DIFFICULT TO FERMENT JUICES: STRATEGIES FOR FERMENTATION MANAGEMENT Linda F. Bisson Department of Viticulture and Enology, UCD

Types of Difficult to Ferment Juices High Brix High Rot/High Bioload Vineyard Site Issues Varietal/Rootstock Issues

High Brix (Long Hang Time) High sugar means high ethanol Increased demand for nutrients with increasing Brix, may be as much as two-fold Long Hang Time means more juice seepage Increased potential for inhibitory lactic acid bacteria populations on surface of fruit Higher pH of juice, greater activity of spoilage microbes in winery Higher SO 2 demand of juice

High Rot High microbial bioloads in juice Greater competition for nutrients Increased production of inhibitory compounds negatively impacting fermentation progression Higher SO 2 demands Nutrient level and timing of addition critical to assure feeding the right population Temperature critical to fostering development of right population (too warm favors bacteria, too cold favors spoilage yeast)

Vineyard Site Issues Poor Soils Chronically Nutrient Deficient Juices Nutrient supplementation not always effective Complex nutrients needed Presence of fermentation/growth inhibitors from the vine High Disease/Pest Pressure Poor fruit nutrient content Presence of fermentation/growth inhibitors from the vine

Variety/Rootstock Issues Variation in fermentation progression as a function of rootstock Often a soil composition component More severe with some varietals/clones than others

First Study Nitrogen Status and Fermentation Dynamics for Merlot on Two Rootstocks Christine M. Stockert, Linda F. Bisson, Douglas O. Adams and David R. Smart AJEV

Outline of Study Compare impact of N fertilization at two seasonal time points: fall and spring on two rootstocks, Mgt and 1103P Merlot clone 1 used as scion Assessed leaf %N and fruit amino nitrogen composition Monitored fermentation dynamics

Questions to be addressed: Is Leaf %N correlated with amino acid composition of grapes? Can Leaf %N predict fermentation performance? Do rootstocks differ in uptake and utilization of N with respect to berry composition?

Details of Merlot Trial Experiment was carried out in the UCD vineyard in Oakville, California The vines were in their tenth year and trained as bilateral cordons with vertical shoot positioning (VSP) The trellis height was 1.6 m and the canopy was hedged to 2.2 m. The rows were oriented SE to NW and spaced 2.4 x 2.2 m between and within rows respectively Vines on 1103P were established and managed with 28 nodes while those on Mgt were established and managed with 24 nodes A randomized complete block design with six blocks was used. Each block consisted of subplots of six vines per rootstock x treatment combination

Details of Experimental Design The Spring fertilized treatment was 16.8 kg N/ha applied on 18 May 2005 and the Fall fertilized treatment was 16.8 kg N/ha applied on 7 October 2004 using potassium nitrate (36.94% K, 13.75% N) applied through the drip line The vines were deficit irrigated bi-weekly with 40% replacement of crop ET c, which totaled 60 mm over the course of the summer. Irrigation water and fertigation solution were delivered via one 3.8 L/hr drip emitter per vine, located 50 cm from each trunk.

Results Leaf N levels similar for both rootstocks Mgt had fewer leaves, less total canopy nitrogen Leaf number but not nitrogen level per leaf associated with nutrient deficiency caused by rootstock

Results: Fermentation

Results: Juice Nitrogen Analysis Nitrogen1103 Control Spring N Fall N Mgt Control Spring N Fall N Total Free AA, mg/L Arginine, mg/L Proline, mg/L YAN/YNAN Pro/Arg

Questions to be addressed: Is Leaf %N correlated with amino acid composition of grapes? NO Can Leaf %N predict fermentation performance? NO Do rootstocks differ in uptake and utilization of N with respect to berry composition? YES

Conclusions Grape/Juice N varies by rootstock Nitrogen additions in vineyard might not impact juice YAN as much as thought Yeast YAN not predictable from Vineyard N assessments, although there is often a trend Sluggish juices are characterized by low YAN/YNAN and high Proline/Arginine ratios

Second Study Difficult to Ferment Coastal Chardonnay Juices Priyanka Dhar, Aline Cresswell, Vidhya Ramakrishnan, Gordon Walker

The Issues: Vineyard blocks characterized by low vine N Vine N less responsive to N application than other blocks in vineyard Chronic issues with fermentation progression Yeast fermentation does not respond to yeast nutrient addition

Fermentation Results: Yeast Strains Used in Study Yeast Strain Restart Stuck Temp. Range Ferm. Speed Competitive Factor Alcohol Tolerance Relative Nitrogen Needs Lalvin ICV- D254 Lowest12-28ModerateNeutral16Medium Lalvin Rhone 2226 Moderate15-28FastActive18High Uvaferm 43Highest13-35FastNeutral18+Low

Fermentation Results

Easy to ferment juices generally finished in 8 days at fermentation temperatures of 60° F UV43 in Napa juice took 12 days In difficult to ferment juice, strains took days to complete fermentation

Amino Acid Composition of Juices 2010 Vintage JuiceFANYAN/YNANProline/ Arginine Dry Creek Napa J Lohr Difficult J Lohr Easy KAC

Amino Acid Composition of Juices 2011, 2012 Vintages JuiceFANYAN/YNANProline/ Arginine J Lohr 2010 Difficult J Lohr 2011 Difficult J Lohr 2012 Difficult J Lohr 2012 Easy

Fermentation Results 2012

Conclusions from Chardonnay Study Difficult to ferment Chardonnay juices also show low YAN/YNAN ratios and high Proline/Arginine ratios Nutrient supplementation does not affect rate of fermentation of difficult to ferment juices Also a rootstock effect? Difficult to ferment Chardonnay is Clone 5 on 5C

Overall Conclusions Difficult to ferment juices are challenging to yeasts regardless of innate nutritional requirements Difficult to ferment juices do not respond to typical yeast nutrient additions in winery Although low in N, it is not clear low N is the reason difficult to ferment juices are so difficult to ferment Correction of problem in vineyard may be challenging as it requires high N applications

Cause of Difficulty in Fermentation? Not chloride or other inhibitory ion Does not respond to ammonium addition Metabolome analysis: yeast have high concentrations of stress-associated metabolites, especially mannitol Not associated with wild lactic activity Oxidative stressors? Inhibitory phenolics/plant metabolites?

Acknowledgements Funding American Vineyard Foundation USDA Viticulture Consortium California Grant Program for Research in Viticulture and Enology Maynard A. Amerine Chair Endowment VEN Department Scholarships