Evaluation of select cider apple (Malus domestica Borkh.) cultivars grown in Ontario. II. Juice Attributes

Twenty-eight apple cultivars were selected for their potential for hard cider production in Ontario and their juice characteristics were measured in 2017 and 2018, beginning two years after planting in 2015. After being harvested and pressed, each juice sample underwent analyses to determine soluble solids concentration (SSC), titratable acidity (TA), pH, yeast assimilable nitrogen (YAN), and polyphenolic concentration. SSC ranged from 10.6° Brix in Brown’s Apple to 18.3° Brix in Ashmead’s Kernel. TA ranged from 31 as mg malic acid 100 mL-1 juice in Sweet Alford to 191 as mg malic acid 100 mL-1 juice in Bramley’s Seedling. The pH ranged from 2.88 in Breakwell to 4.76 in Sweet Alford. YAN concentration ranged from 60 mg YAN L-1 juice in Medaille d’Or to 256 mg YAN L-1 juice in Bulmers Norman. Polyphenols in juice ranged from 131 µg gallic acid equivalents mL-1 juice in Tolman Sweet to 1042 µg gallic acid equivalents mL-1 juice in Stoke Red. Firmness ranged from 6.3 kg in Yarlington Mill to 11.7 kg in GoldRush. The relationships between these variables were also analyzed, showing a connection between acidity and juicing efficiency as well as a relationship between polyphenol concentration and fruit weight. Exploratory analyses indicated that juice attributes can be used to distinguish between cultivars and their origins. Cider producers can use these data to determine what to expect in juice from these cultivars.

Juice Attributes of Ontario-Grown Culinary (Dessert) Apples for Cider

Continued interest in the commercial production of cider in Ontario has revealed there is a lack of information available to apple producers and cidermakers on the juice attributes of culinary dessert apple for making cider and how they may vary from orchard to orchard. A two-year study was conducted to characterize the juice characteristics of 18 common culinary dessert apple cultivars grown at several locations in Ontario. Juice was assayed for soluble solids concentration, pH, titratable acidity (TA), juice extraction efficiency, yeast assimilable nitrogen (YAN), polyphenols and soluble solids-to-TA ratio. Significant differences among cultivars were observed for all parameters, which varied by orchard and year, except juice extraction efficiency. These data underly the importance of assaying juice every growing season prior to fermentation. Cidermakers should focus on juice characteristics from culinary apples that are more difficult to alter (with amendments), and use juice with lower pH, higher TA and polyphenols, and moderate to higher YAN to optimize cider quality and flavour. Overall, this study will inform cidermakers of which culinary apple cultivars might be preferable for fermentation as well as how they might be blended to optimize cider quality. Notwithstanding annual and orchard variation, cultivars that meet these criteria include Cortland, Crimson Crisp, Honeycrisp, Jonagold, McIntosh and Northern Spy. If making cider from Ambrosia, Crispin, Empire, Fuji, Gala, Golden Delicious or Idared, cidermakers should expect to blend the juice from these cultivars to create a more fully balanced juice prior to fermentation.

Soil Nitrogen Fertilization Increases Yeast Assimilable Nitrogen Concentrations in ‘Golden Russet’ and ‘Medaille d’Or’ Apples Used for Cider Production

The recent growth in the U.S. hard-cider industry has increased the demand for cider apples (Malus ×domestica Borkh.), but little is known about how to manage orchard soil fertility best to optimize horticultural performance and juice characteristics for these cultivars. To assess whether nitrogen fertilizer applied to the soil can improve apple juice and cider quality, calcium nitrate (CaNO3) fertilizer was applied at different rates to the soil beneath ‘Golden Russet’ and ‘Medaille d’Or’ trees over the course of three growing seasons. The experiment started when the trees were in their second leaf. The trees were cropped in their third and fourth leaf. At the end of the first growing season of the experiment, the greatest fertilizer rate increased tree trunk cross-sectional area (TCSA) by 82% relative to the control, but this difference did not persist through to the end of the study. Yield and crop load were unaffected by the nitrogen fertilization treatments. Increasing the nitrogen fertilizer rate correlated positively with more advanced harvest maturity in ‘Golden Russet’ fruit, which resulted in greater soluble solid concentration (SSC). Fruit from the greatest fertilizer rate treatment had an average starch pattern index (SPI) that was 1 U greater than in the control, and an SSC that was 3% greater than the control. The fertilizer treatments did not affect juice pH, titratable acidity (TA), or total polyphenol concentrations. Yeast assimilable nitrogen (YAN) concentrations were increased by nitrogen fertilization for both cultivars in both harvest years. The greatest fertilizer treatment increased juice primary amino nitrogen by 103% relative to the control. Greater nitrogen fertilization rates correlated positively with less hydrogen sulfide production during the fermentation of ‘Golden Russet’ juice from the first, but not the second, harvest. During the first year, cumulative hydrogen sulfide production for the ‘Golden Russet’ control treatment was 29.6 μg·L–1 compared with the ‘Golden Russet’ high treatment, which cumulatively produced 0.1 μg·L–1. Greater maximum fermentation rates and shorter fermentation durations correlated positively with increased fertilization rate for both cultivars after the second harvest. High treatment fermentations had maximum fermentation rates 110% greater, and fermentation durations 30% shorter than the control. Other horticultural and juice-quality parameters were not affected negatively by the CaNO3 treatments. In orchards producing apples specifically for the hard-cider industry, nitrogen fertilizer could increase juice YAN, thus reducing the need for exogenous additions during cider production.

