Wine chemistry Flashcards
What are the main components of wine
- water (85%)
- Alcohol (mostly ethanol)
- Acid (malic and tartaric)
- Residual Sugar
- Aromatics
- Glycerol
- Phenolics
Aromatics can be derived from four main groups - what are they?
1) aromas from the grape (Methoxypyrazine, rotundone from Syrah)
2) Aroma precursors that are triggered by fermentation (Thiols and terpenes)
3) aromas directly from fermentation (esters)
4) Aromas from other sources, such as the barrel
A thiol is an aroma building block which becomes aromatic during fermentation. What is an example of a well-known thiol
the box-tree aroma in Sauvignon Blanc known as 4MMP
What command is responsible for fruit, floral aromas such as linalool or citronol
Terpenes.
What delicate, volatile aromas are formed during fermentation
esters
How are esters formed
alcohol (produced by the yeast) and acid (present in the grape)
Why are there lots of different esters
lots of acids and lots of alcohols in the ferment
Give an example of two common esters
isoamyl acetate in beaujolais nouveau ethyl acetate (ethanol + acetic acid) -> pear drops
What is Ethanal
Oxidated ethanol - also known as acetaldehyde
Which wine type requires oxidised ethanol to achieve its characteristic style
Fino sherry
diacetyl is produced by what acid
lactic acid. IT is recognised for its buttery, creamy notes.
What is a reductive aroma? Is it good or bad?
A reductive aroma is. result of the sulfur let off by yeast during fermentation or lees ageing, without O2 to dissipate it. In small amounts, it can give a struck match aroma which is agreeable, while in larger amounts it is considered a fault (rotten eggs)
Which element is essential in fermentation
Nitrogen. It feeds the yeast and ensures fermentation starts promptly. This is why natural wines from soils that are low in N sometimes struggle with fermentation
Explain the difference between primary, secondary and tertiary flavours
Wine aroma is composed of primary, or varietal, aromas that arise directly from the grapes;
secondary, or fermentation aromas, aromas produced by yeasts during the alcoholic fermentation;
tertiary, or maturation bouquet that results from chemical reactions during wine ageing
How does Eucalyptol get into grapes
In the heat, volatiled eucalyptol from trees is absorbed in the waxy layers on the skin of grapes
What RS level do off-dry / sweet styles of wine (eg Sauternes) typically have
150g/L
What European region requires that sweetness levels are printed on the label
Alsace. The rest of EU doesn’t.
Which is sweeter:
- Moelleux or Doux
- Lieblich or Süss
- medium dry or medium
Doux
Süss
Medium (also known as medium sweet)
How much residual sugar can a half-trocken (demi-sec/medium-dry) wine have?
[4g/L; x; 12g/L], going up to 18, so long as total acid is less than or equal to 10g/L of RS
How much residual sugar can trocken (sec/dry) wine have?
[0; x; 4g/L[ going up to 9g/L os long as total acid is less than or equal
What is the third most abundant constituent of wine
Glycerol, after h20 and alcohol
Which wines have the highest level of glycerol
Botrytised wine. Beaujolais nouveau as well, but less.
What does glycerol bring to a wine
a little sweetness, sensation of fuller body and smooth texture
Where are phenolics found
skins, seeds, stalks
What is the chemistry behind the drying sensation of tannins
they bind to proteins in the mouth
How much residual sugar is allowed in medium / moelleux/lieblich wine?
[12;x;45] g/L
