Hard cider is an alcoholic beverage produced from fermented apple juice or apple juice concentrate. Domestic cider consumption has increased more than 850% in the last 5 years and there are now over 550 cider producers in the United States (TTB, 2007–14; Brown, 2016). The vast majority of cider produced in the United States is made from apple cultivars that were originally planted for fresh or processing markets (Peck and Miles, 2015). Culinary apples do not have all of the fruit quality characteristics desired by cider producers, but many of the desired cider apple cultivars have not been documented as being widely planted in the United States (Miles et al., 2015; Peck, 2012; U.S. Apple Association, 2015). In the United States, where the production of traditional hard cider apple cultivars has lagged behind the increase in cider sales, methods to increase cider quality from existing apple cultivars are needed.
Fruit quality attributes that are important for culinary apple production include low incidence of damage and decay, fruit shape and size (typically measured by fruit mass), peel color, flesh firmness, soluble solid concentration (SSC), titratable acidity (TA) and pH, and flavor (La Belle, 1981). Along with the starch pattern index (SPI) and internal ethylene concentration (IEC), fruit quality factors are often measured to gauge harvest maturity (Watkins, 2003). For cider production, fruit quality attributes also include polyphenol and YAN concentrations in the fruit, and juice yield, while cosmetic attributes such as color, shape, and size are much less important (Lea, 1996).
Apple orchard management practices that focus on fruit quality characteristics that are desirable for cider production are needed. Specifically, most apples commercially grown in the United States have low YAN and polyphenol concentrations (Thompson-Witrick et al., 2014). While both exogenous nitrogen and polyphenols (i.e., “enological tannins”) may be added to increase their concentration in cider, the sensory impact of addition of these products to cider warrants further investigation. For example, the addition of commercially available exogenous tannins to red wine has been shown to increase the measured total polyphenol concentration, but they did not always lead to improvement in sensory character (Harbertson et al., 2012). As such, increasing endogenous polyphenol concentration in fruit remains the generally preferred approach to achieve desired sensory characteristics for wine and cider.
In European wine grape (Vitis vinifera L.) production, measurable improvements in fruit quality have been achieved through adjusting the relationship between fruit yield and vegetative growth, often referred to as crop load. Grape cluster crop load has been shown to impact secondary metabolism in grape berries, which can in turn impact wine chemistry, aroma, and flavor. For example, SSC was greater in ‘Chambourcin’ grapes that were from vines with reduced fruit clusters (Dami et al., 2006). Similarly, lower crop loads for ‘Sauvignon blanc’ grapevines resulted in wine that had more favorable sensory scores (Naor et al., 2002). A study of ‘Shiraz’ grapevines under five training systems in the Barossa Valley of Australia demonstrated that grape berry anthocyanin and polyphenol concentrations decreased with increasing crop load (Wolf et al., 2003). However, a point is reached when continuing to decrease crop load results in decreased yield and increased production cost, but no further increase in wine quality (Berkey et al., 2011; Bravdo et al., 1985; Preszler et al., 2010). Although horticultural practices for apples and grapes are quite different, wine grape growers exert a tremendous amount of effort optimizing fruit quality to make their crop more desirable to their buyers. For these reasons, crop load targets are often specified in vineyard management with the goal of maintaining optimal fruit quality for winemaking (Wolf, 2008).
With the increased utilization of apples for cider production, it is necessary to more fully understand how orchard management decisions, such as crop load density, impact cider quality. The development of crop load management practices can be used by orchard managers to improve cider produced from culinary apples. The goal of this project was to assess the impact of three different crop load densities on fruit and cider quality.
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