Chitosan's Surprising Role in Winemaking

When it comes to winemaking, Brettanomyces bruxellensis (Brett for short) is a notorious troublemaker. This wild yeast, if left unchecked, can wreak havoc during wine aging, causing off-flavors and aromas that mask the varietal characteristics of the wine. But fear not, winemakers have a secret weapon in their arsenal—chitosan. Let's delve into the world of Brett and how chitosan is helping winemakers keep this pesky yeast at bay.

Understanding Brettanomyces

Brettanomyces is not your friendly neighborhood yeast like Saccharomyces cerevisiae, the superstar behind alcoholic fermentation. Instead, Brett is known for its ability to produce undesirable compounds such as phenols, pyridines, acetic acid, and fatty acids. These compounds can overshadow a wine's natural bouquet with off-putting notes like barnyard, band-aid, and sweaty saddle. Not exactly the tasting notes a winemaker strives for!

Brett thrives in oak barrels, which are commonly used for aging wines. The porous nature of oak provides an ideal sanctuary for Brett, offering a shielded environment where it can flourish away from the sanitizing treatments used in wineries. Combine this with Brett's resilience to ethanol and sulfur dioxide (SO2), and you have a recipe for potential wine spoilage, especially during prolonged barrel aging.

Enter Chitosan

Chitosan, a biopolymer derived from chitin, is found in the exoskeletons of crustaceans like crabs and shrimps. It also occurs in the cell walls of fungi. Industrially, chitosan is produced by deacetylating chitin. This natural polymer has found a variety of applications in medicine, agriculture, and now, winemaking.

The Many Faces of Chitosan

Chitosan's versatility is a key part of its appeal in winemaking. Here's how it works its magic:

• Clarifying Agent: Chitosan has a high affinity for oxidized and oxidizable polyphenols, causing them to precipitate out of the wine, often more effectively than traditional agents like gelatin or casein.
• Antiseptic Properties: It exhibits powerful antimicrobial action against lactic and acetic bacteria, indigenous yeasts, and of course, Brettanomyces.
• Metal Chelator: Chitosan binds to metals and heavy metals, preventing potential spoilage reactions.

Using chitosan not only helps inhibit malolactic fermentation but also reduces the need for sulfur dioxide, which is often added as a preservative.

How Does Chitosan Tackle Brettanomyces?

Research into chitosan's effect on Brettanomyces has yielded promising results. For instance, a study by Gómez-Rivas et al. (2004) demonstrated that high concentrations of chitosan (300-600 g/hL) could inhibit Brettanomyces growth without affecting Saccharomyces cerevisiae. Similarly, Ferreira et al. (2013) found that even lower concentrations (30-32.5 g/hL) were effective against Brettanomyces, with lower molecular weight chitosans showing greater efficacy.

A pivotal study published in 2016 in the Journal International des Sciences de la Vigne et du Vin explored how chitosan's performance varies with factors like alcohol content, pH, and type of chitosan. This research revealed that chitosan derived from crab shells outperformed its fungal counterpart, especially in more acidic and higher alcohol environments. The study also noted that while chitosan initially reduces Brett populations, these stubborn yeasts can sometimes make a comeback, indicating that chitosan doesn't completely eradicate the problem but significantly mitigates it.

The Future of Chitosan in Winemaking

While chitosan is not a silver bullet, its multifaceted capabilities make it an invaluable tool for winemakers. Continued research is crucial to optimize its application and understand its interactions in various wine conditions. As our understanding deepens, the hope is to develop even more effective strategies to keep Brett at bay, ensuring that our wines can express their true character without unwanted interference.

In the meantime, chitosan stands as a testament to the innovative spirit of winemaking, blending tradition with modern science to tackle age-old problems. So, the next time you savor a beautifully aged wine, you might just have a tiny polymer from a crab shell to thank for its pristine taste.