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Impact of Severity and Timing of Basal Leaf Removal on 3-Isobutyl-2-Methoxypyrazine Concentrations in Red Winegrapes


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Field studies were conducted on Vitis vinifera L. cvs. Cabernet franc and Merlot to evaluate the effects of basal leaf removal timing and severity on 3-isobutyl-2-methoxypyrazine (IBMP) concentration in grape berries. Treatments consisted of removing either 50% or 100% of leaves from the fruiting zone at either 10 days after anthesis, 40 days after anthesis, or 60 days after anthesis. In the second year of the Cabernet franc study, a 15-day postveraison leaf removal treatment was also included. In both years of the Cabernet franc study, significant reductions in IBMP (range = 28 to 53%) were observed before veraison compared with the control in both 10 days after anthesis treatments (50% and 100% leaf removal). In 2007, all leaf removal treatments significantly reduced IBMP concentrations compared with the control (46 to 88%) in Cabernet franc berries at harvest, with the greatest reduction observed in the 100% leaf removal treatments at 10 days after anthesis and 40 days after anthesis. In 2008, the 100% leaf removal treatment at 10 days after anthesis and the 50 and 100% leaf removal treatments at 40 days after anthesis significantly reduced IBMP concentrations (34 to 60%) in mature Cabernet franc berries. In the Merlot trial, all leaf removal treatments significantly reduced IBMP concentrations (38 to 52%) at harvest. In summary, early season (10 to 40 day after anthesis) basal leaf removal reduced IBMP accumulation preveraison compared with the control in both studies, suggesting that early leaf removal is a more effective management strategy to reduce IBMP accumulation in grape berries than leaf removal later in the season.
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Am. J. Enol. Vitic. 61:3 (2010)
The 3-alkyl-2-methoxypyr azines (M Ps) are a class of
odorant s associated wit h “g reen,” herbac eous aroma s of
some Bo rd ea ux w inegr ap e (Viti s vin ifer a L.) culti va rs.
Qu antitatively, 3-isobut yl-2-methoxypyr azine (IBMP) is
the predominant MP in grapes and wine, typically an order
of magnitude h igher i n concentration t han 3-isopropyl-2-
methox ypyr az ine (I PMP) and 3-sec -butyl-2-met hoxypyr-
azine (sBM P) (Alberts et al. 2009). The sensory detection
threshold for IBMP is re por ted to range from 0.5 to 2 pg/g
in water ( Butter y et al. 1969, Kotseridis et al. 1998, Seifert
et al. 1970) and 10 to 15 pg/g in red wine (de Boubee et al.
1Graduate Student, Cornell University, Field of Horticulture, Plant Sciences
Building, Ithaca, NY 14853; 2Assistant Professor of Enology, 3Former Postdoc-
toral Scient ist, Cornell University, Depar tment of Food Science and Technol-
ogy, 630 W. North Street, Geneva, NY 14456; 4Former Postdoctoral Scientist,
Cornell University, Depart ment of Horticultural Sciences, Geneva, NY 14456;
5Research Technician, 6Viticultu rist, Cornell Cooperat ive Extension Suffolk
County, Long Island Horticultural Research and Extension Center, 3059 Sound
Avenue, Riverhead, NY 11901; 7Research Suppor t Specialist, Depa rtment of
Horticultural Sciences, Geneva, N Y 14456; and 8Assistant Professor of Viti-
culture, Cornell University, Depar tment of Hor ticultural Sciences, Geneva,
NY 14456, and Department of Hor ticulture, Ithaca, NY 14853.
*Corresponding aut hor (email:
Acknowledgments: The authors thank Sheldrake Point Vineyard and Pellegrini
Vineyard s for cooperation on this project, Imeld a Ryona for assistance with
sample preparation, and Terry Bates for assistance in editing this manuscript.
Manuscript submitted Nov 2009, revised Mar 2010, accepted Apr 2010
Copyright © 2010 by the American Society for Enology and Viticulture. All
rights reserved.
Impact of Severity and Timing of Basal Leaf Removal
on 3-Isobutyl-2-Methoxypyrazine Concentrations
in Red Winegrapes
Justin J. Scheiner,1* Gavin L. Sacks,2 Bruce Pan,3 Said Ennahli,4
Libby Tarlton,5 Alice Wise,6 Steven D. Lerch,7 and Justine E. Vanden Heuvel8
Abstract: Field st udies were condu cted on Vitis vinifera L. cvs. Cabernet fr anc and Merlot t o evaluate the ef-
fects of basal leaf removal timing and severity on 3-isobutyl-2-methoxypyrazi ne (IBMP) concent ration in g rape
ber ries. Treatments consisted of removing either 50% or 100% of leaves from t he f ru iting zone at eit her 10 days
after anthesis, 40 days after anthesis , or 60 d ays after anthesis. In the second year of the Cabe rnet franc st udy, a
15-day postveraison leaf removal treatme nt was also included. In both years of the Cabernet franc study, signifi-
cant reductions i n I BMP (range = 28 to 53%) were observed b efore veraison compared with the control in both
10 days aft er anthesis treat ments (50% and 100% leaf removal). In 2007, all leaf removal treatments significantly
reduced IBMP concentrations compared with the control (46 to 88%) i n Cabernet franc berr ies at har vest, w ith
the greatest reduction observed in the 100% leaf removal tre atments at 10 days aft er anthesis and 40 days after
ant hesis. In 2008, the 100% leaf removal t reatment at 10 days after anthesis and the 50 and 100% leaf removal
treatment s at 40 days after anthesis sig nificantly reduce d IBMP concentrations (34 t o 60%) in matur e Caber net
franc berries. In the Me rlot tr ial, all leaf removal treatments signif icantly reduced I BMP concentrations (38 to
52%) at ha rve st. In summary, early season (10 to 40 day af ter anthesis) basal leaf removal reduced I BMP accu-
mulation preveraison compared w ith the cont rol in both studies, suggesting that early leaf re moval is a mor e ef-
fective management strategy to reduce IBMP accu mulation i n grape berries than leaf removal later in the season.
Key words: IBMP, accumulation , cluster exposure, methoxypyra zine
2000, Kotseridis et al. 1998). When present at concentra-
tions near sensory threshold, MPs may contribute positively
to wine quality by adding complexity and , in some cases,
var ietal cha racter (Allen et al. 1991). At higher concent ra-
tions, MPs can result in excessive herbaceousness and sup-
pressed fruitiness in wines (Allen and Lacey 1999, Hein et
al. 2009, Pickering et al. 2005). MPs are efficiently ext ract-
ed by conventional red wine practices, and their concentra-
