How do you know the bottle of sparkling wine you’ve just paid good money for hasn’t been ‘manufactured’ to match marketing requirements? The answer my friend, isn’t blowing in the wind, but it may be in the bubbles - or an isotope of bubbles.
As an avid reader of this website, you’ll know sparkling wines are produced using a second fermentation. If it’s done in the bottle it’s termed Traditionalle or Chapmenoise. If it occurs in a large pressurised tank it’s termed Charmat. Like many things we consume, wines which were once produced in very traditional ways are now possible to replicate by all manner of food science technologies. Evidence for this comes from the third method of producing sparkling wines: pump CO2 gas into the wine under pressure. In an effort to control the many pretenders, most wine producing countries have legislation to describe how the fermentation steps are done and the final composition of the wine. For example, Brazil allows sugar to be added in the first fermentation to increase the alcohol content. It also allows sugar to be added to the second fermentation to adjust the sweetness to match the wines description. Californian producer in the US are only allowed to add sugar during the second fermentation. European legislation is stricter still, allowing sugar to be added only in accordance to local wine types and method of production.
One way to determine the history of a sparkling wine is to see if the sugar has been added at the right stage of the process. The difficulty with this fine idea is knowing if the sugar came from the grapes (the first fermentation) or from added sugar (the second fermentation). As it turns out, the common sources for added sugar are sugar cane and corn starch, or sugar beet. The first two plants are C4 plants, mainly tropical grasses, the first organic molecule they from from atmospheric CO2 contains four carbon atoms. Sugar beet belongs to a group of with a less efficient photosynthetic pathway termed C3 plants. Most temperate plant species, including grapes, belong to this group. Incase you’ve had a long day, their first organic molecule in the photosynthetic process contains three carbon atoms.
Normal run of the mill carbon is C12, but a small proportion of carbon is C13, which means its atom contains 13, rather than the usual 12 neutrons in its nucleus (C14 is the radioactive form). The usual proportions of C12 is 98.89%, and C13 - 1.11%. Due to their slightly different photosynthetic pathways, C3 and C4 plants accumulate C13 in different proportions from the atmosphere. C4 plants incorporate less C13 than C3 plants. Therefore if cane sugar or corn starch has been added to the second fermentation it will alter the C13:C14 ratio. If the CO2 comes from a pressurised gas bottle, that too will leave a C13 signature in the wine consistent with fossil fuels. It must then be clearly labelled as a gassified wine, not a sparkling wine. In this detective story, the bubbles themselves can also give the game away.
Studies have shown that many sparkling wines have mixed sugar parentage in both the first and second fermentations. The C4 plant signature shows many of them also have added cane sugar in the second fermentation.
So, science can help you rest assured your vino is what it says it is. But if the label says $5.99, you sure as hell don’t need stable isotope analysis to know what you’re getting.