Post-Fermentation

Diffusion of water, ethanol, and oxygen into and out of barrel-aging wine creates changing environmental conditions which may support or hinder growth of AAB. Depending on the relative humidity (RH) in the cellar, water (at RH 60%) or alcohol (at RH 60%) preferentially is lost 

Although not recommended, processing requirements may occasionally necessitate storage in partially filled containers. Stainless steel or other containers that can be sealed effectively should be used in this case. After transfer, such containers should be topped with nitrogen gas and sealed. In this case, nitrogen, rather than carbon dioxide gassing, is recommended. The limited solubility of N2 (14 mg/L) compared with COg (1500 mg/L) in wine means that the former remains as a layer on and above the wine s surface for a longer period of time compared with CO2, which rapidly solubilizes. 

Volatile acidity may have abiotic origins as well. Increases of 0.06-0.12 g/L have been reported after 1 year s storage in new wood (Chatonnet, 1993). In this case, the origin was hydrolysis of acetyl groups of hemicel-lulose. Additionally, acetic acid may result from coupled oxidation of wine phenolics (Zoecklein et al., 1995), initially yielding hydrogen peroxide which, in turn, oxidizes ethanol to acetladehyde and subsequently acetic acid see Fig. 2-3. 

The distribution of yeast species in cellar-aging wine includes Dekkera/ Brettanomyces (Section 11.2.2), film yeasts (Section 11.2.3), Saccharomycodes (Section 11.2.4), and Zygosaccharomyces (Section 11.2.5), all of which can result in serious wine spoilage. 

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In China some teas, such as Pu-er tea, are made through microbial fermentation and called post-fermented teas. The typical characteristic of these teas is a mouldy or aged flavour the more intense this flavour, the better the quality. Other kinds of tea, such as white, yellow and dark, are produced in small quantities and consumed locally. Further processing of these teas produces scented and brick teas. 

Special Organic Solvents (e.g., CH.CN) for post-fermentation modification or conjugation reactions such as PEGylation... 

Bacteriological Stability. The bacteriological stability provided by malo-lactic fermentation is its most important attribute. Wines aged before bottling (and which are susceptible to the fermentation) will nearly always be fermented during the first or second year. With proper post-fermentation treatment, these wines can be safely bottled without fear of further bacterial attack. We have seen no instances where a second bacterial fermentation has occurred once the malo-lactic fermentation was completed unless additions had been made to the wines or they had been blended. 

Zoecklein, B.W., Marcy, J.E. Jasinsky, Y. (1997a). Effect of fermentation, storage sur lie or post-fermentation thermal processing on White Riesling (Vitis vinifera L.) glycoconjugates. Am. J. Enol. Vitic., 48, 397-402. 

Consequently, pre-fermentation maceration at low temperature increases the level of anthocyanins and flavanols from pulp and skins while post-fermentation maceration increases that of proanthocyanidins, as a result of enhanced extraction from seeds (Cheynier et al. 2006). 

Pezet, R. and Cuenat, P. 1996. Resveratrol in wine Extraction from skin during fermentation and post-fermentation standing of must from Gamay grapes. Am. J. Enol. Vitic. 47(3) 287-290. 

Post-fermentation maceration continues after the completion of alcoholic fermentation and is specific to wines with aging potential. Its length is highly variable, from a few days to a few... 

Fig. 6.41. Influence of vatting on the extraction of various compounds from grapes. A, anthocyanins T, tannins P, Polysaccharides Cl, color intensity MpF, maceration prior to fermentation AF, alcoholic fermentation PfM, Post-fermentation maceration...

Off-line measurements of state variables are more difficult to integrate into control schemes due to the typically long delays in sample analysis. However, they are still crucial in post-fermentation analysis of the performance of the system, and can be used in the vaHdation of both predictive and interpretive models. They may also be important to provide a check on on-hne measurements, since off-line methods typically suffer from less noise than on-hne methods. The most important off-line measurements are discussed below. 

The Dranco process (Dry anaerobic composting) (De Baere and Six, 1988) also utilises the segregated organic fraction of MSW. This is mixed with recycled effluent, and fed to the reactor. The retention time is 18 days, and after post-fermentation processing, dewatering, and drying, the final product is marketed... 

The carbon dioxide can of course be recovered readily from the enclosed vessels. For one unit weight of sugar, about half this weight is theoretically recoverable as carbon dioxide and, considering the cost of the gas and the great use for it in the post-fermentation period of beer treatment, the escape from open fermenters appears to be an expensive waste. In practice, the percentage of carbon dioxide recovered is rarely above 50% of the theoretical (see Chapter 20). There is, however, considerable debate on the economics... 

Method Primary fermentation Transfer Post fermentation storage... 

Long-term chemical changes also take place in the maturation vessel such as esterification and certain reductions. During the post-fermenting treatment of beer it is necessary to promote clarification of the beer and, by stabilizing treatment, ensure that turbidity due to chemical precipitation or growth of micro-organisms does not occur. 

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