tions in wine are strongly correlated to their concentrations
in grapes (Ryona et al. 2009). Several studies have evalu-
ated the ef ficacy of vin if ication and cellar ing practices in
reducing MPs (Blake et al. 2009, de Boubee 2003, Marais
1998, Picker ing et al. 2006) and have generally concluded
th at remediation of M Ps is ineffec tive or else re su lt s i n
other nonselective changes to the wine. Vit icultural man-
age ment st rategies th at reduce MPs i n the vineyard have
thus been proposed to be the most effective way to control
MP concentration in wine (Boga rt and Bisson 2006).
In grape b er r ies, IBMP beg ins to a ccumulat e a roun d
10 d ays aft er anthesis with a pea k i n con ce nt ration oc-
cu rring approximately 0 to 14 days before veraiso n, fol-
lowed by a rapid decline during maturation (de Boubee et
al. 20 00, Hashizume and Samuta 1999, Ryona et al. 2008,
Sala et al. 20 04). IBMP concent rations in mature berries
are reported to be less than 10% of their preveraison peak
concent rations. A strong correlation (R2 = 0.936) between
IBMP concentrations in mature Cabernet franc berries and
preveraison peak concent rations has been reported ( Ryona
Am. J. Enol. Vitic. 61:3 (2010)
et al. 2008), suggesting that final IBMP concentrat ion is
primarily deter mined preveraison. Thus, management prac-
tices that affect initial accumulation of MPs in g rapes pre-
verai son ar e ex pected t o more d ramatically impact f in al
MP concentrations at har vest than inter ventions later in the
season, assuming similar maturities.
Fruit-zone leaf removal is a com mon viticultural prac-
tice and has be en de mo ns trated to y ield improved fru it
chem ist ry at harvest ( Percival et al. 1994, Poni et al. 2006,
Rey nolds et al. 1996, Zoecklei n et al. 1992, 1998) and to
improve fungal control (Chellemi and Marois 1992, Percival
et al. 1994, Wolf et al. 1986, Zoecklein et al. 1992). T hese
effects are generally hypothesized to be mediated through
an increase of sunlight reaching the f ruiting zone. Several
gr oups h ave observed t hat cluster light exposu re results
in lowe r MP concentration s in mature fru it (Allen et al.
1996, de Boubee et al. 2002, de Boubee 2003, Marais et al.
1999, Noble et al. 1995, Ryona et al. 2008). Rece nt work
suggests that sun- exposed clusters accumulate less IBMP
pr ever aison tha n sha de d cluste rs w it hin the same v ine
(Ryona et al. 2008) and that the propor tional differences
pe rsist until harvest, alt houg h the physiolog ical mecha -
nisms behind these effects are not understood. Most of the
aforementioned studies have observed differences between
shaded and exposed f ruit by using artificial shading or tak-
ing advantage of natural variation in light exposure within
the canopy, but little work has been published on the effec-
tiveness of specif ic vineyard practices (e.g., leaf removal)
to reduce M P a ccumulation preveraison and subs equent
levels at harvest. A 68% reduction in IBMP concentration
of Cabernet Sauvignon at harvest resulted from removal of
lateral shoots and basal leaves on the east side of the f ruit-
ing zone at fruit set compared to an unthinned control (de
Boubee 2003). A similar t reatment imposed postver aison
resulted in only a 10% reduction in IBMP at harvest. How-
ever, that repor t did not consider more than one preveraison
leaf removal timi ng, the period when the accumulation of
MPs is greatest (Ryona et al. 2008), nor did it i nvestigate
the effects of the severity of leaf removal. We are unaware
of a ny other literatu re that has quantif ied the i mpac t of
leaf removal on M Ps in grape berries. The objective of this
study was to investigate the impact of timing and severity
of leaf removal on IBMP concentration in Cabernet franc
in the Finger Lakes and Merlot on Long Island, New York.
Materials and Methods
Experimental design. Two commercial v ineyards lo-
cated in Ovid, New York (42.67°N, 76.82°W; Fi nger Lakes
AVA, Cay uga Lake) and Cutchogue, New York (40.99°N,
72.48°W; Long Island AVA, North Fork) were used in this
st udy. The soil ty pe s we re classified by t he U.S. D.A. as
Howard ser ies with a g ravelly loam structure, well drained,
an d a de pt h of >2 m a nd as Have n ser ie s with a loa my
st r uct ure, well d rai ne d, a nd a de pt h of >2 m at Fi ng er
Lakes and Long Island, respectively. Vines at the Finger
Lakes site were Vitis vinifera L. cv. Cab er net franc cl. 1
grafted on 3309C rootstock trained to a Scott Henry system
with four canes. The upper canes were at 1.3 m height and
shoots vertically positioned. The lower canes were at 1.0 m
height and shoots downward positioned. Vines at the Long
Isla nd site were Merlot cl. 181 grafted on 3309C rootstock
trained to a combination of low wire cordon and a f lat cane
system with either two cordons or two canes at 1.0 m height
and shoots vertically positioned. Vine spacing for both sites
was 2.0 m between vi nes and 2.5 m betwee n rows. Vine
management was performed according to the standard viti-
cult ural practices for vinifera in the Finger Lakes and Long
Island regions. The experimental design was a randomized
complete block with fou r re plications. The expe rime nt al
plot at each site consisted of fou r rows, and each exper i-
mental unit consisted of eight contiguous vines in each row.
Treatments consisted of a control (no leaf removal); re-
moving the first, third, and f ifth leaf from the base of each
shoot at 10 days af ter anthesis (10 DA A 50%), 4 0 d ay s
after ant hesis (40 DAA 50%), or 60 days after a nthesis (60
DAA 50%); and removing the first five leaves beginning
at the base of each shoot at 10 days after anthesis (10 DAA
100%), 40 d ays after anthesis (40 DAA 100%), or 60 days
after a nthesis (60 DAA 100%). Two additional treatments
were added at the Cabernet franc site in the second year of
the st udy: removi ng the first, thi rd, and f if th leaf from the
base of each shoot at 15 d ays after veraison (15 DAV 50%)
or removi ng the f i rs t five leaves from the base of e ach
shoot at 15 days after veraison (15 DAV 100%). All basal
leaf removal treatments were applied by hand on all f ruit-
ing and nonfruiting shoots of each vi ne. The beginning of
bloom was noted on 18 June 2007 and 19 June 2008 (Cab-
er net f ra nc), and 22 Ju ne 20 08 (Merlot). Time of anthesis
was determined as the date on which 50% capfall wa s vi-
sually estimated. In 2007, the calendar dates for the treat-
