Three Cheers for the Holidays!: The Foamability of Sparkling Wine

We are nearing the end of another year, and what better way to celebrate the holidays and ring in the New Year with some bubbles!  Well, in all honesty, I think bubbly wines should be consumed at any time, and not just reserved for special occasions, but alas, the latter seems to be the way things end up in general.

One thing about sparkling wines that you may or may not have known is that there are several factors that influence the “foamability” of the wine.  After a sparkling wine is poured into a glass, it creates bubbly foam, the characteristics of which depend on many things, including changes in the wines’ chemical composition due to grape variety, viticulture management, and winemaking technique.  So far, nearly all

of the studies examining foamability of sparkling wines have dealt with those wines made in the traditional method (“méthode Champenoise”), used to create Champagne and Cava wines, however, none have looked at the foamability of sparkling wines creating using other methods such as the “bulk method”, which is used in Italy to create Prosecco wines.

Those studies on sparkling wines created in the méthode Champenoise have found that various proteins, polysaccharides, and iron are very important in the foamability of Champagne wines.   Basically, proteins in wine have been shown to act like surfactants (think soap or liquid dish detergent), which increases foamability as well as elasticity and strength of the bubbles.  In other words, the concentration of protein in a sparkling wine has been closely associated with the quality of the foam produced from the wine being poured into a glass, with greater protein levels yielding greater foamability.

One commonly used winemaking technique for still wines could actually be a detriment to the final characteristics and quality of the foam in a glass of sparkling wine.  Bentonite or other protein-removal compounds are often used during still winemaking, in order to remove excess proteins from the wine that may cause haziness or other off organoleptic characteristics.  Since sparkling wine starts off as a still wine, whatever is done to the wine during this first stage of winemaking can have an effect on the foamability of the finished sparkling wine once the whole process is complete.

More specifically, further studies have shown that glycoproteins may contribute more to foamability, indicating that the polysaccharide/protein combination may have more of an influence on foamability of sparkling wines than “naked” proteins alone.  Other more complicated protein compounds known as yeast mannoproteins, released during the fermentation process, also have been linked to improved foamability in sparkling wines, again hinting at the fact that synergistic effects between different types of proteins and other compounds in the sparkling wine may occur to produce a particular size and quality of the foam produced when a glass of bubbly has been poured.

The purpose of the study today was to take what is known about the foamability of sparkling wines made in the traditional method and apply it to wines made in the bulk method, specifically focusing on Prosecco from Italy.  Specifically, the study examined what components of Prosecco, both before and after aging on the lees, contribute to the foamability of the wine.

Methods

The wine used for this experiment was made from Glera grapes (Prosecco) from the 2009 vintage, and was made employing standard white winemaking techniques, but without using bentonite or any other protein fining treatment.  Standard “bulk method” procedures were used for secondary fermentation, which finished in about 25 days. Wines were left in contact with their lees for 1 and 18 months.  1 month of aging on the lees is typical for “bulk method” Prosecco aging, while 18 months is sometimes used when more complex organoleptic characteristics are desired.

At 1 month and 18 months, wines were filtered with GF/A filters, followed by 0.45μM cellulose acetate filters.  Some of this wine was stored for analysis at this stage, while some of this wine was removed to undergo ultrafiltration (3.5kDa size cut off).  This allowed for the analysis of wine with specifically sized proteins present.

“Wine foamability” was measured at the maximum height reached by the foam during the experiment.

Protein and polysaccharide content was analyzed for all experimental wines, as well as foam qualities.  Foam height was measured every 15 seconds for 15 minutes, as well as foam decay.

I can provide a few more details if you need them—just ask in the comment section if you need clarification on something.

Highlighted Results

• Yeast mannoprotein concentrations increased in wines as time on the lees increased.
• Greater concentrations of sugars and other glycocompounds were found in wines that spent a longer period of time on their lees.
• Grape-derived proteins such as Thaumatin-like proteins and chinases were found in all experimental wines, though more degraded fragments were noted in the wines aged on their lees for 18 months compared with those aged for 1 month.
• Foamability:
  • Ultra-filtered wines (that were filtered so that no molecules larger than 3.5kDA were present) did not produce any measurable amounts of foam, indicating that compounds larger than 3.5kDA (i.e. glycoproteins, mannoproteins, and other macromolecules) are required for producing foam in sparkling wines.
  • Foamability in wines decreased with increased aging time on the lees.
    • This result has also been found in sparkling wines made in the traditional method, and is thought to be due to either the chemical composition changes over aging time, or perhaps as a result of the loss of macromolecules by adherence to the bottle over storage time. More research is needed to pinpoint this.
  • Glycolated compounds had the greatest influence on wine foamability.
    • Specifically, yeast mannoproteins and grape invertase had significant influence on the wine’s foamability.
      • Grape invertase is rich in hydrophilic sugars and has good surface properties that allow it to act as a decent surfactant for wine foam formation and stability.
      • Yeast mannoproteins are considered to be proteoglycans  with a 10% by weight protein content, and are able to interact strongly with the bubble walls, allowing it to significantly contribute to foam formation and stabilization.
  • Grape proteins, such as Thaumatin-like proteins and chinases, alone did not contribute to the formation and stabilization of foam, however when synergistically acting with other compounds (such as glycolated proteins), foam height was found to be maximized.
    • In other words, by themselves, grape proteins can’t make foam, though when combined with the glycolated compounds like the ones I described above, the result is even more foam than the glycolated compounds alone.

Conclusions

This research seemed to confirm similar findings with Prosecco wines (bulk method) as have already been seen with wines made in the traditional method (Champagne, Cava, etc).  In simple terms, foamability of the wine when poured from the bottle into the glass depends chemically on larger glycolated proteins in conjunction with other grape-derived non-glycolated proteins.

What does this mean as a winemaker?  Well, if you want a wine that creates lots of foam when you pour it into a glass, you’ll need to perform viticulture management practices as well as winemaking techniques that maximize glycolated protein concentrations in your finished wines without compromising other aspects of wine quality.  Adding bentonite or other compounds used to reduce protein haze in wine is

effectively going to decrease the foamability of your finished wine, so if you’re aiming to maximize foam levels, perhaps consider using less of these protein-clearing compounds.  Of course, if you prefer less foam, then you can take steps to do that by decreasing larger macromolecules and other protein levels in the wine prior to bottling.

I hope your holidays are filled with lots of bubbles, family, friends, and joy!

Source: Vincenzi, S., Crapisi, A., and Curioni, A. 2014. Foamability of Prosecco wine: Cooperative effects of high molecular weight glycocompounds and wine PR-proteins. Food Hydrocolloids 34: 202-207.