Wine Basics – Bubbles

In “Wine Basics – From Vine to Wine Part 3” I mentioned that the bottling of sparkling wines is different from that of still wines and promised a posting on them.

As with beer and soda, what makes a sparkling wine sparkle is carbon dioxide (CO2).  CO2 is a natural product of fermentation.  In still wines almost all of the CO2 is naturally allowed to escape from the wine.  You would think that sparkling wines are simply wines that are bottled before all the CO2 escapes and in some wines that is the case.  The majority of time, however, CO2 is reintroduced into the wine using one of three methods.

The first, least common, and generally not well regarded, method is to inject CO2 from a tank into the wine.  This is the method used for almost all soda, most beer, but very few wines.

The second and third methods both use a technique called secondary fermentation.  When the wine has finished fermenting, sugar is added.  It can be in the form of a sugar syrup or sometimes grape juice concentrate.  This gives the yeast some new food and they start fermenting again.  In some cases, fresh yeast is added to help the process along.  From here the methods diverge.

For many wines, such as Asti (F/K/A Asti Spumante), the process takes place in a sealed tank.  The wine is bottled using a sophisticated machine called a counter-pressure filler.  This allows the bottles to be filled with minimal loss of CO2 and minimal contact with oxygen.  The advantages are that the wines can be bottled when younger as they are separated from any sediment in the tank.  Although the equipment is expensive, the method is less labor intensive than the one outlined below.  Some people say that it makes for a fresher tasting wine.  I am not so sure.

The last method is to add the sugar into the bottle itself.  This is a labor intensive and thus more expensive.  It is the method used in Champagne.  Because the fermentation takes place in the bottle, there will be sediment from spent yeast (i.e. dead or dormant yeast).  Since most people find an excess of sediment unpleasant, particularly in a sparkling wine, it has to be removed.  The trick is to remove the sediment without losing the CO2.

The method used involves gradually moving the bottle from a near horizontal position to one were the opening is pointed mostly down.  The bottles are also turned to encourage the sediment to come to rest on the cork.  This is known as riddling.  When ready, the cork is quickly removed, any lost wine is replaced, and the bottle quickly re-corked.  This is known as disgorgement.

A final note:  Being much influenced by French traditions, many in the wine world tend to think of wine as sparkling or still.  In truth there is a wide range of levels of CO2 in wines.  Some wines, such as Portugal’s Vhino Verdes have a barley perceptible amount that adds a certain zippiness to the wine.  Italy’s Moscato d’ Asti has more CO2 than Vhino Verde but less than Champagne.  The Italians call this Fizzante.  Finally there are full blown sparklers like Champagne.  Once again the Italians have a term, Spumanti.

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2 Responses to Wine Basics – Bubbles

  1. The Whiner says:

    How do champagne houses achieve differing classifications of sweetness (e.g., brut, demi-sec) while maintaining the same level of “bubbliness”?

    • admin says:

      Great Question. They vary the amount of added sugar at the dosage. They then bottle before the yeast has “eaten” all the sugar. Most of the yeast is ejected during the disgorgment. That combined with the low levels of oxygen and high levels of carbon dioxide prevent the remaining yeast from converting the sugar into alcohol and carbon dioxide so the level of sweetness is maintained.