Grape ripening –
and how to manage it
Markus Keller
Growing
g grapes
g p for profit
p
What we want:
• Balanced vines
• Ideal microclimate
• Open, productive canopy
• High yield and quality
• Low disease pressure
p
• Vineyard access and mechanization
The management toolbox
•
•
•
•
•
•
Site/variety/clone selection
Trellis design,
g , training
g system
y
Pruning strategy
Nutrient/floor management
Water management
Canopy management
The ‘how to’ for dummies
Principles:
p
• Lower yield → better quality
WRONG!
• More stress → better quality
Quality
It ain’t necessarily so…
95
10
5
90
48
85
36
80
24
12
75
r = 0.13
70
Q
Quality
(Soth
heby's v
vintage rrating)
12
6
Qu
uality
re)
Yie
eld (t/acr
(T/ha
a)
Yield
Yield
0
1960
1970
CA North Coast (Napa, Sonoma)
1980
1990
65
2000
Mean harvest Brix: 20.5 (1971) – 24.2 (2001)
Change is in the air
Color ((A520/mL)
25
20
Season and Cluster thinning
1998 1999
(t/ha)
Tons/acre
Early (13.7/5.2)
6.1 - 2.3
Late (13.7/6.1)
6.1 - 2.7
None 11.3
(25.4/8.8)
- 3.9
15
2876
2243 GDD (°F)
10
5
0
10
15
20
25
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
Berry Growth
Xylem flow reverses
Cell expansion
Cell division
Ripening: A trade deficit?
(modified from
Coombe 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)
Ü xylem flow reversed
• Veraison: phloem flow Ü,
→ Berry less sensitive to soil moisture
H 2O
Xylem
Phloem
Transpiration
Sugars: sweet seducers
Sug
gar per berry (mg)
• Sweet taste and alcohol
• > 90% of soluble solids (Brix)
• Glucose + fructose (> 95%,
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%
450
400
350
300
250
200
150
100
50
0
Year 1
Year 2
Year 3
5
10
15
20
Soluble solids (ºBrix)
25
30
Acids: sour repellents
4.0
22
20
18
16
14
12
10
8
6
4
2
Year 1
Year 2
Year 3
Year 1
Year 2
Year 3
3.8
3.6
pH
Titrata
able acidity (g L -1)
• Sour taste, mask sweetness
• Tartrate & malate (70-90%)
• Also citrate
citrate, succinate
succinate, phenolics
phenolics,
amino acids, fatty acids
Tartaric
• From glucose before veraison
• Ripening: tartrate → little turnover but dilution
malate → respiration & gluconeogenesis
• High
g ac
acidity
d y → low
o p
pH (3
(3-4 a
at harvest)
a es )
• Temperature!
3.4
3.2
3.0
2.8
14
16
18
20
22
24
Soluble solids (ºBrix)
26
28
22
20
18
16
14
12
10
8
Titratable acidity (g L -1)
6
4
2
Malic
Nitrogen: fuel for yeast
Free amino acids (50-90%), proteins, NH4+, NO3Main 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)
• Disease susceptibility
•
•
•
•
Phenolics: repulsion and attraction
• Color, astringency (texture), flavor, oxidation
• From amino acid phenylalanine
+
• Stored as glycosides: bound to glucose
Glu
(and acetate/coumarate) or tartrate
• 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
N, light
light, temperature
temperature…
Volatiles: pick me!
•
•
•
•
Smell: aroma, flavor, odor, bouquet
p
100s of compounds
Volatile profile is variety-specific → varietal aroma
Post-veraison: norisoprenoids (from carotenoids),
monoterpenes (bound to glucose)
• Methoxypyrazines… (volatile)
g fruit-to-fruit variation due to location,, light,
g ,
• Large
temperature, nutrition, harvest date, post-harvest handling
Harvest time: the challenge
Maximum fruit q
quality
y at optimum
p
stage
g of maturity
y
• Rule: The sooner grapes reach optimum, the better the wine
• Challenge: Determine optimum precisely, objectively, rapidly
• Final judgment: Taste end product (fruit, juice, wine)
late, too slow,
slow expensive,
expensive subjective
• Problem: Too late
…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
polymerize,
y
, bind to cell walls?
