Crushed Grapes Research Articles

High Power Ultrasound Treatments of Red Young Wines: Effect on Anthocyanins and Phenolic Stability Indices.

Polyphenols, especially anthocyanins, play an important role on red wine sensory qualities and their evolution during storage. High Power Ultrasound (HPU) has been recognized as one of the most promising technologies which can be applied in winemaking processes for several purposes, and it is recently officially approved for crushed grapes treatments. The effect of ultrasound amplitude (41 and 81%) and treatment time (1, 3, and 5 min) has been studied on anthocyanins, flavan-3-ols, tannins, polymerized pigments, HCl index, and the color intensity of two finished red young wines. Anthocyanins and phenols compounds were not degraded with an increase in amplitude and sonication time, and the chromatic properties of the selected wines were preserved. Amplitude and ultrasound time were also evaluated considering their effect on evolution of anthocyanin content and phenolic stability indices during the first thirty days of storage. The higher level of amplitude (81%) induced a higher percentage decrease in tannins, 15% and 40% after 15 and 30 days of storage, respectively, compared to untreated wine which did not show a significant change during storage. HPU shows a possible chemical effect on the evolution of some analytical indices during bottling maturation, but their effectiveness could be strictly linked with the initial phenolic profile and ratios between polyphenol classes.

Exploring potentials of indigenous yeasts in fermentation of Chambourcin Grapes

Background: Indigenous yeasts present on grape berries have been shown to impact the winemaking process and final wine quality. In this study, we used Chambourcin, a hybrid grape cultivar, to isolate indigenous yeasts for potential use in winemaking. Hybrid grapes are of particularly interest due to higher resistance to cold temperature and fungal diseases. Methods: Yeasts were isolated from spontaneous fermentation of crushed grapes by plating on Dichloran Rose Bengal Chloramphenicol agar and identified by Sanger sequencing. Yeast candidates were selected for their ability to grow in Yeast Extract-Peptone-Dextrose broth supplemented with varying ethanol concentration. Candidate yeasts were chosen for mock fermentation using sterile Chambourcin juice. Volatile and non-volatile compounds that predict wine quality (flavor and aroma) were measured by UPLC and GC-MS. Results: Hanseniaspora uvarum, Starmerella bacillaris, Candida californica, and Zygoascus meyerae were predominantly isolated from Chambourcin. S. bacillaris isolate 180002 and C. californica isolate 180004 were able to tolerate up to 10% ethanol compared to S. cerevisiae (ethanol tolerance up to 12%). Our results demonstrate that isolate 180002 grown in ethanol supplemented medium is comparable to the commercial S. cerevisiae. Various aroma profiles of three main chemical families – esters, higher alcohol and volatile acids in products fermented by S. bacillaris and other isolates were observed. Conclusion: Starmerella bacillaris isolate 180002 demonstrates potential for use in winemaking with hybrid grapes based on ethanol tolerance and production of wine related chemical compounds. This study further supports the application of indigenous grape-associated yeasts in creating flavor and aroma diversity of wine.

Grape Must Processed by Pulsed Electric Fields: Effect on the Inoculation and Development of Non-Saccharomyces Yeasts

Pulsed electric fields (PEFs) are an emerging cold technology capable of reducing wild yeast in either musts or crushed grapes, facilitating the implantation of starters while increasing the extraction of both phenols and aroma compounds. PEFs with an intensity of 20 kV/cm, 150 pulses, and 3 μs were applied continuously to the must of Vitis vinifera L. cv Garnacha, reducing the initial population by 1-log CFU/mL and, in most cases, maintaining a high viable population at the end of fermentation of the inoculated non-Saccharomyces. Several specific yeast metabolites produced by the inoculated non-Saccharomyces yeasts were found at higher levels in the PEF-processed musts, thus indicating a better implantation of these yeasts. The main differences have been found not only in some esters such as ethyl lactate, 2-phenyl ethyl acetate, and ethyl acetate but also in the lactic acid concentration for Lachancea thermotolerans inocula.

