It’s bottling season! Wineries are gearing up for the current growing season and another harvest. Now is the crunch time to get everything from last year’s vintage out of tank and barrel, and into bottle. Bottling is time intensive and tedious for a winery of any size, and it’s easy to leave the bottling line with contaminated wine bottles.
In fact, previous research has shown that even when sterile filtration steps are properly performed, over between 39-58% of the bottles leaving the bottling line end up with yeast in the bottle (Neradt 1982). Renouf et al. (2007) found that using sterile filtration (0.45 micron absolute filter or lower) was the only way to eliminate most microorganisms from the wine during bottling. However, in bottles that contained microbial populations upon bottling, Brettanomyces was able to bloom in the bottle after 6 months of storage, and increase 4-EP and 4-EG volatile phenol concentrations within 10 months post-bottling (Renouf et al. 2007). In fact, long term storage of red wines infected with Brettanomyces found this spoilage yeast became the dominate microbial population in the bottle, outcompeting most other microorganisms (Renouf et al. 2007). Yikes!
Bottling is one of the most important steps to retain wine quality at the winery. Therefore, this blog post will focus on a number of bottling considerations for wineries:
- Make pre-bottling additions before bottling day
Most product additions, including sulfur dioxide, potassium sorbate, gums, sugar, etc. require at least 24 hours of stabilization in wine before it can be sterile filtered and bottled. There are some exceptions, and some products may require longer stabilization time or need to be added during bottling, after filtration. You should rely on the advice of your product supplier when working with new additives. Additionally, some filter suppliers recommend making large sugar additions to wine at least a week before filtration.
If you are making the final sulfur dioxide addition the day before bottling, make sure you measure the concentration of free sulfur dioxide in the tank prior to bottling. Take multiple samples throughout the tank to ensure that the sulfur dioxide has penetrated all sections of the wine. If the sulfur dioxide is not high enough to reach the 0.85 ppm molecular level, it is best to alter additions and wait to bottle another day.
Whether you have a manual bottling and capping system, or a high-tech bottling line, physically cleaning the bottling line is essential to maintaining proper hygiene in the winery. Bottling is one of the key areas where the quality of the product can greatly be degraded. Have brushes specific for the bottling line, and utilize detergents that break down wine debris or environmental dust.
Some bottling lines will require personnel to remove valves, hose lines, etc. to physically clean off debris or biofilms. Following cleaning operations, proper sanitation is essential to reduce microbial contamination through the bottling process.
*Note: The use of potassium sorbate will not inhibit contamination of your wine through bottling. Only proper sanitation techniques can reduce microbial populations and minimize risk of microbial spoilage in the bottle.
- …and Sanitation of the Bottling Line
As mentioned above, proper sanitation reduces microbial populations within food equipment and the surrounding environment, in order to reduce the risk of potential contamination within the packaged product – in this case, wine. While greatly underestimated, the surrounding environment is a potential contamination point in wineries, especially during bottling. Aseptic bottling operations are not necessary to maintain good hygiene, but it is often recommended that the bottling line be isolated within the winery to avoid large air movements while wine is packaged. This helps to avoid yeast, which are ubiquitous, contamination during the bottling process.
Floors, walls, and drains should be easily accessible and cleaned in the bottling area to help reduce environmental contamination. Routine environmental sanitation will also help reduce the risk of contamination.
Additional primary sources of contamination on the bottling line have previously been identified by Neradt (1982):
- Filler/Fill spouts
- Bottle sanitizer
- Bottle mouth
Proper sanitation of the bottling line first requires proper cleaning to remove all physical dirt and debris. Otherwise, the sanitation step is literally “cleaning dirt.”
Water chemistry, temperature, and contact time all affect the efficacy of sanitation. The use of soft water is often recommended for sanitation to avoid hard water residues that can harbor microbial populations.
The minimal temperature-time combination to sanitize equipment using hot water is 180°F (82°C) for at least 20 minutes. This temperature must be obtained at the coldest point in the bottling line. For bottling operations, this will be where water leaves the system. Butzke (2010) notes: “…that humans perceive water as painfully hot at temperatures just above 42°C (108°F).” Therefore, temperature readings should be taken with a calibrated, food-grade thermometer.
