© The Authors, published by EDP Sciences, 2023

1 Introduction

SO₂ is an antioxidant which is able to avoid developing oxygen aroma, and its capacity of antimicrobial restrains unwanted bacteria cultivating. Based on those advantages, SO₂ has become an important protection tool of road usage in conventional winemaking process. However, SO₂ may cause allergy and other health problems. It’s a trend to reduce the usage of SO₂ in winemaking. A contrastive study of red wine with and without SO₂ added was carried out in Bordeaux, which shows a larger number of “non-added” wines with defects [1]. In order to improve the quality of SO₂ “non-added” wine, non-saccharomyces yeasts were used for bioprotection in recent year, results from which has shows that bioprotection has a significant impact on the aromatic profile of wine [2].

Traditional winemaking processes massively rely on the ambient yeast especially Saccharomyces cerevisiae on the grape surface [3]. It plays a principal role in wine fermentation, producing various chemical compositions, makes the wine show different “terrior” [4]. Nowadays, with a growing concern about food safety, winemakers are trying to return to tradition, consequently “natural wine” gets more and more popular. Although there is not an unambiguous definition of natural wine, it is considered a type of wine with low input.

This research aims at the approach to producing “natural wine”, two objects were studied:

How does the wild yeast from local grapes work.

Compare the bioprotection wine and the SO₂ protection wine from physicochemical and sensory aspects.

2 Materials and methods

2.1 Experimental procedure

This research was carried out with Rara Neagra grapes from Olanesti, PGI Stefan Voda, and Moldova. Grapes were harvested from an organic vineyard at the moment when they reached the optimal must weight. For each type of wine, 7000 kg grapes were used, 80% of which crushed and destemmed while 20% were whole bunches grapes. The grapes were fermented together. For wine A, Saccharomyces cerevisiae authorized for organic wine were inoculated, meanwhile wine B inoculated the wild yeast from itself, they are both protected by SO₂ (PMS 400 g). For wine C, the same Saccharomyces cerevisiae inoculated with Torulaspora delbrueckii and metschnikowia pulcherrima for bioprotection. The density measured twice a day after each punching down. Each type of wine with duplication (n = 2).

2.2 Physicochemical properties analysis

The FTIR spectroscopy method was used for general physico-chemical analysis: alcohol and pH. Capillary electrophoresis was used to detect and quantify the organic acid. The composition of volatile substances was determined by gas chromatography, the polyphenolic pole was determined with the help of UV spectrophotometry, and the component of anthocyanins was established by the HPLC method refer to Ribereau-Gayon. The total fenolice was measured by method Folin-Ciocaleteu.

Color Intensity (CI) was calculated by summery of absorbance value of 420 nm, 520 nm and 620 nm. The method refers to what Glories described. The A420/520 represent hue which is determined ratio between value at 420 nm and 520 nm.

In addition, the CIELAB analysis followed what Ayala mentioned.

2.3 Sensory analysis

The sensory analysis was carried out in the specialized tasting room of the National Center for checking the quality of wine products. The samples were served together at a temperature of 20 degrees in individual booths and in ISO-INAO glasses into which about 75 ml of wine was poured. Each of the analyzed samples was coded with a three-digit code.

The samples were evaluated by ten panelists (women 4/men 6, average age 37.4) from the professional wine industry who have worked for at least 5 years in different spheres of the value chain of the wine industry: winegrowers, oenologists, marketers and traders, logistics, catering, and hospitality (wine tourism).

The sheet below was applied to the sensory analysis:

The sheet contains the usual sensory descriptors that must be developed according to an intensity scale from 0 (no sensation) to 5 (very strong sensation). Besides these descriptors, there are 2 positions that contain a binary answer and refer to the purity of aroma and taste (absence or presence of a defect). If present, the taster was asked to identify this defect. Also the ladder of appreciation of the quality of the tannins in the taste to limit to three levels: dry, pronounced and supple.

2.4 Statistical analysis

Statistical analysis was performed by R.4.04 for IOS. ANOVA (one-way analysis of variance) and Tukey test were used to compare differences between samples, when p < 0.05, it regarded as significant.

3 Results and discussion

As Figure 1 shows, both the musts density of Wine A and Wine C (inoculated with commercial yeast) falling faster than Wine B, and the end of alcoholic fermentation analysis showed Wine B with a lower alcohol level. But after MLF, three wines didn’t show significant difference, refer to Table 1.

