# Analytical Methods to Assess Polyphenols, Tannin Concentration, and Astringency in Hard Apple Cider
## 3 Results and Discussion
In comparison among the classifications as juice, dessert, or crab apple, the main assumptions regarding phenolic composition could be confirmed. While dessert apples contain the lowest levels and crab apples the highest concentrations, juice or cider apples show a wider range. For example, Black Limbertwig as a cider apple is analytically similar to the dessert apple group, while Horse, also a cider apple, is indistinguishable from the crab apples with more than 2 g/L total flavanols. Some of the variability within the dataset could also be related to processing steps during cider production. Previous studies reported mostly data that were analyzed in fresh apples prior to any processing [9; 34; 38]. Compounds such as catechin, epicatechin, or caffe acid are very sensitive to oxidation and fairly reactive with other juice components [8]. This could lead to a loss of these compounds during juicing, fermentation, and bottling. The concentrations shown in Table 2 should therefore not be used to categorize the apple but rather to classify the cider. However, the correlations between the photometric data described above and the concentrations determined by HPLC-DAD are highly significantly positive. The Spearman Correlation Coefficient for the comparison between FolinC and total flavanols is 0.83 with a \(p\)-value of <0.001. Similarly, when comparing FolinC to total hydroxcinamic acids, the Spearman Correlation Coefficient is 0.91 with a \(p\)-value of <0.001. This supports the working hypothesis that apple ciders can be classified and categorized with sufficient accuracy using grape wine-related methods. We therefore suggest including total polyphenols (FolinC) and total tannins (using the MCP assay) in the classification attributes for cider apples. Figure 6 summarizes the most relevant analytical data for cider production and groups the samples by category. Juice and cider apples are expected to have very little color and a more balanced sugar to acidity ratio, while dessert apples for direct consumption are usually characteristically sweeter, mildly acidic, with very low astringency, and hold up well during storage. These simple classifications based on sugar and total acidity have been used in the industry for a long time; however, in dry hard apple cider where residual sugar does not mask any bitterness or astringency, polyphenols and tannins play an important role in the overall perception of the product. The apple varieties included in this study demonstrate the characteristics that could be expected from cider apples and dessert apples. While the sugar levels are slightly higher on average in dessert apples, the average acidity is higher in cider apples. This can be explained by the technical necessity to keep the pH of the cider low during and after fermentation for microbial and chemical stability. As already mentioned earlier, the level of polyphenols correlates well with the color of the cider but the concentration of tannins is considerably lower in dessert apples compared to juice varieties. The exception to all these patterns is crab apples. Even though the sample size in this study is relatively small, crab apples display a wide range in most attributes and generally higher concentrations of all solutes. This illustrates their great potential as a blending partner for cider production to build structure and mouthfeel in the beverage. Using different apple cultivars instead of oenological tannins or additives might provide the same effect with the potential for improvements in production and cost efficiency. The analytical tools to evaluate the composition of hard ciders and to make these production decisions are reasonably accurate except for the analysis of astringency. Some changes to the assay are required to better capture astringency without the disrupting effect of polysaccharides. The main assays that can be recommended for apple cider are the Folin Ciocalteu method and Iron Reactive Phenolics to analyze polyphenols and the Methylcellulose Precipitation assay to analyze tannins.