5 Use of Enological Additives for Colloid and Tartrate Salt Stabilization 133
Although this can significantly reduce the bentonite’s binding ability (−50%), it
often produces about one half of the normal lees volume. Bentonite may also be
counterfined with kieselsol (aqueous silicon dioxide) to aid in lees compaction.
Gelatin is a positively charged protein which will bind with negatively charged
species such as tannins kieselsols and bentonite. Gelatin can be used to help ben-
tonite flocculation and possibly aid in lees compaction. Additionally, fining juice
or wine that is already relatively freefrom suspended solids will minimize lees
formation and, consequently, the bentonite requirement. Some winemakers prefer
multiple finings with bentonite rather than a single large addition. This approach
may be successful in reducing the overall bentonite requirement, particularly if the
wine to be fined is free from suspended solids.
A method used to solve the problems of excessive lees and flavor stripping caused
by fining wine with bentonite is to ferment in contact with bentonite. Fermentation
in the presence of bentonite is an old practice used in Europe for protein stabiliza-
tion. Such a practice avoids or minimizes the need for subsequent bentonite addition
into wine. Fermentation in contact with bentonite has several advantages: (1) only
juice components are adsorbed onto bentonite and not the fermentation-by products
or barrel-aging constituents and (2) fermentation lees have a lower monetary value
than do finished wine lees. Thus, protein stabilization or partial stabilization during
fermentation may be an important economic consideration.
Nevertheless, addition of bentonite at the beginning of the alcoholic fermentation
may deplete the assimilable nitrogen content of the must due to electrostatic binding
and adsorption. This may result in fermentation sticking and/or hydrogen sulfide
production. Addition of an exogenous source of nitrogen eliminates these potential
problems.
5.1.1.6 Dosage of Bentonite
The quantity of bentonite to be added to the juice to reach a protein-stable wine is
generally determined using a heat test (Dubourdieu et al. 1988; Marchal et al. 2002d).
In addition to protein stability, juice bentonite fining can help to enhance wine filter-
ability via general removal of suspended solids. Protein removal is not proportional
to the amount of bentonite added, but follows a power law (Marchal et al. 2002d).
Although complete removal of wine proteins can generally be achieved by the
use of bentonite (except for yeast proteins but the latter do not really partici-
pate to protein haze), it has been recognized that this may not be necessary to
obtain protein stability and may have detrimental effects on the sensory qualities
of wine (wine body, color, and possibly imparting an earthy, freshly “laundered”
smell).
Care must be taken when fining a sparkling wine with bentonite in order to pre-
serve its foaming properties. Excessive use of bentonite for the fining of sparkling
winecuvees ́ can produce a finished product that has a large bubble size and a poor
bubble stability as a result of a reduction inboth protein and peptide contents. Cold
stabilization procedures cause both a precipitation of potassium bitartrate crystals as
well as proteins because of the downward shift in pH. This precipitation of proteins