Impact of Must Replacement and Hot Pre-Fermentative Maceration on the Color of Uruguayan Tannat Red Wines

This research aimed to evaluate the impact of different options for winemaking on the color composition of Uruguayan Tannat red wines. The techniques evaluated were the substitution of ripe grape juice with immature grape juice and the heating of the crushed grapes before fermentation, called must replacement and hot pre-fermentative maceration, respectively. These procedures were proposed to reduce the alcohol content and increase the phenolic composition of the wine, according to the expected effects of climate change and current trends in consumer preferences. The investigation was made over three consecutive years (2016, 2017, and 2018). Both winemaking techniques allow the enhancement of the chromatic characteristics of wines via the modification of the phenolic composition. Additionally, such techniques allow the overcoming of the well-known limitations in the extractability of anthocyanins presented by the Tannat cultivar. Hot pre-fermentative maceration increases the proportion of the most oxidizable molecules delphinidin-3-O-glucoside, cyanidin-3-O-glucoside, and petunidin-3-O-glucoside, suggesting heat inactivation of polyphenoloxidases enzymes. Must replacement and hot pre-fermentative maceration are technological alternatives that could significantly improve the intensity and chromatic characteristics of red wines.

Evaluation of Volatile Metabolites Emitted In-Vivo from Cold-Hardy Grapes during Ripening Using SPME and GC-MS: A Proof-of-Concept.

In this research, we propose a novel concept for a non-destructive evaluation of volatiles emitted from ripening grapes using solid-phase microextraction (SPME). This concept is novel to both the traditional vinifera grapes and the cold-hardy cultivars. Our sample models are cold-hardy varieties in the upper Midwest for which many of the basic multiyear grape flavor and wine style data is needed. Non-destructive sampling included a use of polyvinyl fluoride (PVF) chambers temporarily enclosing and concentrating volatiles emitted by a whole cluster of grapes on a vine and a modified 2 mL glass vial for a vacuum-assisted sampling of volatiles from a single grape berry. We used SPME for either sampling in the field or headspace of crushed grapes in the lab and followed with analyses on gas chromatography-mass spectrometry (GC-MS). We have shown that it is feasible to detect volatile organic compounds (VOCs) emitted in-vivo from single grape berries (39 compounds) and whole clusters (44 compounds). Over 110 VOCs were released to headspace from crushed berries. Spatial (vineyard location) and temporal variations in VOC profiles were observed for all four cultivars. However, these changes were not consistent by growing season, by location, within cultivars, or by ripening stage when analyzed by multivariate analyses such as principal component analysis (PCA) and hierarchical cluster analyses (HCA). Research into aroma compounds present in cold-hardy cultivars is essential to the continued growth of the wine industry in cold climates and diversification of agriculture in the upper Midwestern area of the U.S.

Lachancea thermotolerans as a tool to improve pH in red wines from warm regions

In warm regions, a typical problem is to reach high pH in must together with excessive sugar concentration, this problem is being increased by climatic change. In most of the wine regions of the south centre of Spain, it is easy to find red musts with pH values in the range 3.8–4.0 that after fermentation frequently exceed pH 4. This low acidity is accompanied by alcoholic degrees that are often higher than 14% vol. By yeast selection, we have obtained one strain of Lachancea (formerly Kluyveromyces) thermotolerans that reduces pH value approximately in 0.5 units making unnecessary the use of chemical acidification. The production of lactic acid by this strain is done using sugars as precursors, thus affecting the final alcoholic degree. Some collateral reduction of ethanol can be achieved, up to 0.5% v/v. The efficiency of this strain is higher than that of others commercially available today. The use of L. thermotolerans sequentially with Saccharomyces cerevisiae is a powerful tool to modulate acidity and ethanol in warm areas. In this work, the effectivity to reduce pH of a specific strain of L. thermotolerans has been verified in low and high pH musts in lab trials but also in semi-industrial fermentations with crushed grapes.

