Wine Chemistry and Biochemistry

90 R. Peinado and J. Mauricio

Acetic

Acid

Glycerol Ethanol

L-Proline

Acetic

Acid

Ethanol

Dihydroxyacetone

Acetaldehyde

Piruvic acid

Oxalacetic Acid

Acetoin

Butanedione

2,3 Butanediol

Polysaccharide Hexose +CO 2

Fumaric Acid Aconitic Acid

2-Ketoglutaric Acid

Malic Acid Citric Acid

Succinic Acid Isocitric Acid

Glutamic Acid

CO 2 + H 2 O + ATP

Acetic Acid

Acetyl-CoA + CO 2

Fatty Acids Cycle

Fatty Acid Saturated

Fatty Acid Unsaturated

Sterols

CO 2 +H 2 O

Glycerol

Phospholipids

Amino Acids

Protein

L-Proline

O 2 O 2

O 2

O 2

O 2

O 2

O 2

Fig. 3B.4General scheme of the flor yeast metabolism

diacetyl and acetoin, and theremainder is metabolizedvia the tricarboxylic acid

pathway for incorporation as carbohydrates, lipids and proteins into cellular material

(Su ́arez-Lepe and I ̃nigo-Leal 2004). The ethanol uptake is governed by various fac-
tors such as the dominant yeast race in the flor film, film formation stage and aging

stage. Thus, ethanol is consumed in increased amounts at the film formation stage,

and also in the scales containing the youngest wine (Mart ́ınez et al. 1993, 1998).

Usually, up to 1 vol.% ethanol can be used during the aging process - nearly 4 vol.%

has been lost in some laboratory tests.

3B.3.2 Glycerol

Glycerol is the third most abundant component of wine after water and ethanol.

Yeasts use it as a carbon source and reduce its concentration with time. This has

prompted the use of the glycerol content of wine as a measure of its degree of aging

(Cort ́es et al. 1998; Moreno et al. 2001).

3B.3.3 Acetaldehyde

Acetaldehyde is one of the most special compounds in the biological aging process
and influences the sensory properties of wines by introducing a typical pungent