Ch 1: Wine Composition + Chemistry Flashcards
- Recognize the main categories of chemical compounds in wine - Identify the approximate concentrations of the major components of wine. - Describe specific types of alcohols, acids, and sugars that are most prominent in wine. - Discuss the types of phenolic compounds that are important in wine.
1
Q
What is the most simple definition of wine?
A
The fermented product of grapes.
2
Q
What is a scientist’s definition of wine?
A
A complex blend of chemicals that collectively give the liquid its visual, olfactory, and tactile characteristics.
3
Q
Why does wine have an ever changing character?
A
Chemical reactions expand and evolve over time. Some concentrations of compounds increase and others decrease.
4
Q
What inevitably happens to all wines with sufficient time?
A
Nearly all wines are overcome by undesirable components as chemical reactions reach their final stages.
5
Q
What are the 5 major components of wine?
A
- Water (80 - 90%)
- Sugar
- Alcohol (10 - 15%)
- Acid (0.5 - 0.75%)
- Phenolic compounds
6
Q
What percentage of a wine’s volume is made up of water?
A
80 - 90%
7
Q
Why would a winemaker intentionally add water to wine during the winemaking process?
A
To dilute wine when potential alcohol, actual alcohol, or phenolic compounds are beyond desired levels.
8
Q
What percentage of a wine’s volume is made up of alcohol?
A
10 - 15% (typically)
9
Q
What is ethyl alcohol (ethanol)?
A
The principal alcohol found in wine and the primary result of alcoholic fermentation.
10
Q
True or false:
Ethanol is a volatile compound.
A
True
11
Q
What is a volatile compound?
A
A compound (such as ethanol) prone to evaporation and carries the wine’s aromas to the nose.
12
Q
What are the 3 non-principal types of alcohol that occur in wine?
A
- Glycerol
- Methyl alcohol (mentanol)
- Fusel alcohols (fusel oils or higher alcohols)
13
Q
What is alcohol’s effect on the palette?
A
Weight or body (the mouth-filling, tactile sensation)
14
Q
Wines with ____ levels of alcohol tend to be ____ in weight. Wines with _____ levels of alcohol tend to be ____ in weight.
A
Wines with HIGHER levels of alcohol tend to be HEAVIER in weight. Wines with LOWER levels of alcohol tend to be LIGHTER in weight.
15
Q
What are ‘tears’ or ‘legs’?
A
Streaks produced by viscous droplets of liquid that run slowly down the interior of a glass of wine after swirling.
16
Q
What contributes to slow, thick-appearing tears (legs) when the wine is swirled?
A
High levels of alcohol
17
Q
What percentage of a wine’s volume is made up of acid?
A
0.5 - 0.75%
18
Q
What are the 6 principal acids in wine?
A
- Tartaric
- Malic
- Citric
- Lactic
- Acetic
- Succinic
19
Q
Which of the 6 principal acids in wine are derived from fermentation?
A
- Lactic acid
- Acetic acid
- Succinic acid
20
Q
Which principal acids can be found in grapes?
A
- Tartaric acid
- Malic acid
- Citric acid (in trace amounts)
- Succinic acid (in trace amounts)
21
Q
What is acid’s effect on wine?
A
Acids give wine much of its:
- structure
- balance
- thirst-quenching refreshment
22
Q
What is the most common acid in grapes and wine?
A
Tartaric acid
23
Q
Which is the acid with the strongest pH?
A
Tartaric acid
24
Q
What is a tartrate?
A
A crystalline compound that is formed when wine contains more tartaric acid than it can retain in a dissolved state (particularly when the wine is chilled)
25
What is the proper name for a wine diamond?
A tartrate
26
What effect do wine diamonds have on a wine?
The tartaric acid will not re-dissolve into the liquid and the wine becomes noticeably less acidic.
27
True or false:
| Tartrates (wine crystals) are considered a defect in most wines.
False
28
Which winemaking process can minimize tartrate formation?
Cold stabilization
29
What is malic acid?
- Moderately strong acid
- Sharp, green apple taste
- Found in unripe and cool-climate grapes
- Primary input to malolactic fermentation
30
True or false:
| Malic acid decreases as grapes ripen.
True
31
Which winemaking technique can assuage high levels of malic acid?
Malolactic fermentation
32
What is citric acid?
