Transcript Must And Wine Composition

Must And Wine Composition
General Background
0.6
5
4
20
16
75
juice
skins
stems
seeds
The weight % of the grape
component parts of a cluster
0.2 0.5
79
water
sugars
organic acids
inorganic
others
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
Tartaric
acid
Occuring
solely in
vine fruits
Development of acids during ripening
(Cabernet Sauvignon)
• 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
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 αketoglutaric 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.
C6H12O6
MW=180
91.5
℃
2CH3-CH2-OH + 2CO2
MW=46
Alcohol concentration
in wine is by
measuring its boiling
point
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
Formation of methanol during fermentation
treated with heat and enzyme
Pectin enzyme
treatment before
heating
Heated grapes,
fermentation
Hot pressed juice
Pre-heated must
produced very
low methanol
content
• The toxicity methanol as a fatal(lethal)
dose is 100-250 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: ①originally produced ②from the fermentation
process(neutral esters) ③aging 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
•
1.
2.
3.
4.
Total phenol extraction in red wines
depends on many factors
Grape variety: some have very high
phenol content while others do not.
Climate: high temperature during
ripening tend to reduce phenolic
content.
Maturity state
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.