Grape ripening –and how to manage it

Markus Keller

Growing grapes for profitg g p p

What we want:What we want:• Balanced vines

• Ideal microclimate

• Open, productive canopy

• High yield and quality

• Low disease pressurep

• Vineyard access and mechanization

The management toolboxThe management toolbox• Site/variety/clone selection• Trellis design, training systemg , g y• Pruning strategy• Nutrient/floor management• Water management• Canopy management

The ‘how to’ for dummies

Principles:• Lower yield → better quality

p

WRONG!• More stress → better quality

WRONG!

It ain’t necessarily so…Qua

lity

12 95Yield

6

10

a)

90

ratin

g)

re)

5

6

8

eld

(T/h

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80

85

Qua

lity

vint

age

r

eld

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r

4

3

4

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75

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by's

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ualit

y

Yie

2

2 70 (Sot

h

Yield

Qu

r = 0.131

CA North Coast (Napa, Sonoma) Mean harvest Brix: 20.5 (1971) – 24.2 (2001)

1960 1970 1980 1990 20000 65

Change is in the air

20

25 Season and Cluster thinning1998 1999 (t/ha)

Early (13.7/5.2)Tons/acre6.1 - 2.3

15

20

(A52

0/mL) Late (13.7/6.1)

None (25.4/8.8)6.1 - 2.7

11.3 - 3.9

2876 2243 GDD (°F)

5

10

Col

or (

10 15 20 250

5

Soluble solids (Brix)

• Color varies >2-fold at the same Brix level• Too much (or too little) heat slows ripening• Temperature trumps crop load → nature trumps nurture

Xylem flow reversesBerry Growth

Cell expansionCell divisionCell division

Ripening: A trade deficit?

(modified fromCoombe 2001) SEED FORMATION BERRY RIPENING

What’s in a grape? Mostly water• Berry water content 70-80% at harvest• In: xylem and phloem• Out: transpiration and xylem backflow→ Berry very sensitive to temperature (+25ºF)• Veraison: phloem flow xylem flow reversedVeraison: phloem flow , xylem flow reversed→ Berry less sensitive to soil moisture

H2OXylem Phloem

Transpiration

Sugars: sweet seducers• Sweet taste and alcohol• > 90% of soluble solids (Brix)• Glucose + fructose (> 95% 1:1 ratio)• Glucose + fructose (> 95%, 1:1 ratio)• From sucrose via phloem• Sugar accumulation → veraison (~9 Brix)• Physiological maximum ~25 Brix→ Shrinkage increases concentration

( 10% weight → +2 Brix)(-10% weight → +2 Brix)

g) 350400450

Year 1 Year 2Year 3

gar p

er b

erry

(m

100150200250300

Year 3

Soluble solids (ºBrix)

Sug

5 10 15 20 25 300

50100

Acids: sour repellents• Sour taste, mask sweetness• Tartrate & malate (70-90%)• Also citrate succinate phenolics

Tartaric Malic• Also citrate, succinate, phenolics,

amino acids, fatty acids• From glucose before veraison• Ripening: tartrate → little turnover but dilution

malate → respiration & gluconeogenesis• High acidity → low pH (3-4 at harvest)g ac d y → o p (3 a a es )• Temperature!

1 ) 182022

Year 1Year 2 3.8

4.0 Year 1Year 2

able

aci

dity

(g L

-

81012141618 Year 2

Year 3

pH

3.2

3.4

3.6

Year 2 Year 3

Soluble solids (ºBrix)

Titra

ta

14 16 18 20 22 24 26 28246

Titratable acidity (g L -1)

2468101214161820222.8

3.0

Nitrogen: fuel for yeast

• Free amino acids (50-90%), proteins, NH4+, NO3

-

• Main amino acids: proline & arginine (>70%)Main amino acids: proline & arginine (>70%) • From NO3

- (via xylem) and glutamine (via xylem & phloem)• Ripening: mostly glutamine import,

proline & PR proteins accumulate (osmotic stress?)• Yeast uses arginine but not proline• PR proteins → protein haze (heat stability)• PR proteins → protein haze (heat stability)• Disease susceptibility

Phenolics: repulsion and attraction• Color, astringency (texture), flavor, oxidation• From amino acid phenylalanine• Stored as glycosides: bound to glucose

(and acetate/coumarate) or tartrate• Pre-veraison: tannins (skin and seeds) → astringency

+Glu

• Pre-veraison: tannins (skin and seeds) → astringency• Post-veraison: anthocyanins (skin) → color• Flavonols (skin: sunscreen) → copigmentation• Hydroxycinnamates (pulp), decline

post-veraison → volatile phenols• Sensitive to N light temperatureSensitive to N, light, temperature…

