5 Use of Enological Additives for Colloid and Tartrate Salt Stabilization 129
Fining is one of the least expensive operations in wine production but one that
can have the greatest impact on wine quality. Fining trials should always be done
at several intervals in the winemaking process to ensure that the fining objective
is achieved using the smallest possible amount of fining agent. Considering all the
changes to color, flavors and aromas that occur during laboratory trials, fining is
often a trade off between achieving a specific goal, such as protein stability, and pro-
ducing a palatable wine. Many different fining agents can often be used to achieve
the same goal. If a winemaker is not satisfied with the results of the fining trials,
it is always possible to test another fining agent. To achieve consistent results, it
is essential that the preparation methods, temperature, mixing and timing are the
same between laboratory fining trials and winery applications. Bentonite, protein
and polysaccharide fining agents must be prepared just prior to use. The efficacy of
these fining agents can be reduced by 50% or more by improper preparation. Fining
agents always have to be prepared in exactly the same way for both laboratory and
winery uses. Preparation equipment, temperatures and timing are critical. The dif-
ference between a blender in the laboratory and a paddle mixer in the winery can be
overfining.
Fining agents have to be removed from wine as they are not additives but tech-
nological “assistants” or adjuvants. Most fining agents react within seconds and the
contact time between the fining agent and the wine should be as short as possible.
Carbon and PVPP can be filtered out immediately or a few hours after fining. At the
opposite extreme, formation of flocculates requires a few days when proteins are
used (depending on wine temperature) and they require a week or two to settle.
5.1.1 Bentonite Fining of White Juices and Wines
Bentonite has been the most commonly used fining agent in the wine industry since
the works of Saywell (1934) in the USA and Rib ́ereau-Gayon and Peynaud (1935)
in Europe. Authorization for the use of bentonite followed the contribution of
Milisavljevic (1963). The main bentonite usesare clarification and protein stability.
A major problem encountered in juice and wine production (white and ros ́ewines)
is protein stability, that is, removal of heat-unstable proteins (Hsu and Heather-
bell 1987; Waters et al. 1992). This form of instability together with potassium
bitartrate precipitation (see the section “Use of adjuvants for stabilizing wine with
respect to tartrate salt crystallization”) are the most common non-microbiological
defects in commercial wines. Bentonite fining removes both stable and unstable
proteins. The goal is to lower the unstable protein content to a level at which pre-
cipitation in the bottle will not occur, while using as little bentonite as possible
(Zoecklein 1988c). The use of bentonite toobtain protein stability is a somewhat
confusing issue due to the variation in bentonite characteristics, the nature of wine
proteins, and the different phenomena by which protein stability is determined.
Bentonite is a volcanic material which was deposited millions of years ago in
broad layers, which weathered and changed from a fragile glassy state into a min-
eral one. This mineral is classified as a montmorillonite, which referred to the small