Wine Chemistry and Biochemistry

408 V. Ferreira and J. Cacho

1. Impact or highly active compounds, that are the compounds which can effec-

tively transmit their specific (impact) or primary (highly active) aroma nuance

to a given wine without the need of the support of more aroma chemicals. An

example is linalool in Muscat wines.

2. Impact groups of compounds. These are families of compounds usually having

similar chemical structures (chemical homologous series) and with quite close

odor properties that can impart to the aroma of a wine the specific notes of the

family. An example is theγ-lactones.

3. Subtle compounds or families. These are the compounds or groups of compounds

which fail in transmitting their specific aroma nuances to the wine, but contribute

decisively to the development in wine of some secondary-generic aroma nuance

(for instance fruity, sweet), always with the need of more chemicals bearing a

similarity in such odor notes. Compounds in categories 1 and 2, which do not

reach enough concentration, or even ifreaching it, theyco-occur with many

other powerful odorants (such as happens in complex wines), may fall into this

category.

4. Compounds forming the base of wine aroma. These are the compounds, present

in all wines at concentrations above their corresponding odor thresholds, which

are no longer perceived as single entities because their aromas are fully integrated

to form the complex concept of wine aroma. Within this group different roles can

be found:

a. Aroma enhancers

b. Aroma depressors

The problem is that many wines, particularly the most complex, do not have clear
impact compounds but rather families of compounds contributing to a given aroma

nuance, and this fact must be considered for the design of the sensory experiments

to assess the role of the different aromas.

A classical strategy makes use of odor thresholds calculated in matrix as similar

as possible to the wine subject of the study. This strategy, for instance, demonstrated

its usefulness for assessing the importance of wood constituents on wine aroma

(Boidron et al. 1988) or for establishing the maximum limits beyond which some

odorants exert a negative effect on wine aroma (Chatonnet et al. 1993). However,

this strategy is quite limited in scope and can only be applied to those compounds

that really play the role of impact compounds and to those cases in which is pos-

sible to find wines free from such substances. It is, therefore, very well suited to

characterize taints and off-flavors.

A second more rigorous strategy is that proposed by Grosch (1993). This strategy

first converts the concentration data into Odor Activity Values just normalizing the

concentration by the corresponding odor threshold, calculated in a simple matrix

similar to that of the product (in the case of wine the matrix could be a simple

ethanolic solution with pH adjusted at 3.4). Second and most important, the odor-

ants are mixed in a synthetic medium (this is called the model) to evaluate the

degree of similarity between the model and the original product. And third, new

models from which some of the odorants have been omitted are again prepared to