Certified Specialist of Wine (CSW) Practice Exam

In-bottle secondary fermentation under pressure, as used in the traditional method, yields the finest, most persistent bubbles. When the wine undergoes a second fermentation inside each sealed bottle, CO2 is produced and remains dissolved under the bottle’s pressure. The wine is often aged on its lees, which adds complexity and creates countless tiny nucleation points for gas, producing very small bubbles that last longer after pouring.

The Charmat method ferments the secondary phase in large tanks, not in individual bottles, and the resulting CO2 bubbles form under lower pressure with less aging on lees, so the bubbles tend to be larger and less persistent. Direct CO2 injection and bulk tank carbonation bypass natural fermentation altogether, introducing gas directly into the wine, which creates coarser, quickly dissipating bubbles.