Postharvest wine grape dehydration: ethanol dissipation from grape and biochemical changes.

BACKGROUND: During postharvest dehydration, grapes are subject to metabolic changes including ethanol anabolism and catabolism. These changes affect the quality of the final product and ethanol production is a key step. Ethanol dissipation has never been measured during postharvest wine grape dehydration. Thus, the present study aimed to: (i) monitor ethanol dissipation and (ii) investigate chemical-biochemical changes in berries during dehydration. RESULTS: Ethanol dissipation from Raboso grapes, under controlled postharvest dehydration, was found to comprise up to 36% of weight loss (w.l.). Moreover, the activity of enzymes involved in the anaerobic metabolism of grapes was investigated. Ethanol dissipation was highly correlated with grape weight loss (r2 = 0.989). Alcohol dehydrogenase activity, responsible for the reduction of ethanol to acetaldehyde, declined significantly with w.l. Similarly, pyruvate decarboxylase and lactate dehydrogenase reduced their activity. High lipoxygenase activity was measured at 27% w.l., whereas polyphenol oxidation was constant and declined in the last sampling. CONCLUSION: Ethanol dissipation during postharvest dehydration allows for reducing anaerobic metabolism and promotes oxidative metabolism. The sensor used can be a useful commercial tool for monitoring berry metabolism. © 2023 Society of Chemical Industry.

Novelty of Italian Grape Ale (IGA) beer: Influence of the addition of Gamay macerated grape must or dehydrated Aleatico grape pomace on the aromatic profile.

A new category of fruit style beer resulting from the addition of grape matrices is named Italian Grape Ale (IGA). In this paper, we report data on an experimental work to produce IGA beers, adding macerated (CO2 or N2) red Gamay grape must or Aleatico grape pomace resulting from a grape dehydration process. Our hypothesis, that these wine processes can produce volatile organic compounds (VOCs) to characterize these IGA beers which was confirmed by chemical, sensory and aromatic results. IGA beers especially the one with gas-macerated grape musts (IGA-C and IGA-N) showed higher alcohol content than ALE beer (Control) and a higher polyphenol content and antioxidant activity. As regards VOCS, IGA beers increased the concentration of some classes (i.e., alcohols, esters, norisoprenoids) and IGA-N was better characterized by specific compounds such as isobutyric acid, phenylacetate, tyrosol, ethyl hydrogen succinate. Finally, E-nose and sensory evaluation discriminated significantly all the IGA beers.

Air speed and plastic crate vent-holes for wine grape quality during postharvest dehydration: commercial and laboratory studies.

BACKGROUND: Airflow is an important issue to favor postharvest dehydration keeping wine grape quality. The aim of this experimental work was to analyze the grape quality during postharvest dehydration: (i) in a commercial facility ('fruttaia') by monitoring the efficiency of the ventilation system and (ii) at laboratory level, studying the influence of crate type and airflow direction. RESULTS: In the fruttaia, the airflow was provided by an air duct hanging from the ceiling, and by floor fans. A great gap in air speed from 0 up to 3.7 m s-1 was measured in different sectors of the fruttaia, leading to a different weight loss and grape quality in crates, depending on crate stack height and sector. At the laboratory level, two tunnels, with exhaust or supply fans, were used and four crate types with different percentages of vent-holes were adopted. A decrease of about 5% delayed the weight loss rate depending on the type of crate, and the exhaust fan guaranteed a faster dehydration. CONCLUSION: The results clarified the inefficiency of the commercial ventilation system in ensuring homogeneous grape weight loss in all crates. In addition, the exhaust fan guaranteed a more uniform air distribution around crates, and a slightly higher air speed. © 2023 Society of Chemical Industry.

Nitrogen maceration of wine grape: An alternative and sustainable technique to carbonic maceration.

Carbonic maceration (CM) consists in placing intact grape bunches into a sealed tank to have a natural or artificially created carbon dioxide atmosphere. No articles have been published on the comparison between CM and nitrogen maceration (NM). Therefore, the present study aimed at testing the use of alternative maceration technique (NM) in alternative to CM, to create the conditions of anoxia on the Gamay variety. The results showed a higher concentration of polyphenols and anthocyanins in the macerated wines, especially in NM wine. Concerning VOCs (Volatile Organic Compounds), the CM wine showed the highest content in esters while the total alcohol content was slightly higher in the NM wines. The CM wine had the highest content in volatile medium chain fatty acids (MCFA). E-nose measurements revealed a clear separation among the samples, and the E-nose data, in PCA computation, were generally overlapped by the PCA of VOCs analysis. The NM showed a potential as environmentally sustainable technique useful to produce a new style of macerated and aromatic wines.