Colloids are aggregates of polyphenols, polysaccharides, proteins, and other wine constituents ranging in size from 1 nanometer (small molecules) to 1 micrometer (microorganisms). Winemaking techniques, especially those employed for stabilization, directly impact colloidal properties in wine. In many ways, our exploration of colloids lends an alternative perspective to the true nature of wine stabilization and its relationship to quality.

Flavor

Colloids are the intersection between flavor and mouthfeel. Phenolics, in particular, play a key role in binding flavors altering their stability in wine’s matrix (Wang et al., 2022). One fundamental pathway for colloid formation begins with the polymerization of bound anthocyanins in wine. Within the 100-day post-crush window, a wine is primed for colloid formation due to abundant free anthocyanins, high tannin activity, and favorable environmental conditions (warm temperatures and oxidation). An abundance of wine flavor also coincides with this period immediately following fermentation. Like free anthocyanins, many of these flavors are subject to oxidative decay thus making it the winemaker’s prerogative to stabilize these compounds. Colloids are such a solution. Once bound anthocyanins form, they aggregate with other wine constituents, snowballing into large conformations of polyphenols, polysaccharides, proteins, and flavor compounds. These structures protect wine flavor from oxidation and will persist into the finished wine unless disrupted by filtration or other stabilization techniques.

Stability

While modern winemaking has largely advocated for wine stability, it’s worth considering the qualitative changes at risk. One study evaluating the impact of crossflow and lenticular filtration between 0.45-0.65 μm showed that filtration significantly decreased colloid particle size and polysaccharide concentrations (McRae et al., 2017). Even though the colloid particle size of the filtered wines reassembled after 18 months, the study found significant differences in the flavor attributes of the filtered wines. Whether flavor perception increased or decreased was dependent on the lot and the filtration method, but overall, the results indicated a significant change suggesting a disjointing of flavor incorporation from wine colloids.

Figure 1. Intensity ratings of sensory attributes showed significant differences between filtration grades for (A) Cabernet Sauvignon 2013 and (B) Shiraz 2013. Pre-crossflow (PreX), post-crossflow (PostX), nylon (0.45N). Significance level: * p < 0.05, ** p < 0.01, *** p < 0.001 (McRae et al., 2017).

A second study found the addition of pectolytic enzymes to reduce colloid concentrations by disrupting polysaccharides and their aggregation properties (Kassara et al., 2019). The chart below shows a complete reduction of intermediate colloid size and a spike in low molecular weight colloid size in both red and rose wines. Particle concentration in the red control wine was also three times greater than for the enzyme treatment.

Figure 2. Size exclusion chromatography of polysaccharides isolated from wine. Comparison of enzyme-treated and control rosé and red wines (Kassara et al., 2019).

Conclusion

Colloids are important compounds in white, rose, and red wines. While they play a significant role in mouthfeel and flavor incorporation, colloid instability can also lead to wine defects such as haze and precipitation. Fining, filtration, and stabilization are powerful stylistic tools to manage such defects, but with lesser-known side effects. It is worth reconsidering whether a wine aged for 1-2 years at 10-15°C (50-59°F) still requires tartaric stabilization. Premium wines tend to be highly concentrated with the precursors for colloid formation. Even so, it is common for these wine producers to abstain from such treatments due to organoleptic changes perceived in their wines.

References

Kassara, S., Li, S., Smith, P., Blando, F., & Bindon, K. (2019). Pectolytic enzyme reduces the concentration of colloidal particles in wine due to changes in polysaccharide structure and aggregation properties. International Journal of Biological Macromolecules, 140, 546–555. https://doi.org/10.1016/j.ijbiomac.2019.08.043

McRae, J. M., Mierczynska-Vasilev, A., Soden, A., Barker, A. M., Day, M. P., & Smith, P. A. (2017). Effect of Commercial-Scale Filtration on Sensory and Colloidal Properties of Red Wines over 18 Months Bottle Aging. American Journal of Enology and Viticulture, 68(3), 263–274. https://doi.org/10.5344/ajev.2017.16095

Wang, S., Zhang, Q., Zhao, P., Ma, Z., Zhang, J., Ma, W., & Wang, X. (2022). Investigating the effect of three phenolic fractions on the volatility of floral, fruity, and aged aromas by HS-SPME-GC-MS and NMR in model wine. Food Chemistry: X, 13, 100281. https://doi.org/10.1016/j.fochx.2022.100281

COLLOIDS