Browsing by Author "Boudreau, Thomas F. IV"
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- Crop Load Density Affects 'York' Apple Juice and Hard Cider QualityPeck, Gregory M.; Boudreau, Thomas F. IV; McGuire, Megan N.; Stewart, Amanda C. (2016-09-01)To assess the impact crop load has on hard cider chemistry, ‘York’ apple (Malus3domestica Borkh.) trees were hand thinned to three different crop loads: low [two apples per cm2 branch cross-sectional area (BCSA)], medium (four apples per BCSA), and high (six apples per BCSA). Higher crop loads produced smaller, less acidic fruit that were slightly more mature. In juice made from fruit from these treatments, the total polyphenol content did not differ at harvest, but, after fermentation, the medium crop load had 27% and the high crop load had 37%greater total polyphenol content than the low crop load. Yeast assimilable nitrogen (YAN) concentration in juice made from fruit from the low crop load treatment had 18%and 22% greater than the medium and high crop load, respectively. YAN concentrations in juice from the medium and high crop load treatments were similar. Our results provide apple growers and hard cider producers with a better understanding of how apple crop load impacts YAN concentrations in juice and total polyphenol concentrations in juice and cider.
- The Effect of Fungicide Residues and Yeast Assimilable Nitrogen on Fermentation Kinetics and H2S Production during Cider FermentationBoudreau, Thomas F. IV (Virginia Tech, 2016-07-06)The Virginia cider industry has grown rapidly in the past decade, and demands research-based recommendations for cider fermentation. This study evaluated relationships between the unique chemistry of apples and production of hydrogen sulfide (H2S) in cider fermentations. Yeast assimilable nitrogen (YAN) concentration and composition and residual fungicides influence H2S production by yeast during fermentation, but these factors have to date only been studied in wine grape fermentations. This study surveyed 12 Virginia-grown apple cultivars and found that the majority were severely deficient in YAN. The effects of three fungicides on cider fermentation were investigated; elemental sulfur, fludioxonil and fenbuconazole. Fenbuconazole adversely impacted fermentation kinetics. Sulfur and fludioxonil marginally impacted fermentation kinetics. Sulfur increased H2S production, but fludioxonil and fenbuconazole did not affect H2S production. There was no difference in fermentation kinetics and H2S between nitrogen sources arginine (approximating grape), asparagine (approximating apple) and ammonium (YAN supplement). Supplementation with methionine resulted in increased fermentation rate and decreased H2S production. The detrimental effects of fenbuconazole and beneficial effects of methionine were diminished with increasing total YAN. Contrary to previous findings, the most H2S was formed at 153 mg/L YAN which is above the generally recommended minimum to prevent H2S formation. These results indicate that apple juice chemistry may influence yeast metabolism during cider fermentation, in ways that have not been previously studied in grape fermentation. Our findings indicate the need for and contribute to the development of targeted fermentation management practices for cidermaking.
- Free amino nitrogen concentration correlates to total yeast assimilable nitrogen concentration in apple juiceBoudreau, Thomas F. IV; Peck, Gregory M.; O'Keefe, Sean F.; Stewart, Amanda C. (Wiley, 2017-09-12)Yeast assimilable nitrogen (YAN) is essential for yeast growth and metabolism during apple (Malus x domestica Borkh.) cider fermentation. YAN concentration and composition can impact cider fermentation kinetics and the formation of volatile aroma compounds by yeast. The YAN concentration and composition of apples grown in Virginia, USA over the course of two seasons was determined through analysis of both free amino nitrogen (FAN) and ammonium ion concentration. FAN was the largest fraction of YAN, with a mean value of 51 mg N L⁻¹ FAN compared to 9 mg N L⁻¹ ammonium. Observed YAN values ranged from nine to 249 mg N L⁻¹, with a mean value of 59 mg N L⁻¹. Ninety-four percent of all samples analyzed in this study contained <140 mg N L⁻¹ YAN, a concentration generally considered the minimum level needed in grape-based wines for yeast to fully utilize all of the fermentable sugars. FAN concentration was correlated with total YAN concentration, but ammonium concentration was not. Likewise, there was no correlation between FAN and ammonium concentration.
- Hydrogen sulphide production during cider fermentation is moderated by pre‐fermentation methionine additionBoudreau, Thomas F. IV; Peck, Gregory M.; Ma, Sihui; Patrick, Nicholas; Duncan, Susan E.; O'Keefe, Sean F.; Stewart, Amanda C. (Wiley-Blackwell, 2017-08-15)Yeast assimilable nitrogen (YAN) concentration and composition impact hydrogen sulphide (H2S) production and fermentation kinetics during wine fermentation, but this phenomenon has not been extensively studied in cider fermentation. Our hypothesis was that H2S production during cider fermentation could be decreased through pre‐fermentation modification of concentrations of individual amino acids. Apple juice (53 mg L−1 YAN) was supplemented with asparagine, arginine, methionine or ammonium and fermented with EC1118 and UCD522 yeast strains. No difference in H2S production among fermentations was observed with addition of asparagine, arginine or ammonium. Methionine addition of 5 mg L−1 decreased H2S production by yeast strain EC1118 at 53 mg L−1 YAN. With 153 mg L−1 initial YAN, only methionine addition of 50 mg L−1 decreased H2S production, and no tested methionine rates decreased H2S production with 253 mg L−1 initial YAN. Supplementation to 153 mg L−1 YAN resulted in increased H2S production at all methionine concentrations tested. Sensory differences in aroma were detected in samples supplemented with ammonium and methionine, and these differences were correlated with observed differences in H2S production. Our results indicate that supplementing cider fermentations with methionine leads to lower H2S formation, especially in apple juice containing low YAN.
- The interactive effect of fungicide residues and yeast assimilable nitrogen on fermentation kinetics and hydrogen sulfide production during cider fermentationBoudreau, Thomas F. IV; Peck, Gregory M.; O'Keefe, Sean F.; Stewart, Amanda C. (Wiley-Blackwell, 2017-01-30)BACKGROUND Fungicide residues on fruit may adversely affect yeast during cider fermentation, leading to sluggish or stuck fermentation or the production of hydrogen sulfide (H₂S), which is an undesirable aroma compound. This phenomenon has been studied in grape fermentation but not in apple fermentation. Low nitrogen availability, which is characteristic of apples, may further exacerbate the effects of fungicides on yeast during fermentation. The present study explored the effects of three fungicides: elemental sulfur (S⁰) (known to result in increased H₂S in wine); fenbuconazole (used in orchards but not vineyards); and fludioxonil (used in post-harvest storage of apples). RESULTS Only S⁰ led to increased H2S production. Fenbuconazole (≥0.2 mg L⁻¹) resulted in a decreased fermentation rate and increased residual sugar. An interactive effect of yeast assimilable nitrogen (YAN) concentration and fenbuconazole was observed such that increasing the YAN concentration alleviated the negative effects of fenbuconazole on fermentation kinetics. CONCLUSION Cidermakers should be aware that residual fenbuconazole (as low as 0.2 mg L⁻¹) in apple juice may lead to stuck fermentation, especially when the YAN concentration is below 250 mg L⁻¹. These results indicate that fermentation problems attributed to low YAN may be caused or exacerbated by additional factors such as fungicide residues, which have a greater impact on fermentation performance under low YAN conditions.