Grape Berry Ripening: Environmental Drivers and Spoilers Bogs et al. (2007) Markus Keller
A winemaker s dream Loose clusters Small berries Uniform composition
Nature s reality Large spatial and temporal variation
Grape berry: A job description Seed production and dispersal Color, aroma = Advertising Sugar = Ticket price photo courtesy B. Bondada
Physiological maturity? Cabernet Sauvignon Normal ripening 25 Brix 1-2 seeds/berry 25 mg/seed 34% seed germination Berry shrivel disorder 14 Brix 1-2 seeds/berry 22 mg/seed 31% seed germination Maturity: State in which fruit is best suited for intended use Hall et al. (2011)
a Solutes (ºBrix) b ph 26 22 18 14 10 6 4.0 3.6 3.2 2.8 2.4 Concord Merlot Concord Merlot Change happens early Rapid changes as berry turns from hard-green (1) to soft-blue (4): Sugar: <8 >18 Brix ph: 2.6 3.1 to 3.7 (cultivar!) Titratable acidity: >25 ~10 g/l Slow changes as berry turns ripe (5: 20-24 Brix), and then overripe (6: >24 Brix) Physiological maximum 23-25 Brix c Organic acids (g/l) 30 25 20 15 10 Concord Merlot Keller & Shrestha (2014) 5 1 2 3 4 5 6 S S Maturity group
Berry size: Much ado about water Berry contains 70-80% water at harvest Water in: Xylem and phloem inflow Water out: Transpiration and xylem backflow Balance between ins and outs determines berry size (limited by skin extensibility) Véraison: Phloem flow, xylem flow reverses Berries less sensitive to soil moisture H 2 O Xylem Phloem Transpiration Ins Phloem inflow V: Xylem inflow V: Outs Transpiration V: - Xylem backflow V:
Berry transpiration facilitates ripening Transpiration is mostly cuticular, increases with berry size, and changes with berry development VPD (temperature, RH) drives transpiration Berry transpiration discharges surplus phloem water Low transpiration rate Phloem pressure release Phloem unloading Sugar accumulation Anthocyanin accumulation Low VPD (low temperature, high humidity) Slow ripening Berry transpiration (μmol m -2 s -1 ) 140 120 100 80 60 40 20 0 Berry transpiration VPD 0:00 16:00 8:00 0:00 16:00 8:00 0:00 16:00 8:00 0:00 16:00 8:00 0:00 16:00 8:00 Time of the day Control Restricted transpiration 2.7 2.4 2.1 1.8 1.5 1.2 0.9 0.6 0.3 0.0 VPD (kpa) Zhang & Keller (2015)
Temperature and water limit berry size Harvest berry weight (g) 1.4 1.2 1.0 0.8 0.6 r = 0.43*** 0.4 Spring Cool 0.2 Warm Hot 0.0 0.2 0.3 0.4 0.5 0.6 Harvest berry weight (g) 2.2 2.0 1.8 1.6 1.4 r = 0.84*** 50-100% ET 100-100% ET 1.2 2010 1.0 2011 2012 0.8 0.4 0.5 0.6 0.7 0.8 0.9 Flower cap weight (mg) Lag-phase berry weight (g) Berry size is determined early It is difficult to manipulate berry weight after véraison Cool spring temperatures Small flowers Small berries Water deficit before véraison Small berries Keller et al. (2010) Keller (2015)
Diluting fruit quality really? Berry weight (g) 1.4 1.2 1.0 0.8 0.6 Merlot (r = 0.53**) Syrah (r = 0.43*) Chardonnay (r = 0.51*) -1.4-1.2-1.0-0.8 Pre-veraison Ψ stem (MPa) More water after véraison decreases berry shrinkage -5% weight +1 Brix Berry weight loss (%) More water before véraison increases berry size 50 40 30 20 10 0-10 -20-30 Merlot (r = -0.45*) Syrah (r = -0.41*) Chardonnay (ns) -1.2-1.0-0.8-0.6 Post-veraison Ψ stem (MPa)
Rainfall: Berry splitting (cracking) Critical pressure (kpa) Water through skin Berries swell, may split Sugar may leach Split berries may shrink 600 500 400 300 Concord Merlot Syrah Zinfandel 25 Concord, r = -0.80*** Merlot, r = -0.88*** 200 Berry sugar (Brix) 20 15 10 5 0 0 100 200 300 Leached sugar (mg) 100 0 0 5 10 15 20 25 30 Soluble solids (Brix) Splitting due to: Rainfall Sprinkler irrigation High humidity Preveraison drought
Water deficit impacts berry development C fruit (g shoot -1 ) 18 16 14 12 10 8 6 4 r = 0.77 2 P < 0.001 0 Keller et al. (2015) 100 150 200 250 300 g max (mmol H 2 O m -2 s -1 ) Water deficit g s Pn C partitioned to fruit Water deficit before véraison Smaller berries Skin:juice Stimulation of anthocyanin biosynthesis (sugar + ABA) Water deficit after véraison Less sugar, berry shrinkage
Wine and water deficit: Timing matters Tannin variation due to water and weather; anthocyanin variation dominated by weather (more in cool vintage, less in warm vintage) Full-season deficit Higher anthocyanins and tannins More LPP Prevéraison deficit Intermediate tannins Postvéraison deficit No gain Dehydration does not make berries more mature Casassa et al. (2015)
