Chapter 1 - Wine Composition and Chemistry Flashcards
What are the major components of wine?
water, alcohol, acid, sugar, phenolic compounds
What are the types of alcohols in wine?
Ethyl Glycerol Methyl Fusel Higher
How is wine’s aroma carried to the nose?
Through ethyl alcohol which evaporates easily and carries the wine’s aromas to the nose.
What causes wine to have weight or body?
Alcohol
Acid is what percentage of wine’s volume?
.5%-.75%
What types acid in wine are caused by the grapes?
Tartaric
Malic
Citric
Succinic
What types acid in wine are caused by fermentation?
Lactic, acetic, succinic
Describe some aspects of tartaric acid in wine.
most common, strongest pH, can form wine diamonds (tartrates) at low temps., (tartrates can be minimized through cold stabilization)
Describe aspects of malic acid in wine.
Sharp tasting (green apple), found in wine made with underripe grapes or cool-climate grapes, can be mitigated using malolactic fermentation.
Describe aspects of citric acid in wine
Is not naturally found in wine, sometimes added to increase total acidity, generally not found in quality wines.
Describe lactic acid in wine.
Not naturally found in wine. Created by lactic acid bacteria (converts malic acid into lactic acid in malolactic fermentation). Results in a softer and smoother mouthfeel in wine.
Describe acetic acid in wine
Type of acid found in vinegar. It is volatile, so you can smell it in the aroma. In higher concentrations it can cause a chemical reaction which will make the wine undrinkable.
What pH level scale is used to measure wine?
Between 2.9 and 3.4. (2.9 is more acidic than 3.4)
What does a lower pH mean?
Stronger acid content. (2.9 will have more acid than 3.4)
Why do winemakers care about pH?
It gives an indication of stability
Helps determine sulfur additions
What percentage of sugar do wines typically contain at harvest?
15%-28%
What types of sugar is in wine?
Glucose
Fructose
Name phenolics that are found in wine
Anthocyanins Flavonols Tannins Vanillin Resveratrol
What are anthocyanins?
Compounds that give red wine its color
color is also influenced by acidity levels - more acidic wines are redder in hue, less acidic wines appear bluer
What are flavonols?
Yellow pigments found in white wines. They increase in grapes with increased exposure to sunlight.
(Sunnier climates tend to have wines with more golden color than wines from cooler climates)
What are tannins?
Astringent, bitter compounds found in the skins, seeds, and stems of grapes. Also found in oak and oak barrels. They help form the structure of big red wines. Natural preservative which helps protect wines from oxidation.
What is vanillin?
Aromatic phenolic compound in oak that imparts a vanilla scent to barrel-aged wines.
What is resveratrol?
A compound in wine believed to have several beneficial health effects in humans.
Where to phenolics come from?
The grape skins and seeds.
How is sediment in wine formed?
The phenolics in wine (tannins and pigments) polymerize (combine into long molecule chains). THe chains become too heavy to stay suspended and drop out of the liquid. This creates sediment which will cause a wine to be lighter in color and less astringent.
What are aldehydes?
Oxidized alcohols that are formed when wine is exposed to air. (This is also what gives fino Sherry its distinctive aroma.)
What are esters?
Molecules that result from the joining of acid and alcohol. Can result in nice aromas at lower concentrations or faulty aromas at higher concentrations.
What is ethyl acetate?
A type of ester formed when acetic acid and ethanol combine.
What type of aromas does ethyl acetate impart to a wine at low concentrations?
Fruity, flowery aroma
What type of aromas does ethyl acetate give to a wine at high concentrations?
Nail polish remover, varnish, or glue.
What are dissolved gases?
They are present in any liquid, but not in high concentrations. Examples: dissolved oxygen and CO2.
What are sulfites?
A class of chemicals based on sulfur. It is an important preservative widely used to keep wines stable after fermentation. Produced in minute quantities and is a natural by-product of fermentation. (Some people are extremely allergic to it – wines in the US need to be labeled, “contains sulfites”)
When do wines need to carry a label “contains sulfites” in the US?
When a wine has more than 10 ppm of sulfur dioxide