In the general analysis results, the pH among three wines has a significant difference, where wine B is larger than others. What more interesting is that Wine C with a significantly larger value in volatile acidity.

The volatile acidity is considered with an important contribution for aroma, when it was more than 1.2 g/L, the unpleasant vinegar aroma will appear [5]. The volatile acidity of Wine C (0.45 g/L) was still at a normal level.

As the Table 1 shows, the phenolic and anthocyanins have significant difference between bioprotection wine and others. It is widely accepted that they contribute to the quality of wine, especially astringency, bitterness and color. There are lots of factors that affect the color of wine: grape variety, winemaking practice, the strain of yeast and lactic acid bacteria. Lb.plantarum and O.oeni modify the wine color, astringency and bitterness[6]. But significant differences in taste and color haven’t been detected by panelist.

As the Table 1 shows, the phenolic and anthocyanins have significant difference between bioprotection wine and others. It is widely accepted that they contribute to the quality of wine, especially astringency, bitterness, and color. There are lots of factors that affect the color of wine: grape variety, winemaking practice, the strain of yeast, and lactic acid bacteria. Lb.plantarum and O.oeni modify the wine color, astringency, and bitterness. But significant differences in taste and color haven’t been detected by panelist.

As the secondly important compound of volatile acidity of wine, ethyl acetate affected by the yeast strain selected, this makes different results from wine A and wine B. Another important reason for variation amount of ethyl acetate is aeration, the more aeration protection is, the smaller the value. Previous research pointed out that a concentration of ethyl acetate less than 70mg/L contributes positive aroma [7]. But from sensory analysis results, aroma defect was not detected by panelists.

The sensory analysis evaluations are listed with average value and standard deviation. Different letters are significantly different between the samples (p < 0.05).

As another important influence factor to aroma, the phenolic substance also enjoys a significant difference between Wine A and Wine C. From Table 2, the smell intensity difference was detected by panelist, especially the fruity aroma.

Non-Saccharomyces enhancing complexity and fruity characters has been provided by many researches. The Impact from Metschinikowia pulcherrima as a bioprotection hasn’t found on wine quality. But Torulaspora delbrueckii is always linked with “fruitness”, which has a good consistence with sensory analysis results in this research [8].

The sensory analysis didn’t show significant difference of gustative characteristics, but from the radar graph, a little variation can be observed, especially from the perspective of body and structure.

The color study results are listed with average value and standard deviation. Different letters are significantly different between the samples (p < 0.05)

In contrast with sensory analysis, the results of CIELAB and A420/A520 show that bioprotection wine is significantly different from conventional wine. As mentioned previously, MLF modifies wine color, bioprotection wine permits simultaneous MLF and alcoholic fermentation, as a result that even it has an obviously different color from conventional wine is not remarkable. Considering the complexity of microorganism activities, samples of must from different stages of winemaking process were took for microbiology study in future. From what Table 3 shows, wine C is significantly different from A and B on Lightness (L) and Hue angle (H), the H from 0-60 represents red, and H > 60 means yellow. The CIELAB result is the same as sensory analysis that bioprotection wine is of darker red hue. The evaluation from the panelists didn’t show significant difference, however, the hue value measured by A420/520 shows that significant difference exists only between Wine A and Wine C.

Figure 1 Sensory analysis sheet.

Figure 2 The dynamic of alcoholic fermentation. End of alcoholic fermentation analysis: Wine A with 14.3±0.28, Wine B 13.1±0.14, Wine C 14.8±0.

Figure 3 Radar graph of gustative characteristics.

4 Conclusion

This research is based on a real production scale of vinification, chemical-fizico and sensory analysis that were done with three types of wine. Firstly, in terms of conversion the commercial yeast worked better than wild yeast in the alcoholic fermentation, but after MLF, they get similar alcohol level. From other perspectives, except pH, ethyl acetate and TPI, the qualities of wine made from commercial yeast and wild yeast are almost the same. Secondly, from the comparison between bioprotection wine and conventional wine:

The former has obviously higher concentration of volatile acidity, TPI, phenolic, anthocyanin and ethyl acetate. And it also has more fruit aroma and higher smell intensity.

References

All Tables

All Figures

	Figure 1 Sensory analysis sheet.
In the text

	Figure 2 The dynamic of alcoholic fermentation. End of alcoholic fermentation analysis: Wine A with 14.3±0.28, Wine B 13.1±0.14, Wine C 14.8±0.
In the text

	Figure 3 Radar graph of gustative characteristics.
In the text