High power ultrasounds: A powerful, non-thermal and green technique for improving the phenolic extraction from grapes to must during red wine vinification

Wine color is one of the main organoleptic characteristics influencing its quality. It is of especial interest in red vinifications due to the economic resources that wineries have to invest for the extraction of the phenolic compounds. To increase this extraction, some chemical (maceration enzymes) or physical technologies (thermovinification, criomaceration, flash-expansion) can be applied. In this work, the results of the application of high power ultrasounds to the crushed grapes to increase the extraction of phenolic compounds are presented. Crushed grapes (400 kg) from the 2017 harvest were treated with ultrasound, and three different lengths of skin maceration period (2, 3 or 7 days) and the results were compared with a control vinification, where grapes were not subjected to any treatment and were skin macerated during 7 days. The wine chromatic characteristics and the individual phenolic compounds were followed during all the maceration period, at the end of alcoholic fermentation and after bottle storage. The wines made with ultrasound treated grapes presented differences with control wine, especially as regard color and total phenol and tannin content, the wines with three days of maceration time presenting similar chromatic characteristics than control wines with 7 days of maceration time.

Application of high‐power ultrasounds during red wine vinification

SummaryWine colour is one of the main organoleptic characteristics influencing its quality. It is of special interest in red vinifications due to the economic resources that wineries have to invest for the extraction of the phenolic compounds responsible for wine colour, compounds that are mainly located inside the skin cell vacuoles, where the volatile compounds are also found. The transfer of phenolic compounds from grapes to must during vinification is closely related to the type of grapes and the winemaking technique. During traditional winemaking, grapes are crushed and skin macerated for several days, with pumps overs to facilitate the colour extraction. To increase this extraction, some chemical (maceration enzymes) or physical technologies (thermovinification, cryomaceration, flash‐expansion) can be applied. In this work, a new methodology has been tested. This methodology consists in the application of high‐power ultrasounds to crushed grapes to increase the extraction of phenolic compounds. Crushed grapes were treated with this non‐thermal technology and vinified, with 3, 6 and 8 days of skin maceration time, and the results were compared with a control vinification, where crushed grapes were not subjected to any treatment and were skin macerated during 8 days. The wine chromatic characteristics (determined spectrophotometrically) and the individual phenolic compounds (anthocyanins and tannins, determined by HPLC) were followed during the maceration period, at the end of alcoholic fermentation and after two months in bottle. Also, the wine volatile compounds were determined by GC‐MS. The wines made with ultrasound‐treated grapes showed differences with the control wine, especially regarding total phenol content and tannin content. The wines elaborated with sonicated grapes and with only three days of skin maceration time presented similar concentration of anthocyanins and twice the concentration of tannins than control wines elaborated with 8 days of skin maceration.

Chemical Gradients in Pilot-Scale Cabernet Sauvignon Fermentations and Their Effect on Phenolic Extraction

The phenolic content of red wine is responsible for the color and mouthfeel of the wine. Phenols are extracted from the skins and seeds of the crushed grapes through contact with the juice. Formation of a skin cap at the top of the fermentation decreases this contact, necessitating cap management techniques such as punch-downs or pump-overs. While it is clear that these techniques are necessary for extraction, the kinetics of phenolic release, adsorption, and reaction in this heterogeneous system are not well understood. To better understand these kinetics, pilot-scale (2000 L) Cabernet Sauvignon fermentations were performed in two consecutive harvests (2011 and 2012) using a tank modified with a custom sampling array that allowed sampling of the fermentations at four depths (two in the cap and two in the liquid), with three replicate sampling points at each depth. Chemical gradients were observed for several phenolics, including gallic acid, (+)-catechin, (−)-epicatechin, caftaric acid, malvidin-3-O-glucoside, total anthocyanins, and condensed tannins. Chemical gradients for skin phenolics, such as the anthocyanins, were observed to develop early during fermentation and to diminish as fermentation progressed. Phenolics found primarily within the seed, such as (+)-catechin, exhibited chemical gradients throughout the fermentation. Seed extraction trends were confirmed with phloroglucinolysis. Interestingly, the phenolic gradients were eliminated following a pump-over event, but were re-established during the subsequent few hours and approached a saturation point ~8 hrs after the pump-over for skin phenolics, while saturation behavior was not as pronounced for the seed phenolics.

