CIDER PRODUCTION FROM VIRGINIA-GROWN APPLES: DEVELOPMENT OF RESEARCH-BASED FERMENTATION AND FLAVOR IMPROVEMENT STRATEGIES

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1012969
• Project Start Date: Oct 1, 2017
• Project End Date: Sep 30, 2022
• Program Code: [(N/A)]- (N/A)

Recipient Organization
VIRGINIA POLYTECHNIC INSTITUTE
(N/A)
BLACKSBURG,VA 24061

Performing Department
Food Science & Technology

Non Technical Summary
Virginia apple growers work diligently year in and year out to produce high quality fruit. By improving process yield, tannin retention and fermentation management in cider production, Virginia apples will be consistently transformed into world-class cider. The proposed five year project will lead to reliable, optimized processing and tannin management strategies for cider production and will increase the value of specialty crops in Virginia. The expansion of cider production supports existing farmers by providing additional value-added outlets for specialty crops grown in the Commonwealth. The project we are proposing will make Virginia's cider producers and apple growers more competitive by providing research-based processing and tannin retention strategies for production of consistent, high quality cider from Virginia-grown apples.

Animal Health Component

80%

Research Effort Categories

Basic

20%

Applied

80%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
701	1110	2000	50%
501	1110	1000	50%

Knowledge Area
501 - New and Improved Food Processing Technologies; 701 - Nutrient Composition of Food;

Subject Of Investigation
1110 - Apple;

Field Of Science
1000 - Biochemistry and biophysics; 2000 - Chemistry;

Keywords

malus xdomestica

apple

cider

fermentation

polyphenol

Goals / Objectives
ObjectivesThe three main objectives for this project are:1. Yeast assimilable nitrogen optimization for cider fermentation.(a) Survey yeast assimilable nitrogen concentration in Virginia cider apples, and determine pre-fermentation amino acid profiles in juice from apple cultivars used for cider production.(b)Evaluate the impacts of differences between grape and apple YAN composition and concentration on fermentation performance.(c) Based on the outcomes of these experiments, develop practical recommendations specific for nitrogen management in cider fermentation.2. Improve tannin concentration in apples used for cidermaking.(a) Work collaboratively with horticulture researchers for improved cultivar selection and development of orchard management strategies to increase tannin concentration in fruit from existing dual-purpose plantings, and to improve tannin retention through the cider production process. (b) Evaluate tannin analytical techniques and make practical recommendations for tannin analysis procedures in cider production research.3. Communicate the results of this research within a framework of cider fermentation best-practices to Virginia cidermakers through at least two Extension workshops on Cider Production and Cider Fermentation organized by Virginia Tech research and extension faculty from Food Science & Technology and Horticulture Departments, and through numbered Virginia Cooperative Extension publications, and the Virginia Tree Fruit Horticulture website.

