Aroma Chemistry And Perceptions Flashcards
Sources of Wine Aromas and Compounds (5)
- 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
Methoxypyrazines (5)
- Grape -derived
- Vegetative, herbaceous, bell pepper or earthy aroma
- Cab Sauv, Cab Franc, Merlot
- From grape skins
- Tomato leaf, bell Pepper, grass
Thiols (importance, where its derived, and profile)
7
- 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
Thiols (Chemical compound, role of Sulphur)
4
- 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
Terpenic alcohols
6
- From Grape skins (muscat, traminer)
- Primary source is grapes, not fermentation
- Linalool
- Flowers, lemon peel, lemon, lavendar
- Isoprenoids
- C-13 Norisoprenoids
C-13 Norisoprenoids
- Released as the free aroma compound through fermentation and ageing
- Contribute tea, honey, violet, tobacco, kerosene flavours
Hexanol (5)
- Grape derived
- Cut grass
- Herbaceous
- Vegetal
- Higher Alcohol
Fermentative Aroma Compounds
Yeast and fermentation – volatile metabolites (there are 5)
¡ Esters
¡ Higher alcohols
¡ Carbonyls
¡ Volatile acids
¡ Volatile fatty acids
Esters (basic Info) 4
- 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
5 types of Esters
*Acetates
* Propanoates
* Hexanoates
* Octanoates
* Succinates
Esters (more detailed) 3
- 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.
Higher Alcohols (3)
- They have more carbon atoms than ethanol and can support fruitiness.
- Also called Fusel Alcohols
- Made from Amino acids
Higher Alcohols thresholds and yeast (4)
- < 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
Volatile Acids range and 2 important ones
- 500-1000mg/L
- Volatile fatty acids (propionic and hexanoic acid)
- Acetic Acid
Volatile fatty acids (3)
- 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
Acetic Acid (3)
- High concentration vinegar-like aroma
- Too much can be from metabolism of ethanol by aerobic acetic acid bacteria
- From Acetaldehyde
Carbonyl compounds (2)
- Acetaldehyde (bruised apple, nutty)
- Diacetyl (butter or butterscotch)
Acetaldehyde (2)
- Increase over time due to oxidation of ethanol - due to aeration
- Acetaldehyde in white wine is indication of oxidation
Diacetyl
- Significant production during MLF by lactic acid bacteria
*Increased production under aerobic conditions
Lactones (5)
*A subclass of esters where the esterification is internal, forming a cyclic compound
* From the grape, synthesised by yeast during fermentation
* Extracted from oak – oaky/coconut
* From grape precursors - characteristic of Riesling and Muscat (Dried Fruit perceptions)
* Because the fermentation is kept at a low temperature, it takes a long time for the dried fruit component to come put, but if it is a sweet wine it can come out sooner
