Wine Composition & Chemistry

Question 1

What “wine” means legally in the US

4 aspects of grapes that make them ideal for winemaking

Answer 1

a beverage made from grapes.

grapes have the most valued combination of

1) fermentable sugars
2) significant acidity
3) desirable flavors
4) liquid content

Question 2

5 major components of wine

3 other components that may be present

Answer 2

Water 
Alcohol 
Acid 
Sugar 
Phenolic 

bacteria
yeast
proteins

Question 3

% of wine that is water

3 sources of water in wine, with primary first and rarest last

Why the last source is performed

Answer 3

80–90% water

1) from the grapes themselves
2) small amounts of water may be added incidentally during winemaking.
3) intention addition of water

to dilute grape juice or wine when potential alcohol, actual alcohol, or phenolic compounds are beyond desired levels.

Question 4

What is the most prevalent ingredient in wine after water

Usual percentage of it in wine by volume, with caveat

Specific type of this ingredient (scientific name)

Answer 4

alcohol

10–15%

Ethyl alcohol

Question 5

AKA for ethyl alcohol

Process it is a product of

3 other kinds of alcohols that occur in smaller amounts

Answer 5

ethanol

alcoholic fermentation

glycerol
methyl alcohol (or methanol)
fusel alcohols (fusel oils) or higher alcohols.

Question 6

What does volatile mean when used to describe ETOH

What olfactory quality these lends to wine

What tactile sensation ETOH lends to wine, with term used to describe it (2)

Note about ETOH and wine weight

Visual sign of high alcohol content in wine

Answer 6

it evaporates easily

it carries the wine’s aromas to the nose.

contributes to the mouth-filling, tactile sensation of a wine as it rests on the palate; this sensation is often referred to as a wine’s “weight” or “body.”

Wines with higher levels of alcohol tend to be heavier in weight than wines with lower levels of alcohol, all other things being equal.

slow, thick-appearing “tears” or “legs” in the glass after the wine is swirled.

Question 7

6 kinds of acids found in wine, with most prevalent first

Answer 7

Tartaric
Malic
Citric
Lactic
Acetic
Succinic

Question 8

General wine type in which acid can make the most difference

3 things that a variety of acids can lend to wine

% of wine in volume made up by acids

Answer 8

white wines

structure
balance
thirst-quenching refreshment

0.5% and 0.75%

Question 9

2 places where tartaric acid is the most prevalent acid

2 unique properties of tartaric acid

Name for second phenomenon

Answer 9

in both grapes and grape juice/wine

1) It’s the strongest in terms of pH.
2) It forms solid crystals at low temperatures.

“wine diamonds”

Question 10

Note about tartaric acid “wine diamonds,” with result

Are wine diamonds considered a defect?

How they can be avoided or minimized in the winemaking process

Answer 10

They will not redissolve into the liquid, and the wine will become noticeably less acidic.

Not technically

cold stabilization

Question 11

Taste of malic acid, and what it is often associated with

Two types of grapes typically high in malic acid

How malic acid decreases

2 types of wine that are low in levels of malic acid

How to reduce malolactic fermentation in wine

Answer 11

sharp-tasting; green apples.

1) Underripe
2) cool-climate grapes

during the ripening phase of the grapes on the vine.

1) Wines made from overripe grapes
2) grapes grown in hot climates

malolactic fermentation.

Question 12

Note about prevalence of citric acid in wine

Usual impact of it on wine

Why it is sometimes added, but usually not

Answer 12

Citric acid is not usually considered to be a normal component of grapes, as it exists in such minute quantities that specialized equipment is required to measure it.

It has no sensory impact on the majority of wines.

to increase the total acidity in a wine, although its distinctive citrus fruit flavor makes it generally unsuitable for quality wines.

Question 13

Is lactic acid usually found in grapes?

