Must And Wine Composition

General Background The weight % of the grape component parts of a cluster The general weight composition of the juice

Sugars The relative sweetness vs. sucrose at a 10% water solution which assigned as 100 The relative concentrations in order to have same sweetness as glucose (iso-sweet)

The concentrations of glucose and fructose in grape juice are about the same, where the ratio of glucose/fructose depending on such factors as maturity state, climatic conditions and grape variety. During fermentation the consumption of glucose by the yeast is slightly faster then fructose, so the ratio of glucose/fructose gradually declines.

Pectins and gums may form gels that are quite stable in water solution(and in must). They less soluble in alcohol, hence during fermentation they tend to precipitate up to 50-60% of their initial concentration. In botryized grape, their concentration is much higher, especially gums, which may cause cloudiness problems.

Measuring sugar content in grape juice Baume It is approximately the potential alcohol(in mL/100mL wine). For example, a must with 12 Baume will have about 12% alcohol. Oechsle It is direct hydrometer reading translated to more workable numbers. Oechsle = (density-1.0)*1000 Brix (B°) It is the % of total solids in solution, in grams of solute/100g of solution. Recent year it is the most used unit for sugar content in the wine industry.

The relations between the density(20 ℃ ) and the Baume(or Brix) For example, 10 Baume leads upwards to its equivalent value 18 Brix.

Temperature corrections of Brix values For example, 22.3 B° at 26 ℃, then correct Brix content is 22.7 B°

Acids Acidity It is one of the most important factors in wine. -Microbial stability -Malolactic fermentation -Color and aging rate -Tartrate and protein stability -Tasting balance perception Sources of Acidity in wine -Tartaric acid, malic and citric : acids developed in the grapes and were carried forward into the wine - Lactic, succinic, acetic and others : acids which are formed through the process of winemaking

Grape acids Three major acid: tartaric acid, malic acid and citric acid Tartaric acid concentration is unchanged, while malic acid concentration is gradually and consistently decreasing by respiration Development of acids during ripening (Cabernet Sauvignon) Tartaric acid Occuring solely in vine fruits

Wine acids Succinic acid It is formed during fermentation as a by-product in all alcoholic fermented beverages. Its concentration is about 1%. The acid is very stable and does not change during aging. Lactic acid It is formed in wine from two sources : ① as d by-product of yeast fermentation ② as the main product of malolactic(ML)-fermentation of malic acid. Acetic acid It is the main volatile acid in wine(other volatile acids-formic, propionic and butyric). It if formed during yeast fermentation. The side reaction of acetaldehyde oxidation. Other acid Formic, oxalic, pyruvic, butyric, isobutyric, hexanoic, octanoic and α- ketoglutaric acid

Acidity and pH changes The total acidity is steadily decreasing as the grape mature, the wine TA is almost equal or greater than must. The pH of the must is steadily increasing during maturity, and the wine pH is almost epual or lower than must The TA has sourness impact then the pH. The pH is the dominate factor on wine microbial activity and stability.

Alcohols Ethanol Main product of alcoholic fermentation. The concentration of alcohol depends on the initial sugar concentration and the completeness of the fermentation. C 6 H 12 O 6 2CH 3 -CH 2 -OH + 2CO 2 MW=180MW=46 Alcohol concentration in wine is by measuring its boiling point 91.5 ℃

Methanol Methanol is not a direct product of fermentation. The source for methanol in wine is pectin, which is hydrolyzed by methylesterase pectin enzymes. Methanol production comparisons of control( ○ ) and pectin enzyme treatment( ● )

Formation of methanol during fermentation with and without skin Pectin is found more in the skin Hot pressed juice Heated grapes, fermentation Pectin enzyme treatment before heating Pre-heated must produced very low methanol content Formation of methanol during fermentation treated with heat and enzyme

The toxicity methanol as a fatal(lethal) dose is mL or 340 mg/kg body weight from another source. Methanol content in wine : 100 mg/mL Strict toxicity value : 340 mg/kg (body wight) If a person whose weight is 140 lb(~70kg), it has toxicity when drinking about 200 L of wine.

Higher alcohol (Fusel oils) The major source for higher alcohols is amino acid which by a sequence process of trans-amination, decarboxylation and reduction

2,3-Butandiol is the major di-alcohol in wine. It is a by-product of fermentation from pyruvic acid, or by reduction of acetoin. Glycerol is the major trialcohol found in wine. its content is related to the amount of alcohol formed to the temperature of fermentation and to the yeast strain. (it is higher at higher temperatures and it is synthesized by the Botrytis cinerea fungi ) Glycerol is very viscous and sweet, it was believed that it contributes to the wine body and mouthfeel

Aldehydes and ketones Aldehydes and ketones are formed during alcoholic fermetation. Acetaldehyde, acetoin and diacetyl are the main representatives in wine. Esters Esters are the reaction product between alcohols and acid. Esters have three sources: ① originally produced ② from the fermentation process(neutral esters) ③ aging of the wine during a very slow chemical esterification(acid esters) -Volatile esters Organoleptic perception is described as a fruity-type aroma. Ethyl acetate has the highest concentration in wines, its contribution to the wine quality is considered negatively. Ethyl acetate is always accompanied by acetic acid. Spoiled wines with acetic acid bacteria have much higher concentration of ethyl acetate. -Nonvolatile esters This class of esters includes mainly ethanol reaction products with the major wine acids such as tartaric, maric, lactic and succinic.

Nitrogen components Nitrogen compounds have a special interest to wine production mainly because of two reason: (1) if there a deficiency in nitrogen component in the must, the fermentation probably will not proceed (2) in case where there is too much protein, there might be some clarification difficulties and protein instability of the wine. -Amino acid Proline and arginine are the dominate amino acid found in grape. Not used as nitrogen nutrient Except proline, almost all the amino aicd is used by the yeast during fermentation

- Ammonia It can easily be used as a nutrient for yeast growth. - Protein protein nitrogen in wine is only about 2% of the total nitrogen contents Vitamins Vitamins are very important micro nutrients for yeast growth. Some of the most valuable vitamins found in must are thiamin(B1), riboflavin(B2), pyridoxin(B6), cobalamine(B12), pantothenic acid, nicotinic acid, biotin and choline.

Phenolics

White wine phenols

SO2 200ppm SO2 100ppm SO2 50ppm SO2 0ppm and oxygenaed

The temperture of maceration has a great influence on phenol extraction

Their concentration increases at veraison and then gradually decreases towards full maturation.

Red wine phenolics

Anthocyanin Typical phenolic

Total phenol extraction in red wines depends on many factors 1.Grape variety: some have very high phenol content while others do not. 2.Climate: high temperature during ripening tend to reduce phenolic content. 3.Maturity state 4.Vinification practiced

Inorganic constituents Cations Anions

Cations -Potassium: the most abundant metal in grapes. It plays a major factor in wine pH and in tartrate stability -Calcium: It cause tartrate instability -Iron: it plays a part in wine oxidation processes as a catalyst. -Copper: it plays a similar part as iron Anions - Phosphate: it plays a very important part in wine fermentation and in many case it is added to wine by diammonium phosphate to increase nitrogen content for smooth fermentation. -Sulfate: sulfate ion might be an end product when sulfur is oxidized during wine processing.