ments in Caber net franc were ant hesis (17 June), 40 d ays
after anthesis (27 July), 60 days after anthesis (16 Aug), and
harvest (21 Oct). In 2008, the calend ar dates for the treat-
ments i n Cabernet franc and Merlot were anthesis (18 June
and 21 Ju ne, respectively), 40 days after anthesis (28 July
and 31 July), 60 days after anthesis (17 Aug and 20 Aug),
and harvest (20 Oct and 16 Oct). The 15-day post veraison
treatment was performed on Cabernet franc on 6 Sept 2008.
Sampling and har vest. Five days after each basal leaf
remov al tr eatment was i mpos ed in 2007 (15, 45, and 65
days after a nthesis) a nd 5 to 15 d ays after ea ch basal leaf
re moval treat me nt wa s i mposed in 2008 (15, 50, 75, 85
days after a nthesis) in Cabernet f ranc, 50 -ber ry samples
were collected at random f rom each experiment al unit for
IBMP quantif ication. At har vest, 150 berries were collected
at random from each exper imental unit in Cabernet f ranc
and Merlot for IBMP qua ntification and chemical analysis.
The berr y samples were placed in plastic storage bags and
immed iat ely frozen followed by storage at -23°C for later
Yield components wer e ass es sed in the 20 08 Ca ber-
net f ranc and Merlot studies. At har vest, yield (measured
with a hanging scale accurate to 0.01 kg; model SA3N340,
Salter Brecknell, Fairmont, MN) and cluster counts we re
Am. J. Enol. Vitic. 61:3 (2010)
deter mined for each vine and an average was recorded for
each replication. Crop weight and number of clusters were
used to calculate average cluster weight. Yield data was not
recorded in the 2007 Cabernet franc st udy as there was a
significant “green har vest” of fruit by the grower several
wee ks before harvest . In the 20 08 Cab er ne t franc study,
cluster thinning at veraison was performed by the grower in
all treatments to eliminate the least mature clusters.
Berry analysi s for Br ix , titrat able acid it y, and pH.
A subsample of 100 mat ure berries per experimental u nit
was removed f rom the -23°C freezer, placed in a 250-mL
beaker, and heated to 65°C for one hour in a water bath to
redissolve tartrates, pressed through cheesecloth with a pes-
tle, and the juice was collected for analyses. Soluble solids
(Br ix) were measured using a digital refractometer (model
300017; SPER Scientific, Scottsdale, AZ) with temperature
cor rection. Tit ratable acidity (TA) and pH were measured
with a n automat ic tit rate r (Titri no model 798, Metr ohm,
Riverview, FL), and TA wa s mea sured w ith a 5.0-m L ali-
quot of juice by tit ration against 0.1 N NaOH to pH 8.2.
Berry analysi s for IBMP. 3-Isobutyl-2-methoxypyr-
azine analysis was conducted using 50-berry samples. The
extraction method was head-space solid-phase microext rac-
tion (HS–SPME) and quantif ication was performed by com-
prehensive two-dimensional gas chromatography time-of-
flight mass spectromet ry (GCxGC–TOF–MS) as descr ibed
elsewhere (Ryona et al. 2009). In brief, HS–SPME was con-
ducted using a LEAP CombiPAL Autosample r (Carrboro,
NC) fitted with a th ree-phase fiber ( DVB/CA R/PDMS). A
10-min online incubation at 650 r pm agitation rate and an
incubation temperature of 80°C wa s applied before head-
space-fiber insertion and equ ilibrium. Following f iber in-
se rtion , the vi al wa s agit at ed at 100 r pm for 30 mi n at
80°C. Quantif ication was performed by GCxGC–TOF–MS
(Pegasus I V, Leco Cor p, St. Joseph, MI). SPME inject ions
were splitless with a desor ption temperature of 270°C. The
first capi llar y column (30 m × 0.25 mm × 0.50 μm) was
an RTX5 (Restek, Bellefonte, PA), and the second colu mn
(2.5 m × 0.10 mm × 0.10 μ m) was a VF-WAXms (Varian,
Palo Alto, CA). Helium was used as a car rier gas at a f low
rate of 1 m L/min. The temperatu re program was as fol-
lows: initial hold for 5 min at 40°C, followed by a 5°C/min
ramp to 120°C; then 2°C/min to 150°C, no hold; then 10°C/
min to 250°C, 15 mi n hold. The G CxGC modulation t ime
was 3 sec. The MS transfer line temperature was 230°C.
The TOF–MS was operated in EI mode with an ioni zation
energy of 70 eV. T he electron multiplier was set to 1680 V.
The TOF–MS data were st ored at an effective acquisition
rate of 12 0 Hz over a mass ra nge of m/z 20 to 40 0. The
qualifier ions were m/z = 124, 151, 166 for IBMP a nd m/z
= 126, 153, 168 for [2H2]-IBMP. The quantif ier ions were
m/z = 124 and 126, respectively.
Statistical analysis. Statistical analyses were conducted
with SAS statis tical sof tware (SAS Instit ut e, C ar y, NC ).
Data was subjected to the Proc GLM procedure and means
were separated using the Fisher’s protected least significant
difference (LSD) at the 5% sign if ica nce level. I BMP data
for harvested Cabernet franc berries in 2007 and 2008 were
not c ombined over yea rs due to significant yea r by t reat-
ment interaction.
Leaf removal in Cabernet franc. Leaf removal timing
and severity impacted the concent rat ion of IBMP preverai-
son and at ha rvest in both 2007 and 2008. In 20 07, at 15
days after anthesis, IBMP was present at quantif iable con-
centrations (data not shown), but no significant difference
was observed in IBMP between the 10 DAA leaf removal
treatment and the untreated vines. At 45 days after anthe-
sis, both the 10 DAA 50% and 10 DA A 100% treatments
significantly reduced IBMP concentrations by 52 and 53%,
respect ively, compared to the control (Fig ure 1A). At 65
days after anthesis, t he concentration s of IBMP in the 10
DAA 50% and 10 DAA 100% treatments were 55 and 65%,
respectively, lower than the control (Figure 1B). The period
bet ween veraison (65 days af ter anthesis) and harvest (125
days after ant hesis) was marked by a decline in IBMP con-
cent rat ion. The IBMP concentration in mature fruit ranged
from 0.5 to 4.3 pg/g (Fig ure 1C) and averaged 1.1% of the
observed max im a (65 days aft er anthesis). Although the
only significa nt reduc tion in IBM P concentratio n at the
th ree preha rvest sample timings was observed for the 10
DAA 50%, 10 DAA 100%, and 40 DAA 100% treat ments,
all leaf removal t reatments significantly reduced IBM P in
mature berries with respect to the control (Figu re 1C). The
range in Bri x of t he C aber net fr an c be rries at harvest in
2007 was 19.4 to 22.3 (Table 1). The 10 DAA 50% and 10
DAA 100% t reatments signif icantly increased Bri x com-
pared to the control by 5 and 10%, respectively. TA ranged
from 6.4 to 8.6 g/L across treat me nts. Al l leaf removal
