VITIS viniferaGRAPE COMPOSITION

Milena Lambri

Enology Area - DiSTAS Department for Sustainable Food ProcessUniversità Cattolica del Sacro Cuore - Piacenza

GRAPE (and WINE) COMPOSITION

Chemical composition of grape juice:1. water2. sugars3. organic acids4. inorganic compounds 5. phenolic compounds 6. nitrogenous materials7. vitamins8. pectic substances9. enzymes 10. volatile flavor compounds

The Composition of the “Grape” is based on several factors including: CULTIVAR SOIL ROOTSTOCK CLIMATIC CONDITIONSMATURITY CROP YIELD POST-HARVEST HANDLING

GRAPE (and WINE) COMPOSITION

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

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.

WATER and SUGARS

ALCOHOLIC

FERMENTATION

C6H12O6 2 C2H5OH + 2 CO2 + heat

1 g sugar (glucose or fructose) 0,6 ml ethanol

100 ml must 100 ml wine

Saccharomyces cerevisiae INDIGENOUS OR SELECTED STRAINS

=

Sugar % (g/100 ml) x 0.6 = Potential alcohol degree of wine

Sugar (g/1 litre) x 0.06 = Potential alcohol degree of wine

56 l of CO2 /l of must at 20 °C

Increasing temperature:

0.65 °C / 1 % w/v of sugar

0.25 °C / 1 % w/v of sugar

ALCOHOLIC

FERMENTATION

C6H12O6 2 C2H5OH + 2 CO2 + heat

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

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)

OCM 1493/1999 E.C. Regulation - Italian Legislation

A

B

C I C II

C IIIb

C IIIa

SUGARS

Immature grape: glucose > fructoseMature fruit: glucose ~ fructose 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 METHANOLHydrolysis by natural pectinmethylesterase and

polymethylgalacturonase enzymes

O-methyl groups form methanol in alcoholic solution

METHANOL (30-35 mg/l)

Major: tartaric acid (H2T) and malic (H2M)

Immature grape: the H2M/H2T is just below 1 to over 2 Mature grape

malic acid 1 - 10 g/l tartaric acid 2 - 10 g/l total acidity 4 – 18 g/l

Other acids include citric, ascorbic, oxalic, succinic, “lactic”, glutaric, alpha-ketoglutaric, pyruvic, oxalacetic, galacturonic and phenolics.

ORGANIC ACIDS

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)

ORGANIC ACIDS and their SALTS

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

Minerals and metals

Metals and legal limits

Copper 1 mg/l Zinc 5 mg/l Lead 0.2 mg/l Arsenic 0.2 mg/l Mercury 5 µg/l Cadmium 5 µg/l

The Malo-Lactic Fermentation

After alcoholic fermentation, the enzymatic conversion ofmalic to lactic acid and CO2 in the wine by lactic acidbacteria can occur.

Initially, malic acid is decarboxylated, via malatedehydrogenase, to pyruvic acid. Immediately afterdecarboxylation, pyruvic acid is rapidly converted to lacticacid by lactate dehydrogenase.

Since malic acid has 2 carboxyl groups and lactic acid hasa single carboxyl group, conversion of malic to lactic acidreduces the titratable acidity and increases the pH.

MALOLACTICFERMENTATION

COOH COOHMalolactic Enzyme (NAD+ Mn2+)

HO C H HO C H + CO2

CH2 NADH + H+ CH3

COOH

L (-) malic acid L (+) lactic acid

LACTIC ACID BACTERIA (Lactobacillus spp., Oenococcus oeni)

INDIGENOUS OR SELECTED STRAINS

PHENOLIC COMPOUNDSFLAVONOIDS

Flavonols (aglycons and glycosidated derivatives)

Anthocyanins

Flavan-3-ols

PHENOLIC COMPOUNDS

Anthocyani(di)ns

Anthocyanins - red and blue pigments widelydistributed in plants.

The base structure consists of 2 aromatic rings (A andB) connected by a pyran ring.

The anthocyanins are polar, flavonoid derived,pigments. There are five anthocyanidins in grapes:delphinidin, petunidin, malvidin, cyanidin andpeonidin.

HO

OH

R

OH

R’O

O-Gluc

O-Acyl

+

Pelargonidin: R=H; R’=H Cyanidin: R=OH; R’=H Delphinidin: R=OH; R’=OH

Malvidin: R=OCH3; R’=OCH3 Peonidin: R=OCH3; R’=H Petunidin: R=OCH3; R’=OH

Anthocyani(di)ns

STABILITY

Anthocyanidins

The non-glycosylated (no sugar attached) form isthe aglycone.

The anthocyanidins can be glycosylated oracylated. Primarily with glucose, at one or twoselected hydroxyls or with the addition of someother compound, such as p-coumaric acid.

The concentration range for young red wines is ingeneral 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.

PHENOLIC COMPOUNDS

O

O

Anthocyanin Structures and Equilibrium

O

ROH

R

OH

HO

OHOH

O

R

R

O-Gluc

+

O-Gluc

H+

Quinoidal base Flavylium cation

HO

OH

OHR

R

O-Gluc

OHOH O

O-Gluc

HO

OH

R

R

OH

Chalcone Carbonyl pseudo-base

H2 O H+

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 SO2disappears, the sulfite addition product is dissociated and the red color intensity returns.

PHENOLIC COMPOUNDS

O

O

SO2: Bleaching of Anthocyanins

OH

HO

OH

R

R+

O-Gluc

Flavylium cation

O-Gluc

HO

OH

R

R

OH

H SO3 H

SO2

Flavene Sulfonate

PHENOLIC COMPOUNDSTannins Tannins affect an important flavor characteristic of red wine

termed “astringency” that creates a mouth feel characterizedas a “puckering” sensation.

Tannins can either be of the:

“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 asgallic acid or ellagic acid. They are coming from wood or theyare added.

Condensed TanninPolymers of the flavan-3-ols (epicatechin, catechin and gallocatechin) and of the flavan-3,4-diols. GRAPE

Hydrolizable TanninDerived from phenolic acids (gallic and ellagic acids). WOOD

Tannins

PHENOLIC COMPOUNDSTannins

The flavan-3,4-diols (procyanidins) differ fromcatechin due to an additional hydroxyl group atposition 4. Flavan-3,4-diols are important precursorsto polymeric tannins in wine.

The tannins present in grapes and wine areprimarily of the condensed tannin type.

The total tannin concentration for red wines is in~2-4 g/l range.

Taste/Body are affected by tannins which, if toomuch, can cause astringency.

0.01 to 0.04% w/v - white wines 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, othersare anti-oxidative (not flavonoids type).

PHENOLIC COMPOUNDS

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.

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.

NITROGENOUS MATERIALS

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

VITAMINS

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