Lect 10&11 wine
- 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 1
- 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. 2
- 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. 3
- 4. 10/2/2012 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! 4
- 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. 5
- 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. 6
- 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 7
- 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 8
- 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 9
- 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 10
- 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. 11
- 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 12
- 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 13
- 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! 14
- 15. 10/2/2012 Very late harvest Riesling -Eiswein 15
- 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 16