Good cellar practices to prevent spoilage during aging
Joy Ting
November 2018
It is always important to maintain good cellar practices to prevent spoilage during aging. In years like 2018, these practices become essential during elevage. Wines with higher pH, lower tannin content and higher VA than usual are especially susceptible to oxidation and microbial spoilage. Good cellar practices can help protect your wines during this critical period.
This is the time to make sure that you are not skimping on any general hygiene procedures in the cellar. Some general practices to make sure you have in place include:
- Timely topping of all storage vessels to prevent oxygen ingress
- Adjusting acid early to keep molecular SO2 at acceptable levels and aid in anti-microbial control
- Managing oxygen ingress by racking as anaerobically as you can, using inert gas as a blanket. AWRI suggests 50 ppm tannin addition at racking for antioxidant protection
- Keeping partial tanks gassed and sealed
- Maintaining storage vessels at a DO level less than 0.8 ppm (check weekly)
- Checking DO during cellar operations and adjusting as needed by bubbling inert gas to displace oxygen
It is also important to manage any potential for microbial growth. It is probable that some spoilage microbes came into the winery with the grapes. Preventing their growth and spread can keep a bad situation from getting worse.
The first thing to do is consider inoculating for malolactic fermentation. If you already have high VA, a laborious malolactic will only exacerbate the problem. Inoculating allows you to select a strain that fits well with the chemical environment of your wine (pH, alcohol tolerance), as well as completing fermentation and adding SO2 sooner (Chauffour 2018).
Clean
Preventing the spread of contaminating microbes through the winery is essential. This includes making sure surfaces are properly cleaned before sanitization. Dr. Randy Worobo has an excellent webinar on hygeine(insert hyperlink: https://www.youtube.com/watch?v=2oq4r2bWNDM) that is worth watching if you are experiencing microbial problems, or if you want to prevent these problems.
Barrels are one of the hardest areas to clean and sanitize. Once they are infected, it is very difficult to remove spoilage organisms. Taking the proper steps to clean and sanitize barrels thoroughly during racking operations is an excellent opportunity to allow for longer aging. Cartwright et al (2018) found that 12 minutes of steam is needed to kill Brett impregnated in the staves of barrels while Wilker and Dharmadhikari (1997) found 20 minutes of hot water (88 degrees C) are needed to inactivate acetic acid bacteria already in the barrel. (In this study, sanitizing treatments of SO2, chlorine, heat and potassium bicarbonate were all tested and only hot water was shown to consistently inactivate acetic acid bacteria.)
Fine
Chitosan provides another tool in microbial management. Most enological companies now carry a version of chitosan. The chitosan used to treat wine is a biopolymer obtained from Aspergillis niger that shows a broad range of anti-microbial action. It has been shown to bind to negative charges on the cell walls of microbes and cause sedimentation, allowing removal by racking. Binding also leads to leakage of cell membranes, including ATP loss and eventual death. Cell mortality is concentration dependent, so racking off chitosan is still recommended for highest efficacy of the treatment. Specialized chitosan products can be used prior to fermentation to remove spoilage organisms, while a different formulation is recommended after fermentation is complete. Chitosan will bind to malolactic bacteria, so if you use this product prior to fermentation you will need to inoculate for malolactic fermentation. Also, do not add this product to your finished wine until you confirm the completion of malolactic fermentation. (Chung et al 2004, Taillandier et al 2014)
Monitor
It is very important to monitor SO2 and VA regularly. If SO2 is dropping faster than normal, or VA is accumulating too quickly, you will know to intervene. Scottlabs recommends you measure each parameter monthly until you achieve stable levels, and bimonthly after that. As already stated, it is also important to monitor SO2 during cellar operations as oxygen pickup during racking will bind SO2 and leave your wine more susceptible to oxidation as well as increase the action of acetic acid bacteria.
Rack?
Care should be taken in deciding when and how often to rack, depending on the situation. Racking can be very useful in removing yeast and bacterial cells from the bottom of the barrel. If spoilage organisms are suspected, and especially if chitosan has been used, racking can reduce the microbial population significantly (Jackson 2014). Scottlabs recommends racking 3-4 times in the first year, after primary, secondary, and several times in first and second years, managing SO2 additions along the way. To offset oxygen pickup, they suggest using the AWRI recommendation of adding 50 ppm tannin addition with each racking.
However, racking itself introduces oxygen and removes lees that themselves (if non-spoilage organisms) can serve as anti-oxidants and help integrate tannins. In Enology Notes #106, Zoecklein describes a study by Delteil (2002) comparing two Syrah wines, one aged on light lees for 9 months while the other was racked several times prior to storage in barrel for 9 months. The wine stored on lees had better structural integration and higher perception of higher varietal fruit than the wine that was racked and stored without lees. Ultimately, the decision of when and how much to rack depends on your particular wine.
References
Cartwright, Z.M., Glawe, D.A., & Edwards, C.G. (2018). Reduction of Brettanomyces bruxellensisPopulations from oak Barrel Staves Using Steam. AJEV, 69(4), 400-409.
Chauffour, E. (2018, October 22). Microbes Management in Winemaking. Lecture presented by Enartis: http://www.enartis.com/upload/images/12_2017/171228002113.pdf
Chung, Y, Su, Y, Chen, C, Jia, G, Wang, H, Wu, JCG, & Lin, J. (2004). Relationship between antibacterial activity of chitosan and surface characteristics of cell wall. Acta Pharmacol Sin, 25 (7) 932 – 936.
Jackson, R. S. (2014). Wine science: Principles and applications. London: Elsevier/Academic Press.
Scottlabs (2018). Post Fermentation Management Plan. Personal Communication with Megan Hereford, Oct 2018.
Taillandier, P, Joannis-Cassan, C, Jentzer, J.B., Gautier, S., Sieczkowski, N, Granes, D. & Brandam, C. (2014) Effect of a fungal chitosan preparation on Brettanomyces bruxellensis, a wine contaminant. J Appl Microbiology 118: 123 – 131
Wilker, K. L., & Dharmadhikari, M. R. (1997). Treatment of Barrel Wood Infected by Acetic Acid Bacteria. AJEV, 48(4), 516-520.
Worobo, R. (2012, June 12). Winery Sanitation Basics. The Northern Grapes Project Webinar Series. http://northerngrapesproject.org/northern-grapes-webinar-series/recorded-webinars
Zoecklein, B. (2005). Lees management. Enology Notes, (106). Retrieved October 22, 2018.