Individuals should take caution when working with scalding material or any chemical agent during the sanitation step. Always remember to ensure that employees have proper safety equipment and adequate ventilation.
Note that if you are using hot water, heat, or steam to sanitize the bottling line, you will need to bring the equipment back to the temperature of the wine to avoid cooking the first few gallons of wine that flow through the bottling line. Do not use tap water to change the temperature, as this will ruin the purpose of the sanitation step. Some wineries prefer to lose the first few gallons of wine, while others will follow a heat step with cold acidulated-sulfur dioxide mix.
Fill heads are an easy source of potential contamination. Periodically throughout bottling (i.e., every hour, or every time that breaks are taken), these can be sprayed or misted with 70% food-grade ethanol to ensure proper sanitation. Allow the ethanol to evaporate before proceeding. Wineries could also dip the ends in a properly made acidulated-sulfur dioxide mix. Do not wash off sanitized equipment with a towel or “clean” paper towel.
Always remember that the efficacy of cleaning and sanitation is dependent on the processor to complete this task correctly. Both cleaning and sanitation should take place immediately before bottling and immediately after bottling is completed. For more information on proper sanitation techniques, wineries can attend the Penn State Food Safety and Sanitation Short Course, which emphasizes key concepts related to sanitation processes.
Additionally, the book, Winemaking Problems Solved, has an entire chapter designated to trouble shooting during bottling operations, and is recommended for any winery.
- Checking sterile filtration integrity
Filter integrity is an easy step that wineries can take to ensure their sterile filtration unit is working properly. Remember that sterile filtration requires the use of a 0.45 micron (or smaller) absolute filter cartridge. The Bubble Point Test is an integrity test that should be applied to a filter before and after bottling to ensure filter integrity.
- Bottle washing
While bottles are sterile when they are formed, many retain cardboard dust (“case dust”) in the bottles by the time they reach the bottling line in the winery, and this acts as a contamination point. Wineries should also be aware of tiny glass shards that may be retained within the bottle during glass manufacturing.
The best way to remove dust and debris in the bottle is by gas jetting: injecting a small stream of inert gas (e.g. nitrogen) prior to the bottle’s use.
As this is not a sanitation step, it is recommended that bottles also undergo a pre-rinse step with an approved no-rinse sanitizer. Many wineries utilize an acidulated-sulfur dioxide rinse or ozonated water.
- Inspecting filled bottles
Many wine microbiology text books recommend sampling one or two filled wine bottles every hour during bottling. There are several things that wineries can look for including using a microscope to scan for potential contamination, using membrane filtration to enumerate yeast and bacteria on a Petri Dish (pg. 236-238 in Wine Microbiology), or sending samples away to test for bottle sterility. This quality control step can help minimize worry post-bottling and provide ample feedback regarding bottle efficacy.
- Checking sulfur dioxide depletion
The use of sulfur dioxide is the last line of defense in terms of microbial stabilization while wine is in bottle. Many refermentation incidents are a result of too little free sulfur dioxide in the bottle.
During bottling, the wine will lose a little bit of the free sulfur dioxide concentration. Typically, this is around 10 ppm of free sulfur dioxide concentration, but it will vary from winery to winery, and bottling line to bottling line. Wineries should sample the sulfur dioxide concentration about 24 hours post bottling to evaluate the average loss of sulfur dioxide during the bottling process. Extra additions of sulfur dioxide can be made beforebottling to compensate for the loss during the bottling process.
Resources & Literature Cited
Butzke, C. “How long do I need to disinfect my bottling line if my hot water is less than 82°C (180°F)?” in Winemaking Problems Solved
Neradt, F. 1982. Sources of reinfections during cold-sterile bottling of wine. Am. J. Enol. Vitic. 33(3):140-144.
Renouf, V., M.-C. Perello, G. de Revel, and A. Lonvaud-Funel. 2007. Survival of wine microorganisms in the bottle during storage. Am. J. Enol. Vitic. 58(3):379-386.