VITIS vinifera GRAPE COMPOSITION Milena Lambri Enology Area - DiSTAS Department for Sustainable Food Process Università Cattolica del Sacro Cuore - Piacenza
GRAPE (and WINE) COMPOSITION Chemical composition of grape juice: 1. water 2. sugars 3. organic acids 4. inorganic compounds 5. phenolic compounds 6. nitrogenous materials 7. vitamins 8. pectic substances 9. enzymes 10. volatile flavor compounds
GRAPE (and WINE) COMPOSITION The Composition of the Grape is based on several factors including: CULTIVAR SOIL ROOTSTOCK CLIMATIC CONDITIONS MATURITY CROP YIELD POST-HARVEST HANDLING
COMPOSITION (W/W) OF GRAPE BUNCH STEM 2,5 8 % GRAPE Berry 92 97 % of which skin 6 10% seeds 2 15 % must 60 80 %
DISTRIBUTION OF THE GRAPE COMPONENTS INTO THE FRUIT Phenolic compounds
Grape maturity & Wine type
WATER and SUGARS WATER 65-85% weight of grapes SUGARS fructose and glucose (15 25 %). Technological or pulp maturity is based on measure of sugar (Babo or Brix degree) of acidity (g/l expressed as tartaric acid) and of ph. Ethanol concentration in wine is a function of sugar. A theoretical maximum 51.1% (w/w) of the sugar can be converted to alcohol. Usually g/l of sugar x 0.06 gives potential ethanol in wine as % v/v.
ALCOHOLIC FERMENTATION Saccharomyces cerevisiae INDIGENOUS OR SELECTED STRAINS C 6 H 12 O 6 2 C 2 H 5 OH + 2 CO 2 + heat 1 g sugar (glucose or fructose) 0,6 ml ethanol = 100 ml must 100 ml wine Sugar % (g/100 ml) x 0.6 = Potential alcohol degree of wine Sugar (g/1 litre) x 0.06 = Potential alcohol degree of wine
ALCOHOLIC FERMENTATION C 6 H 12 O 6 2 C 2 H 5 OH + 2 CO 2 + heat v 56 l of CO 2 /l of must at 20 C v Increasing temperature: 0.65 C / 1 % w/v of sugar 0.25 C / 1 % w/v of sugar
ALCOHOLIC FERMENTATION OCM 1493/1999 E.C. Regulation - Effective alcohol degree (% v/v) It is the ethanol present in wine - Potential alcohol degree (% v/v) It is the ethanol developping from residue sugars - Total alcohol degree (% v/v) The sum effective ethanol + potential ethanol
Corrective actions of must composition OCM 1493/1999 E.C. Regulation - Italian Legislation Sugars - Increasing concentration by means of concentrated and rectified must - Increasing concentration by under vacuum concentration or inverted osmosis of the must to correct Acids - Increasing concentration by addition of tartaric acid - Decreasing concentration by addition of salts (potassium hydrogen carbonate, calcium carbonate or potassium tartrate)
A B C I C II C IIIa C IIIb
SUGARS ü Immature grape: glucose > fructose ü Mature fruit: glucose ~ fructose ü Overly mature: glucose < fructose (ratio as low as ~0.85) Glucose: 5.6 to 8.5 g/100 ml (5.6-8.5%) Fructose: 6.4 to 10.6 g/100 ml (6.4-10.6%) Sucrose: 0.02 to 0.18% Raffinose: 0.015% to 0.34% Sugar content directly affects wine sweetness Ethanol enhances sweetness and softness of wine
PECTIC SUBSTANCES Pectic substances present in grape include protopectin, a water insoluble material and soluble pectin. Pectin is the component in jams and jellies that makes the product thick and is a polymer of galacturonic acid. An average pectin content < 1 g/l was reported for grapes.