Project Methods
Procedures for Objective 1: Yeast assimilable nitrogen optimization for cider fermentation.Pursuant to Objective 1a, we will collect fruit grown in the cider apple variety trial at the Virgina Tech Alson H. Smith, JR Agricultural Research and Extension Center (AREC) in Winchester, VA. We will use fruit from a variety of cultivars (targeting 8-15 cultivars, depending on availability in Year 1 and Year 2). These fruit will be milled and pressed to yield juice, comparable to juice that would serve as the starting material for cider production. The yeast assimilable nitrogen (YAN) concentration will be measured in the resulting juice pre-fermentation using a commercially available kit to determine the primary amino nitrogen concentration, and the ammonium ion concentration will be determined using an ion-specific electrode. This data set will add to the very limited information currently available on YAN concentration in apples, and will serve to provide a baseline for YAN concentration in apples grown in Virginia. Two-way ANOVA (analysis of variance) followed by Tukey's HSD (honest significant difference) will be used to determine whether there are differences in total YAN concentration among cultivars grown under the same conditions within a single year, and whether there are differences in YAN between the two growing seasons. These data will be published in an appropriate peer-reviewed journal targeted for beverage fermentation. Amino acid concentrations will be determined using fruit from 8-15 cultivars (depending on availability) from one growing season, also sourced from the Alson H. Smith, Jr. AREC. A Waters AccQ-Tag amino acid analysis kit will be used in conjunction with a Waters UPLC-PDA system (Waters Corporation, Milford, MA) to identify and quantify 18 amino acids in each sample. One-way ANOVA followed by Tukey's HSD will be used to determine whether there are differences in the concentration of each amino acid among the cultivars included in the study. The amino acid profiles by cultivar will also be published in an appropriate peer-reviewed journal. This information will add to the limited body of knowledge on amino acid composition of apples.Pursuant to Objective 1b, we will compare amino acid composition of apples determined in Objective 1a to that of grapes (data available in peer-reviewed literature, and from prior work in our lab, unpublished). This will provide a starting point for investigations of how differences in YAN concentration and composition between grapes and apples may impact fermentation through influencing the production of volatile aroma compounds by yeast. This work will address aroma compounds imparting both positive and negative characteristics to cider. Based on the results of Objective 1a, we will investigate the impact of amino acid composition on yeast metabolism during fermentation. The specific experiments to be conducted will be defined based on the results of Objective 1a, but will involve pre-fermentation modification of amino acid concentration and composition in apple juice, followed by fermentation monitoring and analysis of finished cider. We will evaluate both analytical and sensory outcomes. One-way ANOVA followed by Tukey's HSD will be conducted to determine if modification of amino acid profiles results in differences in the observed outcomes. If differences are observed, we will use sensory preference tests to determine which treatment resulted in cider most preferred by consumers, and then make practical recommendations for pre-fermentation juice chemistry adjustment that will result in the most preferred cider.Procedures for Objective 2: Improve tannin concentration in apples used for cidermaking.For Objective 2a, we will work with horticulture researchers to evaluate the extent to which orchard management practices impact tannin (polyphenol) concentration and composition in fruit. Management practices we will evaluate include: crop load, sunlight exposure, foliar nitrogen applications. Whenever possible given the plantings available to work with during each season, we will employ three treatment levels per experiment in the field. We will then harvest the fruit and perform fruit maturity analyses on a representative sample of apples in each treatment lot. Juice will then be made from the bulk fruit for each treatment, and that juice will be fermented to produce cider. We will evaluate juice and cider chemistry parameters including Brix, titratable acidity, pH, residual sugar, yeast assimilable nitrogen (YAN) concentration, and total polyphenols. One-way ANOVA followed by Tukey's HSD will be used to determine whether there are differences between the treatments. We will then make practical orchard management recommendations for cider chemistry improvement to growers interested in selling fruit for cidermaking. Pursuant to Objective 2b, to ensure that the outcomes of these experiments are relevant and translatable to other researchers, we will also assess the differences in results obtained when four common tannin analytical techniques are applied to cider and apple juice. Six commercially available ciders of different styles will be selected for analysis. Two apple juice samples will also be included. Juice will be prepared using a bench scale Champion Juicer (Champion, Lodi, CA). One sample will be prepared under oxidative conditions (no antioxidant), and another sample will be prepared from the same fruit but with an antioxidant added at pressing.We will compare the following analytical methods for cider and juice tannin analysis:Lowenthal Permanganate Titration (Lea et al., 1978)Folin-Ciocalteu (Waterhouse, 2002)DMAC (Payne et al., 2010)BSA protein precipitation (Boulet et al., 2015)The above standard analytical methods are described in detail in the cited references. All of these methods with the exception of the Lowenthal permanganate titration have been performed on grape, apple, or cocoa substrates in Dr. Amanda Stewart's and/or Dr. Andrew Neilson's laboratories in prior work, and are simple and economical enough to be employed in routine horticultural and cider fermentation research. We will also determine the mean degree of polymerization (mDP) of polyphenols in each sample, as described by Dorenkott (Dorenkott et al., 2014). The mDP results will provide information about the relative size of polyphenol polymers in the sample and provide insight as to how the size of the tannin complexes in the sample, may influence the results among the analytical methods evaluated in this study. Data will be analyzed using one-way ANOVA followed by Tukey's HSD to determine whether tannin concentration results differ among analytical techniques, and if so, which results are significantly different. We will assess the correlations between results from the four techniques using linear regression. We will then use the preferred analytical method moving forward with investigations of the impact of processing methods on tannin improvement in cider apples and retention through the cidermaking process. Tannin retention improvement strategies we will investigate include (1) pre-fermentation maceration of milled fruit, (2) purging the headspace with nitrogen gas or CO2 gas during pressing to displace oxygen and reduce losses of tannins to oxidation, and (3) fermentation on skins.Procedures for Objective 3: Communicate the results of this research to stakeholders Effective communicationand practical recommendations derived from these results will involve several modes of dissemination of information. We anticipate holding workshops and field days open to cider industry members in Virginia and the region, and publishing research reports and extension publications on the Virginia Tree Fruit Horticulture website, and numbered Extension publications published by Virginia Cooperative Extension, as well aspublicationsin relevant peer-reviewed journals.