Water deficit: It s not just about berry size 50 47 C Temperature ( C) 40 30 20 10 0 Ambient Fruit exposure 25% ET c Exterior Interior 100% ET c Exterior Interior 245 246 247 248 249 250 Day of year Water deficit Small berries, low vigor Open canopy, restricted shoot growth High cluster sun-exposure 32 C High light and high temperature Exposed berries are warm berries 35 C Anthocyanin optimum 20 C Keller et al. (2016)
Weather causes vintage variation Titratableacidity(g/L) 30 25 20 15 10 5 197 198 19 20 201 6 8 10 12 14 16 18 Solublesolids( Brix) Fruit color (A 520 ) 12 10 8 6 4 2 0 Season (Yield rank) 1997 (1) 1998 (3) 1999 (4) 2000 (2) 2001 (2) 6 8 10 12 14 16 18 Soluble solids ( Brix) Climate variation and vineyard location: By far the strongest determinants of fruit composition Acidity and color vary >2-fold, aroma volatiles >10-fold at similar Brix level and yield Temperature trumps soil moisture and crop load Keller et al. (2004, 2005)
Soluble solids (Brix) Temperature limits fruit ripening Brix 28 26 24 22 Control 1st Cold Treatment 2nd Cold Treatment 5 Nights <10 C 20 18 16 14 Hall (2010) 231 236 243 247 281 Aug 19 Day DOY of year Oct 8 No berry growth or sugar accumulation at <10ºC and >40ºC
Temperature: West Side Story Disentangling the light from the heat Photosynthesis - Sugar ( - ) (20-30 C) Acids: Tartrate (?) Malate ph (?) K + +15 C! Amino acids (proline, arginine) Phenolics: Anthocyanins - (days: 30-35 C) Tannins (?) Volatiles (?): Methoxypyrazines Sunburn: >42 C + UV/visible light partly from Spayd et al. (2002)
Light: Visible and UnVisible Photosynthesis - -99% light! Sugar Acids: Tartrate ( ) Malate ph (?) K + (?) Amino acids (arginine ), N Clouds vs. canopy shade Phenolics: Anthocyanins (color) (visible >100 µmol m -2 s -1 ) Flavonols (color cofactors) (UV-B) Cinnamic acids (lignin, Brett ) (visible) Tannins (astringency) (visible?) Volatiles: Norisoprenoids, monoterpenes Methoxypyrazines Wine sensory properties -
Sun exposure: More is better? Sun-exposed berries: More UV light + heating (+15ºC) Chardonnay, Riesling: Sun-exposed berries with 6-8 times more flavonols and 2-4 times more flavan-3-ols (monomers, dimers, trimers, polymers) than shaded berries + Sunburn Smaller, open canopy More sun-exposed fruit More bitter and astringent phenolics Skin contact White wine?
Nitrogen: Moderation is a virtue Soluble Soluble solids ( Brix) 2820 2719 2618 2517 2416 Hot 2315 Warm no N Ambient Cool 100 kg N/ha r = r -0.65*** = -0.47*** 2214 0 2 4 65 8 10 10 12 14 161518 20 22 20 24 26 25 28 30 Growing tips/shoot Yield (t/ha) at veraison Total anthocyanins (mg/l) Fermentation etc. Keller et al. (1999, 2001, 2010) More N Higher yield, more lateral growth, denser canopy Growing shoot tips compete with fruit Delayed ripening N suppresses secondary metabolism (phenolics) Bad recipe: Apply N fertilizer, then hedge away excess growth 200 150 100 N (and S) enhance aroma precursors (volatile thiols) 50 0 ST/noN RT/noN ST/90kgN/ha RT/90kgN/ha ST: Single hedging RT: Repeated hedging Day 0 Day 4 After press After coldst. Day 2 Day 6 After MLF
Nitrogen: Interaction with light 50 Increasing N at bloom N1 N5 N10 Anthocyanins (mg/g skin fw) 40 30 20 10 0 50 40 30 20 10 0 50 40 30 20 10 Delphinidin-3-glc Cyanidin-3-glc Petunidin-3-glc Peonidin-3-glc Malvidin-3-glc 100% 20% 2% Decreasing light at veraison 0 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 Weeks after veraison Light drives anthocyanin accumulation, but N modulates it Keller & Hrazdina (1998)
Juice amino ug/ml acids (mg/l) Nitrogen: Yeast cannot live by sugar alone 350 Arginine-N 300 Proline-N 250 200 150 100 50 0 N40+0 N20+20 STD N0+40 N40+0 N20+20 PRD N0+40 N40+0 N20+20 RDI STD PRD RDI N0+40 Proline and PR proteins accumulate during ripening Water deficit N deficit Risk of stuck fermentation H 2 S N deficit High phenolics but low aroma precursors Wade et al. (2004)
Potassium and the ph conundrum Metal cations (K +, Na + ), may counter the influence of organic acids by substituting for H + Juice ph Variation in juice ph is driven by variation in both TA and K + Late harvest TA, K + ph Crop load K + (phloem import) ph Juice ph is not very responsive to soil K + ( Malate ) Ca 2+ and K + compete for root uptake: Soil ph Juice ph Juice ph 3.9 3.8 3.7 3.6 3.5 3.4 Merlot Syrah Chardonnay 3.3 3.2 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Juice K + (g/l)
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