Wine Science: Principles and Applications, Third Edition - Vinum Vine

Prefermentation Practices 351
cfu ml
0.8% 0.9%
0.1%
1
95.2%
96.5%
10
2.5%
0.3%
0.2%
0.3%
0.2%
2.7%
0.2%
0.04%
93.5%
6.5%
3
104 105 (0%
EtOH)
106 107 108 0 mg l1SO4 added to must 20 mg l1SO4 added to must 50 mg l1SO4 added to must
0–5 days
(0–4%
EtOH)
104 105 106 107 6–15 days
10 3
(4–12%
EtOH)
103 102 104 105 106 107 15 days
0.4%
Candida guilliermondii
Cryptococcus laurentii
Zygosaccharomyces sp.
0.2%
0.1%
28.0%
0.9%
0.3%
71.1%
99.1%
Metschnikowia pulcherrima
Kloeckera apiculata
Several unidentified
Saccharomyces cerevisiae
25.1%
Figure 7.10 Predominance (% colonies recovered) and total cell numbers (cfu ml -1 ) of all yeasts during uninoculated
fermentations at 16 ºC with three sulfi te treatments. (From Henick-Kling et al., 1998, reproduced by permission)
Lactobacillus spp. (Davis et al., 1986a, b). Occasionally,
though, sulfur dioxide can aid malolactic fermentation,
by inhibiting endemic lactic acid bacteria infected with
bacteriophage (Davis et al., 1985).
If added, sulfur dioxide is usually supplied several
hours before yeast inoculation, usually at crushing.
During the settling period, the free SO 2 content declines
(as it binds with sugars, carbonyls and phenolics in the
must). Thus, the antimicrobial effect of sulfur dioxide
is much reduced when, and if, the must is inoculated
with one or more cultured yeast strains. For musts
derived from moldy grapes, the dose of sulfur dioxide
may need to be increased. Not only are the numbers of
microbial contaminants much higher, but the presence
of microbial by-products, such as glucuronic and galacturonic
acids, can markedly reduce the antimicrobial
infl uence of sulfur dioxide.
There is even more doubt about the advantages of adding
sulfur dioxide to inhibit the action of grape polyphenol
oxidases in white musts. Depending on the variety,
between 25 and 100 mg SO 2/liter may be required to
inhibit the early (enzymatic) oxidation of phenolics
(White and Ough, 1973). As a result, these phenolics
remain in the must, leading to an increased susceptibility
0.3%
74.6%
100%
Candida guilliermondii
Cryptococcus laurentii
Zygosaccharomyces sp.
Metschnikowia pulcherrima
Kloeckera apiculata
Several unidentified
Saccharomyces cerevisiae
1.0%
9.2%
89.8%
100%
Candida guilliermondii
Cryptococcus laurentii
Zygosaccharomyces sp.
Metschnikowia pulcherrima
Kloeckera apiculata
Several unidentified
Saccharomyces cerevisiae
to serious in-bottle browning. Regrettably, the undesirable
oxidation, induced by fungal laccases (found in
moldy grapes), is not controlled by commercially acceptable
sulfur dioxide additions. In the past, ascorbic acid
was added along with sulfur dioxide to limit early phenolic
oxidation. Although effective in this regard, ascorbic
acid induces even further delays in the oxidation and
precipitation of readily oxidized phenolics, delaying the
process until after bottling (Peng et al., 1998). Ascorbic
acid addition to white wine after crushing is now generally
not recommended.
With red wines, sulfur dioxide can bleach anthocyanins.
Although the bleaching is reversible, sulfur dioxide
also binds to fl avonoids, delaying the formation of
stable colored complexes between anthocyanins and
tannins. In addition, by binding with acetaldehyde and
pyruvic acid, sulfur dioxide can delay the formation of
vitisins (Morata et al., 2006).
The effect of sulfur dioxide on the synthesis of fl avorants
by Saccharomyces cerevisiae and other yeast
species (Herraiz et al., 1990), as well as its potential to
impart a metallic taste are additional points of concern.
Thus, whether the antimicrobial and antioxidant effects
of sulfur dioxide addition are benefi cial or detrimental