Aroma Chemistry And Perceptions Flashcards
1
Q
Sources of Wine Aromas and Compounds (5)
A
- Directly from the grape
- From non-volatile grape precursors - (many grape aroma compounds occur in a ‘bound’ form – not able to be smelled until they are converted to a ‘free’ form)
- Yeast and bacterial metabolism
- Oak wood extraction
- Chemical reactions
during wine ageing
2
Q
Methoxypyrazines (5)
A
- Grape -derived
- Vegetative, herbaceous, bell pepper or earthy aroma
- Cab Sauv, Cab Franc, Merlot
- From grape skins
- Tomato leaf, bell Pepper, grass
3
Q
Thiols (importance, where its derived, and profile)
7
A
- Grape derived
- Very low thresholds
- Cat Urine, sweat, broth, passion fruit, grape fruit, gooseberry, guava
- Important for Sauv Blanc
- More important in White wines
- Seen as a positive
- Formed during fermentation
4
Q
Thiols (Chemical compound, role of Sulphur)
4
A
- Mercapto
- Thiols contain a terminal sulphur group
- Derived from S-containing amino acids broken down by yeast during fermentation
- May also be sourced from the degradation of S-containing fungicides
5
Q
Terpenic alcohols
6
A
- From Grape skins (muscat, traminer)
- Primary source is grapes, not fermentation
- Linalool
- Flowers, lemon peel, lemon, lavendar
- Isoprenoids
- C-13 Norisoprenoids
6
Q
C-13 Norisoprenoids
A
- Released as the free aroma compound through fermentation and ageing
- Contribute tea, honey, violet, tobacco, kerosene flavours
7
Q
Hexanol (5)
A
- Grape derived
- Cut grass
- Herbaceous
- Vegetal
- Higher Alcohol
8
Q
Fermentative Aroma Compounds
Yeast and fermentation – volatile metabolites (there are 5)
A
¡ Esters
¡ Higher alcohols
¡ Carbonyls
¡ Volatile acids
¡ Volatile fatty acids
9
Q
Esters (basic Info) 4
A
- Formed from acid and alcohol
- Most esters are from alc fermentation, we can also get them from aging
- Exist in equilibrium – hydrolysis reaction will split the ester back into the parent alcohol and acid
- 160 have been found in wine
10
Q
5 types of Esters
A
*Acetates
* Propanoates
* Hexanoates
* Octanoates
* Succinates
11
Q
Esters (more detailed) 3
A
- A combination of ethanol + hexanoic/octanoic/decanoic acids give ‘fruity’ flavours
- Higher alcohols (isobutyl, isoamyl) + acetic acid (floral and fruity flavours)
- Ester retention requires the wine to be kept cold as these compounds are highly
volatile.
12
Q
Higher Alcohols (3)
A
- They have more carbon atoms than ethanol and can support fruitiness.
- Also called Fusel Alcohols
- Made from Amino acids
13
Q
Higher Alcohols thresholds and yeast (4)
A
- < 300 mg/L add complexity (fruity characteristics)
- > 400 mg/L (strong, pungent smell and taste)
- Different yeast strains contribute
variable amount of fusel alcohols - Non-Saccharomyces yeast – higher levels of fusel alcohols
14
Q
Volatile Acids range and 2 important ones
A
- 500-1000mg/L
- Volatile fatty acids (propionic and hexanoic acid)
- Acetic Acid
15
Q
Volatile fatty acids (3)
A
- Produced by fatty acid metabolism of yeast and bacteria
- They are particularly important to get esters
- Antibacterial compounds, produced from yeast compounds to fight lactic acid compounds