treatments except the 60 DAA 50% treatment significantly
reduced TA compared to the control.
In 2008, the 10 DAA 50% and 10 DAA 100% treatments
signif icantly reduced the concent ration of IBMP i n Caber-
net franc ber ries at 50 days after anthesis by 28% and 36%
(Figure 1D). At 75 days after anthesis the 10 DAA 100%
and 40 DAA 100% t reatments reduced I BMP concent ra-
tions by 25% and 48%, respectively (Figure 1E). At 85 days
after anthesis, there were no significant differences among
treatments (data not shown). At harvest (124 days after an-
thesis), the range in IBMP concent ration acros s all treat-
ments was 1.2 to 3.5 pg/g (Figu re 1F) and averaged 1.3% of
the obser ved preveraison (50 days after anthesis) maxima.
Although the 10 DAA 50% and 100% treat ments signif i-
ca nt ly reduced I BM P concent ra tion s at the preve raison
sample timing, t he 10 DA A 100%, 4 0 DAA 50%, and 40
DAA 100% leaf removal t reatments significantly reduced
IBM P concentrations (ra nge = 34 to 60%) at har vest. The
range in Brix was 21.1 to 22.5, with no significant differ-
ences among treatments (Table 1). TA ranged f rom 5.5 to
6.8 g/L among treatments. All treatments except 10 DAA
50% significantly reduced TA below the control. No dif-
ferences in juice pH were observed among the leaf removal
treatments. Yield, number of clusters, and average cluster
Am. J. Enol. Vitic. 61:3 (2010)
weight per vine in 2008 ranged from 3.4 to 4.1 kg, 21.6 to
26.1, a nd 145.7 to 181.8 g, respectively, with no significant
differences among t reatments (data not shown).
Leaf removal in Merlo t. At harves t (117 days after
ant hesis), the range in I BMP concentration i n Merlot ber-
ries across treatments was 3.2 to 6.7 pg/g (Figure 2). Leaf
removal at all timings and severities significantly reduced
IBMP by a r ange of 37 t o 52% compa re d to the cont rol.
Leaf removal timing and severity had no signif icant impact
on Brix, TA, and pH (Table 1). T he 10 DAA 50% t re at-
ment had sign if icantly lower yield (1.9 k g/vi ne) t han the
control and other t reatments (ra nge = 2.1 to 2.4 kg /vine).
No signif icant differences were observed among treatments
for nu mbe r of clusters pe r vine (12.8 to 14.8) and average
cluster weight (143.2 to 172.9 g).
The highest concentrations of I BMP in Cabernet franc
were observed at the preveraison sample tim ings (65 days
after anthesis sa mpling in 2007, and at the 50 days aft er
anthesi s sampli ng i n 2008 (Figure 1). Differ ences in re -
por ted peaks between yea rs are likely a function of differ-
ent sample timings. In ag reement with our results, previous
research has demonstrated that IBMP reaches a maximum
in the 2 to 3 weeks before veraison (de Boubee et al. 2000,
Lacey et al. 1991, Ryona et al. 2008).
In both 2007 a nd 20 08, signif icantly lower IBM P con-
ce nt rations were observed in Caber net fr anc berries in
the 10 DAA 50% a nd 10 DAA 100% treatments compared
to the control at t he time poi nts ju st before or just aft er
veraison (65 days p osta nt he sis in 20 07, 50 days postan -
thesis in 20 08). No significant effe ct of leaf r emoval was
observed at these poi nts with the 40 DAA 50% or the two
60 DA A t reatments in either yea r, although the 40 DAA
100% treat ment had lower IBMP than the control in 2007.
These results are in concordance with a recent observation
that clu ster light exposu re preveraison reduces IBMP a c-
cumulation (Ryona et al. 2008). Because basal leaf removal
is widely shown to improve light penetration to the fruit-
in g z one ( Reyn olds et al. 1996, 20 06, Wolf et al. 1986,
Zoecklein et al. 1992), the reductions in IBMP concentra-
tion that we obse rved are likely due to incre ased cluste r
light exposure. Generally, we did not obser ve a significant
decrease in IBM P at the time point i mmediately following
the treatment application. We did not observe signif icantly
lower IBMP in the 40 DAA 50% treat ment at 45 d ays after
anthesis in 2007 or at 50 days after anthesis in 2008 nor did
we observe a significant effect for the 40 DAA 100% treat-
ment at 50 days after anthesis i n 20 08. We d id, however,
observe sign if icantly lower IBMP in the 40 DAA 100%
treatment at 75 days after anthesis in 2008, and at 65 days
after anthesis in 2007. Similarly, no significant difference
Figure 1 A 
Am. J. Enol. Vitic. 61:3 (2010)
in IBMP was ob se rved between the 10 DAA treatments
and t he control at 15 days after anthesis in both years nor
was a difference observed at 75 days after anthesis between
the 60 DAA treatment s and the control. Thus, exce pt for
one case (40 DA A 100% in 2007), the impact of t he leaf
removal treat ment was not obser vable until >15 days after
the treatment was imposed.
Across all three stud ies, the largest and most consistent
dec reases for IBMP at har vest were observed in t he ea rly
leaf removal treatments. In the 2007 Cabernet franc study,
all t reatments had signif icantly lower IBMP than the con-
trol at harvest, with the g reatest reduction i n the 10 DAA
100% and 40 DAA 100% t reat ment s ( Fig ure 1C). I n the
2008 Cab er net f ranc st udy, the 10 DAA 100%, 4 0 DA A
50%, and 40 DAA 100% treatments contained significantly
lower IBMP at harvest compared to the control (Figure 1F).
In the 2008 Merlot study, all t reatments resulted in lower
IBMP than the control at har vest (Figure 2). These results
support t he previous hy pothesis t hat cluster light exposu re
pr ever ai so n inhibits ac cumulat ion p re vera ison, but has
lit tle effect postveraison, and that the relative differences
in I BMP established before f ruit mat urat ion per sist unti l
harvest (Ryona et al. 2008).
Althoug h preveraison leaf removal (10 or 40 days post-
anthesis) resulted in the largest decrease in I BMP levels
at har vest compared to the control i n the Cabernet f ranc
studies, we also observed a smaller but still sign ificant de-
crease in IBMP for the 60 DAA treatments in both the 2007
Cabernet franc and 2008 Merlot stud ies. Previou s wo rk
(Allen et al. 1996, Marais et al. 1999, Ryona et a l. 2008)
indicates t hat clu ster exposure reduc es IBM P accu mula-
tion preveraison, but does not increa se IBMP degradation
postveraison on a percentage basis. A p otent ial explana-
tion is that IBMP sy nthesis and degrad ation are occurring
simultaneously, at similar rates, in ber ries 40 to 60 days
Figure 3
Table 1 
Treatment Brix TA (g/L) pH
2007 Cabernet franc
  
