5 Use of Enological Additives for Colloid and Tartrate Salt Stabilization 149
5.2.2 Use of Yeast Mannoproteins for Stabilization of Tartrate Salt
Precipitation
Traditional practices, such as white wine aging on lees in barrels for several months,
confer the wine’s tartaric salt stability, which dispenses them from any cold sta-
bilization treatment. It has indeed been observed (Moine-Ledoux and Dubour-
dieu 2007) that, in the Bordeaux wine-growing area, the majority of dry white wines
aged on lees which are not stable in March after their first winter but become stable
in June or July without any supplementary cold treatment (Table 5.1). In contrast,
wines within the same crus which are not aged on lees systematically undergo cold
treatment to obtain stability regarding tartaric salt crystallization.
It is well established that, during wine aging on lees, yeasts release mannopro-
teins that are able to prevent tartrate salt precipitation as was demonstrated first
by Lubbers et al. (1993) in model wine solutions. Lubbers et al. (1993) used heat-
extracted mannoproteins in alkaline buffers, that is, conditions very different from
the spontaneous release of proteins during aging on lees. Nevertheless, Moine-
Ledoux and Dubourdieu (1999) reported that heat-extracted mannoproteins added
at a dose of 25 g/hL do not show any stabilizing effect as regard to tartrate salt
precipitations in red, ros ́e and white wines.
Discovery of the potent crystallization inhibitor effect of mannoproteins extracted
with enzymes (EEM) from yeast cell walls can be seen as an unforeseen conse-
quence of the work of Moine-Ledoux and Dubourdieu on protein stabilization of
wines. The mannoproteinfractions used for tartrate salt stabilization studies were
indeed the same as those they used to reach protein stability: cell walls were
treated at 40◦C with an industrial preparation of theβ-glucanase ofTrichoderma
sp (Glucanex-Novo), the use of which is authorized in enology forBotrytis cinerea
β-d glucane hydrolysis (Dubourdieu et al. 1981). The resulting hydrolysate puri-
fied after ultra-filtration is a colorless and odorless solid, known as MannostabTM,
perfectly soluble in water and wine. EEM used at a dose of 25 g/hL were shown
to inhibit bitartrate salt precipitation in red, ros ́e and white wines even after having
been kept at− 4 ◦C for six days (Moine-Ledoux and Dubourdieu 1999). Moreover,
these authors observed that EEM are stable over time in contrast to metatartaric
acid. Within 10 weeks at 30◦C, wines treated with EEM remain stable as regard to
Ta b l e 5. 1 Evolution of tartaric salt stability estimated by cold testing (six days at− 4 ◦C) of
different white wines aged on lees throughout two vintages (Reprinted with authorization from
Moine-Ledoux and Dubourdieu 2007)
Sample March June
Graves 1–94 Crystals present Crystals absent
Graves 2–94 Crystals present Crystals absent
Bordeaux 94 Crystals present Crystals absent
Graves 1–95 Crystals present Crystals absent
Graves 2–95 Crystals present Crystals absent
Bordeaux 95 Crystals present Crystals absent