MODE OF ACTION OF THE MAIN PECTOLITIC ENZYMES
ORIGIN OF METHANOL Hydrolysis by natural pectinmethylesterase and polymethylgalacturonase enzymes O-methyl groups form methanol in alcoholic solution METHANOL (30-35 mg/l)
ORGANIC ACIDS Major: tartaric acid (H 2 T) and malic (H 2 M) Immature grape: the H 2 M/H 2 T is just below 1 to over 2 Mature grape 7 malic acid 1-10 g/l 7 tartaric acid 2-10 g/l 7 total acidity 4 18 g/l Other acids include citric, ascorbic, oxalic, succinic, lactic, glutaric, alpha-ketoglutaric, pyruvic, oxalacetic, galacturonic and phenolics.
ORGANIC ACIDS and their SALTS Organic acids and their salts affect: Wine acidity (4-8 g/l expressed as tartaric acid) ph 2.9 3.4 Freshness perception Sapidity perception Hardness perception (together with tannins)
Minerals and metals At grape maturity: Potassium: 1000-1500 mg/l Calcium: 20-100 mg/l Sodium: 20-80 mg/l Phosphate content: 0.02 to 0.05%. Problems cloudiness 1) Tartrate solubility: super-saturated potassium bitartrate. It can be removed via chilling then filtering or by ion exchange chromatography, to obtain clarity. 2) Iron and Copper: complex with tannins and/or proteins
Metals and legal limits n Copper 1 mg/l n Zinc 5 mg/l n Lead 0.2 mg/l n Arsenic 0.2 mg/l n Mercury 5 µg/l n Cadmium 5 µg/l
The Malo-Lactic Fermentation After alcoholic fermentation, the enzymatic conversion of malic to lactic acid and CO 2 in the wine by lactic acid bacteria can occur. Initially, malic acid is decarboxylated, via malate dehydrogenase, to pyruvic acid. Immediately after decarboxylation, pyruvic acid is rapidly converted to lactic acid by lactate dehydrogenase. Since malic acid has 2 carboxyl groups and lactic acid has a single carboxyl group, conversion of malic to lactic acid reduces the titratable acidity and increases the ph.
MALOLACTIC FERMENTATION LACTIC ACID BACTERIA (Lactobacillus spp., Oenococcus oeni) INDIGENOUS OR SELECTED STRAINS COOH COOH Malolactic Enzyme (NAD + Mn 2+ ) HO C H HO C H + CO 2 CH 2 NADH + H + CH 3 COOH L (-) malic acid L (+) lactic acid
PHENOLIC COMPOUNDS FLAVONOIDS Flavonols (aglycons and glycosidated derivatives) Flavan-3-ols Anthocyanins
PHENOLIC COMPOUNDS Anthocyani(di)ns Anthocyanins - red and blue pigments widely distributed in plants. The base structure consists of 2 aromatic rings (A and B) connected by a pyran ring. The anthocyanins are polar, flavonoid derived, pigments. There are five anthocyanidins in grapes: delphinidin, petunidin, malvidin, cyanidin and peonidin.
Anthocyani(di)ns + HO O R OH R OH O-Gluc O-Acyl STABILITY Pelargonidin: R=H; R =H Cyanidin: R=OH; R =H Delphinidin: R=OH; R =OH Malvidin: R=OCH 3 ; R =OCH 3 Peonidin: R=OCH 3 ; R =H Petunidin: R=OCH 3 ; R =OH
PHENOLIC COMPOUNDS Anthocyanidins The non-glycosylated (no sugar attached) form is the aglycone. The anthocyanidins can be glycosylated or acylated. Primarily with glucose, at one or two selected hydroxyls or with the addition of some other compound, such as p-coumaric acid. The concentration range for young red wines is in general of 0.2 to 0.7 g/l.
PHENOLIC COMPOUNDS Anthocyani(di)ns Color dependence on ph Weakly acidic conditions - the red oxonium form is in reversible equilibrium with the colorless pseudo-base. The position of the equilibrium depends upon the ph. For example, the color intensity of mixture of anthocyanidins is 6 fold greater at ph 2.9 than at 3.9.