  
  
   
   
  
  
  
2008 Cabernet franc
   
   
   
   
   
   
   
   
   
  
2008 Merlot
   
   
   
   
   
   
   
  
  
Figure 2    
         
   
      
Am. J. Enol. Vitic. 61:3 (2010)
postanthesis. Thus, IBMP synt hesis may still be occu rring
around ver aison although the berry IBMP concent rat ion is
unchanged. In s uppor t of this hypothesis, we observe d a
sizeable decrease (41%) in 2008 Cabernet franc for the 40
DAA 100% treatment at Day 75 compared to the control,
even though no significant decrease was observed at Day
50. However, IBMP synthesis li kely does not persist late
into the season. In the 15-day postveraison treatments (50%
and 100%) in the 2008 Caber net f ranc study, we observed
no signif icant change in IBMP levels at harvest compared
to the control (Figu re 1F). Sim ilarly, post veraison clust er
sha ding has been repor ted to have no impact on I BMP in
Cabernet Sauvignon (Sala et al. 2004).
Several st udies have reported that g rowing season tem-
peratu re a nd MP cont ent in mat ure ber ries are inversely
correlated (Allen et al. 1991, 1994, Falcao et al. 2007). The
total growing deg ree d ays (GDD, base 10°C) accumulated
at t he Finger La kes site i n 2007 and 20 08 from 1 Jan to
harvest (17 and 16 Oct) w as 1552 and 1410, r es pect ively
(Figure 3). Although there were 142 more tot al GDD accu-
mulated in 2007, there was less than 1% difference between
years in GDD accumulated f rom 10 days af ter anthesis to
veraison. The p er io d bet ween ver aiso n a nd harvest was
much warmer in 2007 (492 GDD during ripen ing) than in
2008 (349 GDD). Thus far, the relative importance of pre-
veraison versus postveraison growing season temperat ure
in deter mining IBMP cont ent in grapes has not been re -
ported. Althoug h we obser ved large diffe rences in GDD
between years, the average IBMP concentrations measured
at har vest in Cabernet franc (2.0 pg/g in 2007 and 2.3 pg/g
in 20 08) we re si milar, suggesti ng that the postveraison
GDD a ccumu la tion d id not have a strong inf luence on
final IBMP concentr ation. A st rong correlation has been
noted between IBMP concent rations at veraison and harvest
(Ryona et al. 2008), suggesting that final concentration is
dependent upon preveraison conditions.
Althoug h the harvest concentrations of IBMP observed
in this study are below repor ted sensory thresholds in red
wi ne (de Boubee et al. 20 00, Kotseridis et al. 1998), the
leaf removal t reatments in 2007 and 2008 reduced the final
IBMP concent ration in Cabernet franc by up to 88% and
60%, re spect ively, and in Merlot by up to 52% compared
to the control. In Caber net franc, IBMP accumulation was
reduced by up to 65% (2007) and up to 36% (2008) by the
10 DAA 50% and 10 DAA 100% treatments at the observed
maximum IBMP concentrations. Although we did not mea-
sure cluster light exposure for the various treatments in this
st udy, ou r f indi ngs may be consistent with oth er group s
that have evaluated t he effects of preveraison cluster light
exposu re on IBMP concent ration (Allen et al. 1996, de
Boubee 2003, Marais et al. 1999, Ryona et al. 2008).
Preveraison basal leaf removal treatments reduced IBMP
concent rat ion in Cabernet franc and Merlot berr ies at har-
vest. In Cabernet franc, accumulation of IBMP in the pre-
verai son pe riod was red uced by leaf removal, likely due
to improved lig ht intercept ion by the clusters. In a situa-
tion where IBMP is present in concentrations near sensory
threshold, leaf removal during the growing season could be
critical in reducing accumulation of I BMP. The earliest (10
days after anthesis and 40 days after anthesis) leaf removal
treatments yielded the greatest benef it in reducing IBMP.
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... Since MPs are influenced by the cultivar, temperature, and sunlight, research has been conducted to address the management of MPs-as with other secondary metabolitesthrough viticultural practices [13,51,54]. Several studies have examined the effects of cluster exposure on MP levels. ...
... Several studies have examined the effects of cluster exposure on MP levels. The training system [13], vine spacing [51], row orientation [55], leaf removal [32,54,56], and irrigation [51,57] can all impact MP levels and the potential wine quality through their influence on fruit cluster exposure. Training systems that increase temperature and light exposure both in the canopy and in the fruiting zone have been associated with a lower MP content [13]. ...
... Defoliation via leaf removal to expose grape clusters has also become a widely used method in cool climate regions to reduce the MP content in red Bordeaux grape cultivars. Early defoliation can reduce the concentration of MPs in grapes at harvest [32,54], particularly under poor growing conditions such as in cool, wet years [56]. Early leaf defoliation (10-40 days after flowering) reduced the IBMP content by 28-58% at veraison and 34-88% at harvest compared to the non-defoliated vines [54]. ...
Full-text available
Alkyl-methoxypyrazines are an important class of odor-active molecules that contribute green, ‘unripe’ characters to wine and are considered undesirable in most wine styles. They are naturally occurring grape metabolites in many cultivars, but can also be derived from some Coccinel-lidae species when these ‘ladybugs’ are inadvertently introduced into the must during harvesting operations. The projected impacts of climate change are discussed, and we conclude that these include an altered alkyl-methoxypyrazine composition in grapes and wines in many wine regions. Thus, a careful consideration of how to manage them in both the vineyard and winery is important and timely. This review brings together the relevant literatures on viticultural and oenological inter-ventions aimed at mitigating alkyl-methoxypyrazine loads, and makes recommendations on their management with an aim to maintaining wine quality under a changing and challenging climate.
... IBMP content in all treatments was below the sensory threshold in red wine (Roujou de Boubée et al., 2000). While leaf removal at full bloom has been shown to reduce IBMP content in 'Cabernet Franc' (Scheiner et al., 2010), defoliation at any time did not impact IBMP levels in 'Chambourcin'. In another study, IBMP concentration at harvest decreased in 'Merlot' fruit in response to post-fruitset (fruit exposure response) but not pre-bloom defoliation (crop level response) . ...
Several winegrape cultivars grown in cool climates, including Vitis sp. ‘Chambourcin’, are highly productive and require crop regulation to ensure timely fruit maturation and improved fruit quality. Balanced pruning and cluster thinning are the cultural practices used to attain the desired crop load in ‘Chambourcin’. However, crop reduction by cluster thinning is labor intensive, costly and typically not mechanized for winegrapes. In this study, the practice of early season leaf removal was investigated as an alternate tool to reduce crop level, thereby optimizing crop load and fruit quality in ‘Chambourcin’. The specific objectives were to determine the effects of the timing of leaf removal (pre-bloom, bloom, fruitset, no removal) on yield components, crop load, fruit composition, and cold hardiness. Leaf removal at pre-bloom and bloom reduced yield and crop load (Ravaz index) as compared to control (no defoliation). However, leaf removal did not impact fruit composition. Furthermore, defoliation at pre-bloom and bloom reduced bud cold injury during the dormant season. Therefore, early season leaf removal is a viable alternative to cluster thinning as a vineyard practice for yield regulation in ‘Chambourcin’ grapevines.
... Several environmental factors such as cluster shading, water availability and nitrogen fertilization can affect the accumulation of IBMP in grapes. Basal leaf removal performed at 10-40 days after anthesis may to reduced IBMP synthesis in grapes (Scheiner et al., 2010). Cluster shading carried out since veraison, using pieces of sackcloth, resulted in wines with lower IBPM concentration than the sun exposed clusters (Sala, Busto, Guasch, & Zamora, 2004). ...