A Traditional Turkish Fermented Non-Alcoholic Grape-Based Beverage, “Hardaliye”

Hardaliye is a non-alcoholic fermented beverage produced in a traditional way in Thrace, the European part of Turkey. The nutritional value of hardaliye is derived from the grapes and the fermentation process. Health benefits of hardaliye are also related to etheric oils present in mustard seeds. Hardaliye is a lactic acid fermented traditional beverage produced from grape juice and crushed grapes with the addition of different concentrations of whole/ground or heat-treated mustard seeds and sour cherry leaves. The color of hardaliye reflects the original color of the grapes and has a characteristic aroma. Dark red grape is preferred. Benzoic acid is used as preservative during production. Benzoic acid inhibits or decreases alcohol production by affecting the yeast. Fermentation occurs at room temperature for 7–10 days. If the ambient temperature is low, fermentation process can be extended until 20 days. Once fermented, the hardaliye is stored at 4 °C for three to four months. The hardaliye is consumed either fresh or aged. If it is aged, hardaliye may contain alcohol. The industrial production is just in small-scale and it must be developed. More studies are required to determine characteristic properties of hardaliye. Identification of the product properties will supply improvement for industrial production.

Production of White Wine from Grapes Using Sacharomyces cervisiae

Wine is an alcoholic beverage often made of fermented grape juice. The natural chemical balance of grapes is such that they can ferment without the addition of sugars, acids, enzymes or other nutrients. Wine is produced by fermenting crushed grapes using various types of yeast which consume the sugars found in the grapes and convert them into alcohol. Different varieties of grapes and strains of yeasts are used depending on the types of wine being produced. Although other fruits such as apples and berries can also be fermented, the resultant wines are normally named after the fruit from which they are produced (for example, apple wine or elderberry wine) and are generically known as fruit wine or country wine. Wine is an undistilled product obtained after normal alcoholic fermentation of grapes by yeast. Wine is basically the transformation of sugars of grapes by yeast under anaerobic conditions in to ethanol, co2, and small amounts of byproducts like D-Glucose, D-fructose. In our project, for the extraction of juice grapes must be stemed, cleaned, and crushed and then sodium or potassium metabiosulphate is added to check undesirable organisms. The crushed grape is called must. Fermentation is carried out by adding 2–5% of wine yeast namely sacharomyces cervisiae, anaerobic conditions favors the alcoholic fermentation liberating ethanol, co2. Main aim of this work is to produce white wine from grapes. A detailed study on grapes and different methods to produce wine is also reported. By analysis of wine, we reported the percentage purity, alcohol percentage in produced wine and different compound compositions.

Extraction of Bioactive Compounds from Two Grape Varieties Using Pulsed Electric Field

In this paper, our objective was to investigate extraction efficiency of polyphenols with antioxidant capacity from two varieties of grapes (white-Muscat Ottonel (MO) and red-Pinot Noir (PN)) using pulsed electric field (PEF). Grapes were harvested in the Crisana Santimreu vineyard in 2015. The grapes were declustered and crushed, and have been divided into three parts. A part was treated in PEF, the second one was homogenized, and then was treated in PEF and the last part remained untreated, representing the control samples. The bioactive compounds, like total polyphenol content and total flavonoid content, were determined by the spectrophotometric method. The antioxidant capacity of the samples was determined by three methods (DPPH, FRAPand TEAC). Our results show that the application of PEF to the crushed grapes increases the total polyphenol content 2.28 and 3.15 times and the total flavonoid content 7.17 and 5.29 times for MO and PN, respectively. Also, the antioxidant capacity was significantly increased when it was compared with the control sample. When the treatment in PEF was applied on homogenized grapes both bioactive compounds and antioxidant capacity were significantly increased compared to the samples treated in PEF for crushed grapes. In the present research work, we demonstrated that the application of PEF to two different grape varieties significantly increased the level of total polyphenols and flavonoids and also the antioxidant capacity. The application of PEF to homogenized grapes was more efficient.

