Differentiation of Wines Treated with Wood Chips Based on Their Phenolic Content, Volatile Composition, and Sensory Parameters

Trials of Commercial- and Wild-Type Saccharomyces cerevisiae Strains under Aerobic and Microaerophilic/Anaerobic Conditions: Ethanol Production and Must Fermentation from Grapes of Santorini (Greece) Native Varieties

In modern wine-making technology, there is an increasing concern in relation to the preservation of the biodiversity, and the employment of “new”, “novel” and wild-type Saccharomyces cerevisiae strains as cell factories amenable for the production of wines that are not “homogenous”, expressing their terroir and presenting interesting and “local” sensory characteristics. Under this approach, in the current study, several wild-type Saccharomyces cerevisiae yeast strains (LMBF Y-10, Y-25, Y-35 and Y-54), priorly isolated from wine and grape origin, selected from the private culture collection of the Agricultural University of Athens, were tested regarding their biochemical behavior on glucose-based (initial concentrations ca 100 and 200 g/L) shake-flask experiments. The wild yeast strains were compared with commercial yeast strains (viz. Symphony, Cross X and Passion Fruit) in the same conditions. All selected strains rapidly assimilated glucose from the medium converting it into ethanol in good rates, despite the imposed aerobic conditions. Concerning the wild strains, the best results were achieved for the strain LMBF Y-54 in which maximum ethanol production (EtOHmax) up to 68 g/L, with simultaneous ethanol yield on sugar consumed = 0.38 g/g were recorded. Other wild strains tested (LMBF Y-10, Y-25 and Y-35) achieved lower ethanol production (up to ≈47 g/L). Regarding the commercial strains, the highest ethanol concentration was achieved by S. cerevisiae Passion Fruit (EtOHmax = 91.1 g/L, yield = 0.45 g/g). Subsequently, the “novel” strain that presented the best technological characteristics regards its sugar consumption and alcohol production properties (viz. LMBF Y-54) and the commercial strain that equally presented the best previously mentioned technological characteristics (viz. Passion Fruit) were further selected for the wine-making process. The selected must originated from red and white grapes (Assyrtiko and Mavrotragano, Santorini Island; Greece) and fermentation was performed under wine-making conditions showing high yields for both strains (EtOHmax = 98–106 g/L, ethanol yield = 0.47–0.50 g/g), demonstrating the production efficiency under microaerophilic/anaerobic conditions. Molecular identification by rep-PCR carried out throughout fermentations verified that each inoculated yeast was the one that dominated during the whole bioprocess. The aromatic compounds of the produced wines were qualitatively analyzed at the end of the processes. The results highlight the optimum technological characteristics of the selected “new” wild strain (S. cerevisiae LMBF Y-54), verifying its suitability for wine production while posing great potential for future industrial applications.

Browning Development and Antioxidant Compounds in White Wines after Selenium, Iron, and Peroxide Addition

The effect of oxidation on the organoleptic properties of white wines mostly involves increased browning color, loss of the fruity aromas, and appearance of unpleasant odors. Browning, however, is known to be related with polyphenol oxidation and therefore it may be delayed by the presence of antioxidants such as selenium (Se) and SO2. On the other hand, the presence of oxidants such as metal ions and H2O2 can accelerate browning and oxidation phenomena. The browning capacity, the phenolic composition (both total and individual contents of flavanols and hydroxycinnamic acids), the antioxidant activity, and the SO2 content of Assyrtiko white wines were studied after the addition of Fe2+ and H2O2 and Se at two temperatures, employing an accelerated test. Browning was approached from a kinetic point of view, and the study was focused on the implication of oxidants and antioxidants on browning rate, paying particular attention to the content of major redox-active polyphenols, including substances with an o-diphenol feature, such as flavanols and hydroxycinnamic acids. The results showed that after the addition of oxidants it was possible to significantly accelerate the rate of browning development (up to 4.7 and six times) depending on the temperature and the concentration of the added compounds. The presence of Se protected wine color and preserved total SO2 at 35 °C, while at 50 °C, these effects were not observed. Total flavanol content decreased upon heating, while total hydroxycinnamic content showed a slight increase. Similarly, the content of the individual phenolic compounds (with the exception of caffeic acid and (+)-catechin at 35 °C) was decreased with oxidant addition, while Se addition was not adequate to prevent or even promote their oxidation.

