracted from the grape solids during fermentation, those derived from metabolism and, possibly, also those released by the wood. For many of them, the temperature and dissolved oxygen parameters related to technological operations of the winery can have dramatic effects and the quality of the final wine depends on the type and intensity of reactions taking place. 

Commercial 0. oeni strains are selected for their oenological parameters, including the absence of amino acid decarboxylases. According to the in vitro studies done by Moreno-Arribas et al. (2003), none of the four commercial malolactic starter cultures tested could produce histamine, tyramine or putrescine. Martln-Alvarez et al. (2006) also compared inoculation with spontaneous malolactic fermentation in 224 samples of Spanish red wine. They found that inoculation with a commercial starter culture of lactic acid bacteria could reduce the incidence of biogenic amines compared to spontaneous malolactic fermentation in wines. Starter cultures could eliminate indigenous bacteria, or could possibly degrade the biogenic amines produced by the undesirable strains. 

These relationships are independent of the yeast strain and of the fermentation temperature, within normal limits. Typical values of the parameters for natural wines are (D/H), 102 ppm, (D/H)n 131 ppm, (D/H), 160 ppm, (D/H)w — 155 ppm. The deuterium content of methyl and methylene sites is greatly reduced with respect to glucose and starting water, but (D/H), is about 5 times more sensitive to the (D/H) ratio of the glucose than to the starting water, whereas (D/H)n depends almost entirely on the starting water. 

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