Scaled design of PEF treatment reactors for electroporation-assisted extraction processes

In industrial applications electroporation-assisted extraction processes are about to replace conventional extraction. The devices for PEF treatment are designed specifically to the needs of each application. However, the design process of the electrode system and field geometry inside a PEF treatment reactor consists in general of similar steps to scale from laboratory-scale experiments done in batches up to a large-scale device operating continuously. Thereby, the electrode system might be tailored specifically to an application. In contrast to a closed PEF treatment reactor for batch processing with homogeneous electric field distribution an open electrode system with inlet and outlet section involves additional losses due to inhomogeneities of the electric field geometry. The article describes a novel approach to scale up an electrode design and to define for it an optimum operating voltage with respect to high energy efficiency in a straight-forward design process based on scaling laws. Moreover, a new method is presented to derive an efficiency factor for any given electrode geometry. It is based on a comparison of the specific power required for operating the electrode system under investigation inside a PEF treatment reactor to the specific power for a cubical PEF treatment chamber with homogeneous field distribution. Examples are given based on the design of a PEF treatment reactor for crushed grapes. PEF treatment devices for electroporation-assisted extraction are becoming increasingly interesting for industrial applications due to the benefits they offer with respect to product quality and energy savings. Challenges when transferring pulse parameters as obtained from laboratory scale experiments to industrial scale devices arise from electric field inhomogeneities in PEF treatment reactors designed for continuous flow. This work therefore presents a novel method to evaluate the electric field distribution inside the PEF treatment reactor with respect to energy efficiency. The derived scaling laws enable an energy-efficient up-scaling of any given electrode profile towards large scale for products such as sugar beets, potatoes, apples or crushed grapes in a straight-forward design process.

Post-harvest control of wine-grape mycobiota using electrolyzed water

Abstract Electrolyzed water (EW) has recently attracted much attention due to its efficacy against a broad spectrum of microorganisms. In this study, we investigated the impact of two EW treatments (40 and 400 mg/L free chlorine) on grape mycobiota using culture-dependent and -independent approaches. Moreover, the effect of yeast inoculation on treated and non-treated grapes was also considered. At the end of the fermentation, the wines produced were subjected to chemical and aroma analyses. The results revealed a decrease of about 0.5 log CFU/mL of the total yeast population on grapes surface independently of the dose of EW applied. Yeast inoculation and EW treatments shortened the time needed by Saccharomyces cerevisiae to dominate apiculate yeasts, particularly, 2 days for inoculated and 7 days for spontaneous fermentations. A decrease of acetic acid (about 55%) was also observed compared to untreated spontaneous fermentation. In addition, aroma analysis highlighted a positive contribution of inoculated yeast on the wine aromas, since they had approximately 50 % higher pleasant esters compared to spontaneous fermented wines. Industrial Relevance: Sulfur dioxide is widely used in crushed grapes prior to fermentation due to its antimicrobial and antioxidant activity. However, legislative rules, health risks and negative consumer perception related to its presence and use have resulted in a need to find new sanitizers able to reduce its use. The effectiveness of EW to reduce yeast species able to produce high levels of undesirable compounds was demonstrated. This research introduced an innovative antimicrobial agent, which could assist in the first step of wine production to reduce the use of SO2.

Overwintering of Vineyard Yeasts: Survival of Interacting Yeast Communities in Grapes Mummified on Vines.