Foliar Urea Applications Increase Yeast Assimilable Nitrogen Concentration and Alcoholic Fermentation Rate in ‘Red Spy’ Apples Used for Cider Production

Yeast assimilable nitrogen (YAN) can be a limiting nutritional factor for Saccharomyces cerevisiae yeast when fermenting apple (Malus ×domestica Borkh.) juice into hard cider. Endogenous YAN concentrations in apples are often below the recommended thresholds to completely use all of the fermentable sugar and minimize the production of off-flavors, such as hydrogen sulfide. Cider producers supplement apple juice with exogenous nitrogen to increase YAN. Urea, commonly applied to apple orchards to increase fruit size and yields, was tested for its ability to increase endogenous apple juice YAN. Starting 6 weeks before harvest in 2017 and 2018, a 1% urea solution was applied to ‘Red Spy’ apple trees one, three, or five times to create low-, medium-, and high-rate treatments, respectively. Relative to the control, the high treatment increased YAN by 229% in 2017 and by 408% in 2018. More than 90% of the YAN in all juice samples was composed of primary amino nitrogen (PAN). Among all treatments, PAN mostly comprised asparagine, and as urea applications increased, the relative concentration of asparagine also increased. Aspartic acid and then glutamic acid were the second and third most abundant amino acids in all treatments, respectively, but comprised less of the total PAN as the number of urea applications increased. Soluble solid concentration, pH, titratable acidity, and total polyphenol concentration were not different among treatments. There was a positive correlation between increased urea application rate and the maximum fermentation rate, which resulted in a shorter fermentation duration. Increasing the number of urea applications was also correlated with greater hydrogen sulfide (H2S) production in juice fermented from fruit harvested in 2017 but not for fruit harvested in 2018. No residual H2S was found in the finished cider from any treatment. Increasing the number of urea applications was estimated to be less expensive than supplementing the juice with Fermaid O™. There would have been no cost savings if Fermaid K™ was used as an exogenous nitrogen source. Foliar urea applications were estimated to be more expensive than supplementing juice with diammonium phosphate. This study demonstrated that foliar urea applications can effectively increase YAN concentration in cider apples while not negatively affecting other juice quality attributes.

Foliar Application of an Amino Acid-Enriched Urea Fertilizer on ‘Greco’ Grapevines at Full Veraison Increases Berry Yeast-Assimilable Nitrogen Content

Reaching a sufficient yeast assimilable nitrogen (YAN) content in berries at harvest is considered a main viticultural goal for wine-making, because low YANs can slow down must fermentation and have negative effects on wine sensory attributes. For this reason, many attempts have been made to define correct fertilization strategies to stimulate YAN accumulation in the berries. Foliar application of amino acid-enriched urea fertilizer is considered a promising environmentally friendly strategy for improving the yield and nutrient efficiency of plants. The aim of this two-year research was to study the effects of two fertilizers based on urea enriched with amino acids applied at low doses in diverse phenological stages on berry YAN concentration in ‘Greco’ grapevines. The results of this study indicate that amino acid-enriched urea fertilizers induced an increase in YANs in the ‘Greco’ berries at harvest, but only when the application was undertaken at full veraison. Foliar applications applied at veraison onset or post-veraison appeared to be ineffective. In addition, the fertilizers enhanced YAN accumulation in the berry without modifying the other composition parameters measured in this study (total soluble solids, titratable acidity, pH and malic acid). Therefore, the results of our study suggest that foliar application of urea fertilizers enriched with amino acids is an effective strategy to increase yeast-assimilable nitrogen concentration in grapevine berries at harvest.