Lect 10&11 wine

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Introduction to Vines and Wines

Hort/VE 113 Fall 2012Session 10&11-Grape ripening and

Maturity Estimation I & IIMaturity 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 As grapes grow, several factors influence wine quality.

–Climate–Variety–cultural practices–soil

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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 , gsettle 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

l l t th t l t i th • several solutes that accumulate in the berry during the first growth period reach a maximum around véraison.

• most prevalent are tartaric and malicacid.

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• 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

During the first growth period(cont.)

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.

• Also accumulating during the initial period of growth are the hydroxycinnamic acids.

• distributed in the flesh and skin of the


• distributed in the flesh and skin of the berry

• important because: – involvement in browning reactions– precursors to volatile phenols

• Tannins, including the monomericcatechins 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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• 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 t f t • Red grapes turn from green to purple-red

• Change is quite rapid, sometimes in a few days!

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• Aka fruit ripening (véraison) • Characterized by softening and coloring of

the berry. • Berry approximately doubles in size before

Development during the second growthperiod

y pp yharvest.

• 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.

• Some compounds already produced are reduced on a per-berry basis (not simply diluted)P i i l th i li id

During the second growth period(cont.)

• Principal among these is malic acid– reduction varies considerably – Roughly correlated with climate– grapes grown in cooler regions tend to have more malic acid than those grown in warmer regions

• 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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• Skin tannins decline or remain constant during the second period of growth

• Tannins also change:


• Tannins also change:– Significant modifications that take place for the skin tannins include an increase in their size-less astringent wine flavor, more “body”.

• Notable aroma compounds produced during the first growth period decline (again, on a per-berry basis) during fruit ripening.


• These include methoxypyrazinecompounds– contribute vegetal characters(“green bean”) to some wines (such as Cabernet Sauvignon and Sauvignon Blanc).

• Methoxypyrazine decline is thought to be linked to sunlight levels in the cluster. Th d d d t b


• These compounds are deemed to be undesirable (the current prevailing opinion)

• Canopy management can be used to reduce methoxypyrazine content.

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• 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 i 20 30” t • Grapes require 20-30” water a season

• 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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Compound grape must dry wine

Water 70-85 80-90Carbohydrates-Sugars 15-25 0.1-0.3-Alcohols 0 8-15-Organic acids 0.3-1.5 0.3-1.1Phenolics 0.05-0.15 0.5-0.35Nitrogen compounds 0.03-0.17 0.01-0.09Carbonyl Compounds 0 0.001-0.05Inorganics 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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Sugars

• Main sugars in grapes are fructose and glucose

S i th j l bl lid i th • Sugar is the major soluble solid 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 elsewhereelsewhere

• Baume-percentage of potential alcohol, actually the potential alcohol in gm/100 ml of wine, used in France

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• Oechsle – the density difference between the sample and water (d= 1.000)

Solids concentration measurement units(cont.):

– 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)

• Combining the relationship, we can connect the potential alcohol to the Brix-density relationship:

Solids concentration measurement (cont.):

% alcohol(v/v) = 0.58 x (Brix – 2.1) x density

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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 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 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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C0 F0 15 brix

20 brix

25 brix

30 brix

35 brix

40 brix

Correction factor to be subtracted from observed hydrometer reading:15 59 0.26 0.28 0.30 0.32 0.33 0.3416 60.8 0.22 0.23 0.25 0.26 0.27 0.2817 62.6 0.16 0.18 0.19 0.20 0.20 0.2118 64.4 0.11 0.12 0.13 0.13 0.14 0.14

How to measure Brix and density (cont.)

19 66.2 0.06 0.06 0.06 0.07 0.07 0.0720 68 0 0 0 0 0 0Correction factor to be added to observed hydrometer reading:21 69.8 0.06 0.06 0.07 0.07 0.07 0.0722 71.6 0.12 0.12 0.13 0.14 0.14 0.1523 73.4 0.17 0.19 0.20 0.21 0.21 0.2224 75.2 0.24 0.26 0.27 0.28 0.29 0.3025 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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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 lf di id d b i id K 6 6 ll i sulfur dioxide, and carbonic acid pKa 6.6 all wines

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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Brix- weight method

P = weight of constant number of berries usually 200-500

S = average Brixvalue 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 Least sugar is for Kabinett wines • Spätlese• Auslee• Beerenauslee• Trokenbeerenauslee• Eiswein

Additionally, some rieslings are further described by the winemaking style:May have additional designations indicating that a Spätlese may be:

Example of ripening-related wine styles:(cont.)

indicating that a Spätlese may be:Almost dry– the Spätlese halbtrockenBone dry– the Spätlese trockenits on the label!

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Very late harvest Riesling -Eiswein

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Wine Grape Maturity Groups (from early to mid-season) (NOTE: This material is adapted from Table 5, John Gladstones, 1992, Viticulture and Environment)

Maturity Group

GDD ( °C)

Red wine White or rose´ wines

3 1150 Pinot noirDolcetto

Chardonnay (cool climates) Sauvignon blanc

4 1200 MalbecDurif (Petite Sirah) Tempranillo

Semillon, RieslingCabernet franc (cool climates)

5 1250 Merlot Viognier5 1250 MerlotSyrah (Shiraz) Cabernet francCabernet sauvignon

ViognierRoussaneMarsanne

6 1300 Cabernet sauvignon Nebbiolo

Palomino (sherry)

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.

http://www.youtube.com/watch?v=mrnbSw-3_YE

Grape maturity testing:

U f h d h ld f t thttp://www.youtube.com/watch?v=TfWdLNVJMA4&feature=related

Use of hand-held refractometer

Sonoma County Wine Chronicles:The Life of a Winegrape:http://www youtube com/watch?v=EABxSDosafUhttp://www.youtube.com/watch?v=EABxSDosafU

Lect 10&11 wine

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