The conversion of grape must into wine involves the development and succession of yeast populations differing in species composition. The initial population is formed by vineyard strains which are washed into the must from the crushed grapes and then completed with yeasts coming from the cellar environment. As the origin and natural habitat of the vineyard yeasts are not fully understood, this study addresses the possibility, that grape yeasts can be preserved in berries left behind on vines at harvest until the spring of the next year. These berries become mummified during the winter on the vines. To investigate whether yeasts can survive in these overwintering grapes, mummified berries were collected in 16 localities in the Tokaj wine region (Hungary-Slovakia) in early March. The collected berries were rehydrated to recover viable yeasts by plating samples onto agar plates. For the detection of minority species which would not be detected by direct plating, an enrichment step repressing the propagation of alcohol-sensitive yeasts was also included in the process. The morphological, physiological, and molecular analysis identified 13 basidiomycetous and 23 ascomycetous species including fermentative yeasts of wine-making relevance among the 3879 isolates. The presence of viable strains of these species demonstrates that the grapes mummified on the vine can serve as a safe reservoir of yeasts, and may contribute to the maintenance of grape-colonizing yeast populations in the vineyard over years, parallel with other vectors and habitats. All basidiomycetous species were known phylloplane yeasts. Three Hanseniaspora species and pigmented Metschnikowia strains were the most frequent ascomycetes. Other fermentative yeasts of wine-making relevance were detected only in the enrichment cultures. Saccharomyces (S. paradoxus, S. cerevisiae, and S. uvarum) were recovered from 13% of the samples. No Candida zemplinina was found. The isolates with Aureobasidium morphology turned out to belong to Aureobasidium subglaciale, Kabatiella microsticta, or Columnosphaeria fagi. The ascomyceteous isolates grew at high concentrations of sugars with Wickerhamomyces anomalus being the most tolerant species. Complex interactions including antagonism (growth inhibition, contact inhibition, competition for nutrients) and synergism (crossfeeding) among the isolates and with Botrytis cinerea shape the composition of the overwintering communities.

Bactericidal Action of Photo-Irradiated Aqueous Extracts from the Residue of Crushed Grapes from Winemaking.

Our previous studies revealed that photo-irradiation of polyphenols could exert bactericidal action via reactive oxygen species (ROS). In the present study, the photo-irradiation-induced bactericidal activity of the aqueous extract from the residue of crushed grapes from winemaking was investigated in relation to ROS formation. Staphylococcus aureus suspended in the extract was irradiated with LED light at 400 nm. This solution killed the bacteria, and a 3-4 log and a >5-log reduction of the viable counts were observed within 10 and 20 min, respectively. LED light irradiation alone also killed the bacteria, but the viable counts were 2-4 log higher than those of the photo-irradiated extract. In contrast, almost no change occurred in the suspension without LED irradiation. When hydroxyl radical scavengers were added to the suspension, the bactericidal effect of the photo-irradiated extract was attenuated. Furthermore, electron spin resonance analysis demonstrated that hydroxyl radicals were generated by the photo-irradiation of the extract. The present study suggests that polyphenolic compounds in the extract exert bactericidal activity via hydroxyl radical formation upon photo-irradiation.

Profiling the Hydrolysis of Isolated Grape Berry Skin Cell Walls by Purified Enzymes.

The unraveling of crushed grapes by maceration enzymes during winemaking is difficult to study because of the complex and rather undefined nature of both the substrate and the enzyme preparations. In this study we simplified both the substrate, by using isolated grape skin cell walls, and the enzyme preparations, by using purified enzymes in buffered conditions, to carefully follow the impact of the individual and combined enzymes on the grape skin cell walls. By using cell wall profiling techniques we could monitor the compositional changes in the grape cell wall polymers due to enzyme activity. Extensive enzymatic hydrolysis, achieved with a preparation of pectinases or pectinases combined with cellulase or hemicellulase enzymes, completely removed or drastically reduced levels of pectin polymers, whereas less extensive hydrolysis only opened up the cell wall structure and allowed extraction of polymers from within the cell wall layers. Synergistic enzyme activity was detectable as well as indications of specific cell wall polymer associations.