Progress 10/01/19 to 09/30/20

Outputs
Target Audience:Students, Agricultural producers, fellow scientists, faculty, rural commodity group leaders & groups, agricultural consultants, food processors, educators (extension agents), academic peers/researchers Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project provided an opportunity for two MS students to conduct research in cider processing and fermentation. These students have presented their work at a variety of local, state and national industry meetings, academic conferences, and even to an international industry partner through web-based meetings. Students were provided guidance in analytical techniques as well as in preparation and presentation strategies for communicating to different audiences. The project has also allowed Dr. Stewart to take a leadership role in program development for the World Brewing Congress through her service in the American Society for Brewing Chemists, wherein she will organize a session on cider production for this international meeting in 2021. This project allowed her to build a broad base of cider research projects, and thus gain the international recognition for expertise in cider production and cider fermentation research required to provide this international professional service. How have the results been disseminated to communities of interest?We have presented these findings in several different venues, to reach a broad section of our stakeholder audience. Venues include: Cider Institue of North America (CINA) Foundations of Cider and Perry Production Workshop (Blacksburg, VA March 2020; online courses in summer and fall 2020) World Brewing Congress (hosted by the American Society for Brewing Chemists) (online Aug. 2020) What do you plan to do during the next reporting period to accomplish the goals?Objective 1: Yeast assimilabe nitrogen optimization in cider fermentation. In the next reporting period, we intend to evaluate the effects of yeast assimilable nitrogen concentration and composition on the chemical and sensory characteristics of ciders produced using un-inoculated or "ambient" fermentations. Objective 2: Improve tannin concentration in apples used for cidermaking. In the next reporting period, we intend to evaluate different types of exogenous tannin additionsin ciderand theeffects of these additions on sensoryperception of bitterness and astringency in cider. Objective 3: Dissemination of information to stakeholders In 2020 Ipartnered with the Cider Institute of North America (CINA) to bring their popular international curriculum for Cider and Perry Production Foundations to Virginia Tech, through a week-long Virginia Cooperative Extension workshop in Blacksburg, VA. This was very well-received and has continued in the online format. I plan to continue to work with the online CINA team, and bring in-person workshops back to Virginia as soon as the COVID-19 situation allows. I will continue to move completed research toward publication in peer-reviewed journals. I will continue to move completed research toward publication in numbered Virginia Cooperative Extension publications. I will also continue to mentor one or two graduate students in ongoing research projects pertaining to Objectives 1 and 2 of this project.