Volatiles: pick me!• Smell: aroma, flavor, odor, bouquet• 100s of compoundsp• Volatile profile is variety-specific → varietal aroma• Post-veraison: norisoprenoids (from carotenoids),

monoterpenes (bound to glucose)monoterpenes (bound to glucose)• Methoxypyrazines… (volatile)• Large fruit-to-fruit variation due to location, light, g , g ,

temperature, nutrition, harvest date, post-harvest handling

Harvest time: the challenge

Maximum fruit quality at optimum stage of maturityq y p g y

• Rule: The sooner grapes reach optimum, the better the wine

• Challenge: Determine optimum precisely, objectively, rapidlyChallenge: Determine optimum precisely, objectively, rapidly

• Final judgment: Taste end product (fruit, juice, wine)

• Problem: Too late too slow expensive subjectiveProblem: Too late, too slow, expensive, subjective…and: taste mostly limited to sweet-sour-astringent,

most flavors are ‘locked up’ in grapes

→ Solution: Measure sugar (Brix) throughout ripening…

Hang time: why do it?• Physiological maturity: Seeds able to germinate

• Grapes to specifications: Wine style, price segment…

• Ripening: Physical and chemical changes

• Water increases then decreases → concentration effect

• Natural sugar maximum at 23-25 Brix

• Tannins polymerize, bind to cell walls?p y ,

• Malate, methoxypyrazines decline early, not late

• Terpenes continue to accumulate late → aroma potentialTerpenes continue to accumulate late → aroma potential

• …but so do some volatile phenols → Brett fodder?

• Some ‘fruity’ ester precursors decline → fruit character?Some fruity ester precursors decline → fruit character?

• Danger: high pH → microbial stability?

Temperature: a West Side StoryDisentangling the light from the heat

Ph t th i +25°F!• Photosynthesis -• Sugar ( - ) (68-86°F)• Acids: Tartrate ( ?)

+25 F!

Acids: Tartrate ( ?)Malate

• K+pH (?)

• Amino acids (proline, arginine) • Phenolics: Anthocyanins - (days: 86-95°F)

Tannins ( ?)Tannins ( ?)• Volatiles (?): Methoxypyrazines • Sunscald: >108°F + UV/visible light

partly from Spayd et al. (AJEV, 2002), Tarara et al. (AJEV, 2008)

Light: visible and UnVisible

• Photosynthesis -• Sugar

-99% light!

• Acids: Tartrate ( )Malate

• K+ (?)pH (?)

K (?)• Amino acids (arginine ), N • Phenolics: Anthocyanins (color) (visible > 100 µmol m-2s-1)

Clouds vs. Canopy Shade

Flavonols (cofactors) (UV-B)Cinnamic acids (lignin, Brett…) (visible)Tannins (astringency) (visible?)Tannins (astringency) (visible?)

• Volatiles: Norisoprenoids, monoterpenes… Methoxypyrazines

• Wine sensory properties -

Exposure: how much is too much?

Low N High NIt depends…!Morning sun Afternoon sunIt depends…!

• White grapes cannot make anthocyaninsFair skins don’t tan…?

• White grapes cannot make anthocyanins,but they do make tannins

• Sun: too much of a good thing for white grapes?→ Flavonols → firmness, bitterness → Hydroxycinnamates → volatile phenols

(Smoke wood leather → pharmaceutical medicinal)(Smoke, wood, leather → pharmaceutical, medicinal)• Fruit character • Aromatic varieties sensitive, Chardonnay more forgivingy g g

(flavonoids → ‘structure’)• …but: less need for devigorating trellis, leaf removal, water deficit

Terroir is water:some stress is good more is better ?some stress is good, more is better…?

• Soil moisture determines vigor, canopy density, yield…• Sugar accumulation less sensitive than berry growthSugar accumulation less sensitive than berry growth• Some deficit is beneficial, but too much (too late) is detrimental

→ Berry size → Sugar -→ Seed ‘maturity’ ( ?)→ Acidity (malate )→ Acidity (malate )→ pH → Amino acids (arginine )→ Tannins ( ?)→ Flavonols… ( ?)→ Color (berry size + anthocyanin production)→ Color (berry size + anthocyanin production)→ Carotenoids ( ?)

Don’t let ‘em dry out!