• Tannins p
• Malate, methoxypyrazines decline early, not late
• Terpenes continue to accumulate late → aroma potential
• …but so do some volatile phenols → Brett fodder?
fruity ester precursors decline → fruit character?
• Some ‘fruity’
• Danger: high pH → microbial stability?
Temperature: a West Side Story
Disentangling the light from the heat
+25°F!
+25
F!
• Ph
Photosynthesis
t
th i Ü-Þ
Ü
• Sugar (Ü-Þ) (68-86°F)
?)
• Acids: Tartrate ((Ü?)
Malate ÞÞ
pH (?)
• K+ Ü
• Amino acids (proline, arginine) Ü
• Phenolics: Anthocyanins Ü-Þ (days: 86-95°F)
Tannins (Ü?)
• Volatiles (?): Methoxypyrazines Þ
• Sunscald: >108°F + UV/visible light
partly from Spayd et al. (AJEV, 2002), Tarara et al. (AJEV, 2008)
Light: visible and UnVisible
-99% light!
• Photosynthesis Ü-Þ
• Sugar Ü
• Acids: Tartrate (Ü)
Malate Þ
pH (?)
• K+ Þ(?)
Clouds vs. Canopy Shade
• Amino acids (arginine Þ), N Ü
• Phenolics: Anthocyanins (color) Ü (visible > 100 µmol m-2s-1)
Flavonols (cofactors) ÜÜ (UV-B)
Cinnamic acids (lignin, Brett…) Ü (visible)
Tannins (astringency) Ü (visible?)
• Volatiles: Norisoprenoids, monoterpenes… Ü
Methoxypyrazines Þ
• Wine sensory properties Ü-Þ
Exposure: how much is too much?
High N
Low N
It
depends…!
Afternoon sun
Morning sun
Fair skins don’t tan…?
• White grapes cannot make anthocyanins
anthocyanins,
but they do make tannins
• Sun: too much of a good thing for white grapes?
→ Flavonols → firmness, bitterness Ü
→ Hydroxycinnamates → volatile phenols Ü
(Smoke wood
(Smoke,
wood, leather → pharmaceutical,
pharmaceutical medicinal)
• Fruit character Þ
g
g
• Aromatic varieties sensitive, Chardonnayy more forgiving
(flavonoids → ‘structure’)
• …but: less need for devigorating trellis, leaf removal, water deficit
Terroir is water:
some stress is good,
good more is better
better…?
?
• Soil moisture determines vigor, canopy density, yield…
• Sugar accumulation less sensitive than berry growth
• Some deficit is beneficial, but too much (too late) is detrimental
→ Berry size Þ
→ Sugar Ü-Þ
→ Seed ‘maturity’ (Ü?)
→ Acidity (malate Þ)
→ pH Ü
→ Amino acids (arginine Þ)
→ Tannins (Ü?)
→ Flavonols… (Ü?)
→ Color Ü (berry size + anthocyanin production)
→ Carotenoids (Þ?)
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
Water less before veraison to
limit berry size
1.2
1.0
0.8
50
Merlot (r = 0.53**)
Syrah (r = 0.43*)
Chardonnay
y (r
( = 0.51*))
0.6
-1.4
-1.2
Pre-veraison
-1.0
-0.8
Ψstem (MPa)
40
Berry w
weight loss (%
%)
Berrry weight (g)
1.4
30
20
10
0
-10
-20
Water more after veraison
to prevent weight loss
-30
Merlot (r = -0.45*)
Syrah (r = -0.41*)
Chardonnay (ns)
-1.2
-1.0
Post-veraison
-0.8
Ψstem (MPa)
-0.6
30
Chamber pressure
Bunch Node
Berry - top
Trunk
Berry - middle
Berry - bottom
10
12
10
8
0
6
-10
4
Top
Bottom
-20
2
cham
mber pressure (bar)
20
mV change
Pre-veraison
Middle
-30
0
-40
-2
0
100
200
300
400
500
600
700
minutes
Post-veraison
10
3
5
0
4
-10
2
3
-20
Bar
KPa
change in berry size (mV)
6
2
1
-30
1
Cracked berry
-40
0
Bunch 2
-50
0
0
Non-girdled
Girdled
VPDair
Chamber pressure
100
200
300
time (minutes)
400
500
-1
How to blow up
grape berries
Cracking: low carbs but overweight
Concord, r = -0.80***
Merlot, r = -0.88***
Berrry sugar (Brix)
25
20
15
Leached sugar (mg
g)
200
Water through skin
→ Berry volume Ü
→ Sugar
S
Þ
Concord
Merlot
150
100
50
0
no
yes
Cracking
10
5
0
0
100
200
Leached sugar (mg)
300
• High humidity
• Rainfall
R i f ll
• Sprinkler irrigation
Nitrogen: friend or foe?