Impacts
What was accomplished under these goals? Objective 1: Yeast assimilable nitrogen optimization for cider fermentation. Accomplishments under Objective 1. In this reporting period, nitrogen-rich yeast nutrient productswere evaluated for their potential to decrease the amount of hydrogen sulfide produced during cider fermentation. Hydrogen sulfide is a common off-aroma occurring in cider fermentation,best described as "rotten egg." The aroma isproduced by stressed yeast during beverage fermentation, and the lack of adequate nitrogen for yeast growth and metabolism is believed to be the primary cause of this problem. We evaluated the effects of four different yeast nutrients(including one new experimental nutrient) in three yeast strains commonly used for cider fermentation.We found that while the type of yeast nutrient product used did influencehydrogen sulfide production, the yeast strain selection was actually the mostimportant factor determining the amount of hydrogen sulfide produced during fermentation. This points to the need to emphasize proper yeast strain selectionin cider making as much or even more than yeast nutrient regimes in order to limit hydrogen sulfide production. Another interesting and unexpected development during this reporting period was the discovery that hydrogen sulfide production rates vary tremendously among different types of apple juice concentrate, even when the yeast assimilable nitrogen concentration is equal. This is further evidence that other potentially overlooked juice chemistry paramters also influence hydrogen sulfide production. We are partnering with a group of researchers at Washington State University who have previously worked with vitamins and beverage fermentation to further investigate the potential factors underlying these observations. Objective 2: Improve tannin concentration in apples used for cidermaking. Accomplishments under objective 2: In this reporting period, we submitted a manuscript to a peer-reviewed journal outlining the impacts of high-tannin apple cultivars on cider fermentation and flavor. This manuscript has been accepted with minor revisions, and we expect it to be published in 2021. Objective 3: Communicate the results of this research within a framework of cider fermentation best-practices to Virginia cidermakers through at least two Extension workshops on Cider Production and Cider Fermentation organized by Virginia Tech research and extension faculty from Food Science & Technology and Horticulture Departments, through numbered Virginia Cooperative Extension publications, and the Virginia Tree Fruit Horticulture website. Accomplishments under Objective 3: An update on these research results in the broader context of general education about cider chemistry and cider production was given at the 2020 Cider Institute of North America "Foundations of Cider and Perry Production" courses in March 2020 (Blacksburg, VA), Summer 2020 (online), and Fall 2020 (online).

Publications

• Type: Journal Articles Status: Awaiting Publication Year Published: 2020 Citation: Kessinger, J., G. Earnhart, L. Hamilton, K. Phetxumphou, C. Neill, A.C. Stewart, J. Lahne. 2020. Exploring Perceptions and Categorization of Virginia Hard Ciders through the Application of Sorting Tasks. Journal of the American Society of Brewing Chemists. Published online 17 Dec. 2020. in press
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Karl, A.D., M.G. Brown, S. Ma, A. Sandbrook, A.C. Stewart, L. Cheng, A.K. Mansfield, G.M. Peck. 2020. Soil Nitrogen Fertilization Increases Yeast Assimilable Nitrogen Concentrations in 'Golden Russet' and 'Medaille d'Or' Apples Used for Cider Production. HortScience. 55(8): 1356-1364.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Karl, A.D., M.G. Brown, S. Ma, A. Sandbrook, A.C. Stewart, L. Cheng, A.K. Mansfield, G.M. Peck. 2020. Foliar urea applications increase yeast assimilable nitrogen concentration and alcoholic fermentation rate in 'Red Spy' apples used for cider production. HortScience. 55(8): 1356-1364.
• Type: Theses/Dissertations Status: Other Year Published: 2020 Citation: Moore, Amy. MS Thesis. Deposited April 2020. Impact of Yeast Nutrient Supplementation Strategies on Hydrogen Sulfide Production during Cider Fermentation. MS thesis deposited with VT, embargo for 1yr pending publication in peer-reviewed journal.
• Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Moore, A., J. Lahne, E. Burzynski-Chang, G. Earnhart, B. Wiersema, K. Phetxumphou, L. Hamilton, A. C. Stewart. 2020. Impact of Yeast Nutrient Supplementation on Hydrogen Sulfide Production during Cider Fermentation. World Brewing Congress (poster presentation was online for 2020 due to COVID-19).

Progress 10/01/18 to 09/30/19

Outputs
Target Audience:Students, Agricultural producers, fellow scientists, faculty, rural commodity group leaders & groups, agricultural consultants, food processors, educators (extension agents), academic peers/researchers Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project provided an opportunity for a PhD and two MS students to conduct research in cider processing and fermentation. These students have presented their work at a variety of local, state and national industry meetings, academic conferences, and even to an international industry partner through web-based meetings. Students were provided guidance in analytical techniques as well as in preparation and presentation strategies for communicating to different audiences. One MS student working on this project gave a presentation on cider fermentation to a community group of master gardeners. The project has also allowed Dr. Stewart to take a leadership role in program development for the World Brewing Congress through her service in the American Society for Brewing Chemists, wherein she will organize a session on cider production for this international meeting in 2020. This project allowed her to build a broad base of cider research projects, and thus gain the international recognition for expertise in cider production and cider fermentation research required to provide this international professional service. How have the results been disseminated to communities of interest?An update on theresearch results from this reporting period in the broader context of general education about cider chemistry and cider production was given at the 2019 Virginia Association of Cidermakers annual meeting. This meeting also provided an opportunity for our team to solicit stakeholder feedback to help formulate our plans for 2020. What do you plan to do during the next reporting period to accomplish the goals?Based on stakeholder feedback from the 2019 Virginia Association of Cidermakers annual meeting, I have partnered with the Cider Institute of North America (CINA) to bring their popular international curriculum for Cider and Perry Production Foundations to Virginia Tech, through a week-long Virginia Cooperative Extension workshop in Blacksburg, VA. I will continue to move completed research toward publication in peer-reviewed journals. I will continue to move completed research toward publication in numbered Virginia Cooperative Extension publications. I will also continue to mentor two graduate students in ongoing research projects pertaining to Objectives 1 and 2 of this project.

