1. 10/2/2012
Introduction to Vines and
Wines
Hort/VE 113 Fall 2012
Session 10&11-Grape ripening and
Maturity Estimation I & II
Vinification
• The process of turning grapes into
wine starts with vinification.
• Wine is the result of vinification.
• As grapes grow several factors
grow,
influence wine quality.
–Climate
–Variety
–cultural practices
–soil
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2. 10/2/2012
There are 4 parts of a grape:
Stems: contain a bitter oil which give wine an
unpleasant taste, removed by stemmer
Skins: contain tannin, which is responsible for
coagulation of proteins, enabling the wine to
g p , g
settle and become clear
Seeds: insoluble, yet “harsher” tannins and
phenols can leach into the pomace from testa
Pulp: the part of the grape mainly used in
the production of wine
Development during the first
growth period
• 0-60 days
• the berry expands in volume as
solutes accumulate
• several solutes th t accumulate in the
l l t that l t i th
berry during the first growth period
reach a maximum around véraison.
• most prevalent are tartaric and malic
acid.
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3. 10/2/2012
During the first growth period(cont.)
• Acids distributed in the berry somewhat
differently:
– tartaric acid is highest towards the outside
of the developing berry, and accumulates
during the initial stages of berry
development
– malic acid is highest in the flesh,
accumulates just prior to véraison.
• These acids provide wine with acidity
and are therefore critical to wine
quality.
During the first growth period(cont.)
• Also accumulating during the initial
period of growth are the
hydroxycinnamic acids.
• distributed in the flesh and skin of the
berry
• important because:
– involvement in browning reactions
– precursors to volatile phenols
During the first growth period(cont.)
• Tannins, including the monomeric
catechins also accumulate
• Tannins are present in skin and seed
tissues and nearly absent in the flesh
– Responsible for the bitter and astringent
properties of red wine.
– Also believed to be important in red wine
color stability.
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During the first growth period(cont.)
• Other compounds that accumulate in
the berry during the first phase of
growth:
– Minerals
– amino acids
– micronutrients
– aroma compounds (such as
methoxypyrazines)
• have importance to wine quality.
Verasion-change of grape
color
• White grapes turn from deep green to
yellow-green
• R d grapes t
Red turn from green to
f t
purple-red
• Change is quite rapid, sometimes in a
few days!
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5. 10/2/2012
Development during the second growth
period
• Aka fruit ripening (véraison)
• Characterized by softening and coloring of
the berry.
• Berry approximately doubles in size before
y pp y
harvest.
• Many of the solutes that accumulated in
the grape berry during the first growth
period remain at harvest
• Due to the increase in berry volume, their
concentration is reduced significantly.
During the second growth period(cont.)
• Some compounds already produced are
reduced on a per-berry basis (not
simply diluted)
• P i i l among these is malic acid
Principal th i li id
– reduction varies considerably
– Roughly correlated with climate
– grapes grown in cooler regions tend to
have more malic acid than those grown in
warmer regions
During the second growth period(cont.)
• Tannins decline considerably on a per-
berry basis
• reduction in seed tannin due to
oxidation as they become fixed to the
seed coat.
• results in a change in the composition
of extracted seed tannins
– characterized by a proportional reduction
in the most bitter tannin components.
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6. 10/2/2012
During the second growth period(cont.)
• Skin tannins decline or remain
constant during the second period of
growth
• Tannins also change:
– Significant modifications that take place
for the skin tannins include an increase in
their size-less astringent wine flavor,
more “body”.
During the second growth period(cont.)
• Notable aroma compounds produced
during the first growth period decline
(again, on a per-berry basis) during
fruit ripening.
• These include methoxypyrazine
compounds
– contribute vegetal characters(“green
bean”) to some wines (such as Cabernet
Sauvignon and Sauvignon Blanc).
During the second growth period(cont.)
• Methoxypyrazine decline is thought to
be linked to sunlight levels in the
cluster.
• Th
These compounds are deemed to be
d d d t b
undesirable (the current prevailing
opinion)
• Canopy management can be used to
reduce methoxypyrazine content.
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7. 10/2/2012
During the second growth period(cont.)
• the big story during the second
growth period:
• tremendous increase in sugar
compounds (the major ones being
glucose and fructose)
– occurs as a result of a total biochemical
shift into fruit ripening mode.
Vinification(cont.)
• Grapes ripen early(130) mid-
season(170) or late(200)
• G
Grapes require 20-30” water a season
i 20 30” t
• Optimal temperatures 77-86 °F, good
“vintage” is usually heat-related
Vinification(cont.)
• Higher temps cause sunburn, reduced
growth rates and water stress.
• Excessively high growing
temperatures:
– reduce acids
– increase pH
– inhibit color
– reduce “normal” aromas/flavors
– Low RH stresses vines
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8. 10/2/2012
Compound grape must dry wine
Water 70-85 80-90
Carbohydrates
-Sugars 15-25 0.1-0.3
-Alcohols 0 8-15
-Organic acids 0.3-1.5 0.3-1.1
Phenolics 0.05-0.15 0.5-0.35
Nitrogen compounds 0.03-0.17 0.01-0.09
Carbonyl Compounds 0 0.001-0.05
Inorganics 0.3-0.5 0.15-0.4
All values as % of total
Follow these
parameters for grape
maturity measurement:
1.Sugar content
2.Acid content
3.pH level
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9. 10/2/2012
Sugars
• Main sugars in grapes are fructose
and glucose
• S
Sugar i th major soluble solid i th
is the j l bl lid in the
must
• Concentration measurement is based
on density of the must
So, boss, when do we run the
harvester?