Climate is the main factor affecting grape and wine quality in Mediterranean viticulture. Global warming provokes an increase in the accumulation of soluble solids in grapes, together with a lower content of anthocyanins and acidity. This result in stuck and sluggish fermentations causing economic losses in the winery. Climate adaptation strategies are essential to minimize the detrimental effects of global warming on grape and wine quality. This review summarized the effect of viticultural techniques to delay grapevine ripening with emphasis on canopy management and we overviewed the effects of high temperatures on grape and wine quality. Some viticultural techniques such as severe shoot trimming, minimal pruning, late winter pruning and apical leaf removal may delay grapevine ripening close to 15 days. Forcing regrowth is the most interesting technique since it allows to delay grape ripening at least of two months which can be essential in warm grapevine production areas.
... However, in another study, leaf removal applied at veraison did not affect the content of total soluble solids, whereas it markedly increased the concentrations of C 6 alcohols especially (Z)-3-hexenol (He et al., 2020). Many studies reported that pre-veraison sunlight exposure inhibited the accumulation of methoxypyrazines (Martin et al., 2016;Plank, Hellman, & Montague, 2019;Sivilotti et al., 2016;Suklje et al., 2016) while post-veraison light exposure almost have no impact on methoxypyrazine accumulation (Scheiner et al., 2010). However, Sivilotti et al. (2017) found that the concentrations of IBMP in Sauvignon blanc grapes were not significantly affected by early leaf removal. ...
In this study, fruit-zone microclimate was modified by three treatments, including inter-row mulch (M), the combination of leaf removal applied at the onset of veraison and inter-row mulch (MLR-BV), and the combination of leaf removal applied at complete veraison and inter-row mulch (MLR-EV), in a semi-arid climate in three consecutive years (2015–2017). M decreased fruit-zone reflected solar radiation from vineyard floor and low temperature (10–20 °C) duration, whereas it increased soil temperature and high temperature (> 30 °C) duration. MLR-BV and MLR-EV increased fruit-zone incident photosynthetically active radiation while decreased the duration of 20–25 °C compared to M. Notably, M significantly decreased grape total norisoprenoid concentrations in 2015–2017, and total terpenoid concentrations in 2015–2016. Applying leaf removal applied at the onset of veraison could compensate the decreases of total norisoprenoids and terpenoids caused by M when two treatments were applied together. Besides, M significantly increased grape total C6/C9 compound concentrations, besides, (Z)-3-hexen-1-ol concentrations were significantly higher in grapes of M than those of MLR-BV in 2015–2017. Light exposure and high temperature duration after veraison had strong positive correlations with total norisoprenoids and terpenoids, besides, low temperature duration was positively correlated with total norisoprenoids. In addition, light exposure after veraison had strong negative correlations with total C6/C9 compounds. With respect to the volatile compounds in wines, M significantly decreased the concentrations of isopentanol and ethyl acetate, and the concentrations of ethyl cinnamate, phenylacetaldehyde, phenylethyl alcohol and 3-methylthio-1-propanol were significantly lower in MLR-BV and MLR-EV than in M. The outcome of this study can assist winegrowers to properly adjust vineyard managements to optimize the concentrations of desired volatile compounds in grapes and wines.
... Light exposure and climate seem to have the largest effect on both production and degradation of methoxypyrazines in grapes (Sidhu et al., 2015). Exposing the grape cluster to sunlight can result in a reduced methoxypyrazine concentration in the berries (Noble et al., 1995;Scheiner et al., 2010). It has been observed that methoxypyrazine biosynthesis occurs during the early stages of fruit development, from fruit-set to veraison, and this period might be critical for determining its final concentration at harvest (Hashizume and Samuta, 1999). ...
A new approach for applied research and decision-making in the sector of viticulture related to the mountain territory and the global warming phenomenon is purposed. A high-resolution topoclimate model 5 m × 5 m was applied to classify the different vineyard characters in South Tyrol, an Italian wine region where a considerable dense concentration of different top quality wines is present. Determining the connections between the territory and microclimate can lead to more accurate assessments of the vineyards natural identities and the characteristics of their wines. The results of our geospatial statistical analysis on all the about 26,000 vineyards are used to generate a geographical classification index termed the Solar Radiation Identity (SRI). This quantitative index can characterize the topoclimatic potential of each local vineyard but also be extended to other wine regions with a global perspective. The SRIv index rate can be related to the biosynthetic activity of the vines as well as to the quality of the vineyard's grapes and wine. A qualitative analysis of zones with different SRIv distinguished manifest differences in the concentration of natural polyphenols anthocyanins and tannins in Pinot Noir wines. In the Sauvignon Blanc wines from some specific vineyards with low SRIv, the varietal characteristics that enhance the thiol molecules are quite evident and singular. The proposed analysis method can support the correct matching between vineyard and grape varietals, as well the process of identifying ideal sites for new vineyards, by recognizing original areas that may increase ecological diversity or can favor the quality production. This topoclimate classification can also provide insights into how to reduce the wine product vulnerability, in terms of its protect designation of authentic geographical origin or to better adapt the vine varieties to climate change.
This chapter discusses the impacts of various cultural practices on fruit composition and wine quality, with an emphasis on aroma compounds. It is framed within four basic pillars of the Cool Climate Paradigm of winegrowing: (1) keep the fruit warm; (2) keep the leaves exposed to sunlight; (3) achieve vine balance; (4) minimize water stress. Practices that are particularly relevant to these basic pillars include hedging and basal leaf removal, training systems, vine spacing, crop control and shoot density, vineyard floor management, and irrigation. Fruit exposure, canopy manipulation, prefermentation practices, and vineyard site influence in particular the concentration of aroma compounds in grapes and wines. These differences can sometimes be confirmed organoleptically in wines. The recent literature has displayed greater focus on the effects of viticultural practices on secondary metabolites such as aroma compounds, anthocyanins, and phenolic compounds. In the case of secondary metabolites: (1) many are responsive to viticultural and oenological practices; (2) aroma compounds and phenolic analytes are not always correlated with soluble solids, titratable acidity, or pH, thus cannot necessarily be predicted by standard harvest indices; (3) losses in many aroma compounds can occur between the berry and juice stages, hence the desirability of skin contact; (4) aroma compound and phenolic concentrations can, in some cases, be related to wine tasting results. Recent research in in grapevine cultural practices has included investigations into effects of prebloom leaf removal for reducing berry set and cluster compactness with concomitant improvements in fruit composition. Discoveries have been made in aroma chemistry, such as the confirmation of rotundone as the main source of the black pepper component in Syrah, in addition to vigor-based zonal variation. Recent irrigation research has confirmed much of prior work that focused on fruit composition and wine sensory attributes. Investigations into fertilization and cover crops have uncovered impacts of these variables upon aroma compounds, in particular norisoprenoids.