Impacts
What was accomplished under these goals? Objective 1: Yeast assimilable nitrogen optimization for cider fermentation. Accomplishments under Objective 1. In this reporting period, the interactive effects of apple tannin concentration and composition and yeast assimilable nitrogen requirements were evaluated. We found that for certain high value apples that are very rich in the tannins that impart desirable sensory characteristics of bitterness and astringency, the fermentation rate may be slower than for apples low in tannins. This slow fermentation rate can be improved in some cases through addition of yeast assimilable nitrogen. Perhaps more importantly, we found that when high-tannin apple cultivars are fermentedusing certain yeast strains commonly used in cider production, the aroma of the cider containing high tannins can be dramatically different, taking on notes of smoky, clove and spicy. This demonstrates the potential of fermented beverages made from high-tannin fruit to differ not only in bitterness and astringency, but also in aroma. These effects were also influenced by the type and concentration of yeast assimilable nitrogen added to a given ferment. Objective 2: Improve tannin concentration in apples used for cidermaking. Accomplishments under Objective 2: The project described under Objective 1 evaluated effects of yeast assimilable nitrogen and tannin concentration. It contributes to both Objectives 1 and 2. Objective 3: Communicate the results of this research within a framework of cider fermentation best-practices to Virginia cidermakers through at least two Extension workshops on Cider Production and Cider Fermentation organized by Virginia Tech research and extension faculty from Food Science & Technology andHorticulture Departments, through numbered Virginia Cooperative Extension publications, and the Virginia Tree Fruit Horticulture website. Accomplishments under Objective 3: An update on these research results in the broader context of general education about cider chemistry and cider production was given at the 2019 Virginia Association of Cidermakers annual meeting.

Publications

• Type: Journal Articles Status: Published Year Published: 2018 Citation: Juice Clarification with Pectinase Reduces Yeast Assimilable Nitrogen in Apple Juice without Affecting the Polyphenol Composition in Cider. S. Ma, A. Neilson, J. Lahne, G. Peck, S. O'Keefe, E.K. Hurley, A. Sandbrook, A. Stewart. Journal of Food Science. 83(11): 2772-2781. 2018.
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Management of apple maturity and postharvest storage conditions to increase polyphenols in cider. B. Ewing, G. M. Peck, S. Ma, A.P. Neilson, A.C. Stewart. HortScience. 54(1): 143-148. 2019.
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Comparison of Common Analytical Methods for the Quantification of Total Polyphenols and Flavanols in Fruit Juices and Ciders. S. Ma, C. Kim, A.P. Neilson, L.E. Griffin, G.M. Peck, S.F. O'Keefe, A.C. Stewart. Journal of Food Science. 84(8): 2147-2158.
• Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Polyphenol quantification in fruits: Determination of the contribution of individual polyphenols to quantitative results of four common analytical methods. S. Ma, C. Kim, A. Neilson, S. O'Keefe, G. Peck, A. Stewart. Abstracts of Papers of the American Chemical Society. Vol. 257. Oral presentation at the annual conference of the American Chemical Society.
• Type: Conference Papers and Presentations Status: Other Year Published: 2019 Citation: Chemistry Considerations for Cider Fermentation. Moderated group panel discussion on cider production techniques. Virginia Association of Cidermakers Annual Meeting, North Garden, VA. July 22, 2019.
• Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Cider production from high-tannin cultivars: Improved fermentation management strategies. P. Cairns, K. Racine, K. Phetxumphou, A. Moore, S. Ma, D. Gallagher, J. Lahne, H. Huang, A.C. Stewart. American Society for Brewing Chemists Annual Conference. New Orleans, LA, USA. June 22-24, 2019.