Photosynthesis Ü → growth Ü
Sugar (Ü-Þ)
T t t (?)
Tartrate
Malate Ü
K+ Ü → p
pH Ü
Amino acids (arginine) Ü
Anthocyanins, flavonols… Þ
Carotenoids Ü → terpenes Ü
Other volatiles (Ü-Þ)
Juice am
minoug/mL
acids (mg/L
L)
350
A rgininei i
N
300
P ro line- N
250
200
150
100
50
0
N 40+0 N 20+20 N 0+40
S TD
N 40+0 N 20+ 20 N 0+40
PRD
N 40+ 0 N 20+ 20 N 0+40
RD I
200
Total anthocyanins (m
mg/L)
•
•
•
•
•
•
•
•
•
ST/no N
RT/no N
ST/90 kg N/ha
RT/90 kkg N/h
N/ha
150
100
50
0
Day 0
Day 4
Day 2
After press After cold st.
Day 6
After MLF
How to get poor color
Increasing N at bloom
N1
50
N5
N10
30
100%
20
10
0
50
40
30
20%
20
10
0
50
Delphinidin-3-glc
Cyanidin-3-glc
Petunidin-3-glc
Peonidin-3-glc
Malvidin-3-glc
40
30
20
2%
10
0
0
2
4
6
8
0
2
4
6
8
0
Weeks after
veraison
Weeks
after
veraison
2
4
6
8
Decre
easing ligh
light
ht at
at vera
vera
aison
Decre
easing
aison
Anth
hocyanin
ns (mg/g s
skin fw)
40
Better ways to waste money…
1.5
Soil N 1.0
0 g/vine
3 g/vine
8
50
0
Powdery mildew s
P
severity
af)
(lesions/lea
Berries pe
er cluster
100
0.5
6
0 4
0.2
1
2
0.0
Soil N (g
(g/vine))
2
0
Chardonnay Cabernet S.
Berry w
weight (g)
Botrytized
Healthy
How much N to apply?
Soluble
e solids(°Brix)
24
22
…it depends!
mean = 20.4
20
18
100% Sunlight
N1
N5
N10
20% Sunlight
N1
N5
N10
2% Sunlight
N1
N5
N10
mean = 298
16
50
150
250
350
Yield (g/vine)
450
550
Seeing is believing
?
1 Leaf feeds 5-10 berries
Avoid competition
28
27
26
25
24
23
r = -0.44, p < 0.001
22
0
100
200
300
Berries/shoot
400
500
Soluble solids (°Brix)
Soluble solids (°Brix)
28
27
26
25
24
23
r = -0.47, p < 0.001
22
0
5
10
15
20
25
Growing tips/shoot at veraison
• Too much crop may delay ripening
• Growing shoot tips compete with ripening berries
→ Limit (lateral) shoot growth after veraison
Fruit thinning
Wh ?
Why?
• Regulates crop load (fine-tuning)
→ Prevents overcropping
• May improve fruit composition
• Can increase fruit size
• May promote shoot growth
Wh ?
When?
• Early → shoot growth Ü
• Late → greater effect on yield
• Bloom: cut through flower clusters
→ cluster compactness Þ
• Veraison → quality control?
• Pre-harvest → ??? (BS/BSN)
The ideal vine
•
•
•
•
•
•
•
•
•
Shoots/canopy length
Shoot length
Lateral shoots
Pruning weight
Cane weight
Leaf area/fruit weight*
weight
Yield/pruning weight*
Canopy gaps
Fruit exposure
5/ft
3-4 ft (~15 buds)
5-8 buds/shoot
0.2-0.5 lbs/ft
20-40 g
10-15
10
15 cm2/g
5-10
~ 30%
> 50%
*Measures of crop load