Ch. 1 - Wine Composition & Chemistry

Question 1

What is wine from a scientist’s point of view?

Answer 1

Wine is a complex blend of chemicals that collectively give the liquid its visual, olfactory, and tactile characteristics.

Question 2

What are the major components of wine?

Answer 2

The major components of wine include the
following:
• Water
• Alcohol
• Acid
• Sugar
• Phenolic compounds

Question 3

What % of wine is water?

Answer 3

Wine is typically 80-90% water. The water in wine is
primarily from the grapes themselves, although small
amounts of water may be added incidentally during
winemaking.

Question 4

What type of alcohol is present in wine?

Answer 4

Ethyl alcohol, also referred to as ethanol, is the primary
result of alcoholic fermentation and the main alcohol
component of wine. Other types of alcohol that occur
in smaller amounts include glycerol and methyl alcohol
( or methanol), as well as a group of compounds known
asfusel alcohols (fuse/ oils) or higher alcohols.

Question 5

What carries wine aromas to the nose?

Answer 5

Ethanol is a volatile compound, which means that it evaporates easily. When it does, it carries the wine’s aromas to the nose.

Question 6

What does acid contribute to the wine?

Answer 6

A variety of acids, especially in white wines, give
the wine much of its structure, balance, and thirst quenching refreshment. Acids usually make up
between 0.5% and 0.75% of a wine’s volume.

Question 7

Name the various types of acids in wine.

Answer 7

Grape Acids

• Tartaric Acid
• Malic Acid
• (Citric Acid)
• (Succinic Acid)

Fermentation Acids

• Lactic Acid
• Acetic Acid
• Succinic Acid

Question 8

Which acid is the most prevalent acid in wines?

Answer 8

Tartaric acid is the most prevalent of the acids
found in both grapes and wine. It is also the
strongest in terms of pH. Tartaric acid also has
a unique propensity to form solid crystals at
low temperatures.

Question 9

How can “Wine Diamonds” be avoided in wines?

Answer 9

The formation of tartrates can be avoided
or minimized through the winemaking process of
cold stabilization.

Question 10

How can malic acid be reduced in wine?

Answer 10

High levels of malic acid can be assuaged using the winemaking technique known as malolactic fermentation.

Question 11

Which acid is added in wines for acidification?

Answer 11

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

Question 12

Which acid is not naturally found in grapes but is found in wines?

Answer 12

Lactic acid is not found in grapes; rather, it is
created in wine by lactic acid bacteria, which
convert malic acid into lactic acid in the optional
winemaking process known as malolactic
fermentation.

Question 13

What effect does MLF have on wine?

Answer 13

MLF gives the wine a creamy texture and, in some cases, a “buttery” aroma.

Question 14

Which of the acids found in wines is volatile?

Answer 14

Acetic acid 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.

Question 15

What is Acetobacter?

Answer 15

Higher concentrations of acetic acid typically the result of a chemical reaction between ethanol and oxygen caused by harmful (to wine) bacteria called acetobacter, can be unpleasant and may make a wine undrinkable.

Question 16

What is Total Acidity (TA)?

Answer 16

Total acidity (TA), which is the volume of all the acids in a wine . In general, more acid equates to a more acidic taste.

Question 17

What is pH in wines?

Answer 17

The pH level of a wine represents the combined chemical strength of the acids present. Wine usually measures between 2.9 and 3.9 on the logarithmic pH scale. A lower pH indicates a stronger acid content.
Thus, a wine with a pH of 2.9 will be more acidic than a wine with a pH of 3.4.

Question 18

What sugars are present in wines?

Answer 18

The grapes contain roughly equal amounts of two sugars:
• Glucose
• Fructose

Question 19

Name the phenolic compounds present in wines.

Answer 19

• Anthocyanins
• Flavonols
• Tannins
• Vanillin
• Resveratrol

Question 20

What are Anthocyanins?

Answer 20

Anthocyanins are compounds that give red wine
its color, which in fact ranges from blue to purple
to red. The color of a red wine is influenced by
both the amount of anthocyanins and the acidity
level of the wine; more acidic wines appear redder
in hue, while less acidic ones appear bluer.

Question 21

What are Flavonols?

Answer 21

Flavonols are yellow pigments are found in white wines. Flavonols (sometimes called fiavones) 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 22

What are Tannins?

Answer 22

Tannins are astringent, bitter compounds
found in the skins, seeds, and stems of grapes .
They are also found in oak and oak barrels.
These compounds form part of the structure,
or “backbone,” of big red wines.

Question 23

What is Vanillin?

Answer 23

Vanillin is an aromatic phenolic compound in oak

that imparts a vanilla scent to barrel-aged wines.

Question 24

What causes a wine to throw sediments?

Answer 24

Over time, some phenolic compounds , particularly
tannins and pigments, tend to polymerize, or combine into longer molecule chains. These chains may eventually become too heavy to stay suspended in the liquid and may drop out of the solution as sediment.

Question 25

What causes a wine to throw sediments?

Answer 25

Over time, some phenolic compounds , particularly
tannins and pigments, tend to polymerize, or combine into longer molecule chains. These chains may eventually become too heavy to stay suspended in the liquid and may drop out of the solution as sediment.

Question 26

What are Aldehydes?

Answer 26

Aldehydes are oxidized alcohols that are formed when wine is exposed to air. Some wines such as Sherry and Madeira are made using techniques that encourage the formation of aldehydes.

Question 27

Which is the most common aldehyde present in wine?

Answer 27

The most common aldehyde in wine is acetaldehyde, which is formed by the oxidation of ethanol.Acetaldehyde gives fino Sherries their distinctive aroma.

Question 28

What are Esters?

Answer 28

Esters are molecules that result from the joining of an acid and an alcohol. They represent the largest group of odiferous compounds found in wine.

Question 29

Which is the most common ester present in wine?

Answer 29

The most common esters in wine is ethyl acetate, the ester of acetic acid and ethanol. At low concentrations, ethyl acetate imparts a fruity, flowery aroma; however, at high concentrations, it may impart the faulty aromas of nail polish remover, varnish, or glue.

Question 30

What are Sulfites?

Answer 30

Sulfites are a class of chemicals that are based
on the element sulfur. Sulfur is an important
preservative that is widely used to keep wines
stable after fermentation.

Question 31

What role does sulphur play in winemaking?

Answer 31

Sulfur is an antioxidant and an antibacterial agent, producing wine without the addition of sulfur is very challenging.

Question 32

What is the minimum ppm for sulphur for interstate commerce in US?

Answer 32

Wines destined for interstate commerce in the United
States that contain more than 10 parts per million (ppm) of sulfur dioxide are required to display the “Contains Sulfites” warning on the label.