Process by which it’s created in wine, with chemical description

How wines that undergo this process taste, and why

A second taste by-product of this process

Another way lactic acid is produced in small amounts in wine

Answer 13

No

Through malolactic fermentation, where lactic acid bacteria convert malic acid into lactic acid

by lactic acid bacteria, which convert malic acid into lactic acid in the optional winemaking process known as malolactic fermentation.

They taste softer and smoother in mouthfeel because lactic acid is less intensely acidic than malic acid

Provides wine with a creamy texture and, in some cases, a “buttery” aroma.

during primary fermentation, albeit in very small amounts.

Question 14

In what substance acetic acid is often found

What process in winemaking produces a low level of it in wine

Special quality of acetic acid compared to other wines, with benefit of this quality and wine time in which this quality is most prevalent

How high levels of acetic acid can appear in wine, potentially making it undrinkable

Answer 14

vinegar

fermentation

It is volatile, so it readily evaporates and joins the aromas of the wine, adding to the complexity of a wine’s bouquet, particularly in red wines.

chemical reaction between between ethanol and oxygen caused by harmful (to wine) bacteria called acetobacter

Question 15

Nature of role of succinic acid in wine and how it appears in wine

Describe its taste (3)

Answer 15

a minor component, a by-product of normal alcoholic fermentation.

sharp, slightly bitter, slightly salty flavor.

Question 16

4 grape acids

3 fermentation acids

Answer 16

Tartaric
Malic
Citric
Succinic

Lactic
Acetic
Succinic

Question 17

Two numbers used to describe the acidity level of wine, with definitions, and why second is used more

Answer 17

1) total acidity (TA), which is the volume of all the acids in a wine.
2) The combined chemical strength of all acids present

In general, more acid equates to a more acidic taste. However, TA includes several different acids, some of which are stronger than others.

Question 18

Is a lower pH more or less acidic than a higher pH?

Usual pH of wine

Why winemakers place particular emphasis on pH while looking at both numbers (2)

Answer 18

Lower pH is stronger

2.9 and 3.9

PH gives an indication of stability and plays a role in determining sulfur additions.

Question 19

% of sugar in wine grapes at harvest

Two types of sugars contained in roughly equal amounts in grapes

Chemical type of these sugars with aka

Quality of these sugars in relation to winemaking

Answer 19

15% to 28%

monosaccharides, commonly known as “simple sugars.”

They are highly fermentable

Question 20

Chemical reaction that occurs with glucose and fructose under the right conditions

What will result if the process is allowed to go to completion

What even such a fermented product will contain, and why, and concentration of these

Answer 20

yeast converts these sugars into ethanol, turning grape juice into wine.

the wine will be fermented to dryness

even dry wines contain a trace amount of sugar, as grapes actually contain tiny quantities of unfermentable sugars. These unfermentable sugars generally remain in concentrations below one’s ability to detect them.

Question 21

Define the term “dry”

Why some wines have detectable sugar

2 qualities that residual sugar adds to wine

Answer 21

Wines that have less sugar than a person can taste are described as dry.

because fermentation was stopped, through winemaker intervention or by natural causes, before all of the sugar was converted to alcohol.

1) adds some weight, or “body,” to the wine
2) contributes to slow, thick-appearing tears in the glass after a wine is swirled

Question 22

3 roles (examples) that sugar can play in wine, with % example for first

Answer 22

1) renowned dessert wines are extremely sweet, even up to 24% or more residual sugar
2) sweetness is used to balance high acidity in a wine, or vice versa.
3) In some lower-quality wines, sweetness may be used to hide the wine’s minor flaws.

Question 23

5 primary phenolics found in wine

2 AKAs for phenolics

Answer 23

Anthocyanins
Flavonols
Tannins
Vanilin
Reservatrol

Polyphenolics
Polyphenols

Question 24

What anthocyanins do for wine, with note on range

2 things that influence this property, with note on influence of non-anthocyanin component

Answer 24

give red wine its color, which in fact ranges from blue to purple to red.
amount of anthocyanins
acidity level of the wine

more acidic wines appear redder in hue, while less acidic ones appear bluer.