Solids concentration measurement
units:
• Brix (or Balling) – percentage of soluble
solids in 100 grams of solution(g/g)
common use in US, Australia and
elsewhere
• Baume-percentage of potential alcohol,
actually the potential alcohol in gm/100
ml of wine, used in France
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10. 10/2/2012
Solids concentration measurement
units(cont.):
• Oechsle – the density difference
between the sample and water (d=
1.000)
– Oechsle = (density – 1.000) x 1000
– Example: in a sample with d = 1.074,
oechsle reading is 74. Units used in
Germany, Switzerland and Austria
Solids concentration
measurement (cont.):
• Using brix values, the approximation of pure
sugar content (±0.5%) in growth stages III
and IV (15-25 % Brix) can be calculated:
% sugar = (Brix – 2.1) x density
As can the potential alcohol in the finished
wine:
Each 1.7% sugar (w/v) = 1% alcohol (v/v)
Solids concentration
measurement (cont.):
• Combining the relationship, we can
connect the potential alcohol to the
Brix-density relationship:
% alcohol(v/v) = 0.58 x (Brix – 2.1) x
density
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11. 10/2/2012
http://www.youtube.com/watch?v=-FLJN2kSr0k&feature=related
How to measure Brix and
density
• Refractometer
• Hand-held
• Good field measurement
tool
• Needs to be corrected
for temperature
• General conversion of
sugar to alcohol is
approximately 58%
(0.575%~).
• A brix of 21 degrees
yields around 12%
alcohol.
How to measure Brix and
density (cont.)
• View the hydrometer
floating in the juice sample
at eye level.
• Take the reading from the
bottom of the meniscus (see
illustration). The balling/
brix scale is the brix or
sugar percentage.
• a triple scale hydrometer
also offers a scale for
specific gravity and one for
potential alcohol.
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12. 10/2/2012
How to measure Brix and
density (cont.)
C0 F0 15 20 25 30 35 40
brix brix brix brix brix brix
Correction factor to be subtracted from observed
hydrometer reading:
15 59 0.26 0.28 0.30 0.32 0.33 0.34
16 60.8 0.22 0.23 0.25 0.26 0.27 0.28
17 62.6 0.16 0.18 0.19 0.20 0.20 0.21
18 64.4 0.11 0.12 0.13 0.13 0.14 0.14
19 66.2 0.06 0.06 0.06 0.07 0.07 0.07
20 68 0 0 0 0 0 0
Correction factor to be added to observed
hydrometer reading:
21 69.8 0.06 0.06 0.07 0.07 0.07 0.07
22 71.6 0.12 0.12 0.13 0.14 0.14 0.15
23 73.4 0.17 0.19 0.20 0.21 0.21 0.22
24 75.2 0.24 0.26 0.27 0.28 0.29 0.30
25 77 0.31 0.32 0.34 0.35 0.36 0.38
Changes in Sugar measured as Brix
Maturity testing
• Highly specific and variable season to season
• Don’t bother looking until Brix reaches 14-
16˚
• Measurable things also include acidity and pH
• Common measures are:
– sugar/acid ratio-look for slope change
– Brix x Weight – look for curve flattening
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13. 10/2/2012
Total acidity
• Also known as titratable acidity, is determined by
neutralization, usually to pH 8.2 via indicating dyes
or a pH meter
• Corrections need to be made re: contribution of
sulfur di id and carbonic acid pKa 6 6 all wines
lf dioxide, d b i id K 6.6 ll i
need to be degassed before TA and VA analyses.
• VA is usually acetic acid from a variety of sources:
– ML fermentation
– Acetobacter contamination “acessence”—ethyl
acetate
Changes in Acid species
Changes during and after
veraison
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14. 10/2/2012
Brix- weight method
P = weight of
constant number of
berries usually 200-
500
S = average Brix
value of combined
sample
Example of ripening-related wine styles:
German Rieslings are classified in relation
to degree of harvest ripeness. In order
of ripeness:
• Least sugar is for Kabinett wines
• Spätlese
• Auslee
• Beerenauslee
• Trokenbeerenauslee
• Eiswein
Example of ripening-related wine styles:
(cont.)
Additionally, some rieslings are further
described by the winemaking style:
May have additional designations
indicating that a Spätlese may be:
Almost dry– the Spätlese halbtrocken
Bone dry– the Spätlese trocken
its on the label!
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16. 10/2/2012
Wine Grape Maturity Groups (from early to mid-season)
(NOTE: This material is adapted from Table 5, John Gladstones, 1992, Viticulture and
Environment)
Maturity GDD Red wine White or rose´ wines
Group ( °C)
3 1150 Pinot noir Chardonnay (cool climates)
Dolcetto Sauvignon blanc
4 1200 Malbec Semillon, Riesling
Durif (Petite Sirah) Cabernet franc (cool
Tempranillo climates)
5 1250 Merlot Viognier
Syrah (Shiraz) Roussane
Cabernet franc Marsanne
Cabernet sauvignon
6 1300 Cabernet sauvignon Palomino (sherry)
Nebbiolo
7 1350 Grenache (not commonly grown in WA)
NOTE: Washington varieties are generally in groups 4 and 5, with the exception of ‘Cabernet
sauvignon’, which may be harvested quite late (October) for increased sugar levels.
Grape maturity testing:
http://www.youtube.com/watch?v=mrnbSw-3_YE
Use f h d h ld f
U of hand-held refractometer
t t
http://www.youtube.com/watch?v=TfWdLNVJMA
4&feature=related
Sonoma County Wine Chronicles:
The Life of a Winegrape:
http://www.youtube.com/watch?v=EABxSDosafU
http://www youtube com/watch?v=EABxSDosafU
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