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Grapevine productivity, and berry and wine flavonoid concentration, depend on the interactions of cultivar, environment, and applied cultural practices. We characterized the effects that mechanical leaf removal and irrigation treatments had on the flavonoid concentration of ‘Merlot’ (Vitis vinifera, L.) grape berries and wines in a hot climate over two growing seasons with contrasting precipitation patterns. Leaves were removed by machine, either pre-bloom leaf removal (PBLR), or post-fruit set leaf removal (PFLR), or not removed (control) and irrigation was either sustained deficit irrigation (SDI) at 0.8 of crop evapotranspiration (ETc) from budbreak to fruit set, or regulated deficit irrigation (RDI) at 0.8 ETc from bud break to fruit set, 0.5 ETc from fruit set to veraison, and 0.8 ETc from veraison to harvest, of ETc In 2014, PFLR reduced the leaf area index (LAI) compared to control. The RDI decreased season-long leaf water potential (Ψint) compared to SDI. However, in 2015, none of the treatments affected LAI or Ψint. In 2014, berry flavonoid concentrations were reduced by PBLR as well as SDI. SDI increased the flavonoid concentrations in wine, and PFLR increased some wine flavonols in one season. No factor affected the concentrations of wine proanthocyanidins or mean degree of polymerization. Thus, mechanical PFLR and RDI may increase berry flavonoid accumulation without yield reduction, in red wine grapes cultivars grown in hot climates when precipitation after bud break is lacking. However, spring precipitation may influence the effectiveness of these practices as evidenced by this work in a changing climate.
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Teve-se como objetivo do trabalho comparar diferentes épocas de desfolha e o seu efeito nas características químicas e físicas dos cachos da variedade Chardonnay em região de elevada altitude de Santa Catarina. O presente estudo foi realizado nas safras 2018 e 2019, em um vinhedo comercial, situado no munícipio de São Joaquim – Santa Catarina. Foi utilizado vinhedo da variedade Chardonnay enxertada sobre ‘Paulsen 1103’. Os tratamentos consistiram na realização da desfolha, expondo a região dos cachos em cinco diferentes estágios fenológicos: plena florada, baga chumbinho, baga ervilha, virada de cor e plantas sem desfolha (testemunha). Avaliou-se índices produtivos, arquitetura de cacho e maturação tecnológica. As variáveis foram submetidas à análise de variância (ANOVA) e quando detectados efeitos de tratamento, procedeu-se o teste de comparação de médias pelo Teste Scott Knott a 5% de probabilidade de erro. A realização do manejo da desfolha da videira ‘Chardonnay’ não influenciou variáveis relacionadas a arquitetura de cachos (massa de cacho, comprimento de cachos e número de bagas). No entanto, quando realizada após o estádio fenológico baga chumbinho propicia aumento do índice de compactação. Os resultados obtidos no presente trabalho demonstram que o manejo da desfolha aumentam os índices produtivos (produção por planta e produtividade) e melhora da maturação tecnológica da videira (sólidos solúveis), sendo recomendado sua realização até o estádio fenológico virada de cor.
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In commercial wine grape production, canopy management practices are applied to control the source-sink balance and improve the cluster microclimate to enhance berry composition. The aim of this study was to identify the optimal ranges of berry solar radiation exposure (exposure) for upregulation of flavonoid biosynthesis and thresholds for their degradation, to evaluate how canopy management practices such as leaf removal, shoot thinning and a combination of both affect the grapevine (Vitis vinifera L. cv. Cabernet Sauvignon) yield components, berry composition and flavonoid profile. Three experiments were conducted in Oakville, CA U.S.A. First experiment assessed changes in the grape flavonoid content driven by four degrees of exposure. In the second experiment, individual grape berries subjected to different exposures were collected from two cultivars (Cabernet Sauvignon and Petit Verdot). The third experiment consisted of an experiment with three canopy management treatments i) LR (removal of 5 to 6 basal leaves), ii) ST (thinned to 24 shoots per vine) and iii) LRST (a combination of LR and ST) and an untreated control (UNT). Berry composition, flavonoid content and profiles and 3-isobutyl 2-methoxypyrazine were monitored during berry ripening. Although increasing canopy porosity through canopy management practices can be helpful for other purposes, this may not be the case of flavonoid compounds when a certain proportion of kaempferol was achieved. Our results revealed different sensitivities to degradation within the flavonoid groups, flavonols being the only monitored group that was upregulated by solar radiation. Within different canopy management practices, the main effects were due to the ST. Under environmental conditions given in this trial, ST and LRST hastened fruit maturity; however, a clear improvement of the flavonoid compounds (i.e. greater anthocyanin) was not observed at harvest. Methoxypyrazine berry content decreased with canopy management practices studied. Although some berry traits were improved (i.e. 2.5 Brix increase in berry total soluble solids) due to canopy management practices (ST), this resulted in a four-fold increase in labor operations cost, two-fold decrease in yield with a 10-fold increase in anthocyanin production cost per hectare that should be assessed together.
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Bloom (20 mg/L) and various postbloom (40 to 100 mg/L) applications of gibberellic acid (GA) ± basal leaf removal (BLR) were imposed on Sovereign Coronation vines over a three-year period. GA increased yield in one of three years and berry weight in all three years, while vestigial seed development decreased in two of three years as a linear function of the concentration of GA applied. Brix was reduced linearly with increasing GA in two of three years, pH was generally unaffected, but titratable acidity decreased with increasing GA. Color intensity and anthocyanins increased relative to GA in 2002 only. Methyl anthranilate increased relative to GA in one season while total volatile esters also increased with increasing GA. Treatments involving 40 mg/L GA led to higher fruity and labrusca flavor, sweetness, persistence of flavor, and overall impression, as well as lower acidity and bitterness. Basal leaf removal delayed berry maturity slightly but increased light penetration into the canopy. Berries from non-GA-sprayed control treatments ± BLR were separated into several maturity categories (based on berry Brix) by sucrose buoyant density gradients and were thereafter subjected to sensory evaluation. Increased berry maturity was associated with decreased berry weight and titratable acidity, and increased color intensity, anthocyanins, phenols, methyl anthranilate, and total volatile esters. Principal component analysis coupled with discriminant analysis suggested that soluble solids ≥17 Brix was associated with sweetness, fruity, labrusca, and overall impression. Copyright © 2006 by the American Society for Enology and Viticulture. All rights reserved.
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The precise location of 2-methoxy-3-isobutylpyrazine in Cabernet Sauvignon grape bunches was identified before véraison, after véraison, and when grapes were picked. Regardless of ripeness, the compound was mainly located in stems, then in skins and seeds, while the flesh contained very little. During ripening, the proportion of 2-methoxy-3-isobutylpyrazine in stems and seeds decreased, while it increased in skins. During the winemaking process, this methoxypyrazine was easily extracted from Sauvignon blanc (at the beginning of pressing) and Cabernet Sauvignon grapes (after 24 hours in vat). The concentration in Sauvignon blanc must may be reduced by settling (decreasing by half). The 2-methoxy-3-isobutylpyrazine content of Cabernet Sauvignon wines varied relatively little during vatting, irrespective of the length of time or the number of times it was pumped over. Press wines, however, had higher concentrations of this compound than free-run wines. Although settling white must and careful addition of press wine to blends had a certain impact, the 2-methoxy-3-isobutylpyrazine content of the wine depended primarily on the composition of the grapes.