Question 25

Aka for flavonols

What are they, and where are they found

How they increase, with related note on climate

Answer 25

Flavones

yellow pigments are found in white wines.

They increase in grapes with increased exposure to sunlight; therefore, white wines from sunnier climates tend to have a more golden color than white wines from cooler (or cloudier) climates.

Question 26

How do tannins taste (2)

4 places they are found

Role they have in big red wines

Benefit they have for wines

Why tannins are easily detected when drinking winee

Answer 26

astringent

skins
seeds
stems of grapes
oak and oak barrels

form part of its structure, or “backbone,” of big red wines.

They are a natural preservative and help to protect red wines from oxidation during the aging process.

by the textural, drying sensation they create in the mouth.

Question 27

Describe vanillin

Note about relationship between barrels and beans

Answer 27

an aromatic phenolic compound in oak that imparts a vanilla scent to barrel-aged wines.

The vanillin found in oak barrels is the same compound found in vanilla beans.

Question 28

Where grape phenolics are concentrated and implication of this for grape/wine type

What some phenolics can do over time (name and description), especially with aging, with 2 particular phenolics that undergo this process

Chemical result of this process, and effect this can have on wine properties

Answer 28

in skin and seeds; therefore, red wines, which are fermented in contact with the grape solids, are much richer in phenolic compounds than white wines.

Polymerize, or combine into longer molecule chains. Tannins and pigments in particular.

The chains may eventually become too heavy to stay suspended in the liquid and may drop out of the solution as sediment.
the production of sediment renders a wine lighter in color and less astringent.

Question 29

Four other chemical components found in wine (OK to read)

Answer 29

Aldehydes
Esters
Dissolved gases
Sulfites

Question 30

Define aldehyde

Two alcohols where development of aldehydes is encouraged

Term for development of aldehydes in alcohol and why it is avoided in other wines

3 ways wine can oxidize

Answer 30

Oxidize alcohols that are formed when wine is exposed to air

Sherry
Madeira

Maderized: unpleasant character of wines that underwent aldehyde production from exposure to O2.

1—exposure to O2 during production of storage
2—bottle being open too long
3—exposure of wine to heat

Question 31

Most common aldehyde, and where it comes from

Alcohol to which aldehydes give a distinctive aroma

Answer 31

Acetaldehyde, from oxidation of ethanol

fino Sherries

Question 32

Define ester

Esters honor

Note about ester concentration

Answer 32

Molecules that result from the joining of an acid and an alcohol.

They represent the largest group of odiferous compounds found in wine

Most are desirable at low concentrations, but can give wine an “off” character at high concentrations

Question 33

One of the most common esters in wine, and what it is a product of

What it imparts to wine at low concentrations

What it imparts at high concentrations (3)

Answer 33

Ethyl acetate, an ester of acetic acid and ethahol

A fruity, flowery aroma

A faulty aroma of nail polish remover, varnish or glue

Question 34

What dissolved O2 promotes in wine

How it is avoided (2)

Answer 34

Promote many chemical reactions through oxidation

1—avoid exposure to air
2—add sulfur in order to absorb free O2 molecules before they have a chance to alter the wine

Question 35

How CO2 is created in wine

4 benefits of it, with term for second

Answer 35

1—creates bubbles in sparkling wine

2—gives still wines petillance (slight bubbling under the surface)

3—keeps a wine feel fresh and lively in the mouth

4—promotes release of wine’s aromatic compounds

Question 36

What element are sulfites based on?

Two ways they appear in wine

Action they have, and how they are used as a result

Answer 36

Sulfur

1—added by winemaker
2—produced in minutes quantities as a natural by-product of fermentation, so a trace amount of it is present in all wine

It is an antioxidant and antibacterial agent and thus used to keep wines stable after fermentation. Producing wine without it is very challenging.

Question 37

Problem with sulfites in some people

Resulting law

Answer 37

Some people are extremely sensitive to sulfite and can have a negative reaction to it

In US, all wines with more than 10 ppm must display a “Contains Sulfites” warning on label