- Minor acid
- Found in grapes in trace amounts
- Sometimes used for acidification
- Not considered appropriate for quality wines
33
Why is citric acid considered inappropriate for quality wines?
It's distinctive citrus fruit flavor
34
True or false:
| Citric acid has no sensory impact on the majority of wines.
True
35
What is lactic acid?
- Mild acid
- Not found in grapes
- Created primarily via malolactic fermentation
- Note: Very small amounts are created during primary fermentation
36
How is lactic acid created?
Lactic acid bacteria is converts malolactic acid into lactic acid during malolactic fermentation.
37
True or false.
| Lactic acid is more intensely acidic than malic acid.
False
38
What is lactic acid's effect on the palette?
Creamy texture, buttery aroma
39
What is acid?
The class of chemical compounds that produce a tart, sharp, or biting character in wine
40
How is acetic acid created?
Created during fermentation by a specific bacteria (acetobacter) when wine is oxidized or exposed to air.
41
True or false:
| High concentrations of acetic acid is considered a fault.
True
42
What is acetobacter?
The type of bacteria that may cause wine spoilage in the presence of oxygen by producing acetic acid.
43
Which acid is found in most types of vinegar?
Acetic acid
44
Which acid is volatile (and therefore adds complexity to a wine's bouquet)?
Acetic acid
45
What is acetobacter's effect on wine?
Can make a wine unpleasant and undrinkable
46
What is succinic acid?
- Sharp, slightly bitter, slightly salty flavor
- Minor component in grapes
- By-product of normal alcohol fermentation
47
Which acid has a sharp, slightly bitter, slightly salty flavor?
Succinic acid
48
Which two numbers are used to describe the acidity level of a wine?
Total acidity (TA) and pH
49
What is total acidity?
A measure of the quantity of all the acids in a wine, usually in grams per liter (g/L)
50
What is pH?
A measure of the strength of an acid or of an acidic solution such as wine.
51
In general, ____ acid equates to a ____ acidic taste.
In general, MORE acid equates to a MORE acidic taste.
52
What is the typical pH level of wine?
2.9 - 3.9
53
A ______ pH indicates a _____ acid content.
A LOWER pH indicates a STRONGER acid content.
54
True or false:
| A wine with a pH of 3.4 is more acidic than a wine with a pH of 2.9.
False
55
Why do winemakers emphasize total acidity (TA)?
pH gives an indication of stability and plays a role in determining sulfur additions.
56
Which acid exists in such minute quantities that it requires specialized equipment to measure it?
Citric acid
57
What percentage of sugar do grapes contain at harvest?
15 - 28%
58
Which two sugars do grapes contain equal amounts of?
Glucose and fructose
59
True or false:
| Glucose and fructose are both highly fermentable monosaccharides (simple sugars).
True
60
What happens to sugar during fermentation?
Yeast converts sugars into ethanol (alcohol).
61
How is a wine fermented to dryness?
When the yeast is able (or allowed to) convert all the sugars into alcohol.
62
True or false:
| There is no trace of sugar in dry wines.
False
63
True or false:
| Grapes contain tiny quantities of unfermentable sugars.
True
64
True or false:
| The human palette can detect unfermentable sugars.
False
65
What indicates a dry wine?
Wines that have less sugar than a person can taste.
66
What are the 4 levels of wine sweetness?
1. Dry
2. Off-dry (medium dry)
3. Medium sweet
4. Sweet
67
What is residual sugar's effect on the palette?
Typically: weight and viscosity
| For sweet wines: mouthfeel, body, and texture
68
True or false:
| Some of the world's most renowned dessert wines contain up to 24% residual sugar.
True
69
What is sweetness used to balance in wine?
Acidity
70
True or false:
| Low quality wines sometimes use sweetness to hide the wine's flaws.
True
71
What are phenolic compounds?
| also called phenolics, polyphenols, or polyphenolics
A class of complex carbohydrate molecules often responsible for certain organoleptic properties and other aspects of wine.
72
Phenolics occur in _____ quantities, and have a ____ impact on the sensory profile of a wine.
Phenolics occur in MINOR quantities, and have a MAJOR impact on the sensory profile of a wine.
73
What are the 5 most common phenolics found in wine?
1. Anthocyanins
2. Flavonols
3. Tannins
4. Vanillin
5. Resveratrol
74
What are anthocyanins?
A type of pigment found in plants that gives grapes and wine a blue, purple, or red coloration.