Progress 10/01/17 to 09/30/18

Outputs
Target Audience:Students Agricultural producers fellow scientist, faculty rural commodity group leaders & groups agricultural consultants, food processors educators (extension agents) academic peers/researchers Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project provided an opportunity for a PhD student to conduct research in cider processing and fermentation. This project provided the inspiration for a course module to be developed wherein undergraduate students studied the impact of fruit chemistry on cider fermentation. In this case, cider fermentation research served as a case study in the effects of fruit chemistry on the outcome of fermentation. How have the results been disseminated to communities of interest?The PhD student working on this project presented an educational and research-update talk to a group of approximately 30 cidermakers at an industry forum in the summer of 2018. (Albemarle Cidermakers Forum, North Garden, VA 6/9/2018) An oral presentation on the YAN and amino acid work outlined in Objective 1 was provided to an audience of approximately 100 cidermakers and industry suppliers at CiderCon, the cider industry conference for North America (CiderCon, Baltimore, MD, 2/2/2018) What do you plan to do during the next reporting period to accomplish the goals?We plan to continue to evaluate the impact of differences between grape and apple YAN composition and concentration on fermentation performance, and based on the outcome of projects related to this project we will develop practical recommendations for nitrogen management in cider fermentation. We plan to host a cider production workshop targeting Virginia and regionalcidermakers to disseminate the results of our work to communities of interest.

Impacts
What was accomplished under these goals? Progress report, year 1 of 5 year project. Accomplishments will be listed in relation to the stated objectives and goals: Objective 1: Yeast assimilable nitrogen optimization for cider fermentation. Accomplishments under Objective 1: A survey of yeast assimilable nitrogen concentration in Virginia cider apples was completed. The range of values observed was broad and average values were much lower than the amount of nitrogen typically required by yeast to complete fermentation. This demonstrates the need for cider producers in Virginia to be aware of the potential for nitrogen deficiency in cider fermentation and to take steps to supplement apple juice with exogenous sources of nitrogenprior to fermentation. Amino acid profiles in Virginia cider apples were characterized. Amino acids serve as precursors to aromas developed by yeast during fermentation. The results of this work showed that the amino acid composition of cider apples is different than that of grapes, in ways that have potential to impact the aromas developed by yeast during fermentation. This knowledge will inform the selection of yeast strains and the development of yeast nutrient products specifically for the development of desirable aromas during cider fermentation. Objective 2: Improve tannin concentration in apples used for cidermaking. A study on the effect of harvest maturity and post-harvest storage on tannin content in apples was conducted. Our results indicate that post-harvest storage of apples at 1C and at 10C can lead to significantly increased tannin concentrations in apples, but that the extent of these effects differs by cultivar. This stragegy can be employed by cidermakers seeking to increase the tannin concentration in cider.

Publications

• Type: Journal Articles Status: Published Year Published: 2018 Citation: Free amino acid composition of apple juices with potential for cider making as determined by UPLC-PDA. S Ma, AP Neilson, J Lahne, GM Peck, SF O'Keefe, AC Stewart. Journal of the Institute of Brewing 124 (4), 467-476
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Free amino nitrogen concentration correlates to total yeast assimilable nitrogen concentration in apple juice. TF Boudreau IV, GM Peck, SF O'Keefe, AC Stewart. Food science & nutrition 6 (1), 119-123, 2018
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Hydrogen sulphide production during cider fermentation is moderated by pre-fermentation methionine addition TF Boudreau IV, GM Peck, S Ma, N Patrick, S Duncan, SF O'Keefe, ... Journal of the Institute of Brewing 123 (4), 553-561, 2017
• Type: Journal Articles Status: Published Year Published: 2017 Citation: The interactive effect of fungicide residues and yeast assimilable nitrogen on fermentation kinetics and hydrogen sulfide production during cider fermenation. TF Boudreau, GM Peck, SF O'Keefe, AC Stewart. Journal of the Science of Food and Agriculture 97 (2), 693-704, 2017.