Wood powders of different botanical origin as an alternative to barrel aging for red wine

Wood powders are produced in large quantity as by-product of barrel, staves and chips industry. Differently from larger particles (chips), the use of wood powders in winemaking is not admitted (Regulation (CE) n. 934/2019); however, it could represent a cheap and sustainable alternative for the accelerated aging of red wine. To evaluate their potential use in winemaking, a comparative study on the use of wood powders from oak, chestnut and acacia wood for the accelerated aging of red wine (cv. Aglianico) was conducted. This alternative aging was compared to the aging in wood barrels from the same botanical species. The wine aged in contact with powders underwent a quicker evolution of polyphenolic fraction. After 15 days of contact, the loss of total anthocyanins was higher than that observed after 6 months of aging in barrels (from 4 to 14% with respect to the corresponding kind of barrel). The amount of polymeric pigments tannins–anthocyanins–tannins in wines aged in contact with powders was higher respect to the wines aged in barrels (from 7 to 21% with respect to the corresponding kind of barrel), while the greatest loss of total tannins was detected in the oak barrels (28% less with respect to the control). There were several differences in wine phenolic acids due to wood botanical origin, with the clearest differences being between oak and the alternative wood species (chestnut and acacia). Also, there was a significant botanical effect on sensory profiles. Indeed, both among barrels and among powders, oak wood was the one that gave the strongest wood odor character. However, all the treatments with wood powders (oak, acacia and chestnut) preserved the fruity character of wine, conferring in the meanwhile non-dominant woody notes.

Effect of Barrel-to-Barrel Variation on Color and Phenolic Composition of a Red Wine

Tangible variation of sensory characteristics is often observed in wine aged in similar barrels. Barrel-to-barrel variation in barrel-aged wines was investigated in respect of the most important phenolic compounds of oenological interest. A red wine was aged in 49 medium-toasted oak (Quercus petraea) barrels, from four cooperages, for 12 months. The resulting wines were evaluated for chromatic characteristics, anthocyanin-related parameters, total phenols, flavonoids and non-flavonoids phenols, flavanol monomers, and oligomeric and polymeric proanthocyanidins. PCA and ANOVA were applied to investigate the relationships between barrels and to assess cooperage and individual barrel effect. Three cooperages influenced the wine similarly during aging. Anthocyanin-related parameters showed the highest variation, 25–37%, other phenolics varied 3–8.5%, and with two exceptions, chromatic characteristics changed 1.7–3%. The relationship between the number of barrels and the expected variation for each analytical parameter was calculated, as reference for future measurements involving barrel lots, either in wine production or experimental design.

Application of Ultraviolet-Visible Absorption Spectroscopy with Machine Learning Techniques for the Classification of Cretan Wines

The present study was aimed at the identification, differentiation and characterization of red and white Cretan wines, which are described with Protected Geographical Indication (PGI), using ultraviolet–visible absorption spectroscopy. Specifically, the grape variety, the wine aging process and the role of barrel/container type were investigated. The combination of spectroscopic results with machine learning-based modelling demonstrated the use of absorption spectroscopy as a facile and low-cost technique in wine analysis. In this study, a clear discrimination among grape varieties was revealed. Moreover, a grouping of samples according to aging period and container type of maturation was accomplished, for the first time.

Reusability of Immobilized Cells for Subsequent Balsamic-Styled Vinegar Fermentations

Cell immobilization is a process augmentation technique aimed at improving microbial survival and activity under stressful conditions. It offers the opportunity to reuse the immobilized cells for several fermentation cycles. The present study investigated the use of recycled cells entrapped in calcium-alginate beads and cells adsorbed on corncobs (CC) and oakwood chips (OWC) in subsequent fermentation cycles for balsamic-styled vinegar (BSV) production. Sugars, pH, alcohol and total acidity were monitored during fermentation. Microbial activity and product formation declined when immobilized cells were reused for the second cycle for CC and OWC fermentations. Recycled cells entrapped in Ca-alginate beads completed the second cycle of fermentations, albeit at reduced acetification rates compared to the first cycle. Scanning electron microscope (SEM) imaging results further showed a substantial the structural integrity loss for Ca-alginate beads after the first cycle, and with minor changes in the structural integrity of CC. The OWC displayed a similar morphological structure before and after the first cycle. The sensory results showed that BSV produced using immobilized cells with Ca-alginate beads and CC was palatable, while those produced using OWC had negative attributes. Ca-alginate beads offered better protection for the fermentation consortium for culture reusability in BSV fermentations.

