# Helium Atmospheric Pressure Plasma Jet Source Treatment of White Grapes Juice for Winemaking
## 2 Materials and Methods
### Methods for Characterization of Must and Wine
#### 2.2.3 The pH Value, Brix and Potential Alcohol of Must and Wine  
As general rule, winemakers should keep the pH under recommended ranges and the correction by adjusting free sulfur dioxide should be made quickly because pH plays an important role in the form of SO\({}_{2}\) which inhibits microorganisms. The management of acidity is very important for wine stability and hence for its quality.  
The wine pH values usually range from 2.8 to 3.8. Lower pH 2.8-3.2 ensures the pleasant refreshing taste of wine and the bright color, the wines are easily clarified and are resistant to microorganisms. The low-value pH wine will taste tart/sour, owing to the higher acid concentration. Higher pH values (>3.5) affect the wine quality [82]. High pH values for a grape juice make it less stable to oxidation and microbial spoilage and gives it a flat and unbalanced taste while musts with low pH (naturally occurring or after acid adjustment) require less SO\({}_{2}\) quantity to control the native flora and to ensure the onset of a desired fermentation [89].  
The pH measurements of the pristine and plasma treated samples were performed via a PH-009(I)A Series pen pH and Temperature Tester, the measurements being taken at 20 \({}^{\circ}\)C.  
Brix testing plays a huge role in determining when grapes are at their highest sugar content and suitable for harvest. Furthermore, Brix measurements can also be used with other forms of produce for determine the mineral, protein or amino acid concentration of the plant. Determination of carbohydrates in the samples was performed using the Abbe type refracometer, by determining the refractive index. The reading was made for the Brix index (the unit of measurement of carbohydrates in an aqueous solution), and the conversion was done with the help of a table of transformation in grams of carbohydrates / L: 1 Brix = 10.04 g/L measured at 20 \({}^{\circ}\)C.  
The Brix determination was made by using a portable refracometer (RWN10-ATC, Czech Republic) with five scales: 5-22% VOL (\(\pm\)0.2%); 10-37\({}^{\circ}\) CNM (\(\pm\)0.5\({}^{\circ}\)); 0-30\({}^{\circ}\) KMW (\(\pm\)0.5\({}^{\circ}\)); 0-150\({}^{\circ}\) Oe (\(\pm\)1\({}^{\circ}\)); 0-35\({}^{\circ}\) Bx (\(\pm\)0.5\({}^{\circ}\)).  
The potential alcohol/desitometry determinations were made by using a glass glucometer (GUYOT glucometer, three thermometer bench scales: sugar 0-30, alcohol 0-20% VOL, Baume 0-18\({}^{\circ}\), Enolandia) and a vinnometer (0-25 % VOL, Enolandia). The pH, Brix and alcohol measurements were made in in triplicate, the values being expressed as mean\(\pm\) standard deviation (SD).  
The formula used for estimating the potential alcohol (pa) from Brix measurements [59; 87; 90] of the untreated and plasma treated must samples, is usually referred to: pa (% _v/b_) = 1000(gsi-1.0)/[7.75-3.75(gsi-1.007)], where spi is the initial specific gravity of the must.  
Moreover, according to OIV International Standard for the Labelling of Wines, (Edition 2015) [58], depending on their sugar content, table and quality wines are divided into:  
1. dry, with a sugar content of up to 4 g/L but not less than 2 g/L;
2. medium-dry, with a sugar content between 4.01 g/L and 12 g/L, but can go up to 18 g/L;
3. mellow or semi-sweet, with a sugar content above 18 g/L and up to 45 g/L inclusive;
4. sweet, with a sugar content of more than 45 g/L.