Category Archives: Yeast

The skinny on the bubbly

In the world of enology – the “ology” dealing with wine – sparkling wine is but a small portion of the world’s total wine production. The U.S. sells 150 million bottles annually, with France taking the lead at 500 million. A Wine Business Monthly article on how to make sparkling wine highlights some reasons why the business of sparkling wine is, and shall remain, a small percentage of the wine market.

Among the top reasons: the grapes must be of exceptional quality for a sparkling wine – bubbles intensify a wine’s flaws – and a second fermentation step takes extra time and money.

The seventeenth-century Benedictine monk Dom Pierre Pérignon is erroneously credited with inventing sparkling wine. If alive today, he would argue that bubbles are not meant for wine. Not so, argue many winemakers and wine drinkers today. Sparkling wine has recently surged in popularity, especially among younger drinkers.

According to a recent review article in the journal Trends in Food Science and Technology, our sparkling wine methods have not changed much since Pérignon’s time. Take a base wine, throw in some sugar and yeast, let it sit for a while, bottle it and allow it to pressurize, and presto – you’ve got sparkling wine.

How much sugar you add determines how sweet the sparkling wine is. On average:

    Brut is 1 % sugar
    Extra dry is 2 % sugar
    Sec is 6 % sugar
    Demi-sec is 10 % sugar

The basic technology of sparkling wine production involves two fermentation steps – one produces a base wine and the second yields the bubbly version. Traditionally, the second fermentation occurs directly in the bottle — no filtration, no transfer. The Italian Talento, the Spanish Cava, and, of course, the French Champagne, where sparkling wine was first developed, are made in this fashion.

The wine can be filtered and transferred to a new bottle post-fermentation, or, like the Italian red Lambrusco and white Asti, fermented in a hermetically sealed tank prior to bottling.

The second fermentation step produces the most important visual aspects of a sparkling wine — bubbles and foam. The bubbles and foam are affected by the wine’s chemical composition. This includes how much and what kinds of protein, sugar, fat and nucleic acids are present.

But how do these compounds get into the wine? The yeast do it through autolysis. Autolysis is just what it sounds like: auto (self) and lysis (breaking down). Yeast cells make alcohol out of sugar until they run out of food. Once their food is gone they break down, releasing enzymes that digest them and their nearby neighbors. Their cell walls fragment, and, no longer imprisoned, the proteins, sugar, fat, and nucleic acids can simply diffuse right out.

Proteins, the major compounds released into wine, are foamy; more protein in the wine means more foam. To counteract this, winemakers add stabilizers, which are salts like potassium sorbate, and clarifying agents, like the aluminum silicate compound bentonite.

Sugar comes from the grapes as well as the process of autolysis. The sugar of importance is called mannose, and more is better. Fat content affects foam levels, and nucleic acid content affects flavor.

Research on sparkling wine technology focuses on improving this second fermentation step, namely by speeding up the slow process of autolysis. The current tricks are to add aged lees (these are the dead yeast cells) to the wine and to increase the temperature during aging. Sounds simple, but these tricks affect the aroma and taste of the wine.

The most recent improvements to sparkling wine technology involve genetically engineered yeast strains. These strains are variations of the budding yeast Saccharomyces cerevisiae, which you know from drinking beer and/or eating bread. These same yeast are in wine, engineered by researchers to have improved fermentation abilities. They have enhanced autolysis capacity, better foaming capability, increased mannose release, and less aggregation.

Genetically engineered yeast strains are not yet approved for use in winemaking, but it’s only a matter of time before wine joins the list of genetically modified foods. In the meantime, pour yourself some champagne and enjoy the 20 million bubbles in your glass. After all, that’s 20 million more than Pérignon ever relished.