Odor Characterization of White Wines Produced from Indigenous Greek Grape Varieties Using the Frequency of Attribute Citation Method with Trained Assessors

The aim of this study was to investigate the sensory aroma profiles of white wines of the indigenous Greek grape varieties Assyrtiko, Malagousia, Moschofilero, and Roditis. Twenty-three panelists evaluated 17 wines of the aforementioned varieties using the frequency of attribute citation method. Three indices were calculated to assess panel performance in terms of reproducibility. Correspondence analysis and cluster analysis were employed to investigate the sensory space of the wines. Samples of the Roditis variety were characterized mainly by Banana and Vanilla odors; Assyrtiko samples had Earthy, Mushroom, and Nutty odors, as well as Lemon and Honey for some of the samples. Malagousia wines were described as having Lemon, Grapefruit, and Citrus blossom character, and they shared some descriptors with Assyrtiko wines, such as Mushroom and Earthy, and some with Moschofilero samples, i.e., floral and citrus notes. All Moschofilero wines exhibited a floral odor profile: specifically, Rose, Jasmine, or more Citrus blossom-like. Moreover, some Moschofilero samples also revealed a Grapefruit, Lemon, and/or Earthy character, while others expressed Honey notes. In conclusion, despite common characteristics found within varieties, some samples of different varieties exhibited overlapping profiles, and in some cases, samples of the same variety were quite different from each other.

Wine Authenticity and Traceability with the Use of FT-IR

Fourier transform infrared spectroscopy (FT-IR) has gained popularity in the wine sector due to its simplicity and ability to provide a wine’s fingerprint. For this reason, it is often used for authentication and traceability purposes with more than satisfactory results. In this review, an outline of the reasons why authenticity and traceability are important to the wine sector is given, along with a brief overview of the analytical methods used for their attainment; statistical issues and compounds, on which authentication usually is based, are discussed. Moreover, insight on the mode of action of FT-IR is given, along with successful examples from its use in different areas of interest for classification. Finally, prospects and challenges for suggested future research are given. For more accurate and effective analyses, the construction of a large database consisting of wines from different regions, varieties and winemaking protocols is suggested.

Evaluation of Aroma Compounds in the Process of Wine Ageing with Oak Chips

Many modern alcoholic beverages are subjected to ageing processes during which compounds extracted from wood contribute decisively to the overall beverage character. Wines represent a perfect example of beverage in which ageing is a crucial technological manufacturing step. During winemaking, producers accelerate chemical changes in wine composition by traditional and alternative methods, such as the use of oak wood barrels and/or oak wood chips. Our research aimed to investigate the overall volatile composition and sensory quality of red wines aged for two timeframes, namely, 1.5 and 3 months, and with two technological variants, i.e., American and French oak wood chips. Red grapes from the Fetească neagră (Vitis vinifera) variety were harvested from a vineyard in the North-East region of Romania. Stir bar sorptive extraction and gas chromatography coupled with mass spectrometry (SBSE-GC-MS) was used to extract minor aromas present in wine samples. The results showed clear differences between wines treated with American and French oak chips. Furthermore, ageing for 3 months increased the concentration of cis-whiskey lactone and guaiacol in American oak-treated wine samples. For wines aged with French oak chips, we observed higher concentrations of furfural, 5-methylfurfural, 4-vinylguaiacol, and trans-whiskey lactone. The increased presence of chemical compounds in wine aged with French oak chips generated prominent smoky, licorice, and toasty aromas, whereas in wines aged with American oak chips, notes of vanilla, toasty, and cacao aromas were noticed. Moreover, red wines aged with American and French oak chips were discriminated by chemometric analysis, which confirmed the evolution of aroma compounds.

