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
viable but nonculturable [VBNC] cells can pass through a 0.45µ pore size, but this topic will be discussed in more detail in a later column), which makes this a very effective method for treating wine immediately prior to filling bottles.
Yet, many winemakers strongly believe that filtration negatively impacts wine’s organoleptic qualities, stripping flavors, aromas, and/or color. Potentially, this group of winemakers have the option to use a membrane filter with a 0.65µ pore size, which effectively removes yeast cells but does not eliminate all bacteria.
If a winery has any question about wine instability and the effectiveness of its bottling QA/QC program, we recommend sterile filtering the wine. We have experienced many instances in which unstable wines and even wines thought to be stable, developed post-bottling microbiological activity.
Critical QA/QC program
The final preventative strategy is an effective and robust bottling QA/QC program.Without question, the absence of a QA/QC program or an ineffective one will lead to postbottling microbiological activity. An effective program includes routine sanitation, regular monitoring of finished product for microbes, a set of specifications for allowable microbial levels in sanitation and bottled product, and routine monitoring and maintenance of bottling line equipment
For most wineries (those not running 24 hours per day), daily sanitation of bottling line and associated equipment should be employed. Hot water or steam are effective methods for sanitizing bottling line equipment. If hotwater is your choice, we recommend that 180°F/82°C water be used for at least 20 minutes. The temperature of the water must not be measured at the source, but rather at the most distant point from the source.
If steam is the preferred method, the target temperature of the condensate is 180°F/82°C for at least 20 minutes at the most distant point relative to the steam source.
Because it is difficult to sanitize the corker jaws and cork hopper using either of these methods, we recommend that corker jaws be sprayed or soaked in 70% ethanol daily and that the cork hopper be sprayed with 70% ethanol each time new corks are added
On a weekly basis (or a daily basis if time permits), the bottling line should be cleaned with a caustic cleaner followed by hot water sanitation. On a quarterly or semi-annual basis, bottling line equipment should be taken apart and thoroughly cleaned.
Monitoring program effectiveness
In addition to developing and maintaining bottling line sanitation, it is important to monitor the effectiveness of your sanitation process. Use one or more of the following methods: 1) visual inspection; 2) adenosine triphosphate (ATP) testing; and/or 3)microbial swabbing/culturing. (These threemethods were discussed in detail in the September/October 2008 PWV column).
Because the number of potential microbial contamination sources is quite high during bottling, it is also imperative that each winery conduct post-bottling microbial monitoring of its finished products. This is necessary even if wine is sterile filtered, because membrane filters can fail (through loss of integrity or blow-through of filters).
Ideally, bottles should be collected from the line every hour during every bottling run. At minimum, bottles should be collected off the line immediately after start-up, following employee breaks when the bottling line is not operating, and at the end of a run. At start-up and after employee breaks, microbes being retained on filters can be pushed through the membrane filters by the initial surge from the wine pump.
Once effective sanitation and microbial monitoring programs have been established for the bottling process, it is in the best interest of the winery to establish acceptable levels of ATP and/or microbial loads on bottling line equipment and acceptable levels of microbes in bottled product. By establishing these levels, the winery can prevent contaminated product from entering the marketplace, and it can undertake corrective action when levels are found to be too high on equipment or in wine being bottled.
Bottling maintenance program
The final element of a QA/QC program for bottling is a preventive and ongoing maintenance program for bottling line equipment. A lack of diligence in this area can lead to serious microbial contamination problems during bottling. If the equipment is not properly maintained, cleaned, and sanitized, microbes can quickly proliferate in the numerous nooks and crannies available. Once they have established themselves,microbes will continually contaminate your wine until their source is located and eradicated.
Conclusion
The bottling line is literally the last line of microbial defense for each winery. It is critical that this part of the winemaking process be the cleanest and the most sanitary area possible, and that it has the most comprehensive and robust QA/QC program in the winery.
References
  1. Tracy, R., and B. Skaalen. “Instituting a winery sanitation program.” Practical Winery & Vineyard. September/October 2008.
[Dr. Robert Tracy, with nine years of scientific research experience and seven years of winery laboratory and quality control/- quality assurance experience, specializes in wine chemistry and microbiology, winery sanitation, and QA/QC. He is co-founder of BevTrac Mobile Quality Systems LLC, based in Windsor, CA (www.bevtracquality.com), providing a mobile wine laboratory and consulting services to the wine industry. Please direct inquiries to robert.tracy@bevtracquality.com or tel: 707/239-8581.]