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An analytical method to determine the volatile components of wines is proposed for studying Merlot noir cultivar clones (181, 182, 343, 347) produced in 1993 and 1994. The substances were 3-isobutyl-2-methoxypyrazine, three norisoprenoid-ketones, free terpenols and the alcohols with six carbon atoms. Wines made from the 1993 harvest contained more 3-isobutyl-2-methoxypyrazine and fewer norisoprenoids-ketones because of the cooler climatic conditions in that year. The wine of clone 182 had higher levels of 3-isobutyl-2-methoxypyrazine for the two harvests.
Cabernet Sauvignon wines are characterized by berry and vegetative aromas. Winemakers have known for decades that young vines in cool climates and vigorous vines with dense canopies tend to yield very intensely vegetative wines. Only with the advent of a GC-MS method using isotopically labeled methoxypyrazines was it possible to conclusively identify and quantify the potent 2-methoxy-3-isobutyl pyrazine (MIBP) which had long been suspected to contribute to this bell-pepper-like aroma in wines. A review of sensory and chemical studies of Cabernet Sauvignon wine flavor is presented, including a recent study which in which the effect of vine vigor and light on wine flavor and methoxypyrazine levels was investigated. A strong correlation was found between high vine vigor, low light intensity in the canopy and the intensity of the vegetative aroma and flavor by mouth, with the concentration of MIBP.
Sauvignon blanc is one of the most important white wine cultivars grown in South Africa. It is well-known that climatic and viticultural factors have a major effect on Sauvignon blanc grape and wine composition and quality. Of equal importance is the effect of production factors on Sauvignon blanc wine composition and quality. The purpose of this study was to evaluate the effect of such factors. Wines were produced from grapes from two regions that were stored overnight at 0°C and 20°C. Skin contact was conducted for 15 hours at these temperatures, with as well as without SO2 addition prior to fermentation. Free-run juices were used as control. Settled juices were analysed for 2-methoxy-3-isobutylpyrazine (ibMP) and monoterpenes, and the corresponding wines also for ibMP, acetate and ethyl esters, total polyphenols and total flavanoids. The wines were sensorially evaluated for fruitiness and the typical green pepper/grassy aroma of Sauvignon blanc. Grape temperature, skin contact, and oxidative and reductive conditions prior to fermentation affected some of the above-mentioned component concentrations and therefore wine quality. Generally, most component concentrations were increased by skin contact, while polyphenol and flavanoid concentrations were lower in wines produced oxidatively. It appeared that wines produced reductively from free-run as well as low temperature skin contact juices presented the highest quality. Sauvignon blanc is one of the most important white wine cultivars grown in South Africa. The area planted to this cultivar has increased by 99% from 2 255 (1985) to 4 479 hectares (1996) (Booysen & Truter, 1997). The typical cultivar aroma of Sauvignon blanc is described as vegetative, grassy, herbaceous, gooseberry-, asparagus- and green pepper-like. These nuances are mainly caused by a specific group of chemical components, namely methoxypyrazines. The most important contributor appears to be 2-methoxy3-isobutylpyrazine (ibMP), which normally occurs in much higher concentrations in Sauvignon blanc grapes and wine than other methoxypyrazines (Allen et al., 1991). The preference of producers and consumers, however, is that the methoxypyrazine aromas should not be dominant or onesided, but have to be complemented by tropical and fruity aromas. Monoterpenes, norisoprenoids, esters and higher alcohols are among the compounds that may present these types of aromas.
The effects of berry development and light exposure on the concentrations of 2-methoxy-3-isopropyl- and 2-methoxy-3-isobutylpyrazine (isopropylMP and isobutylMP) were examined in grapes. The concentrations of MPs in unripe grapes (at about 30 days after anthesis) of eight cultivars were higher than those in ripened berries, although the concentration was dependent on cultivar. The MPs in unripe Cabernet Sauvignon grapes which had been removed from the cluster and packed in glass vessels increased under fluorescent light. On the other hand, the isopropylMP in grapes sampled at about 50 or 70 days after anthesis, decreased under such light. The MPs in unripe grapes treated with a saturated solution of CaCl2, which might inhibit the formation of MPs in the grapes, were stable in the absence of light, but decreased in the presence of light. Results indicate that light exposure has two opposite effects on the concentration of MPs in grapes: (a) promoting the formation of MPs in immature grapes; and (b) photodecomposing the MPs in ripening grapes.
Grape glycosides are, in part, important aroma and flavor precursors. Their quantification may offer a means of determining the impact of viticultural practices, such as leaf removal, on potential wine quality. Fruit zone leaf removal of Riesling and Chardonnay grapevines grown at two sites for two seasons was evaluated for its influence on total and phenol-free grape glycosides at harvest. Vines were trained to a low bilateral cordon system at one vineyard and a high bilateral cordon at the other. The concentrations of total and phenol-free glycosides were higher in Riesling and Chardonnay fruit from leaf-pulled vs control vines at three of four harvest dates. Phenol-free glycosides averaged 80% of the total in Riesling juice and 66% of the total in Chardonnay. Grapevine canopy microclimate plays an important role in determining fruit composition, although knowledge about the relationship between microclimate and aroma/flavor development is limited. This study illustrates the affect of microclimate manipulation on grape glycosides, important components of fruit quality.
Selective leaf removal from grapevine fruit zones was evaluated for three seasons as a means of improving grape quality, especially with respect to fruit rot control. Mature White Riesling (syn. Riesling) and Chardonnay grapevines, grown in two northern Virginia vineyards, were used. Vines were trained to a high (1.8 m above ground), bilateral cordon at one vineyard and a low (1.2 m), bilateral cordon at the other; spur pruning was used at both vineyards. Two treatments, (1) removal of two to four leaves per shoot from around fruit clusters two to three weeks after bloom, or (2) no leaf removal, were compared. Leaf removal increased fruit zone porosity as measured by percentage sunlight penetration, point quadrat analysis, and air-blast spray penetration. Fruit yield components were generally unaffected by leaf removal, although crop per vine and cluster weight were occasionally increased with leaf removal of Riesling. Fruit soluble solids at harvest were reduced slightly in three instances and increased in one, by leaf pulling, while pH and potassium levels remained unaffected. Leaf removal reduced titratable acidity as well as malic acid, although not consistently. The incidence of botrytis and sour bunch rot, as well as the concentrations of rot organism metabolites (glycerol, acetic acid, gluconic acid, and ethanol) in harvested fruit, were reduced with leaf removal of Riesling vines. The chief benefit of leaf removal in this region appeared to be improved bunch rot control with Riesling.