Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
email: Office@practicalwinery.com
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January/February 2009
WINE MICROBIOLOGY
2,4,6-TBA — Next ‘2,4,6-TCA’ in U.S. wine industry
WINE MICROBIOLOGY
BY

Robert Tracy
with Bevan Skaalen
leadingB 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.
Physically removing microbes through filtration still causes a great deal of debate within the wine community over what effect filtration has on wine quality. However, there is no question that sterile filtration (0.45µ membrane filter) will remove all of the offending microbes (that is all fully viable cells; there is some evidence that
Table I: Potential sources of microbial problems throughout wine bottling process
AREA/LOCATION
  • Potential sources of microbial problem(s)
WATER DISTRIBUTION SYSTEM AT WINERY
  • Can harbor wine spoilage microbes, especially where wine has cross-contaminated water (inadvertent entry of wine into water well head, back-flushing of wine into water piping).
  • Lack of effective and routine cleaning and sanitation of water piping system.
  • Lack of routine microbial monitoring of water at designated locations throughout the water system.
  • Poor sanitary design of piping system (i.e. poor drainage, dead legs, threaded pipes, uneven welds, rough areas, etc.).
BOTTLING TANK
  • Lack of effective and routine cleaning and sanitation.
  • Poor sanitary design (i.e. poor drainage, uneven welds, rough areas, etc.).
  • Lack of routine microbial monitoring of wine prior to bottling.
WINE DISTRIBUTION (PIPING) SYSTEM FROM BOTTLING TANK TO BOTTLING FACILITY
  • Lack of effective and routine cleaning and sanitation.
  • Poor sanitary design of piping system (i.e. poor drainage, dead legs, threaded pipes, uneven welds, rough areas, etc.).
WINE FILTRATION SYSTEM FOR BOTTLING (IF USED)
  • Poor sanitary design of wine filter housings and associated piping (i.e. dead-legs, threaded piping/fittings, uneven welds, rough areas).
  • Lack of routine sanitation (i.e. hot water) of filters and filter housings.
  • Lack of filter regeneration (daily or weekly flushing with cold water in forward flow direction at 1.5 X filtration rate followed by rinse with hot water, dilute caustic, or dilute citric acid solution).
  • Lack of routine filter integrity testing (bubble point test).
  • Lack or inconsistent monitoring of pressure on filters.
WINE PIPING FROM FILTRATION SYSTEM TO BOTTLING LINE
  • Lack of effective and routine cleaning and sanitation..
  • Poor sanitary design of piping system (i.e. poor drainage, dead legs, threaded pipes, etc.).
ADDITION OF CHEMICAL STERILANTS/PRESERVATIVES (VELCORIN™ OR SO2) DURING BOTTLING PROCESS
  • Inadequate addition of chemical sterilant/ preservative due to poor dosage regulation.
BOTTLING LINE
  • Lack of effective and routine cleaning and sanitation for all parts (rinser, sparger, filler, leveler, and corker).
  • Most likely sources of contamination are environmental air, cork hopper, corker jaws, bottles, filler spouts (rubber spacers and gaskets), sparger, and leveler.
  • Poor sanitary design of piping system (i.e. poor drainage, dead legs, threaded pipes, etc.).
  • Sanitary gauges not used.
  • Unsanitary bottles.
  • Unsanitary process for sanitizing bottles (water or air).ue to p
  • Lack of effective and routine microbiology audit process.ue to p
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