Robert Tracy
with Bevan Skaalen
ottling is the final step of wine production during which the
wine can be microbiologically compromised. It is critical that
all necessary steps be taken to establish andmaintain amicrobiologically
stable product. Lack of attention to detail in bottling
will almost certainly lead to a microbiologically unstable
finished wine. If a consumer opens an unstable bottle of
your wine, it is clearly bad for business.
What is microbiologically unstable wine? It is wine containing
viable microbes that have the potential to initiate
post-bottling microbiological activities. These activities could
be secondary fermentation (production of carbon dioxide);
production of off-aromas/off-flavors (acetic acid, mousiness,
4-ethyl phenol/4-ethyl guaiacol); and/or formation of sediments,
viscosity, and/or off-color.
What can you do to protect your wine from microbiological
instability?
Nature of potential problems
Like bottling in all beverage industries, bottling wine is a
complex process that incorporatesmany different disciplines,
including microbiology, chemistry, quality assurance/quality
control, engineering, maintenance, production, and environmental
sciences. Due to this complexity, there is ample opportunity
for problems to arise.
Therefore, both wineries with bottling lines and mobile
bottlers must have systems in place – such as a Quality
Assurance/Quality Control (QA/QC) program, Good
Manufacturing Practices (GMP), and a preventative maintenance
program – to address the multiple areas/locations
that can microbiologically compromise finished product.
Table 1 provides an overview of the potential sources of
microbial problems throughout the wine bottling process.
Microbial defense strategies
Each winery must have a microbial defense strategy for
every wine it bottles to prevent post-bottling microbiological
activity. Even in situations where a wine is chemically and
microbiologically stable, precautions against contamination
must be in place from the bottling tank through closure of the
finished product. These precautions are critical because both
stable and unstable wine can pick up microbial contaminants
throughout the bottling route if preventive strategies are ineffective
or lacking.
A comprehensive microbial defense plan for bottling
involves a two-pronged approach: 1) treatment of unstable
wine (and in some cases stable wine) with preservatives or
sterilants and/or filtration; and 2) a QA/QC program.
When a wine is known to be chemically and/or microbiologically
unstable, it is imperative that the wine be stabilized
with a treatment–such as a chemical preservative/sterilant
or filtration or both – to help prevent downstream microbiological
activity. These treatments are also recommended for
stable wines in situations where a winery is uncertain about
the effectiveness of its bottling QA/QC program.
Currently, winemakers preserve their wines with sulfur
dioxide, sorbate, or Velcorin™ (dimethyl dicarbonate
[DMDC]). DMDC is an effective antimicrobial agent for wine.
It can be lethal to both yeast and bacteria, although higher
concentrations of DMDC are usually required to kill bacteria.
It has been approved to be used in wine at a maximum concentration
of 200 ppm during the winemaking process.