(Lag phase)

Irrigation

(~20 Brix)

Irrigation

Days after irrigation from Keller et al. (JXB, 2006)

Plant water status and berry size

1.4Water less before veraison to limit berry size

1.0

1.2

ry w

eigh

t (g)

0.6

0.8Ber

r

Merlot (r = 0.53**) Syrah (r = 0.43*)Chardonnay (r = 0.51*)

30

40

50

%)

-1.4 -1.2 -1.0 -0.8

Pre-veraison Ψstem (MPa)

y ( )

10

20

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wei

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oss

(%

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0B

erry

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Merlot (r = -0.45*) Syrah (r = -0.41*)Chardonnay (ns)

-1.2 -1.0 -0.8 -0.6

Post-veraison Ψstem (MPa)

-30 Chardonnay (ns)

Water more after veraison to prevent weight loss

How to blow up 10

12

20

30

Chamber pressure Bunch NodeBerry - topTrunkBerry - middle

Pre-veraison

grape berries

mbe

r pre

ssur

e (b

ar)

4

6

8

mV

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minutes

0 100 200 300 400 500 600 700-2-40

Post-veraison

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Cracked berry

Bunch 2

time (minutes)

0 100 200 300 400 500-50 0 -1

Non-girdledGirdledVPDair

Chamber pressure

Cracking: low carbs but overweightWater through skin → Berry volume

S 150

200

g)

Concord Merlot

25 Concord, r = -0.80***

→ Sugar

100

150

sug

ar (m

g

20

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(Brix

)

Merlot, r = -0.88***

50

Leac

hed

10

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ry s

ugar

no yesCracking

0

5

10

Ber

r

• High humidityR i f ll

Cracking

0 100 200 300

Leached sugar (mg)

0• Rainfall• Sprinkler irrigation

Nitrogen: friend or foe?• Photosynthesis → growth • Sugar ( - )

T t t (?)• Tartrate (?)• Malate • K+ → pH p• Amino acids (arginine) • Anthocyanins, flavonols… • Carotenoids → terpenes • Other volatiles ( - )

350A i i NL) m

g/L)

150

200 ST/no NRT/no NST/90 kg N/haRT/90 k N/h

150

200

250

300

ug/m

L

A rginine-NP ro line-N

min

o ac

ids (

mg/

L

thoc

yani

ns (m

50

100

150 RT/90 kg N/ha

0

50

100

N 4 0+0 N 20+ 20S TD

N 0+ 40 N 40+0 N 20+ 20P RD

N 0 + 40 N 40+ 0 N 20+ 20RD I

N 0 +40

Juic

e am

Tota

l an

0

50

Day 0Day 2

Day 4Day 6

After pressAfter MLF

After cold st.

How to get poor color

50

Increasing N at bloomN1 N5 N10

10

20

30

40

Decresk

in fw

)

100%

Decre

0

30

40

50

easing lighns (m

g/g

s

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easing lig

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10

20

30

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aisonAnt

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2%

aison

00 2 4 6 8 0 2 4 6 8 0 2 4 6 8

Weeks after veraisonWeeks after veraison

Better ways to waste money…

100

Botrytized Healthy

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wei

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8 Soil N

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0 g/vine 3 g/vine

Soil N (g/vine)0 0.2 1 2

0 0.04m

ildew

ssi

ons/

lea

(g )

2

Pow

dery

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Chardonnay Cabernet S.0

P

How much N to apply?24

100% Sunlight

°Brix

) 22N1N5N10

20% Sunlight

e so

lids (

20 mean = 20.4

20% SunlightN1N5N10

…it depends!

Solu

ble

18

N102% Sunlight

N1N5

1650 150 250 350 450 550

mean = 298

N10

Yield (g/vine)50 150 250 350 450 550

Seeing is believing

??

1 Leaf feeds 5-10 berries

Avoid competition28 28

26

27

28

(°B

rix)

26

27

28

(°B

rix)

24

25

ble

solid

s

24

25

ble

solid

s

0 100 200 300 400 50022

23Sol

u

r = -0.44, p < 0.001

0 5 10 15 20 2522

23Sol

u

r = -0.47, p < 0.001

Berries/shoot Growing tips/shoot at veraison

• Too much crop may delay ripeningToo much crop may delay ripening

• Growing shoot tips compete with ripening berries

→ Limit (lateral) shoot growth after veraison→ Limit (lateral) shoot growth after veraison

Wh ?Fruit thinning

Why?• Regulates crop load (fine-tuning)

→ Prevents overcropping→ Prevents overcropping• May improve fruit composition• Can increase fruit size• May promote shoot growth

Wh ?When?• Early → shoot growth • Late → greater effect on yield• Late → greater effect on yield• Bloom: cut through flower clusters

→ cluster compactness • Veraison → quality control?• Pre-harvest → ??? (BS/BSN)

The ideal vine

• Shoots/canopy length 5/ft• Shoot length 3-4 ft (~15 buds)• Lateral shoots 5-8 buds/shoot• Pruning weight 0.2-0.5 lbs/ft• Cane weight 20-40 g• Leaf area/fruit weight* 10-15 cm2/gLeaf area/fruit weight 10 15 cm /g• Yield/pruning weight* 5-10• Canopy gaps ~ 30%• Fruit exposure > 50%Fruit exposure 50%

*Measures of crop load