64 A.J. Mart ́ınez-Rodr ́ıguez and E. Pueyo
3A.3 Foaming Properties
The most important sensorial characteristics of sparkling wines include, undoubt-
edly, the foaming properties perceived by the consumer when serving the sparkling
wine and also when drinking it.
A quality foam can be defined as one that causes a slow release of CO 2 ,inring
shapes from the depths of the liquid, with small bubbles that contribute to the for-
mation of a crown over the surface of the wine, covering it completely, with bubbles
two or three rows deep. The permanence of the foam on the surface of the wine
depends on a balance between the rate of foam formation and the rate at which the
bubbles making up this layer are destroyed.
A tasting card has been designed that can be used to evaluate the foaming
quality of a sparkling wine objectively (Obiols et al. 1998). However, it is also
important to have instrumental techniques that can be used to obtain a quantifi-
able value for foam quality, to be able to compare sparkling wines and also to be
able to correlate these foaming properties with the wines’ physical and chemical
characteristics, in order to establish which ofthese variables affect these properties.
With this knowledge, different technological aspects of the production process of
sparkling wines could be modified with the objective of improving their foaming
qualities.
The methods reported in the literature and used to quantify the foaming prop-
erties of sparkling wines can be classified into methods based on measuring the
kinetics of CO 2 discharging, gas sparging methods and image analysis methods.
The method of gas discharging kinetics (Maujean et al. 1988) involves studying
the time course of the mass quantification of the CO 2 discharged spontaneously
from the bottle. When all the free CO 2 has been discharged, the bottle is shaken to
quantify the so-called provoked CO 2.
Gas sparging methods are those most used in the past and still used today, and are
based on the procedure developed by Bikerman (1938). This essentially consists of
making a jet of gas pass at a controlled speed through a volume of wine to generate
a foam. Based on this method, experiments have been carried out with very simple
equipment made in the laboratory, that can be used to measure the height of foam
reached and the time it takes for this foam to collapse after the CO 2 jet has stopped
(Edward et al. 1982; Pueyo et al. 1995). The advantage of this method over that
described previously is that it can even be used to evaluate the foaming capacities
of still wines. In sparkling wine production it is very important since it permits
evaluation of the foaming characteristics of the base wines used to elaborate the
sparkling wines.
Later, Maujean et al. (1990) designed automated equipment to measure the foam-
ing properties of wines, based on Bikerman’s principle, called the Mosalux. This
equipment uses a photoelectric cell to record the height reached by the foam. It
incorporates a personal computer that can be used to control the experiments and,
also, for data acquisition. The foaming properties measured by Mosalux are HM or
maximum height of the foam or foaming power, HS, or stable height of the foam
with time and, TS, or stability time afterstopping the gas flow. This equipment