Aeration, Agitation and Cell Immobilization on Corncobs and Oak Wood Chips Effects on Balsamic-Styled Vinegar Production

Optimum fermentor conditions are essential for desired microbial growth and activity in fermentations. In balsamic vinegar fermentation systems, the microorganisms used must endure several stressful conditions including high sugar concentration, low water activity, high osmotic pressure and high acetic acid concentration. Consequently, the present study was aimed at improving the performance of a microbial consortium of non-Saccharomyces yeast and acetic acid bacteria during balsamic-styled vinegar fermentation. Cell immobilization via adsorption on corncobs and oak wood chips in combination with aeration and agitation effects, have never been tested during balsamic-styled vinegar fermentation. Therefore, fermentations were initially conducted under static conditions without aeration with successive fermentations also being subjected to low (0.15 vvm min^-1) and high (0.3 vvm min^-1) aeration. The results showed improved acetification rates when cells were immobilized on corncobs under static conditions. Low aeration showed better acetification rates (1.45-1.56 g·L·day^-1), while only free-floating cells were able to complete fermentations (1.2 g·L·day^-1) under high aeration conditions. Overall, cells immobilized on corncobs showed higher acetification rates of 1.56 and 2.7 g·L·day^-1 under low aeration and static fermentations, respectively. Oak wood chips were determined to be less efficient adsorbents due to their relatively smooth surface, while the rough surface and porosity of corncobs led to improved adsorption and, therefore, enhanced acetification rates.

Proanthocyanidin content as an astringency estimation tool and maturation index in red and white winemaking technology

Selecting the appropriate type of barrel for wine maturation but also deciding on the optimum maturation length, is a challenge for winemakers. As different types of barrel woods emerge, it is of great importance for a guideline to be established, which could facilitate winemaking decisions. Since the sensory perception of the finished wine, and particularly the intensity of astringency, is a decisive factor for the quality of a barrel-aged wine, in this experiment, the structural characteristics of wine proanthocyanidins were determined and their correlation with astringency was established. According to the results obtained, the proanthocyanidin content and the type of subunit that is dominant in tannin chains could be used to construct an astringency estimation model. The findings could provide winemakers with a useful tool when deciding how long to mature a specific type of wine in a specific wood container without making it appear coarse and astringent.

New Strategies to Improve Sensorial Quality of White Wines by Wood Contact

Ageing wine is a common practice used in winemaking, since the quality and sensory profile increase due to the extractable compounds coming from wood, by means of barrels or chips. The quantitative and qualitative compounds of the wood depend on the species, its origins and the treatments applied in cooperages. Traditionally, oak wood species are most often used in cooperage, specifically Quercus alba (Q. alba), Known as American oak and Quercus robur (Q. robur) and Quercus petraea (Q. petraea), both known as French oak. Although this stage is very common for red wines, its use is still restricted in the case of white wines. However, this topic is particularly interesting, since due to the sensorial benefits of wood contact, the option for ageing white wines in barrels or chips could be chosen by winemakers. This review compiles the novel strategies applied to white wines by means of wood contact in recent years with the aim to increase wine quality and sensorial features.

Pomace limits tannin retention in Frontenac wines

The impact of different factors (must protein treatment: bentonite and heat; pomace: fermented with and without; tannin addition: 0-9 g/L; and time of maceration: 0-11 days) on tannin, pigment, and protein extraction/retention in Frontenac wines was investigated. Wine tannin concentration and composition were determined by HPLC-fluorescence. Protein and pigment parameters were analysed by BCA assay and Boulton's method, respectively, using UV-spectrophotometry. Results: Bentonite and heat significantly reduced wine protein concentration at the end of alcoholic fermentation but heat was less efficient than bentonite (1.8-5.0 times less). Removing wine proteins did not improve tannin retention in wines (p > 0.1032) but fermenting without pomace significantly improved their retention (up to 2.4 times), especially that of polymeric flavan-3-ols (up to 27.8%). An addition of 3 g/L of enological tannins in wines, fermented with or without pomace, was necessary to increase wine tannin concentration significantly.

Toasted vine-shoot chips as enological additive

Different ways of vine-shoots revalorization have been proposed, but not in wine yet, as for example in the same way as oak chips are being used. In this work, vine-shoot samples were submitted to a thermogravimetric analysis to establish the temperature range for its lignin structure decomposition, resulting between 160 and 180 °C. Then, vine-shoot chips from Airén and Cencibel cultivars, with a particle size around 2.5-3.5 cm, were submitted to six toasting conditions: 160 °C and 180 °C for 45, 60 and 75 min. Their volatile composition was very similar to oak chips, being vanillin the most important compound. Moreover, such vine-shoots have an interesting content of prodelphinidins that together with the stilbenes may contribute to wine antioxidant activity. The toasting conditions at 180 °C/45 min were the most suitable one for releasing the mentioned valuable compounds in order to propose vine-shoots as new enological additive similar to oak chips.