Implementation of an on-line near infrared/visible (NIR/VIS) spectrometer for rapid quality assessment of grapes upon receival at wineries

Background and Aims The parameters commonly examined upon receival of grapes at wineries are insufficient for comprehensive quality assessment. Grape quality is mainly determined by the ripeness and phytosanitary status of the grapes and is indicated by changes in chemical composition. Thus, we have evaluated the feasibility of an on-line assessment for real-time analysis of crushed grapes by near infrared/visible (NIR/VIS) spectroscopy at production scale upon their receival. Methods and Results Spectrometers were successfully integrated into the receival lines of two wineries during three vintages. The spectra of 1160 samples were collected. Calibration models were established for the spectral ranges of 450–850 nm (VIS) and 1050–1650 nm (NIR) by partial least squares regressions for ten relevant parameters. A global calibration model and more specific models relying on grape colour, vintage, winery and grape cultivar were established. The best performing models specific to individual cultivars resulted in a coefficient of determination of the validation (R2val) of 0.767, 0.732 and 0.747 for relative density, fructose and glucose concentration; 0.787, 0.540, 0.877 and 0.862 for pH value, tartaric acid and malic acid concentration and titratable acidity; and 0.698, 0.777 and 0.574 for the grape rot indicators glycerol, gluconic acid and acetic acid, respectively. Conclusions Models suitable for semi-quantitative prediction of parameters related to composition were established as being valuable for multifactorial, holistic assessment of the composition of grape deliveries. Specialisation of the calibration models bears the potential for further improvement, thus allowing comprehensive assessment of grape composition by NIR/VIS spectroscopy. Significance of the Study On-line implementation of NIR/VIS spectroscopy was shown to be a promising tool for rapid and objective assessment of the composition of grapes upon receival at wineries, which may enable improved systems for payment and quality management. Further acceptance criteria may be developed and food safety may be improved by detecting and rejecting spoiled grapes potentially containing mycotoxins.

Impact of different vinification techniques on the formation of reductive notes inVitis viniferacv. Vernatsch

The grape variety Vernatsch is prone to the formation of severe reductive notes during alcoholic fermentation (AF), spoiling the fruity aroma characteristic for this variety. We investigated the impact of eight different vinification treatments on the formation of volatile sulfur compounds (VSCs) and their impact on the sensorial quality of the wines in this susceptible grape variety. Without the addition of sulfur under the form of potassium metabisulfite (K2 S2 O5 ) to the crushed grapes, wines were significant less reductive. The clarification treatment showed promising results for the diminution of reductive notes, but might not be a feasible strategy for commercial wineries. Changing fermentation temperature, adding air, bentonite or copper to fermenting wines increased the appearance of reductive notes. The addition sulfur prior AF increased reductive notes in Vernatsch wines and needs to be considered as a crucial factor for the formation of reductive notes.

Effect of alcoholic fermentation on the quality of grape brandies

Grape brandy is a product obtained by fermentation and distillation of crushed grapes of cultivated grapevine Vitis vinifera. Grape brandy quality depends on many factors such as: grapevine varieties, climate, soil, time and method of distillation, storage methods and other distillates. The grapevine variety 'Neoplanta' grown in the experimental field of the PD 'Center for Viticulture and Enology' in Nis was used in the experiment. Tests were performed in the laboratory of the Centre. Healthy grapes of harvest maturity were squashed by a stalk-removing electric crusher. Fermentation was performed in plastic containers in the presence of the indigenous microflora of wine yeasts. This paper presents the influence of pH and inorganic nitrogen added to the fermentation medium on the content of volatile components and concentrations of higher alcohols.