400 V. Ferreira and J. Cacho
Two different alternatives for the evaluation of the magnitude of the odor intensity
of the effluent have been proposed. The first is based on a psychophysical concept
known as cross modality matching (Stevens1975). According to this concept, there
is a connection between the intensity of some basic stimulus, such as visual or olfac-
tory stimulation, and some muscular responses, such as the contraction of the iris or
the separation between the thumb and the index fingers (finger span) (Stevens and
Stone 1959). This property is satisfactorily exploited in the so-called finger-span
method (Guichard et al. 1995; Eti ́evant et al. 1999). The judge fits his/her index and
thumb fingers in a device connected to a resistance which registers when and by
how much the finger span is opened. The judge does not have to try to follow the
intensity as in the initial version of OSME, but to give a simple measurement of the
intensity of the olfactory stimulus as a whole. Therefore, although there is a time-
intensity measurement (because, again, the time the finger span is actuated is also
registered) only the maximum intensity (the measurement of the overall intensity
of the stimulus) is recorded, at least in its original version. The procedure does not
require a sophisticated assessors training (Bernet et al. 2002) and is easy to use. The
finger span device is offered by a chromatographic company as an additional tool
for its GC-olfactometric port (GC-Sniffer 9000. Product brochure 2008)
The second and easiest alternative is to ask the judges just to give a numerical
measurement of the overall intensity of an odor eluted out of the column. Typically
the panelists are asked to measure the overall intensity using a simple five, seven
or nine point scale. The technique is veryeasy to implement and its reproducibility
and quantitative ability have been well demonstrated (Le Guen et al. 2000; Serot
et al. 2001; Ferreira V et al. 2003b); van Ruth 2004; Campo et al. 2005; Pet’ka
et al. 2005).
8E.2.1.4 Overall Evaluation
In general, it must be said that the selection of the technique for recording and
further processing the olfactometric signal is not critical provided that the exper-
iment is carried out correctly. As can be deduced from the large differences in
individual thresholds (Punter 1983; Cain and Gent 1991), and particularly from the
documented existence of many odorants for which a part of the population shows
specific anosmia (Amoore 1977), the use of a sensory panel is crucial. Our personal
experience, however, suggests that the use of posterior intensity methods is most
cost-effective. In these methods, as in all methods involving the use of a single
dilution of the extract, it is important to choose adequately the concentration factor
for such extract in order to ensure that only a reduced number of odorants reach
odor intensities approaching the maximum of the scale.
8E.2.2 Preparation of Extracts for GC-Olfactometry
This is really a major and critical issue in GC-O, particularly in the study of wine
and other alcoholic beverages and, in general, it can be said that there are better and