I heard wine experts say on TV that bubble size in champagne is a mark of quality. This suggests that wine-makers can control the size of the bubbles created when the bottle is opened and the carbon dioxide is released from suspension. Can this be true, or is the bubble size controlled more by the kind of glassware the wine is drunk from?
鈥� The topic of bubbles in sparkling wines is a snare for the naive. Many variables affect the size and stability of the bubbles, and these variables conflict.
Excessive carbon dioxide concentrations generate large, frothy bubbles that suggest a cheap fizzy wine or too high a serving temperature. To give the bubbles the right spacing and lifetime 鈥� neither too frothy nor too dull 鈥� one needs the right content of surfactant molecules, releasing the bouquet without irritating the sophisticate鈥檚 nose, while offering distracting tickles to juveniles. And the vintner can indeed influence the concentration of suitable molecules and microscopic particles in the wine.
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鈥淓xcessive carbon dioxide concentrations generate large, frothy bubbles that suggest cheap fizzy wine鈥�
Certainly the informed imbiber takes the glass into account, too. A champagne glass needs bubble nucleation sites, but not so many as to exhaust the supply of carbon dioxide, frothing over in a burst such as that caused by adding sugar. Traditionally, microscopic cracks in old glasses, or fibres from dishcloths, would supply starter bubbles. Now the bases of upmarket modern champagne glasses have minute laser-etched pits to nucleate bubbles in positions and sizes calculated to gratify people who are more concerned with the manner in which their fizz bubbles, than why it does so.
Jon Richfield, Somerset West, South Africa
鈥� Dissolved carbon dioxide can escape from champagne in a glass directly through the surface, which accounts for 80 per cent of the loss. This is why it鈥檚 best to use a flute not a coupe. The remaining 20 per cent is lost through bubble formation.
Bubble growth occurs as excess carbon dioxide diffuses into the bubble as it heads towards the surface. The rate at which this happens, and thus the size of the bubble, depends on the amount of dissolved carbon dioxide in the champagne.
Champagne bubbles are produced by , a secondary fermentation in the wine created by adding sugar, yeast and yeast nutrients. This produces carbon dioxide. The key difference in sparkling products on the market is what happens after this secondary fermentation 鈥� the process of ageing. Non-vintage champagnes are required by law to undergo at least 15 months of ageing, while vintage wines require at least three years. Good champagnes undergo between seven and 10 years and the greatest 12 years or more.
This ageing period means a loss of carbon dioxide through the imperfect seal between cork and bottle. This subsequently reduces bubble growth in the glass. Thus the better the wine, the smaller the bubbles 鈥� or perhaps more accurately, the more expensive the wine, the smaller the bubbles.
Peter Crawford, London, UK
This article appeared in print under the headline 鈥淏ubbling under鈥