Anthocyanin Structures and Equilibrium O O R OH R H + HO + O R OH R HO O-Gluc O-Gluc OH OH Quinoidal base Flavylium cation R R H OH 2 O H + OH OH OH O HO O R R O-Gluc O-Gluc OH OH Chalcone Carbonyl pseudo-base
PHENOLIC COMPOUNDS Anthocyani(di)ns Bisulfite ions can condense with anthocyanidins to form a colorless compound (which is why some decolorization occurs in red wine after sulfite treatment). The condensation is reversible and as the free SO 2 disappears, the sulfite addition product is dissociated and the red color intensity returns.
SO 2 : Bleaching of Anthocyanins R HO + O OH R SO 2 OH O-Gluc Flavene Sulfonate R OH Flavylium cation HO O R OH H SO 3 H O-Gluc
PHENOLIC COMPOUNDS Tannins Tannins affect an important flavor characteristic of red wine termed astringency that creates a mouth feel characterized as a puckering sensation. Tannins can either be of the: ü ü Condensed type, which is a polymer of the flavan-3-ols (epicatechin, catechin and gallocatechin) and of the flavan-3,4-diols. Condensed type are coming from grape. Hydrolizable type derived from phenolic acids, such as gallic acid or ellagic acid. They are coming from wood or they are added.
Tannins Condensed Tannin Polymers of the flavan-3-ols (epicatechin, catechin and gallocatechin) and of the flavan-3,4-diols. GRAPE Hydrolizable Tannin Derived from phenolic acids (gallic and ellagic acids). WOOD
PHENOLIC COMPOUNDS Tannins The flavan-3,4-diols (procyanidins) differ from catechin due to an additional hydroxyl group at position 4. Flavan-3,4-diols are important precursors to polymeric tannins in wine. The tannins present in grapes and wine are primarily of the condensed tannin type. The total tannin concentration for red wines is in ~2-4 g/l range.
PHENOLIC COMPOUNDS Taste/Body are affected by tannins which, if too much, can cause astringency. ü 0.01 to 0.04% w/v - white wines ü 0.1 to 0.2% w/v - red wines Tannins can cause oxidative browning in white wine, its rate is dependent upon amount of catechin, proanthocyanidins, sulfur dioxide content, iron, copper, citric acid and oxygen. Some phenolics have anti-bacterial properties, others are anti-oxidative (not flavonoids type).
PHENOLIC COMPOUNDS NOT FLAVONOIDS Gallic acid Hydroxycinnamates Stilbens
OXIDATIVE ENZYMES Several different enzymes have been found in grapes, but the enzyme with the greatest deleterious effect is polyphenoloxidase. In grape attached from Botrytis cinerea laccase can appear. These enzymes accelerate oxidative browning and discoloration.
NITROGENOUS MATERIALS Ammonia and ammonium salts are very important for yeast development and reproduction; certain amino acids are a good sources of nitrogen for the yeast Ammonia in grape juice: 10 15 % Total nitrogen content is 100 1000 mg/l Concentration range: some amino acids <0.3 mg/100 ml of grape juice, others >400 mg/100 ml. Some amino acids are a substrate for higher alcohols, called fusel alcohols, which affect flavor.
VITAMINS Ascorbic acid: 1.1 to 11.7 mg/100 ml of juice Riboflavin: 6.3 to 25 µg/100 ml Pantothenic acid: 50 to 100 µg/100 ml Pyridoxine: 16 to 53 µg/100 ml Nicotinic acid: 80 to 375 µg/100 ml Other vitamins: one to several µg/liter juice
VOLATILE COMPOUNDS Certain volatile compounds are directly associated with the flavor and aroma of many fruits. Major volatiles in grapes (max 1000 µg/l) are: Terpens, free and glycosidated forms Norisoprenoids Thiols C6 alcohols and aldehydes originating from enzyme and oxygen action on precursors (herbaceous flavor) Aromatic maturity (accumulation of varietal volatiles)
The yeast secondary or fermentative aroma Ethanol
EVOLUTION OF THE GRAPE COMPONENTS DURING RIPENING