75
More acidic wine appears ____ in hue, less acidic wine appears ____ in hue.
More acidic wine appears REDDER in hue, less acidic wine appears BLUER in hue.
76
What phenolic compound gives red wine its color?
Anthocyanin
77
What is a flavonol (flavones)?
A phenolic compound found in plants that gives grapes a yellow coloration.
78
White wines from ____ climates contain ___ flavonols (and therefore golden color).
White wines from SUNNIER climates contain MORE flavonols (and therefore) golden color.
79
True or false:
| Flavonols decrease with increased exposure to sunlight.
False. Flavonols increase with increased exposure to sunlight
80
What are tannins?
A phenolic compound found in grapes that gives wine a somewhat bitter taste and distinctive mouth-drying feel.
81
True or false:
| Tannins are found in oak and oak barrels.
True
82
What are tannins' effect on the palate?
- Somewhat bitter taste
- Textural, drying sensation in mouth
- Forms part of the structure of a red wine
83
How do tannins act as a preservative?
Tannins help to protect wines from oxidation during the aging process.
84
Which phenolic compound is aromatic?
Vanillin
85
True or false:
| Vanillin impacts a vanilla scent to barrel-aged wines.
True
86
True or false:
| Resveratrol has negative effects on human health.
False
87
Where are the phenolics of a grape concentrated?
Grape skin and seeds.
88
Which type of wines are richer in phenolic compounds?
Red wines
89
What happens when phenolic compounds polymerize?
Phenolic compounds combine into longer molecule chains that become too heavy to stay suspending in liquid and drop out of the solution as sediment.
90
Whic phenolic compounds polymerize most frequently?
tannins, anthocyanins, and flavonols
91
What impact does the polymerization of phenolic compounds have on wine?
Major impact on the flavor of the wine and is one of the main results of the aging process.
92
What does new research suggest about the polymerization of tannins?
Research suggests polymerized tannins can possibly continue to alter in structure and may eventually break down during extended aging. This means it may be impossible to predict how tannins in a well-aged wine will be perceived by tasters.
93
What is an aldehyde?
Any of several chemical compounds caused by the oxidation of wine.
94
Which wines are made using techniques that encourage aldehyde formation?
Sherry and Madeira
95
True or false:
| Any wine will take on a maderized character is it has been exposed to excessive oxygen during production or storage.
True
96
What are two ways your wine can become oxidized at home?
1. Keeping a bottle open for too long
| 2. Exposing a bottle to heat
97
What is the most common aldehyde?
Acetaldehyde
98
What is acetaldehyde?
The most common aldehyde, formed by the oxidation of ethanol.
99
What effect does acetaldehyde have on Sherries?
It gives Sherries their distinctive aroma
100
What are esters?
Any of various chemical compounds that result from the joining of an acid and an alcohol.
101
What represents the largest group of odiferous compounds?
Esters
102
True or false:
| Esters are considered undesirable at low concentrations.
False. Esters are considered desirable at low concentrations.
103
What is the most common ester?
Ethyl acetate (the ester of acetic acid and etholic)
104
What effect does ethyl acetate have on a wine?
In low concentrations: fruity, flowery aroma
In high concentrations: aroma of nail polish remover, varish, or glue
105
What is oxidation?
Chemical changes that take place in the presence of oxygen
106
How do winemakers avoid oxidation?
Add sulfur to absorb any frere oxygen molecules
107
What gives wine it's bubbles?
Carbon dioxide
108
True or false:
| Carbon dioxide is a natural by-product of fermentation.
True.
109
True or false:
| Still wines contain no trace of carbon dioxide.
False. Small amounts of carbon dioxide are present even in still wines.
110
What is petillance?
A slight bubbling under the surface when the wine is poured, created by leaving enough carbon dioxide in the wine.
111
What effect does carbon dioxide have on wine?
- Keeps wine feeling fresh and lively
| - Promotes the release of the wine's aromatic compounds
112
What is the purpose of sulfur?
To act as an antioxidant and antibacterial agent to keep wines stable after fermentation.
113
True or false:
| All wines contain at least trace amounts of sulfites.
True.
| All wines contain at least trace amounts of sulfites even if no sulfur is added during winemaking.
114
When are wines destined for US commerce required to display a "Contains Sulfites" warning?
When wines contain more than 10 part per million (ppm) of sulfur dioxide.
