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Objectives
Assessing the
efficiency of a lyzozyme treatment on the management of the lactic bacterial
microflora. This treatment is applied in the very particular conditions
of carbonic maceration while the grapes are set into the vat. The test
was monitored by classic indicators assessing microbial alterations under
marc : weekly assessment of the volatile acidity, of the malic acid disappearance,
tasting, microscopic observation.
Context of
the experimentation and results
Six sets of
wines were compared. Two levels of contamination by lactic bacteria (105
et 106 bacteria per ml).
Three antibacterial treatments (SO2 : 5 g/hl, SO2 : 10 g/hl, lysozyme
: 20 g/hl). Constant temperature of 25°C (80°F). .
1. SO2 :
5 g/hl + 100 000 bactéries lactiques/ml
Lysozyme : 0. Code : SO2 : 5 B
2. SO2 :
5 g/hl + 1 million bactéries lactiques/ml.
Lysozyme : 0. Code : SO2 : 5 H
3. SO2 :
10 g/hl + 100 000 bactéries lactiques/ml.
Lysozyme : 0. Code : SO2 : 10 B
4. SO2 :
10 g/hl + 1 million bactéries lactiques/ml. Lysozyme : 0. Code
: SO2 : 10 H
5. SO2 :
0 g/hl + 100 000 bactéries lactiques/ml.
Lysozyme : 20 g/hl. Code : Lyso : 20 B
6. SO2 :
0 g/hl + 1 million bactéries lactiques/ml.
Lysozyme : 20 g/hl. Code : Lyso : 20 H
SO2,bacteria and lysozyme are put at the same time as yeast. All
the quantities have been calculated from the initial juice at the bottom
of the vat : adjusted to 10% of the weight of the grapes. Behavior of
the carbonic maceration : totally static during the whole test, with no
rising or leaching of the grapes.
Commentaires
After the first
week, the measured volatile acidity is due to the alcoholic fermentation.
None of the wines has begun its malolactic fermentation. No difference
between the six wines.
After 2 weeks,
only one wine has completed its MLF : the one treated with lysozyme, with
a heavy inoculation of bacteria. At that time, the level of volatile acidity
is still not high. The slight increase of volatile acidity on the whole
body of wine (0,10 à 0,15 g/L) is due to the metabolism of alteration
yeast which has developed on the grapes that have risen up, far from the
competition of the Saccharomyces selected from the juice. Another consequence
of the development of these types of yeast: a strong smell of ethyl acetate
in all the vats.
Figure n°1 : Volatile acidity at the bottom of a vat of wines in
carbonic maceration. Results R&D Department 1998.
After 3 weeks,
only 2 wines have not begun their MLF yet : high SO2 with low contamination,
and lysozyme with low contamination. The volatile acidity of these two
wines is stable. The one set with high SO2 and a high contamination has
just begun its MLF, but the volatile acidity has slightly increased. All
the others have completed their MLF and have a very high volatile due
to the lactic fermentation of the sweet substance which bursting grapes
released too late.
None of the
treatments tested allows to manage thoroughly a large lactic bacterial
population in the long run. This result confirms some previous experimentation.
An initially
high addition of sulfur dioxide is mostly efficient when it comes to contain
a high population of bacteria. This result also confirms some previous
experimentation.
As a preventive,
the lysozyme is definitely efficient to avoid the proliferation of a lactic
bacterial population when the latter is not too high to begin with. These
results confirm those found for the Beaujolais by the ITV. Therefore,
it is of minor interest to use the lysozyme when work and hygiene conditions
are not sufficiently controlled.
Another thing
this test confirms: an Oenococcus oeni population (ex Leuconostoc oenos)
does not burst out when attacking a juice or a wine. Although the temperature
and environment conditions had favored bacteria and that we deliberately
let things take their course, there still was not any actual souring after
two weeks of maceration.
The "sudden
and unexplained" catastrophes that some experience in their cellar are
due to late and important contamination with well-acclimated populations.
This kind of situation can be solved with a better hygiene and work organization
in the cellar, and not with the accumulation of additives such as lysozyme.
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