# Beneficial Effects of _Pistacia__terebinthus_ Resin on Wine Making
## 3 Results and Discussion
### Repeated Fermentation Batches of Must by Immobilized and Free Yeast Cells  
Repeated fermentation batches of white must (12.5 \({}^{\circ}\)Be) for winemaking at 28, 21, 14 and 7 \({}^{\circ}\)C were performed by immobilized and free yeast cells in order to examine the ferentation time, operation stability, productivity, volatile by-products, total phenolics, antioxidant capacity, and preservation of the produced white wines for comparative reasons.  
The fermentation time using immobilized cells was lower than that for free cells at all fermentation temperatures (28, 21, 14 and 7 \({}^{\circ}\)C) as shown in Figure 1, Tables 1 and 2 (total results in Tables S1 and S2). This effect has also been confirmed in other immobilized systems [14, 15, 25]. The immobilized biocatalyst was used for 27 repeated fermentation batches of the must (12.5 \({}^{\circ}\)Be) from 28 \({}^{\circ}\)C down to 7 \({}^{\circ}\)C gradually (Table 2). During these batches the fermentation time, produced ethanol, ethanol productivity, and sugar conversion remained about stable at each temperature due to the immobilized biocatalyst stability. As the fermentation temperature was decreased, the fermentation time was increased as also the residual sugar [15, 26]. Regarding repeated fermentation batches with free cells, although a higher amount of yeast (2 g) was used against 1.724 g of immobilized cells in each batch of 400 mL, the fermentation time and residual sugars were higher, and so the ethanol productivity was lower. Ethanol concentration was at similar levels in wines produced by immobilized or free cells (Tables 1 and 2)  
The concentration of acetaldehyde in the wines derived from fermentation with immobilized biocatalyst was slightly lower than that with free cells and lower than 120 mg/L. A range of acetaldehyde concentrations in wine can be found; concentrations range from 30 to 130 mg/L [26]. This compound in low levels can give the wine fruit notes, but at higher concentrations it is reminiscent of nuts [27], and at still higher levels produces a green, grassy or apple-like off flavor [28].  
The concentration of ethyl acetate in wines is below 50 to 100 mg/L [29]. The produced wines using both methods (Tables 3 and 4) exhibited low concentrations providing them with a pleasant aroma. Regarding propanol-1 and ethyl acetate their concentrations in the immobilized cells were higher than those in the free cells. Ethyl acetate is perceived as the odour of nail polish remover and has a reported sensory threshold of 12 mg/L. Ethyl acetate is the major ester produced by yeast and at low levels can contribute 'fruity' aroma properties and add complexity to wine.  
Quantitatively, the most important higher alcohols are the straight-chain alcohols 1-propanol, 2-methyl-1-propanol (isobutyl alcohol), 2-methyl-1-butanol, and 3-methyl-1-butanol (isoamyl alcohol). Most straight-chain higher alcohols have a strong pungent odor. At low concentrations (\(\sim\)0.3 g/L or less), they generally add an aspect of complexity to the bouquet. At higher levels they increasingly overpower the fragrance [25].  
The concentrations of isobutanol and amyl alcohols (2-methyl-1-butanol and 3-methyl-1-butanol) in the produced wines using immobilized biocatalyst were lower than those with free cells and were decreased as the temperature was decreased. While regarding the 1-propanol, its concentration was increased decreasing the temperature using either free cells or immobilized biocatalyst except in the fermentation temperature of 7 \({}^{\circ}\)C. Either using free or immobilized biocatalyst for the wine making in all conditions, the average total higher alcohol concentration that was detected in the produced wines (isobutanol, amyl alcohols and 1-propanol) was in acceptable levels (140-420 mg/L) with the produced wines using the immobilized biocatalyst exhibiting lower total higher alcohols concentrations.