# The Effect of Apple Juice Concentration on Cider Fermentation and Properties of the Final Product
## 3 Results and Discussion
### Hydrogen Sulfate Production and Off-Flavor Development  
Hydrogen sulfide production in the cider samples was assessed by using indicative lead acetate paper strips in the headspace of fermentation vessels. Due to the limitations of the method, conclusive  
Figure 4: PLS-DA biplots of volatile ester production in cider samples. (**A**) _S. bayanus_ yeasts; (**B**) _S. cerevisiae_ yeasts. Colors correspond to the combinations of juice type and nutritional supplement. Ellipses indicate confidence region at 0.95 level. The number in parenthesis shows variance captured by the component. quantitative decisions on the differences in hydrogen production cannot be made. Hence, the conclusions are provided as estimates only. The H\({}_{2}\)S production determined by the color intensities of the reaction on the lead acetate paper strip and the respective intensities of the sensorially perceived sulfuric off-flavor are provided in Tables 2 and 3, respectively. The pattern of hydrogen sulfide production was strain-specific, which has also been noticed in other studies [43; 44]. Most of the strains used in this study produced hydrogen sulfide during fermentation but generally not enough to produce sulfuric off-flavor of high intensity. Y6 (_S. cerevisiae_ strain) has been declared by a manufacturer as a yeast with a low capacity to produce hydrogen sulfide. According to the results of our experiments, it indeed showed the lowest production of hydrogen sulfide. In general, lower temperature fermentation (18 \({}^{\circ}\)C) resulted in higher production of hydrogen sulfide in the headspace by the end of the fermentation. This can be attributed to the better accumulation of the hydrogen sulfide due to low fermentation speed and prolonged viability of the yeast culture [45]. No notable differences in hydrogen sulfide production (reaction on the test strip) could be observed between apple juice and concentrate. The addition of nutrients prior to fermentation did not reduce hydrogen sulfide formation and, in some cases, even promoted it. For example, hydrogen sulfide production increased with the addition of a nutritional supplement in ciders fermented with Y5 yeast. The increase, however, was intense enough to produce a perceived off-flavor only in the case of DAP addition. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Nutrient** & \multicolumn{3}{c}{**Control**} & \multicolumn{3}{c}{**Fernaid O**} & \multicolumn{3}{c}{**DAP *} \\ \hline
**Matrix** & **Juice** & **Concentrate** & **Juice** & **Concentrate** & **Juice** & **Concentrate** & **Juice** & **Concentrate** \\ \hline \({}^{\circ}\)**C** & **18** & **30** & **18** & **30** & **18** & **30** & **18** & **30** & **18** & **30** \\ \hline Y1 & ++ & \(-\) & ++ & ++ & ++ & ++ & ++ & ++ & ++ & ++ & ++ & ++ & ++ \\ Y2 & ++ & \(-\) & ++ & \(-\) & ++ & \(-\) & ++ & ++ & ++ & \(-\) & ++ & + \\ Y3 & ++ & ++ & ++ & ++ & ++ & ++ & ++ & ++ & + & ++ & ++ & + \\ Y4 & ++ & \(-\) & ++ & + & ++ & \(-\) & ++ & ++ & ++ & - & ++++ & ++ \\ Y5 & \(+\) & \(+\) & \(+\) & \(+\) & ++ & ++ & ++ & ++ & ++ & ++++ & ++++ & ++ \\ Y6 & \(-\) & \(-\) & \(-\) & \(-\) & \(+\) & \(-\) & \(+\) & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) \\ \hline \hline \end{tabular}  
* Diammonium phosphate.  
\end{table} 
Table 2: Color reaction intensity of H\({}_{2}\)S (hydrogen sulfide) formation on the selective lead acetate paper strip during fermentations prepared from fresh juice or juice concentrate with different yeasts (Y1-Y6) at 18 or 30 \({}^{\circ}\)C. \(-\) No color change; \(+\) Low intensity color formation; \(++\) Moderate intensity color formation; \(++\) High intensity color formation.